Earthing Systems for Outbuildings
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- Опубликовано: 31 май 2024
- Considerations for what type of earth connection to use when connecting power to a shed, garage or other outbuilding.
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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👍
"Your house might even have a roof on top", OMG, you crack me up John.
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....😮
John, Thank you for a very good explanation of the requirements for different supply systems.
Many thanks John for your fantastic videos. This video was very informative.
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 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.
Thank you John.. perfect explanation!
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.
Thank you for a very clear explanation video on the types of earthing...Now to check out your other videos...
THANK YOU JW...for the detailed yet easy to understand videos.
This is so clear and easy to understand. From a fellow electrician. Thank you
Great stuff again John, thank you.
Interesting John, thank you for this.
J W YOUR VIDEOS ARE VERY MEANINGFUL,THANKS.
Thank you, very succinct appreciate your delivery as fast
Really informative John. Thank you.
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.
Your explanation is very clear.Thanks a lot.
Brilliant video John, you make things easier to understand.
Please could you do a video of potential difference.
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.
Thank you John, crystal clear.
Very clearly explained.👍Thank you.
0:56 "Your house may have a roof on top" ==> (giggle) "British, much, lately?"
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.
Excellent presentation.
Useful information keep up the good work
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!
Thank you John clear precise and very very helpful
Amazing clear video
Thank you.
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
Excellent: just the information I needed.
Excellent video again. Many thanks.
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 😀
superb - many thanks john
Very helpful - many thanks.
Great channel John. Thanks.
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.
*So* interesting, as usual - thanks!
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).
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?
Questions: I have a metal lamp post outside currently supplied via a 13A spur from an interior ring going outside via junction box to SWA. Not sure what your opinion on that set-up would be .. but my main concern is possibility of lightning strike to the post sending a current back into the house. Is there any reason not to disconnect the exported earth at the exterior junction box and replace the earth with a rod?
Perfectly explained 😁👍👍
Very good video.Thank you
John I have just recently put up a metallic hut. I know this will need 10mm bonding as it's a TNC-S configuration at my cable head. Can I take the 10mm bonding from the water pipe in my kitchen which is at the side where the hut is? Or do I need to take it from the MET or consumer unit which is the opposite side of the house and would mean lifting flooring and stuff?
Kev
Nice little belch at 12:52 😆
Hiya John. My mate has torn down his wooden shed which had power supplied via swa cable but he's gone and bought a metal tool store to replace it. It isn't sitting on the ground; rather, it sits on decking.
What are your thoughts on this arrangement? He requires a socket outlet fitting for gardening purposes etc.
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 John I’m doing an old outhouse up and need electricity in it the outside is 2 metres away from electric can you use power from a wall socket to a consumer board and do it in armoured cable or do i need to get power from mains board all its doing is running a frezzer and garden lights thanks again
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.
Great video (as usual) thanks John.I came across this only recently so I think that the 18th
edition change on bonding insulated section pipes may have overtaken the
description?
I can see that, for the TNC-S case with an open circuit PEN,
the outbuilding feeder earth connection plus the 10sqmm connection to the water
pipe could carry the entire installation neutral load current. I suppose this
would only be so if the house water and gas pipe earth resistances were high
and the outbuilding water pipe earth resistance was low.
Wouldn’t it be easier to insert a piece of (insulating) hose
pipe and avoid having to connect the water pipe to the protective equipotential
bonding?I would be a bit reluctant to supplement the 6sqmm armoured cable
earth core and about 23sqmm of steel armour in parallel. However, I don’t know
if this arrangement would equal the current carrying capability of the 10sqmm
bonding conductor? If the d.c. resistance of the armour is about 6.7ohms/km and
the d.c. resistance of the 6sqmm copper is 3ohms/km with a current carrying
capacity of about 42A, could we assume the armour will have a current capacity
of about 3/6.7 x 42 = 18A? This would give a total rating of 42+18=60A - which
approximates to the 60A rating of the 10sqmm single core.
A bit shaky perhaps - A bit of hose pipe may be safer.Regards
Brilliant video
Thanks John!
Great video john any chance of explaining how to wire a second outbuilding is it ok to take feed from first outbuilding or run separate cable from house cu .
bloody brilliant John, your videos are informative and easy to understand, do you mind if i share with students? I work for a college?
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.
Related question, how to you measure the stray voltage generated when there is a bad Earth bond ?
I know of a commercial building with a stray voltage on anything earthed (sometimes). Thinking I have to report it to power company, as multiple transformers involved.
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.
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.
Magic thank you Sir
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.
Excellent video John. A question, in the case of a garage with a steel sectional door , would that be regarded as extraneous and need bonding ? Also if I have a brass water tap inside the garage fed with a plastic water pipe, how do we view that from bonding perspective?
Regarding the brass water tap, if the plastic comes out the ground and is converted to brass above ground then it should not need bonding. If the brass enters the ground at all then you should bond it.
Just a question. I'm about to connect an earth to my old TT type system, as I have no earthing. Also putting armored cable to shed 10square. Separate rod for shed as u advise. Can the two earth rods be linked at both boards? Thanks John
hi john,
After some advise please. i want to daisy chain two outbuildings from a TT house supply, would i need to fit two more earth rods and would they be linked together ? so all three are in parallel ? also how would I rcd protect them ? would it be better to not fit an RCD at the final DB and use the first outbuildings rcd ? no extraneus metal water pipes but the second outbuilding has a hot tub built on top of a metal tank . any help appreciated, chris
This is the most enlightening lecture I know of after Gautama Buddha’s some time back.
Hi. John,
Can I use a 6mm 3C SWA cable to supply garage with water pipe if the earth core is combined with the armour, TN-C-S system.
So, John. I have a (single PH) 2 cable overhead supply into to a brick building, where the meter is. I need to go from there (via rcd spur) underground 75m to my new house, which will be, yes, steel framed. About as Extraneous as it gets.. What do you feel is best? With the long run, I was going to use 25mm sq cable, but 2 core, as I feel relying on such a long (and old, unknown) earth is maybe risky?
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?
Educational and interesting
Quite good videos.
Hi john
With lots of these steel sheds that are going up now would it be better not to bond the steel frame as they sit on a concrete base and don’t bring in a potential or tt and bond steel frame? Tia
Hi JW,
If the outbuilding is less than a meter away from the main building would you still need another earth electrode (assuming the main building is TT, and the cable supplying the outbuilding is RCD protected at the main building end)? The circuit into the out building would be supplied via 3 core 2.5mm SWA (from a 16amp MCB) and be supplying a 2.5mm radial circuit of not more than a few meters in length.
I would say not
thankyou for the robust explanations of these principals
Great videos👍
Would using MICC cable be a solution to the size of the earth conductor - yes I know you need specialist tools and training to make off the ends successfully, or does this not give adequate protection for buried cables, or should then this be run on a surface instead if possible?
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?
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.
Would it be permissible to use an earth rod/matrix to reduce any resistance on the TNCS earth and bond these together due to long cable runs. Thanks for an informative and educational video.
Great videos. Really informative. Would i be able to use the 10mm2 earth cable separate for a hot tub outside? Or does that definitely need to be set up as a tt system? Im on TN-C-S
You can do that for a hot tub, although the regulations recommend that an earth mat or electrode with low resistance is installed even if TN-C-S is used, so there won't be much difference in cost or installation time. The electrode/mat would need to be connected to the TN-C-S earth via a minimum 10mm cable.
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?
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??
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.
Excellent
John this is very interesting . I hope you will see this as I am kind of late to this , it is 3 years old! . I have a question , or questions for you if that's Ok? .
I am "into" lights , especially old street lamps and have installed a few old , restored , cast iron street-lamps in gardens for people . My question is , would a metal lamp post in a garden, remote from the house, often some considerable distance , need to be treated the same way as an out-building , as if it WERE an out building ? (Albeit a very "narrow" thin one)?
In the past I have always used a relatively small cable to supply lamp posts in gardens like this , (probably a 1.5mm2 three-core SWA) . In the base of the lamp post I would normally connect a bonding conductor to the metal body of the post itself , (often by drilling a hole and fitting a brass earthing bolt). This would be connected to the earth terminal in the fuse / cutout which would be connected to the earth-core in the SWA cable and the armour wires.
However , if I should be treating a lamp post as if it were an out building, and applying what you say in this video , that would mean I would need a minimum 10 mm2 SWA cable , or to provide an earth electrode for the lamp post?
Is this correct? Have I been doing these incorrectly? How would you install a metal lamp post in a garden like this? Would what you have discussed here in the vid apply to this?
Regards . Jerry.
What about using AWA cables (hard drawn aluminium armor?)or MICC cables?
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 ?
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.
Thanks John really useful video. I am installing a feed to the garage, I have bought an earth rod and also have 4mm 3 core armoured cable supply. After watching your video I realise I have no extraneous conductive parts and the 4mm earth supply would be suffice. My question is should I still install the earth rod as I've already purchased it so there will be no additional cost or is the 4mm house earth a better option?
In most cases the earth from the house is the better option.
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’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
Hi JW. On a TN-C-S (PME) system (and a TN-S) if you are exporting the DNO's earth externally to out-buildings etc are you not required to obtain their permission, after all it's their earth and they assume it ends at the intake and rightly so? I would assume this is not good practice in any scenario to export a TN earth, whereas creating a TT system at the outbuilding I thought ticks all the boxes. Similar scenario to EV Charging Points really. Great videos by the way, love your work, keep it up.
Hi John, two questions: For a TT system would you bond the two earths (house and shed) via the armoured cable? Also - aren't you obliged to use an RCD at the house end to ensure safety in case someone sticks a spade through the buried cable?
Yes for both.
John Ward
Hi, thought you didn't need an RCD on the house side to feed the new garage board with its own RCD if its a tn system?
+Alan Allington For TN systems the armoured cable does not need an RCD, as the fault current between line and the earthed armour will be high enough to trip the circuit breaker.
An RCD is required for TT as the fault current between line and the armour will be very small.
Hi John, as i said. Seem to think you said an RCD is necessary both ends? My business is 26 years old and still learning, please keep helping this high class industry prospered.
thanks Alan
Earthing for off grid using inverters would be useful too. And how to connect to house pipes with grid earthing?
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?
Hi John,
I made an installation in a wood cabin at my uncles property.
For gas and water we used PE plastic pipes for the underground runs, and switched to copper pipe after coming inside the cabin.
Should these copper pipes be bonded to earth as extraneous conductive parts?
Or since they are 100% inside the cabin are they potentialfree?
We had an elektrician connect up 3phase run for sauna heater, he has not mentioned bonding at that time.
So this is just curiosity.
Nice video, thx
Bonding not required, as the pipes are not extraneous - they can't introduce any potential from outside.
Could I not wire a wooden shed from a house TT consumer and just rely on the RCD at the house consumer unit?
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
Have you considered using a 4 core SWA 6mm and using 2 conductors joined together as the earth conductor
Hello John, great video but I am slightly confused. In your video it says you can export the earth to an outbuilding no matter what system you have? After a lot of reading online says you should never export the earth on a TNCS system (PME) and should be rodded at the outbuilding? I have recently installed power to my metal shed and on a TNS system in the house so have exported as normal and will put a 6mm bond the metal casing. I have a job at my cousins to look at this week. I'm sure she is on TNCS so I plan to not export the earth and use a rod at the shed which is wood. Any help appreciated 👍
Depends on the risks involved, and whether someone is likely to be in contact with a part of the installation and the Earth outside.
In a wooden shed the risk is no different to being inside any other building. If there were extraneous conductive parts in the shed such as a metal water pipe it would need to be bonded in the same way as in any other building, which for a TN-C-S supply is a minimum of 10mm². The concept being that the pipe in the shed and any exposed conductive parts of the installation in the shed remain at the same potential, even if that potential is different to the Earth outside.
A metal shed is much higher risk as it's very likely that someone could be in contact with the metal parts while standing on the Earth outside, TN-C-S in that situation would not be advisable as there could be a significant potential between the shed and the Earth outside if a fault occurred.
There isn't a single rule for everything - each installation has to be considered on it's own and a decision made as to what is appropriate for that.
However people like easy answers and that's why you can find things which say never to export the earth - even though in many instances there is nothing wrong with doing that.
@@jwflame Many thanks for the reply John, I seem to be slowly getting my head around it now 👍