Great comprehensive, well presented video John, it has covered the info I was after for my son in laws project on his new house and man cave (A "TT" installation as it happens) Many thanks👍
Remote power to sheds and out buildings on PME/TNCS is the bigggest head ache but John nicely clarifying things for new sparkies and anyone diy 😊. Great work and clear as this is often debated and argumented....😮
Thanks John for an incredibly clear and informative explanation. Good to see a You Tube video without bells, whistles and wrapping paper! Just straight to the information required.
Been out of the trade a few years, semi retired, but I had to watch this to recap. I remember in the past I always used minimum 10mm SWA 2c SWA as standard and I don't know why or who told me to and I always used an earth stake completely isolating the earth connection from the house. Also I was taught on PME the mini C/U had to be plastic. I'm going back 30 or so years. Only recently have I seen vids of people connecting and using the house earth in a shed or outbuilding an wondered when this changed. Like we had to earth bond everything in sight at one time now its not the case. Glad I'm out of it now, just do bits at home spurred on after much nagging from her indoors 😀
My grandfather have some talent for electronics. Replaces the ungrounded power outlets with grounded ones, does not connets it to anything (at least he says), and there is 115 and 81 volts to main and neutral from the ground. If I connect my aplifier to the living room, the speaker in the bathroom give me 81V to the case of the washing machine. The next rooms power outlet works fine. It MAYBE connected to the heatin systems radiator. The taps earthing is removed. In the garage we have a power outlet which have main on both terminal. Makes extension cord from 3 color 4 core wire, uses the same color twice. Uses 3 core wire, metal case machine, earth plug, leaves earth wire long and not connect. Doesn't use the strain relief in the plug. Maybe I sould be or get an electrician and redo the whole wiring.
This couldn't come at a better time. I've taken on renovating an old outbuilding on our property and I know I'm going to have to at least add an earth to make the wiring safe.
John, thanks for this video and answering some of the questions below. This has really cleared up confusion I had around TT and the earthing that the electrician put in when he cabled my home office. He didn't connect the armoured cable armour to the outbuilding earth (there is a separate rod) or fit a time delay RCD at the house end. The breaker often trips when I plug in a laptop PSU and have to go dashing off to the house to reset the breaker. I will be having a conversation with him tomorrow.
I solved the problem of getting power to my shed for lighting by fitting a 12V solar system £100 for a 40w panel & charge controller, £15 for two 12v 10w LED floodlights and a used car battery £0.00. Six years later and it's still working fine. It would have been too much hassle to correctly run a mains supply to the shed which is mostly galvanised steel.
I'm glad you didn't title your video "Earthing Systems for Outhouses". That said, I can see a ground loop possibility between the two buildings as a result of the ground rods not being close enough to earth potential within mΩ (i.e., one of the rods has not as good a contact with the earth due to difference in backfill materials).
If you only need modest power requirements for your outbuilding, say lights and a pond pump, then treat the outbuilding as an appliance. Simply connect to the house supply via a standard plug in a convenient socket. Your outdoor wiring is no longer a permanent installation and is treated as an extension lead. Obviously, the connecting cable should be suitably stout to handle the max possible load rating of the plug, even if only as a fault condition. I would still use a small consumer unit in the outbuilding regardless, and protect the connecting cable. Not what you are teaching here, John, I know, and thank you for it, but jogged my memory and I believe is worth keeping in mind.
Particular care is required where conductive pipes and such items as telecommunication cable sheaths , covered walkways, etc may be continuous between separate buildings and thus establish a parallel earth/neutral path
If i install an electrical system in an outbuilding containing extraneous conductive parts, with the main building being TN-C-S, I always install an earth rod at the outbuilding. If there was ever a situation that the mains neutral was to become lost or damaged the earthing can become live at mains potential, which could be dangerous. This would not be a problem at the outbuilding if you made a TT system. I understand that you have multiple earthing steaks on a PME system, so if there was a break in the neutral the system can still be held at earth potential. However if the neutral break was between the last reliable earthing point and the customers home, any extraneous parts will become live at mains potential. I know the chances are slim but its possible. I have looked at the draft of the 18th edition, it looks like we will have to install earthing steaks on all new installations whatever the earthing system. I believe this is because of the points raised above.
+Lester Electronics Additional earth rods would have to be very low impedance to make any significant difference, I thought... In my view some kind of "PME lost neutral detector/3-pole-disconnector" might be needed...
Here's an interesting one: power from an attached garage (where CU is situated) to feed a wooden shed, maximum 6 feet away on a concrete base with concrete path between and a concrete garage floor! Questions 1. Is a catenary supported SWA installation legitimate or MUST the cable be underground? 2. The house is TT so presumably the shed will need to be TT also, or is six feet considered OK to use the same TT earth as the house? Seems undesirable at best to do the latter 3. Presumably also, all circuits will need to be protected overall by RCD anyway or individual RCBO? 4. What are the considerations for avoiding inductive spike loops? The house rod will be connected to the shed rod via the ground and there will be an earth cable running overhead to the CU in the shed. Unless there is an earth break somewhere, a full earth loop with the loop resistance in it will be created. What is the recommended mitigation or avoidance for this? a) Bring the SWA earth connection (3 core cable) into the shed connecting solely to the SWA steel sheath in a separate insulated enclosure and connect the system PE directly to the shed rod? b) Bring the SWA connection into the shed and connect it AND the shed rod to system PE and ignore any possible ground loop effects? c) Bring the SWA connection into the shed and connect the SWA earth to both system PE (including the metal shed CU enclosure and the steel sheath on the SWA and not use a shed rod (due to it's close proximity to the garage and the source power CU)? 5. Presumably NOW (Feb 2020) the 18th edition regs apply and the shed CU must be a metal clad one (earthedto what?) with plastic being non-legit?
Also with equal potential bonding its typically installed as a separate earthing conductor run back to the earth bar at the main switchboard in the house, it's normally not needed to be connected to the feeder earths in the outbuilding as well, But not that it really matters if they are combined or joined to the feeder earths. Its typical to bundle the bonding conductor with the feeders in the same conduit or ducts. If the bonding earth is directly buried, this may be where the 10mm2 min size is coming from, I thought it was 16mm2 however. I never directly bury cables anyway.
John, I am trying to work out the difference between connecting a TN-C-S earth to a metallic outbuilding and the situation everyone is concerned about with EV charging in the event of an open PEN fault. The two circuit diagrams side by side look identical to me. Any pointers as to why the metallic outbuilding is okay but the EV charger is not?
Huh. I'm pretty sure the TN_S configuration is the only type allowed for remote subpanels under the current US NEC, but the third conductor is an actual wire in the cable, not a lead sheath. Mike Holt goes into excruciating detail on this in his videos, which I highly recommend. The TT configuration has far too much ground resistance to reliably trip breakers, and the TN_C_S has the usual sorts of shared neutral/earth issues. Notably a broken or high resistance neutral/earth connection will result in all grounded metal cases going live in the outbuilding as soon as any thing in the outbuilding is turned on.
Working slowly through a lot of your videos. I am not living in the UK but living in Thailand. Working here only with TT. The electrician that was involved during the building of the house wasn't very good. So time to check everything. On this video. If I have a rod both at my house and the barn, would it be beneficial to connect them together? The difference is though that in my case, the electricity comes into the barn and with an underground cable goes to the house. Currently it is 2 wires going into the house with an extra rod for grounding at the house. The situatoin is actually a little more complicated but that I will ask in another related video that comes more close to my question.
the reason I was thinking about that is that in this way, both ground in the house and ground in the barn are basically a single reference to the neutral.
Interesting case for bonding -- if you feed an outbuilding with Unshielded ethernet, and also separate SELV power (e.g. monititoring/alarm) in separate conduit -- all metallic, coming in from outside, but have no ''earthed'' wires at all ?
Hi John.. A great video as always. Could you answer a question for me please... Recently out looking at a job where a new build house is going in.. The supply cable for the new build is actually coming from another house on the site (parents house) So they're new house is titled as an annexed property... The existing house where the supply cable comes from is TT... So my question is.. If wiring the new build property, would it be best to not use the incoming earth on the supply cable from existing property. And to earth rod and TT the new build separately? Keep up the excellent work as always.... Much appreciated by many...
It has been said before that a breakdown in neutral supply can be mitigated by a parallel earth connection In terms of touch voltages being safer. Finally there seems to be more acceptance of this in the new regulations.
if you have done main bonding in the main house and the outbuilding's water and gas supplies are just an extention from the house do you still need to bond these extrenous conductive parts in the outbuilding as they are already bonded??
Hi John, many thanks for another great video. May I ask how this applies to a metal control box? Would it be a TT arrangement as the box itself is like a metal outbuilding? I am looking at running power to a painted IP65 metal control box to facilitate a supply to electric gates to my house, and am curious as to how this compares to the outbuilding scenario you've mentioned. I am using an electrician for this task but i'd like to be in the position to understand what he is doing and to be able to ask the right questions. Thanks in advance!
Great video JW, now I see why you guys call us "convicts", we would certainly be "convicted" if we ever used the armour or lead sheath of a cable as the earth, that's like using the steal conduit for the earth. M.I.M.S cable is one case where we are alowed to use the sheath as the earth and so long as the cable originates at the main switchboard in a M.E.N system, we can also use it as the neutral return path in what we call an E.S.R (earth sheath return system), where a single core M.I.M.S cable provides all three functional conductors to the sub board be it in side the main building or remote.
i miss wiring in nz and oz, far less stupid stuff, like ring circuits, fucken swa cable and multiple earthing systems and some of the dodgyest fuse boards known to man, dont even get me started on chiseling brick walls to bury cables in.
An answer for that TN-C-S water pipe issue will be to replace the section that enters the outbuilding with plastic pipe. The bonding issue then doesn't exist. Of course if the water was supplied via a 15mm copper pipe, with the standard wall thickness of 0.7mm, it has a cross-sectional area of 33mm^2, far greater than any earth bonding cable. It would require a continuity and resistance check back to the bonding point at entry to the property, but as electrical regulations seem to ignore these real world situations, it's not allowable. So, replace that last bit of pipework with plastic. Cheaper and easier than running 10mm cable out to an outhouse just to meet a bonding requirement.
Why in a TT system does shed need its own electrode in ground. Is it because it would be running beside the 230 Volt cable from house. Or is because a fault in house would send all exposed metal in shed to 230 Volts ?
If copper pipes from house go underground and re-enter a ultily room. Does his need additional 10mm bonding at entry at utiliy. The board in ultilty room only has 6mm twin and earth supply. Thanks
John, so if I have a steel frame pergola in a garden that has lights and heaters attached and wired through the frame it would need bonding accordingly as well then?
What's the difference between touching the floor of an outbuilding with a concrete floor, which is the "ground" is it not if the concrete is in direct contact with the earth below, and touching a tap connected to the ground through a metallic pipe ? Surely in both cases you're touching ground ? Or is this just a case of how good the connection is as a conductive path ?
I (think) i worked out that may not in-reality be enough... and in some respects goes down to the regulation-wording. I could also ask after 4mm 4-core , 2 cores + armour to carry the main equipotential bonding? Puzzle!
Come to think of it, probably not as the steel cores would have to be at least 32mm before you even go there, and even then, it may still not comply as it is not one material or the other due to wording of the regs
I’d say not because they would then be parallel conductors and a parallel conductor need to be the same diameter, same length and made of the same material to ensure it has the same resistance I believe.
Thank you John for another very clearly presented topic. With a TT system in the main house would it only be beneficial to connect the 10mm 3core SWA cable (cpc) to the outbuilding (with water and gas services) consumer unit MET where it has its own separate earth rod. I would imagine this setup, rather than keeping the two completely separate as you presented, is beneficial in trying to keep the Ra to a minimum. Or is it a pointlessly small benefit since you are relying on RCD for earth fault protection? I hope that makes sense? Many thanks for my crazy brain working overtime.
Surely most people will want to fit RCBOs or RCDs on all new installations anyway, so TT is the basic way to go to satisfy regs easily. If you supply with say 6mm SWA 3-core and link armour and earth you have more than enough safety at reasonable cost.
Much appreciated. Would you consider inserting an insulated section in to the water pipe itself, breaking the electrical connection to ground("extraneous part").? This would obviate the need for a 10mm bonding cable and possibly work out cheaper?
Hi JW, fab as always. A question if I may. I am off grid completely but running a conventional house. I generate electricity approx 100 metres away where it is also stored in batteries prior to onward transmission to the house. The solar system is earthed via a very effective TT install - there obviously is no other option. My earth and neutral are linked inside the inverter/charger. 3 core 25mm runs from my solar setup to my house. I have treated my house electrical installation as having a TN-S system and regarded my solar system (100m) away as my ‘power or generating station’. Consequently, I use the 3 core incoming earth at the house as my main earth, ie. no TT at the house. I wondered if you had any thoughts as to whether or not that is a suitable arrangement. In my head I can’t see a difference from a city estate house and my set up on a TN-S arrangement. BTW I am a retired electrician. Many thanks.
Your installation is TN-S. There is no TT. TT would mean an earth electrode at the solar/battery, 2 core L&N cable to the house, and another earth electrode at the house.
Hi John In relation to exporting a PME to outbuilding, A question I’ve always wondered is why is outdoor socket or lighting ok which could potentially be or have conductive things plugged into it. Yet if the light fitting was fitted to an out building the building would need an earth rod?
If you do have a stake then you use that as your only earth, as you would create an extended fault loop, if you were connected to the houses earth also..?
in a TT system, one should not have more than one earthing point to avoid ground loops which depending on the fault can cause power to flow from one ground point to the other, which is why the electrical code in my country requires that all earth wires go to a earth bus bar within the DB, before a single earth wire goes to the earthing rod. No looping of earth wires is allowed. So by right, the outhouse should also have an earthing wire going back to the panel in the main building, if it was a TT system
Hi John. Fantastic video's very informative. I see in the video at 13.55 you talk about ignoring the earth connection and driving your own earth rod. I have been asked to fit a new board in an outbuilding. The supply is coming from the dwelling house is a two core SWA cable and the steel wire was not used as an earth. As I see it I have two options. Option 1: Find the SWA back at the house and use the armour as my earth and connect it to the earthing block in the main board and do the same at the new board. The installation in the house is quite old and the size of the cable from the board to the earth rod is not 10 squared. Option 2: Ignore the earth from the earth connection coming from the house and drive my own earth rod and use 10 squared cable to the new board in the shed. What would you recommend and what distance from the building should the earth rod be driven?
With the 18th regs I believe you will require an earth electrode anyway even for TN installations. In which case would and exported earth to an outbuilding require an electrode as well? Rather like a belt and braces approach I guess. Very useful video.
The 18th is only a draft, but one electrode at the origin (in the house) should be sufficient as you are not installing a new supply but just extending an existing one. You could install one if desired, and the existing 17th edition does allow this already.
we use earth rods and bonding because that brings body standing on ground or touching objects into same potential with equipment case's pe and no dangerous currents will flow now you stand in your shed but your pe comes from far away house and has no local connection to actual earth under your feet. that sounds bad even with rcds which would limit fault voltages. if it's any permanent installation i would recommend replicating house's system in there. that is, if tn-c-s, bring either tn-c or tn-s to shed, and ground your pen or pe there. logically thinking, it would be even safer if you ground something that should be at ground level anyway if you dig the cable into ground and path to shed is short, you could improve both buildings earthing by installing vertical and / or horizontal earthing structure along your cabling. if, for god forbid, the buildings miss earth altogether, you could end up with proper electrical system too. later could be case, depending how strict checks your country has. estonia, where i live, doesn't currently have strict checks on existing installations, it's both good and bad
If you’re supplying an outbuilding without extraneous materials or a hot tub, and your have. TNCS system inside, could you just use a 2 core to the building or tub, earthing the armour with the TNCS and then just put a separate cable out to a local earth rod? I’m getting so confused by when to use RCDs with a TNCS system
Cheers John. This seems to be a bone of contention in the sparky world. The DNO don't like you exporting their TN-C-S earth even if your outbuilding doesn't have extraneous conducive parts. I've rang the East Anglian DNO and they said no. However NICEIC technical helpline say crack on, or at least they use none committal wording in that if you think the TNCS earth will be better than a TT rod then use it. Seems to be contradictory. This is also becoming an issue for car chargers. Some car chargers say they have built in tech to allow for exported PME earth but again, DNO say no to using it. My personal opinion is that installing SWA correctly, losing the earth core is more unlikely than damage to a TT rod earth/16mm cable (which already could be up to 200ohms) but if the DNO are insistent then TT it is. Whats your thoughts please?
Put your hand up if you've ever lived in a UK house where the garage wiring was a piece of twin & earth run from somewhere in the house to the garage... Now, my question relates to network cabling... If I wanted to run network cabling between my house and garage (assuming said garage was correctly wired for mains), do I need to do anything special to isolate the network cable between the two buildings? Is it likely that a potential difference between the two buildings would build up, and use the network cabling as some sort of return path, doing horrible things to the network devices? Or is that only an issue for buildings far apart from each other, on totally separate power systems?
That was my understanding too. So what are the "ethernet isolators" for that you can buy? Is that in case the cabling itself somehow picks up a charge? (which is unlikely in a short 20m run from a garage to a house)
Shielded ethernet cables are bonded to the earth of the devices on both ends, so some current could flow down this if you use shielded cable bonded at both sides. It would effectively be in parallel with the the earth used to supply the outbuilding. The isolators (often seen in hospitals) are typically rated for a higher isolation voltage, and isolate the shield.
sure ive seen a lot of garages that have been using a standard extension lead for decades, running it outside along the fence in all weathers, plugged into a spare socket, then wonder why they cant run much at the end of a cheap 30m lead. dread to think how standard flex it stands up to UV and british weather too, my garage was built after the fact of concreting nearer the house, thus could not bury the cable, but in the 80s we wired at along the fence with MIC pyro cable, have had no issues in 30 years, we also have an earth rod along with the pyro is earth in the outer
There are different degrees of isolation. A typical port has a rating of 1500V (which is a TEST voltage not a continuous rating) but the industrial isolator I looked up was rated 4000V.
How would this apply to a series or outside (earthed) metal bollard lights, screwed to concrete slabs, assuming the house is TNCS earthed? Can the house earth be used (as with a wooden shed) or is an earth rod needed for the lights (as they are metal)?
Probably best to convert to a low voltage system to be sure, see David Savery’s recent video on that. Otherwise make sure the circuit is RCD protected and have the 5X disconnect time checked for compliance (within 40mS) at the bollard furthest from the supplying RCD.
I have a wooden summer house with a couple of sockets and a light. I have have connected it to the main house using 3 core armoured cable. It is connected via an RCD and 7 amp breaker off the down stairs ring main. It is all relying on the ring main earth back to the consumer unit. Should there be a supplementary separate 6mm earth cable back to the consumer unit? There are no extraneous metal parts.
John, thanks for this. You did not explain why the earth cable needs to increase from 6 sq mm to 10 sq mm if there were extraneous parts. I presume it is because more current needs to be carried .... but why?
How can you say 6mm2 or 10mm2 without knowing the distance? If I have a metal frame greenhouse 30m from the house connected with 10mm2 3-wire SWA and the frame bonded to the E and armour the frame is in contact with the foundation, especially when raining, whether another Earth rod is added or not. So what happens if there is a close lightning strike and there is 50kV or more gradient between the house rod and greenhouse frame?
In my workshop I have a water pipe which is plastic MDPE pipe coming in from the house (about 10m away) via an underground duct (4” soil pipe) with the armoured cable. Since none of this water pipe is conducting to the actual earth, is it OK not to bond it? What if I took it outside the workshop for a hose tap? The system is TNS and the outbuilding earth is from the house along SWA.
John, this was an interesting presentation, but what if the water pipe into the outbuilding is in plastic and the goes into copper at say an instantaneous heater? Presumably it would then only be necessary to bond the tap pipework to the local earth at the end of the incoming cable, maybe a secondary consumer unit?
I was wondering the same, as most Water and nowadays Gas supplies are in PVC does this then nagate the building from having Extraneous Conductive Parts ?
A shop i worked at had a shipping container out back with a light and socket in it. They just stuck a plastic conduit from the shop to the container. no thought was given to bonding etc.
If you have a TN-C-S or TN-S supply to the house and your taking an earth to the garage there would be no need for an earth rod. As this would continue as a TN-C-S or TN-S system, providing the CPC is appropriately sized.
Jck142 extending the tncs, to an out building, if the neutral goes down, are you not out the equipotential zone? I thought you are, and this is why you don’t use the pme and simply rod it. Slightly confusing. Many people say only use one system, I’ve also read and been told, you can supplement pme with rods. I.e a cabin wired in swa, using the pme, can be supplemented with a rod( in case of neutral fault). Under fault the currents can be large and burn the rod out! So unsure about this too. Very conflicting, wonder if @johnward
Great comprehensive, well presented video John, it has covered the info I was after for my son in laws project on his new house and man cave (A "TT" installation as it happens) Many thanks👍
Remote power to sheds and out buildings on PME/TNCS is the bigggest head ache but John nicely clarifying things for new sparkies and anyone diy 😊.
Great work and clear as this is often debated and argumented....😮
Thanks John for an incredibly clear and informative explanation. Good to see a You Tube video without bells, whistles and wrapping paper! Just straight to the information required.
A great video. Clear, concise and thorough. Thank you!
"Your house might even have a roof on top", OMG, you crack me up John.
Thank you so much for making this. Your description is excellent and extremely useful. You made it sufficiently understandable. Great work.
Certainly clears up the jargon and diagrams in BS7671....Wished i watched this before college ! lol now it's in my head so thank you John as always !
Thanks John excellent video, settles an argument I have been having with some young upstart who is telling me I have been doing it wrong for years.
This is so clear and easy to understand. From a fellow electrician. Thank you
Many thanks John for your fantastic videos. This video was very informative.
Been out of the trade a few years, semi retired, but I had to watch this to recap. I remember in the past I always used minimum 10mm SWA 2c SWA as standard and I don't know why or who told me to and I always used an earth stake completely isolating the earth connection from the house. Also I was taught on PME the mini C/U had to be plastic. I'm going back 30 or so years. Only recently have I seen vids of people connecting and using the house earth in a shed or outbuilding an wondered when this changed. Like we had to earth bond everything in sight at one time now its not the case. Glad I'm out of it now, just do bits at home spurred on after much nagging from her indoors 😀
John, Thank you for a very good explanation of the requirements for different supply systems.
Thank you very much for your service to the industry.....Learnt so much from your videos
My grandfather have some talent for electronics. Replaces the ungrounded power outlets with grounded ones, does not connets it to anything (at least he says), and there is 115 and 81 volts to main and neutral from the ground. If I connect my aplifier to the living room, the speaker in the bathroom give me 81V to the case of the washing machine. The next rooms power outlet works fine. It MAYBE connected to the heatin systems radiator. The taps earthing is removed. In the garage we have a power outlet which have main on both terminal. Makes extension cord from 3 color 4 core wire, uses the same color twice. Uses 3 core wire, metal case machine, earth plug, leaves earth wire long and not connect. Doesn't use the strain relief in the plug. Maybe I sould be or get an electrician and redo the whole wiring.
This couldn't come at a better time. I've taken on renovating an old outbuilding on our property and I know I'm going to have to at least add an earth to make the wiring safe.
John, thanks for this video and answering some of the questions below. This has really cleared up confusion I had around TT and the earthing that the electrician put in when he cabled my home office. He didn't connect the armoured cable armour to the outbuilding earth (there is a separate rod) or fit a time delay RCD at the house end. The breaker often trips when I plug in a laptop PSU and have to go dashing off to the house to reset the breaker. I will be having a conversation with him tomorrow.
THANK YOU JW...for the detailed yet easy to understand videos.
Thank you John.. perfect explanation!
I solved the problem of getting power to my shed for lighting by fitting a 12V solar system £100 for a 40w panel & charge controller, £15 for two 12v 10w LED floodlights and a used car battery £0.00. Six years later and it's still working fine. It would have been too much hassle to correctly run a mains supply to the shed which is mostly galvanised steel.
I'm glad you didn't title your video "Earthing Systems for Outhouses". That said, I can see a ground loop possibility between the two buildings as a result of the ground rods not being close enough to earth potential within mΩ (i.e., one of the rods has not as good a contact with the earth due to difference in backfill materials).
If you only need modest power requirements for your outbuilding, say lights and a pond pump, then treat the outbuilding as an appliance.
Simply connect to the house supply via a standard plug in a convenient socket. Your outdoor wiring is no longer a permanent installation and is treated as an extension lead. Obviously, the connecting cable should be suitably stout to handle the max possible load rating of the plug, even if only as a fault condition. I would still use a small consumer unit in the outbuilding regardless, and protect the connecting cable.
Not what you are teaching here, John, I know, and thank you for it, but jogged my memory and I believe is worth keeping in mind.
Exactly what I did.
0:56 "Your house may have a roof on top" ==> (giggle) "British, much, lately?"
Brilliant video John, you make things easier to understand.
Please could you do a video of potential difference.
Your explanation is very clear.Thanks a lot.
Particular care is required where conductive pipes and such items as telecommunication cable sheaths , covered walkways, etc may be continuous between separate buildings and thus establish a parallel earth/neutral path
Really informative John. Thank you.
Thank you for a very clear explanation video on the types of earthing...Now to check out your other videos...
J W YOUR VIDEOS ARE VERY MEANINGFUL,THANKS.
Thank you John clear precise and very very helpful
Mr Ward is the only person who can tell me this stuff.
If my Dad starts explaining it I go into a deep coma lasting several months.
Thank you, very succinct appreciate your delivery as fast
Excellent video again. Many thanks.
This is the most enlightening lecture I know of after Gautama Buddha’s some time back.
If i install an electrical system in an outbuilding containing extraneous conductive parts, with the main building being TN-C-S, I always install an earth rod at the outbuilding.
If there was ever a situation that the mains neutral was to become lost or damaged the earthing can become live at mains potential, which could be dangerous. This would not be a problem at the outbuilding if you made a TT system. I understand that you have multiple earthing steaks on a PME system, so if there was a break in the neutral the system can still be held at earth potential. However if the neutral break was between the last reliable earthing point and the customers home, any extraneous parts will become live at mains potential. I know the chances are slim but its possible. I have looked at the draft of the 18th edition, it looks like we will have to install earthing steaks on all new installations whatever the earthing system. I believe this is because of the points raised above.
+Lester Electronics
Additional earth rods would have to be very low impedance to make any significant difference, I thought... In my view some kind of "PME lost neutral detector/3-pole-disconnector" might be needed...
Chances are your own house has a PME supply head and I doubt you've TT'd it, why would you bother treating an outbuilding any different?
@R-77 no.
Excellent: just the information I needed.
Great stuff again John, thank you.
Excellent presentation.
Interesting John, thank you for this.
6mm swa 3 core best for future installs. Will support up to 40a mcb at the house and will supply a 32a ring and a 6a lighting circuit.
Very clearly explained.👍Thank you.
*So* interesting, as usual - thanks!
bloody brilliant John, your videos are informative and easy to understand, do you mind if i share with students? I work for a college?
Here's an interesting one: power from an attached garage (where CU is situated) to feed a wooden shed, maximum 6 feet away on a concrete base with concrete path between and a concrete garage floor!
Questions
1. Is a catenary supported SWA installation legitimate or MUST the cable be underground?
2. The house is TT so presumably the shed will need to be TT also, or is six feet considered OK to use the same TT earth as the house? Seems undesirable at best to do the latter
3. Presumably also, all circuits will need to be protected overall by RCD anyway or individual RCBO?
4. What are the considerations for avoiding inductive spike loops? The house rod will be connected to the shed rod via the ground and there will be an earth cable running overhead to the CU in the shed. Unless there is an earth break somewhere, a full earth loop with the loop resistance in it will be created. What is the recommended mitigation or avoidance for this?
a) Bring the SWA earth connection (3 core cable) into the shed connecting solely to the SWA steel sheath in a separate insulated enclosure and connect the system PE directly to the shed rod?
b) Bring the SWA connection into the shed and connect it AND the shed rod to system PE and ignore any possible ground loop effects?
c) Bring the SWA connection into the shed and connect the SWA earth to both system PE (including the metal shed CU enclosure and the steel sheath on the SWA and not use a shed rod (due to it's close proximity to the garage and the source power CU)?
5. Presumably NOW (Feb 2020) the 18th edition regs apply and the shed CU must be a metal clad one (earthedto what?) with plastic being non-legit?
Also with equal potential bonding its typically installed as a separate earthing conductor run back to the earth bar at the main switchboard in the house, it's normally not needed to be connected to the feeder earths in the outbuilding as well, But not that it really matters if they are combined or joined to the feeder earths. Its typical to bundle the bonding conductor with the feeders in the same conduit or ducts. If the bonding earth is directly buried, this may be where the 10mm2 min size is coming from, I thought it was 16mm2 however. I never directly bury cables anyway.
John, I am trying to work out the difference between connecting a TN-C-S earth to a metallic outbuilding and the situation everyone is concerned about with EV charging in the event of an open PEN fault. The two circuit diagrams side by side look identical to me. Any pointers as to why the metallic outbuilding is okay but the EV charger is not?
Thank you John, crystal clear.
Huh. I'm pretty sure the TN_S configuration is the only type allowed for remote subpanels under the current US NEC, but the third conductor is an actual wire in the cable, not a lead sheath.
Mike Holt goes into excruciating detail on this in his videos, which I highly recommend. The TT configuration has far too much ground resistance to reliably trip breakers, and the TN_C_S has the usual sorts of shared neutral/earth issues. Notably a broken or high resistance neutral/earth connection will result in all grounded metal cases going live in the outbuilding as soon as any thing in the outbuilding is turned on.
Useful information keep up the good work
Earthing for off grid using inverters would be useful too. And how to connect to house pipes with grid earthing?
Amazing clear video
Thank you.
thankyou for the robust explanations of these principals
Working slowly through a lot of your videos. I am not living in the UK but living in Thailand. Working here only with TT. The electrician that was involved during the building of the house wasn't very good. So time to check everything. On this video. If I have a rod both at my house and the barn, would it be beneficial to connect them together?
The difference is though that in my case, the electricity comes into the barn and with an underground cable goes to the house. Currently it is 2 wires going into the house with an extra rod for grounding at the house.
The situatoin is actually a little more complicated but that I will ask in another related video that comes more close to my question.
the reason I was thinking about that is that in this way, both ground in the house and ground in the barn are basically a single reference to the neutral.
Interesting case for bonding -- if you feed an outbuilding with Unshielded ethernet, and also separate SELV power (e.g. monititoring/alarm) in separate conduit -- all metallic, coming in from outside, but have no ''earthed'' wires at all ?
Then you have created an Extraneous conductive part into the building.
@@shilks8773 Could you include the 10mm² Earth cable within the conduit ?
Hi John.. A great video as always.
Could you answer a question for me please... Recently out looking at a job where a new build house is going in.. The supply cable for the new build is actually coming from another house on the site (parents house)
So they're new house is titled as an annexed property... The existing house where the supply cable comes from is TT...
So my question is..
If wiring the new build property, would it be best to not use the incoming earth on the supply cable from existing property. And to earth rod and TT the new build separately?
Keep up the excellent work as always.... Much appreciated by many...
It has been said before that a breakdown in neutral supply can be mitigated by a parallel earth connection
In terms of touch voltages being safer. Finally there seems to be more acceptance of this in the new regulations.
Great channel John. Thanks.
if you have done main bonding in the main house and the outbuilding's water and gas supplies are just an extention from the house do you still need to bond these extrenous conductive parts in the outbuilding as they are already bonded??
Hi John, many thanks for another great video. May I ask how this applies to a metal control box? Would it be a TT arrangement as the box itself is like a metal outbuilding? I am looking at running power to a painted IP65 metal control box to facilitate a supply to electric gates to my house, and am curious as to how this compares to the outbuilding scenario you've mentioned. I am using an electrician for this task but i'd like to be in the position to understand what he is doing and to be able to ask the right questions. Thanks in advance!
Very helpful - many thanks.
Have you considered using a 4 core SWA 6mm and using 2 conductors joined together as the earth conductor
Great video JW, now I see why you guys call us "convicts", we would certainly be "convicted" if we ever used the armour or lead sheath of a cable as the earth, that's like using the steal conduit for the earth.
M.I.M.S cable is one case where we are alowed to use the sheath as the earth and so long as the cable originates at the main switchboard in a M.E.N system, we can also use it as the neutral return path in what we call an E.S.R (earth sheath return system), where a single core M.I.M.S cable provides all three functional conductors to the sub board be it in side the main building or remote.
i miss wiring in nz and oz, far less stupid stuff, like ring circuits, fucken swa cable and multiple earthing systems and some of the dodgyest fuse boards known to man, dont even get me started on chiseling brick walls to bury cables in.
An answer for that TN-C-S water pipe issue will be to replace the section that enters the outbuilding with plastic pipe. The bonding issue then doesn't exist.
Of course if the water was supplied via a 15mm copper pipe, with the standard wall thickness of 0.7mm, it has a cross-sectional area of 33mm^2, far greater than any earth bonding cable. It would require a continuity and resistance check back to the bonding point at entry to the property, but as electrical regulations seem to ignore these real world situations, it's not allowable. So, replace that last bit of pipework with plastic. Cheaper and easier than running 10mm cable out to an outhouse just to meet a bonding requirement.
Why in a TT system does shed need its own electrode in ground. Is it because it would be running beside the 230 Volt cable from house. Or is because a fault in house would send all exposed metal in shed to 230 Volts ?
If copper pipes from house go underground and re-enter a ultily room. Does his need additional 10mm bonding at entry at utiliy. The board in ultilty room only has 6mm twin and earth supply. Thanks
John, so if I have a steel frame pergola in a garden that has lights and heaters attached and wired through the frame it would need bonding accordingly as well then?
What's the difference between touching the floor of an outbuilding with a concrete floor, which is the "ground" is it not if the concrete is in direct contact with the earth below, and touching a tap connected to the ground through a metallic pipe ? Surely in both cases you're touching ground ? Or is this just a case of how good the connection is as a conductive path ?
Could you use a 6.mm 3core swa and use one of the inner cores plus the armour to make up the difference ?
*Following this comment*
I (think) i worked out that may not in-reality be enough... and in some respects goes down to the regulation-wording.
I could also ask after 4mm 4-core , 2 cores + armour to carry the main equipotential bonding? Puzzle!
Come to think of it, probably not as the steel cores would have to be at least 32mm before you even go there, and even then, it may still not comply as it is not one material or the other due to wording of the regs
I’d say not because they would then be parallel conductors and a parallel conductor need to be the same diameter, same length and made of the same material to ensure it has the same resistance I believe.
Brilliant video
Thank you John for another very clearly presented topic.
With a TT system in the main house would it only be beneficial to connect the 10mm 3core SWA cable (cpc) to the outbuilding (with water and gas services) consumer unit MET where it has its own separate earth rod.
I would imagine this setup, rather than keeping the two completely separate as you presented, is beneficial in trying to keep the Ra to a minimum. Or is it a pointlessly small benefit since you are relying on RCD for earth fault protection?
I hope that makes sense?
Many thanks for my crazy brain working overtime.
Surely most people will want to fit RCBOs or RCDs on all new installations anyway, so TT is the basic way to go to satisfy regs easily. If you supply with say 6mm SWA 3-core and link armour and earth you have more than enough safety at reasonable cost.
Much appreciated. Would you consider inserting an insulated section in to the water pipe itself, breaking the electrical connection to ground("extraneous part").? This would obviate the need for a 10mm bonding cable and possibly work out cheaper?
Hi JW, fab as always.
A question if I may. I am off grid completely but running a conventional house. I generate electricity approx 100 metres away where it is also stored in batteries prior to onward transmission to the house.
The solar system is earthed via a very effective TT install - there obviously is no other option.
My earth and neutral are linked inside the inverter/charger. 3 core 25mm runs from my solar setup to my house.
I have treated my house electrical installation as having a TN-S system and regarded my solar system (100m) away as my ‘power or generating station’. Consequently, I use the 3 core incoming earth at the house as my main earth, ie. no TT at the house.
I wondered if you had any thoughts as to whether or not that is a suitable arrangement.
In my head I can’t see a difference from a city estate house and my set up on a TN-S arrangement.
BTW I am a retired electrician.
Many thanks.
Your installation is TN-S. There is no TT.
TT would mean an earth electrode at the solar/battery, 2 core L&N cable to the house, and another earth electrode at the house.
Nice little belch at 12:52 😆
Hi John
In relation to exporting a PME to outbuilding,
A question I’ve always wondered is why is outdoor socket or lighting ok which could potentially be or have conductive things plugged into it. Yet if the light fitting was fitted to an out building the building would need an earth rod?
May have a roof on top, thanks for clarifying that one
i wondered what that pointy thing was on my house...now i know ... its the roof..
If you do have a stake then you use that as your only earth, as you would create an extended fault loop, if you were connected to the houses earth also..?
in a TT system, one should not have more than one earthing point to avoid ground loops which depending on the fault can cause power to flow from one ground point to the other, which is why the electrical code in my country requires that all earth wires go to a earth bus bar within the DB, before a single earth wire goes to the earthing rod. No looping of earth wires is allowed.
So by right, the outhouse should also have an earthing wire going back to the panel in the main building, if it was a TT system
Thanks John!
Hi John. Fantastic video's very informative. I see in the video at 13.55 you talk about ignoring the earth connection and driving your own earth rod. I have been asked to fit a new board in an outbuilding. The supply is coming from the dwelling house is a two core SWA cable and the steel wire was not used as an earth. As I see it I have two options. Option 1: Find the SWA back at the house and use the armour as my earth and connect it to the earthing block in the main board and do the same at the new board. The installation in the house is quite old and the size of the cable from the board to the earth rod is not 10 squared. Option 2: Ignore the earth from the earth connection coming from the house and drive my own earth rod and use 10 squared cable to the new board in the shed. What would you recommend and what distance from the building should the earth rod be driven?
With the 18th regs I believe you will require an earth electrode anyway even for TN installations. In which case would and exported earth to an outbuilding require an electrode as well? Rather like a belt and braces approach I guess. Very useful video.
The 18th is only a draft, but one electrode at the origin (in the house) should be sufficient as you are not installing a new supply but just extending an existing one.
You could install one if desired, and the existing 17th edition does allow this already.
we use earth rods and bonding because that brings body standing on ground or touching objects into same potential with equipment case's pe and no dangerous currents will flow
now you stand in your shed but your pe comes from far away house and has no local connection to actual earth under your feet. that sounds bad even with rcds which would limit fault voltages. if it's any permanent installation i would recommend replicating house's system in there. that is, if tn-c-s, bring either tn-c or tn-s to shed, and ground your pen or pe there. logically thinking, it would be even safer if you ground something that should be at ground level anyway
if you dig the cable into ground and path to shed is short, you could improve both buildings earthing by installing vertical and / or horizontal earthing structure along your cabling. if, for god forbid, the buildings miss earth altogether, you could end up with proper electrical system too. later could be case, depending how strict checks your country has. estonia, where i live, doesn't currently have strict checks on existing installations, it's both good and bad
If you’re supplying an outbuilding without extraneous materials or a hot tub, and your have. TNCS system inside, could you just use a 2 core to the building or tub, earthing the armour with the TNCS and then just put a separate cable out to a local earth rod? I’m getting so confused by when to use RCDs with a TNCS system
The takeaway from this is if you want to add a hosepipe to your shed, use pvc.
superb - many thanks john
Educational and interesting
Cheers John. This seems to be a bone of contention in the sparky world. The DNO don't like you exporting their
TN-C-S earth even if your outbuilding doesn't have extraneous conducive parts. I've rang the East Anglian DNO and they said no. However NICEIC technical helpline say crack on, or at least they use none committal wording in that if you think the TNCS earth will be better than a TT rod then use it. Seems to be contradictory. This is also becoming an issue for car chargers. Some car chargers say they have built in tech to allow for exported PME earth but again, DNO say no to using it.
My personal opinion is that installing SWA correctly, losing the earth core is more unlikely than damage to a TT rod earth/16mm cable (which already could be up to 200ohms) but if the DNO are insistent then TT it is. Whats your thoughts please?
He's still thinking
In a TT installation, would you then connect the two earth rods (house and shed) together?
Here for this reason, did you find out?
Put your hand up if you've ever lived in a UK house where the garage wiring was a piece of twin & earth run from somewhere in the house to the garage...
Now, my question relates to network cabling... If I wanted to run network cabling between my house and garage (assuming said garage was correctly wired for mains), do I need to do anything special to isolate the network cable between the two buildings? Is it likely that a potential difference between the two buildings would build up, and use the network cabling as some sort of return path, doing horrible things to the network devices? Or is that only an issue for buildings far apart from each other, on totally separate power systems?
Not a problem, all Ethernet cables are electrically isolated by the devices they connect to.
That was my understanding too. So what are the "ethernet isolators" for that you can buy? Is that in case the cabling itself somehow picks up a charge? (which is unlikely in a short 20m run from a garage to a house)
Shielded ethernet cables are bonded to the earth of the devices on both ends, so some current could flow down this if you use shielded cable bonded at both sides. It would effectively be in parallel with the the earth used to supply the outbuilding.
The isolators (often seen in hospitals) are typically rated for a higher isolation voltage, and isolate the shield.
sure ive seen a lot of garages that have been using a standard extension lead for decades, running it outside along the fence in all weathers, plugged into a spare socket, then wonder why they cant run much at the end of a cheap 30m lead. dread to think how standard flex it stands up to UV and british weather too, my garage was built after the fact of concreting nearer the house, thus could not bury the cable, but in the 80s we wired at along the fence with MIC pyro cable, have had no issues in 30 years, we also have an earth rod along with the pyro is earth in the outer
There are different degrees of isolation. A typical port has a rating of 1500V (which is a TEST voltage not a continuous rating) but the industrial isolator I looked up was rated 4000V.
What if the outbuilding is made of metal? Would you not be able to use Tns or tncs?
How would this apply to a series or outside (earthed) metal bollard lights, screwed to concrete slabs, assuming the house is TNCS earthed? Can the house earth be used (as with a wooden shed) or is an earth rod needed for the lights (as they are metal)?
Probably best to convert to a low voltage system to be sure, see David Savery’s recent video on that. Otherwise make sure the circuit is RCD protected and have the 5X disconnect time checked for compliance (within 40mS) at the bollard furthest from the supplying RCD.
I have a wooden summer house with a couple of sockets and a light. I have have connected it to the main house using 3 core armoured cable. It is connected via an RCD and 7 amp breaker off the down stairs ring main. It is all relying on the ring main earth back to the consumer unit. Should there be a supplementary separate 6mm earth cable back to the consumer unit? There are no extraneous metal parts.
John, thanks for this. You did not explain why the earth cable needs to increase from 6 sq mm to 10 sq mm if there were extraneous parts. I presume it is because more current needs to be carried .... but why?
TN-C-S installations require the main bonding to be at least 10mm.
Could I not wire a wooden shed from a house TT consumer and just rely on the RCD at the house consumer unit?
How can you say 6mm2 or 10mm2 without knowing the distance?
If I have a metal frame greenhouse 30m from the house connected with 10mm2 3-wire SWA and the frame bonded to the E and armour the frame is in contact with the foundation, especially when raining, whether another Earth rod is added or not. So what happens if there is a close lightning strike and there is 50kV or more gradient between the house rod and greenhouse frame?
Very good video.Thank you
In my workshop I have a water pipe which is plastic MDPE pipe coming in from the house (about 10m away) via an underground duct (4” soil pipe) with the armoured cable. Since none of this water pipe is conducting to the actual earth, is it OK not to bond it? What if I took it outside the workshop for a hose tap? The system is TNS and the outbuilding earth is from the house along SWA.
Plastic pipes do not need bonding as they are not conductive.
John, this was an interesting presentation, but what if the water pipe into the outbuilding is in plastic and the goes into copper at say an instantaneous heater? Presumably it would then only be necessary to bond the tap pipework to the local earth at the end of the incoming cable, maybe a secondary consumer unit?
I was wondering the same, as most Water and nowadays Gas supplies are in PVC does this then nagate the building from having Extraneous Conductive Parts ?
Excellent
A shop i worked at had a shipping container out back with a light and socket in it. They just stuck a plastic conduit from the shop to the container. no thought was given to bonding etc.
On a tt system, I don’t understand why you would need a second Earth rod in the ground for the garage if you took an Earth from the house.
from what I get from the video you dont need it - only if there is extraneous metal parts
If you have a TN-C-S or TN-S supply to the house and your taking an earth to the garage there would be no need for an earth rod. As this would continue as a TN-C-S or TN-S system, providing the CPC is appropriately sized.
Jck142 extending the tncs, to an out building, if the neutral goes down, are you not out the equipotential zone? I thought you are, and this is why you don’t use the pme and simply rod it. Slightly confusing. Many people say only use one system, I’ve also read and been told, you can supplement pme with rods. I.e a cabin wired in swa, using the pme, can be supplemented with a rod( in case of neutral fault). Under fault the currents can be large and burn the rod out! So unsure about this too. Very conflicting, wonder if @johnward
Moelwyn, he answered that question elsewhere on this video amongst the other comments, you can export so no need for another earth rod
Perfectly explained 😁👍👍