Transformers & Earth Connections
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- Опубликовано: 29 июн 2024
- Earth connections used with isolating transformers and building site transformers.
An isolating transformer has no connection to earth at all, although the mains earth connection is often continued through to the outlet socket.
A 110V site transformer has the centre of the output winding connected to earth, so that both output conductors are at 55V relative to earth.
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Someone who actually understands isolation. Perfectly nice.
John, These are your best videos. You take us back to basics and do a first class job of explaining (or reminding) us of the fundamentals.
Please do one on joining mains wiring, heat shrink tubing, over tightening brass screws onto copper connectors, terminal screws coming loose, fatigue fracturing of copper wire etc etc.
you are unbelievable ,,,the only specialist which explain everything in detail with no gaps and in such way shows how much you understand the electricity correctly
Great video, helping me understanding transformer windings. I saw videos of people testing voltages and couldn't understand why they weren't being fried
Brilliant I have been a maintenance spark over 35 years still check with this guys videos, john knows his stuff 😀👍
Very interesting thanks, particularly the centre tap earthing for building sites.
Excellent stuff John. I was a little puzzled last time you glanced on this subject but it's all made clear now. Cheers!
Explain speed no sllow
Fantastic video. Very well explained. Thankyou.
I learnt something from this video and I'm a power system engineer by trade. Thanks John, great video!
fantastic, really well explained. I was planning on doing some temp rise testing on an appliance which has the option of taking 110V or 240 V and I have to use the most unfavourable voltage for the test to get the highest temperature rise. I knew that as per P=VI, the lower voltage equates to higher current and thus greater resistive heating but wasn't sure whether the centre tap would have any effect. Many thanks for sharing.
Great video,thanks for sharing.
was so many concepts i had to just go with, transformers was another one
understood windings, changing volts
just never had the visualitionz what was taken palce, really solidified.
This is a good video, but for one serious point that viewers may find misleading. In the centre-tapped earth 55-0-55 volt system the two ends are NOT 'live' and 'neutral', although some 110v connectors are labelled like that for dual use in systems where neutral actually is at or near earth voltage. It would be better to be thought of as 'live' and 'minus live' to indicate it is a split single phase.
Great video as ever John. Very informative and interesting. I learn a lot from you. Do you have any plans to do videos on SPD's?
That was nice to hear that yes, L and N are essentially the same ... one just happens to go to Earth on a mains ... and when they say its safer they mean an isolated transformer .. thanks for explaining. I'm still trying to figure out if center tap can be linked to earth on my transformer/power supply DC i built for my audio.
best video ever answering the question why we do not use isolating transformer everywhere and get rid of all earth reference so no body gets a shock
You can also sometimes find cheap "medical" isolation transformer from dale/fluke and other brands on ebay. Really nice build quality and all you have to do is remove the ground with a set of wrenches/racket set. Most i find seam to be rated for both voltage 240/120v 50/60htz
I picked up a while back at a garage sale a pair of 120V/60H units that I was thinking of doing the exact same thing to, albeit with a switch to select between modes.
Very good video. Nice explanation!
Excellent video!👍
In large power transformers, the unequal voltage distribution caused by voltage surges in the winding is
prevented by the use of
A. static shields. this is correct.
RS used to do a transformer where the link to the centre tap/earth was brought out thru the resin as a loop you could cut to use it for full isolation.
excellent video thank you
the centre tap arrangement is very similar to the American domestic supply set up. apart from the fact that our friends across the pond refer to the centre tap connection as neutral and the two outer conductors as live , which is indeed what they are. maybe the 4th amendment will resolve this
except that it is one step down. 55V L+N vs.120 L+N US.
john, very helpful informations!! are lab power supplies and switch mode transformer (eg for laptop) also connected to earth ?
Not normally, although most lab supplies have a separate earth terminal (usually green) on the front so you can connect the output to earth if required.
😇Starting:While earthing, Neutral to ground, how we get two half waves? Is the second half wave is coming from N to Line?
He confused things here slightly by exampling a 110v site transformer and a 240v isolating transformer. At 8:00 he is talking about working on a site, but its a 240v secondary. If its on site it will be a 110v secondary and so you will get the FULL 110v if there is no earth point on the tranny.
3:59 I'd rather say L1 and L2. In case Earth is connected to center tap then there is no Neutral. Both sides of transformer are Live wires. In this case this is two phase transformer. It is not safe to touch Neutral. That's why it is not Neutral.
Agreed. This is the way i understand it
@@ahmadashirov6330 There is no potential different between earth and neutral. You think its L1 and L2, well throw your probes in parallel to L1 and L2 you would get Voltage difference 400V.
Also im not saying that thisis the fact. Im trying to figure these things out like you people.
please help me: doing kva on center tap, you, earth connection, and the ground distance between you & earth connection loop.
What is the voltage drop across you (what is the current)?
how many watts of power go through you?
If I'm using an isolation transformer in a test bench environment (to power a Device Under Test), I always leave the earth disconnected. A lot of equipment references its internal PSU outputs to chassis ground. If you connect the DUT's chassis to the building earth, every voltage present inside the DUT will have earth reference. Not good if you're working on high voltage equipment. Of course you have the same problem as soon as you connect a scope probe ground clip to the chassis. That's why you should always use a differential probe in these situations.
If the iso. Transformer secondary side live wire somehow gets short with the ground, then does the current flow through the ground?
my favorite solution is cabels in steel tube ! next coaxial cable inner is phase middle is neutral and outer is pe. i read about moister and rcd! i have a custumer he wants on a suptropic ;) area outdoor lightning ! the only solution was to set it to 42 volt ac but he dont like the cost of neu light bulbs! so i stop working on that! i try to pottet all junktion boxes but is was not enough!
Great videos, many thanks. I have a question please..I happen to have the same yellow isolation transformer as seen on your other video and measuring the secondary voltage reads 247v. All well and good, However, measuring the voltage between Live and earth on the secondary is measuring around 117v. Is this normal? Shouldn't it be giving a reading of near )v if there is no reference to ground? Should I be safe and remove the earth connection at the secondary outlet? Thanks
There should be no voltage between earth and the output. Either it's actually a centre tap transformer, or the voltage is capacitive coupling and isn't really there.
If you connect a filament lamp between the L secondary output and E the voltage will disappear if it's capacitive coupling, if the voltage remains (and the lamp glows) then it's a centre tap type.
Hi John thanks for reply and apologies for only replying now. I had a chance to test my transformer this evening and carried out your test. I tested my transformer with a filament lamp and the indeed the lamp did not light up and there was no voltage reading between the line and earth while the lamp was on, however measuring voltage between earth and the neutral gave me a reading of around 238v! Same result when swapping the line with neutral and taking similar readings. I take it it’s safe to leave the earth connected to the secondary socket of the isolation transformer? Thanks again.
I would leave the earth connected. Capacitive coupling will cause the transformer to float at about half the input voltage. However this effect will only allow a very tiny current to flow if you where to touch the output so the transformer should be safe to use. The voltmeter is requires only a very very tiny current to work so can measure the presence of this induced voltage. It is quite normal with transformers of this type.
1:06 - Makes sense when one touches the "Line" conductor but what would happen if one would touch the "Neutral" conductor of the primary transformer while standing on ground?
nothing I guess
Let's say I buy a drill and that drill only has live neutral in the cable does that mean if it's cut it you will only get 110v shock because they have taken out the earth? There for manufacturers have taken away your chance of 55v
Consider this scenario. 120 VAC center tapped step down transformer to 13 V (6.5 V from either line to CT). Transformer is connected to mains via a 2 prong plug so no chance secondary is referenced to earth. Measured voltage between between any secondary winding and earth ground is 135 V. Measured voltage between any secondary winding and line voltage is 50 V and measured voltage between any secondary winding and mains neutral is 14 V. How is this explained?
Voltage measured using a device with a high input impedance (which is most of them now), and capacitance between the transformer windings.
@@jwflame Thanks for your reply but can you elaborate on exactly how the input impedance of the DIMM and coil capacitance cause the voltage to read so high and what, if any, is the significance of that?
Hi John, thank you ever so much for your videos; I've watched dozens of them and understood them all, even as a layman, thanks to your clear communication and presentation. Much appreciated!
Is there any reason why a split-phase 120-0-120 system (like North America uses) wouldn't work here in the UK? Except we would connect all appliances to both live phases and effectively keep at 240V? Would this not be a bit safer in the case of a fault situation? Or is there some blindingly obvious drawback that I have failed to realise?
It would work, the main disadvantage is cost, 3 wires would be required instead of 2.
@@jwflame Thanks for the reply. To mitigate the cost implications, what would be the consequences of continuing to use a two-wire system with split phase so that we could keep our existing infrastructure, plugs and socket outlets? That is, the two phases across L and N pins of a BS1363 plug and a combined neutral/earth across the E pin. I understand plugs would now need to be double-fused but, other than that, nothing would change? I believe some older installations in North America still have this configuration (NEMA 10-30). Would there be safety implications of combined earth and neutral given that earth is combined with neutral at the cutout anyway of a TN-C-S supply?
Hmm, how about 2x 110 volt site transformers wired like: 240v primary -> 110v secondary -> 110v secondary -> 240v primary, then disconnect the earth on the 2nd transformer's 'primary' output (now being used as a secondary). So transformer ratios would be around 2:1 -> 1:2. I guess this would work?
+9ff70f96 Yes, if both centre tap connections were disconnected, and no earth was connected either. It would also be necessary to wire the the two together permanently or change the socket on one for a plug, otherwise you would end up with a lead with a plug on each end, and the output side would need to have a socket as well rather than the plug supplied with it.
+John Ward - Yeah, I was thinking it could be possible to have one site transformer as standard (so it can still be used as normal), then a second transformer with the 13A 240v domestic plug changed to a ceeform 3-pin 110v, disconnect/remove the earth in the plug/lead, then swap the flex internally onto the secondary winding, then swap the 110v output sockets for ceeform 240v 3-pin and wire them to the transformer original primary side, and disconnect any earthing again, then just make-up a ceeform 240v 3-pin plug to domestic 13A double socket or whatever is most desired (or just mount a socket on the box itself if you like). Seems like this could be a decently cheap way to make your own isolation box, particularly as the 1st box could still be used as normal.
Thanks for getting me thinking about this, JW, as it's not something I've considered doing before.
My M300 Harrison lathe has a 440V transformer that uses a single phase to transform to 110V but then connects the earth to one side of the 110V out. Its in the manual at the back. I'm re-wiring for 240V 3PH and will swap the TX for a 240-110 but suspicious about grounding one side ??
Regarding your setup for current testing, have you seen the BoomBoxDeluxe channel? He has built what he calls the Fun Jiggery Pokey Unit. It's two mains sockets in parallel, which are then in turn connected in series with another socket. This can be used to connect a load, in his case usually a water heater, for current limiting in series with the DUD (device under destruction) in case the device fails with a dead short.
The two sockets in parallel also means he can do more advanced things like connecting a transformer that has a sharp inrush current without blowing a fuse. He does this by connecting the water heater on one of the parallel sockets, a pass-through plug (naughty!) on the other parallel socket and the transformer on the series socket. He can then turn on the heater followed by the transformer to provide a limited inrush current. He can then switch to the pass-through plug to use the transformer.
Gurdeep
1:56 Hi John, you made there a little mistake by calling the output leads of this transformer Line and Neutral.
The output of this transformer doesn't have a neutral from nature, because neutral is almost 0 volt, and you can't tranfer 0 volt through a transformer by magnetisme or inductance.
In fact, the outputs of the transformer are both Line, (Line 1 and Line 2), to get a neutral on the output of this transformer, you must bound 1 of the 2 Line's to ground.
2:24 If the metal core of the transformer is grounded, then there is a socalled Ghost / Phantom voltage between ground and each of the 2 Line's.
But from the moment you bound one of the outputs to ground (to create a neutral), the Ghost / phantom voltage becomes almost zero between the core and the just created neutral, but the Ghost / Phantom voltage becomes mains voltage between the core and the remaining Line from the output.
Also to mention, that if you use a isolation transformer, and keep both outputs isolated from ground (so without creating a neutral), that a RCD device won't work against electrocution. A normal RCD needs a neutral to work.
There are devices to detect leakage and to protect against electrocution like a RCD does when using a isolation transformer,
but they called "Isolation Monitor Relay", but are expensive compared to a normal RCD.
Regarding the site Transformer on the Secondary side where the tap is centre making 55V between the 2 outer winding does this not make these winding both Live rather than one being Neutral? because otherwise the Neutral now in the Secondary winding is 55V above Earth, also could this centre tap not become a new Neutral? The reason I ask is I am looking to build a Rotary Phase Converter and am looking to use an old Arc Welder as a set-up Transformer 240V to 415V but then I want to add a centre tap to the secondary winding to split the 415V and then have 2 Lives to attach to L1 & L2 on a 3 Phase Idle motor, I am looking to spin the Idle motor up to speed with a single phase Pony motor before adding power to L1 & L2 once the Idle motor is powered it should generate the ghost leg L3 (but this may need balancing with the use of Run Capacitors) then the 3 Phase machines I want to run will be connected to the Idle motor.
How many volts will be enought to go through your shoes in order to connect to the ground?
Depends on the shoes. Some non-electrician work boots are designed to electrically ground your feet to deal with some other danger, but that is obviously wrong for electrical work. So read carefully when buying OSHA certified footwear to make sure you get the right kind of "electrical safety" for the job and not the complete opposite.
Hello, I read that measuring with an oscilloscope, you need an amplifier, you need galvanic separation, I ask from what point of view, when today's amplifiers have only 2 wires. Thank you for any knowledge
John, if I want my work bench to be isolated from mains power AND also protect my test equipment (=scopes), do I then have to use two isolation transformers?
@Karel van Cooten : Study your setup and learn your current pathways.
Where I worked we were not allowed to use two transformers. There can be a phase difference depending on how they are wired up internal. If one of the transformers gets earthed you can have TWICE mains voltage on the equipment.
Sorry, but around 2:20, I cannot understand why no electric shock results if the L or N wires in the isolation transformer secondary are touched.
Isn't a shock the result of the difference in voltage causing current flow through the body to earth, irrespective of whether it's on the primary or the secondary side ?
The secondary isn't connected to Earth, so there is no path for current if someone touches one of the wires.
@@jwflame Thanks John. I now understand this principle. In other words, "current in a circuit always returns to its' source", and this is not possible if the secondary is not connected to earth.
Hello John
Nice video but some questions
One. Why dont they float they mains anyway, why earth one side to give a neutral anyway??
Regarding the building site transformers you said you get 55v to earth because of the centre tap, this means the secondary winding would only give you 110v anyway. Ie you have a step down transformer with roughly 2: 1 turns ratio.
You then went on to explain that the centre tap is to reduce the shock to ground if one had a fault.
Somehow though you mentioned it was 240 across the coil, surely it is still only the same 110 volts.
Forgive me if I have missed something along the way
Isolated or floating supplies would only be safe if they stayed that way - any fault anywhere to earth will make it into an earth referenced system but with no control over which side is connected to earth.
Site transformers are 110V output, for use with 110V tools.
@@jwflame Thanks John
Also liked you explaination as you drew on paper.
Ur ht supply lines alsoslso act as transformers that's the reason u can connect any no of them w the other side Nd ground on the other side doing the same.... As long as u have ht w resonance u can do same
Interesting, in Finland isolation transformers have no earth at all. One of the uses for them is to connect unearthed (class 0) equipment and those cannot be plugged on a schuko socket.
Mr. Ward, it seems like a lot of people have been questioning the terms “line” (or “live” you might have said) and “neutral” for the ends of the secondary winding. What is the distinction between these two ends and why are they given those names? Much appreciated, and thanks.
In ac which end is neutral.the current generated in power station from generator let have 2 ends (2wires comes out of generator) now both are load or one load one neutral.
As generated and distributed, neither are neutral. One conductor becomes neutral when connected to earth at the final transformer which supplies the end user.
John Ward .thank you brother for your reply.it really help.
The explanation of the Line and Neutral does not make sense to me. The neutral is connected to the center tap and is tied to ground. From my understanding, the start and finish leads should both be line leads.
Why do isolation transforms provide an unreferenced ground output at all ? seem more of a hazard than anything. A DTU likely has a grounded metal case and if I connect my oscilloscope ground lead to that case AND probe the circuit the DTU is no longer isolated? Best I can figure is that it allows you test the transformer itself for isolation.
If you have a transformer with inputs of L & N @240 V with N being bonded to Earth .... and you connect these lines to a transformer which has L1, L2 and a center tap neutral Such that you can now have 120/240 volt split phase on the secondary side ..... Should that secondary side neutral be connected to earth?
Great movie and great channel however i have a question i havn't found the answer yet... why in AC circuit with ground connection, current doesn't flow (escape) by this ground wire but flows in closed "device-transformer" circuit. Thank for all helpfull and "nonhate" replies
I have a question. I recently installed a solar array and i grounded the inverter with a piece of iron rod and used a rccb switch and a fuse on the mains side. My question is is the rccb switch going to work? Voltage on the mains side is 110v live to ground and 110v neutral to ground (220v total) i tryed to trugger the rccb using a 100w lightbulb from phase to ground but nothing happened. Same with the neutral to ground. I didnt directly connect live to ground with a cable because im afraid it might damage the inverter... Please help me
The inverter is seperate from mains input. It os used in a remote wooden cabin with no electricity
Unless that center grounded secondary is stepped down with winding ratio, the output will be 220v across the L and N terminal and will be 110V across either the E/L or the E/N, the way I see it. What am I missing here??
Site transformers have a 110V secondary and 240V primary.
Respect
Even if there is no ground you will receive a shock if you touch the hot conductor.
if you plug an isolation transformer into a piece of equipment that has a step down transformer or smps and that piece of equipment connects the neutral to ground in anyway, you would be connecting the earth point of your isolation transformer back into the neutral of the the line and removing any isolation. I don't believe this how an isolation transformer is setup. The ones I have here are open earth, not connected to anything except the chassis. One of my isolation xfer only has two wire input, Todd systems L1-1000 3lrg. cheers
John,
slightly off topic..
240v inverter found in vans or camper vans; should they be earthed to the ground?
most people seem to it earth the inverter to the chassis of the van. would that not cause an issue?
I'd be interested to hear your thoughts.
regards
J
Enjoying your videos! I am not an electrician so have limited knowledge of these things. Please can you explain something. Why are mains transformers and distributors earthed if it makes a circuit through a human body possible? What us the point of the earth? Sorry if this is a stupid question!
+doughnuts67
See this video:-
ruclips.net/video/Wx_v1-T1gE4/видео.html
Because it is hard to prevent a system becoming earthed so it is better to make an earth in a controlled way. There are other problems with a floating output particularly on a large transformer. Firstly there is capacitive coupling between the primary and secondary which can induce high voltages onto an unearthed secondary and there is the problem of a short putting primary voltage directly onto the secondary. So in the case of an 11kv to 240volt transformer 11kv appearing on the output. With an earthed secondary this is likely to cause a fault current and disconnect the transformer. With a non earthed transformer 11kv gets delivered to someone’s house where it would flash over in a high power electric arc and general unpleasantness would follow.
Does the same principal apply with a toroidal transformer. The 2 wires are your L/N and the secondary winding if it has a centre tap becomes an E connection?
Can do - what matters is how the wires are connected, not how the transformer is constructed.
@@jwflame thanks.:)
Thank you Mr. Ward.
For one of my projects, I have to maintain the Neutral on the secondary side of the isolation transformer (Load: 24VAC, 10A) at zero potential. So, I tied it to the Earth (and then to the building ground-bar) but haven't tested it yet. Is this setup safe to proceed, for permanent usage? Thanks.
Hi did you get a solution this
How can I use center tab ground 55-0-55 vac , with 110 & N instead of just 110 vac & ground . My instrument need 110 vac & 1 neutral. Please advise thank
110V items are connected between the two 55V outputs, (2x55 = 110).
if we connect secondary star neutral to body earthing instead of dedicated eathing ..... is there any issue
Where are the L-E=55V transformer uses? and whats the benefit than L-E=110/220V
Construction sites, the benefit is that any shock between a conductor and the ground will only be 55V. You would still get 110V between the conductors, but someone being in contact with both at the same time is unlikely. Damaged cables and tools getting wet etc. is very likely on construction sites.
What happend with the transformer if the two neutral are connected(primary and secondary) ? there are variation on their voltaje or current?
+Mauricio Ríos With the isolation transformer, output would be the same but not isolated, so no point in doing that at all.
With the site version you would be shorting half of the winding which will cause the transformer to overheat and be destroyed.
What is the hazard if I connect output of transformer to neutral wire?
Question please: Are the two neutrals on the primary and secondary coil connected together?
No, entirely separate.
Why is there usable voltage coming through the so called neutral in my breaker box?
Depends what and where you are measuring. In normal operation the voltage between neutral and ground should be zero, but it can be a few volts if the circuits are heavily loaded.
If the neutral is disconnected, a large voltage will appear, but then it's not really a neutral any more, it's the end of an open circuit.
Hi John, so here in the UK why don't we have isolating transformers in our domestic properties and if a "dangerous" earth fault appears (which can test for) something trips?
Far too expensive to have isolating transformers everywhere, and the monitoring devices which are used with them are more complex than normal RCDs/MCBs. Such things are used, but only in specialised applications such as hospital operating theatres.
Why NO current flow in the E ?
Would you give advice on 72v dc Lithium battery charger I bought from America. The transformer has overheated and the company I bought it from has washed their hands of it and refunded me. I'm trying to find out what went wrong so I can get the appropriate transformer. I live in the UK and am not having much luck.
Why do the transformers not need to have an RCD inside them to stop you connecting between L-E at 55V?
+Simon Howroyd Site transformers can be obtained with RCD protection (generally the much larger ones) but there is usually no point, as 55V is considered to be low enough as to not cause injury.
Another issue with RCDs on a construction site would be unwanted tripping due to moisture ingress.
+John Ward makes perfect sense explained like that. thank you. keep up the good work, excellent videos
+John Ward
I was wondering the related question:-
With transformers with output referenced to mains-earth, in combination without RCDs on the output --
When is the risk of high currents in incoming-EARTH wiring under fault conditions, considered a problem? Imagine one of the 55v output legs being shorted onto the earth-wiring of an "installed" (but isolated) light-circuit 1.0mm cabling elsewhere, returning via earth-lead back into the 55v transformer....
Especially consider transformers with rather high current output capacities (which presumably doesn't include those typical 110v yellow cubes). I'm guessing larger earth-referenced transformers "must"? "should"? have RCD protection (even 100mA S-type) for this reason???
W/ thanks!
+sbusweb The larger transformers have MCBs for each output, so a short to earth should trip the MCB.
Smaller ones do not, as they are intended for use with a single tool, so the risk of a direct short is minimal, and the output current is limited to a modest value as the input is typically fused via a 13A plug.
John Ward a
The building site ones are great until you realise it gives out 2 phases not L and N and your test equipment has a Earth and Neutral on the same connections and goes BANG 🤣
Sorry for stupid question but how does centre tapping earth on secondary change voltage to 55v either side please?
Please tell me why a $15 RCD (residual current device) isn't better than an I/T. The latter saves the scope but not my life, the first saves both. I will be grateful for any comments.
I only read about transformer in school, but practically did not deal with it. May I know the L and N on the left side in 2:05, wouldnt it be effectively shorting L and N together since the copper coil suppose to be near 0 resistance right? Wouldnt it cause a trip in the MCB ?
DC resistance is very low, but with AC the impedance is much higher, as the coil is an inductor.
The building site transformer is 110v, Does it mean powertools used in UK to build houses work 110V AC? It may be a stupid question sorry i'm not from UK, we have 230v in Spain but i have never seen 110v AC tools except for american countries.
Hi John, i work in the HVAC controls industry, we earth the secondary side of the step down transformers negative. its a 240 to 24 volt transformer and we are instructed to earth the negative of the 24 volt side. this transformer powers our PLCs but im trying to figure out why we have to do this, any help would be appreciated thanks.
I'm not trained or certified but I do DIY with tube amps, with multiple supplies the earth can be used as a 0V reference to allow all the power supplies to be relative to 0V and not floating. For example a floating power supply would just provide it's voltage between the two pins but you couldn't say if that's 1000V of -1000V relative to another supply. Tube amp circlotrons use two opposing floating supplies but the two supplies are tentatively balanced at an offset from ground. Hence they 'wobble' and rebalance but are still referenced to ground. Complex and not something you want unless it's in the design!
A hard ground referenced supply means you can state the parameters relative to ground, so if you have stages with different power supplies, you can state the voltages between the stages relative to a common ground - this includes the isolation voltages between stages (isolation transformers, interstage transformers onto-isolators for example). With a fully floating supply you can't rely on this. (this is ignoring potential differences between ground/PE between sites)
OK there's one thing I don't understand here - if the mains Line voltage is 240v in relation to earth (neutral is connected to earth, so it would be, right?), when the output-side earth from an isolating transformer is connected to earth wouldn't there also be a 240v potential (at least roughly) between the output Line and the earth? In this video John says there's no potential between either wire coming out of the transformer relative to the mains earth, but in my interpretation of what's happening there would be 240v between L and E, and only zero between N and E. Where am I going wrong?
The output of an isolation transformer is not connected to earth - that's the whole point. If the output is connected to earth, then it's not isolated.
Is this kind of worksite wiring a British specialty? Because here in Denmark I see full 230V everywhere, but I don't have access to the big restricted worksites.
It's also used in Ireland and perhaps a few other places, but it's mainly a UK thing.
2x modified 110V building site transformers back to back would bring you back to 240V. A little large though.
Dear Sir, in a Step up transformer, is it right to link earth to the body to get '0'
at 1:29 you state that one would not get shocked by touching either lead from the secondary, while standing on the ground. WHY NOT??
Hi there John, I wanted to ask about another way of earthing the secondary side.
Similar to a substation transformer, could you link one output wire (Let's deem this as the neutral) to the output earth connection? So you have 3 wires - Line, Neutral and Earth - all completely isolated from the mains. The input earth would just be connected into a terminal block in the transformer (Or just to the casing if required)
All this essentially creating a transformer like a substation one but without it being also connected to physical earth with a rod. Would this work safely?
In theory yes - however there is then a risk that if the metal casing of the device connected to the transformer was inadvertently connected to another earth connection (such as just being placed against some other earthed equipment), all benefits of the isolation transformer would be lost.
@@jwflame Ah, thank you.
what about electronic components
Why are centre tap transformers not used for the distribution of electricity? If they were, would it not mean you would only receive a 115v shock rather than 230v under live to earth fault conditions?
They are in some countries, such as the USA.
However in most situations it's better to spend the money on preventing exposure to live parts rather than on centre tap transformers and additional wiring.
Besides preventing exposure with no center tapped to earth ( floating ) the center-tapped winding will have better cmrr...
I am working on 230VAC to 24VAC transformer.
The voltage between 24VAC terminal and 0V terminal at secondary side is fine.
But the voltage between 24vac terminal and any other external ground is around 230 volt.
Why is it so? Do I need to earth the secondary side of transformer?
Million dollar question;
Hello, were you ever able to find a solution to this?
Everyone says you cannot use a dimmer switch to make a variac. Is there some kind of switch I can get to do that.I don't have a lot of money and I would like to build one. This here looks kinda like the same thing if you add a switch to control the incoming volts.I am in the u.s. and would like 0 to 110 volts. Thanks for any help.
A variac adjusts the voltage directly, a dimmer cuts the AC waveform into short spikes with gaps between so the average voltage is less. Dimmers will work with basic loads like heaters and incandescent lamps, but other items will not and could actually be damaged.
+John Ward please make a video about this subject (dimmers - to use it or not )
Thanks a lot
So are you saying the output side of the transformer should not be earthed?
Hi John. I bought an used isolation transformer. I am getting a slight higher voltage than the input voltage. The input is 124v and the output is 135v. The hot to ground measures 80v and the neutral to ground measures 50v. What is wrong with this transformer? Thanks
Output voltage will be higher with no load - connect a moderate load to it and the voltage should decrease.
Would it be better to refer to the outputs an L1 and L2?
That is how it would be done in the US. Both sides of our 240V are Line 1 and Line 2. If you measure either side to Earth or Neutral, you find 120V. Center tap at the transformer on the pole splits the voltage. So Line 1 to Neutral/Earth/Ground = 120V, Line 2 to Neutral/Earth/Ground = 120V, Line 1 to Line 2 =240V. It seems in Europe, that the transformer is actually a 480 transformer that is split like our 240V services are. If it is not and the pole transformer is strictly Line 1 and Line 2 with no center tap, what he calls Neutral is not. It is a hot Line lead. On the output of his transformer, he has Line 1, Line 2, And the center tapped Neutral/Earth/Ground. Not a Line, a Neutral, and an Earth. It is a 55V/110V output. The Neutral and the Ground here in the US make the connection at the first service disconnect in most cases. In the 120V inverters, the so called Neutral is indeed hot as it would be with an unbalanced load at the pole transformer. Or in a single branch circuit. That is why GFCI receptacles are so important in wet/damp locations.
+cumberland1234
I think so too. In fact, "N" on an output would be WRONG according to wiring regs definitions -- because that is by definition a Grounded current-carrying (live) conductor.
+gravelydon Hi I am in the UK. The street supply comes from our local substation transformer which are typically in a building or outdoors in fenced off enclosures. Theses are large transformers. We only have pole transformers in rural situations. The supply is a 3 phase 230volt / 400volt supply L1,L2,L3 and N (earthed at transformer) delivered under the street. Each house gets one of the phases (230 volts ref to ground) and the neutral. Larger customers get the full 3 phases and very large customers may get the 11kv or 33kv feeder and have there own substation. We don't have a split phase systems like the USA with its L1 L2 N and P connections. Various earthing arrangements exist. John Ward does a good video on the usual UK ones.
John how are main power supplies grounded on ship board?Bob
John , or anyone knowledgeable, can I ask a related question which is troubling me , I have a step down mains to 24 V AC isolation transformer and on the secondary it has the normal floating outputs. What I can't understand is that when I check the voltage between the output of the secondary and mains ground It shows a potential of about 10V on the multimeter ie from one phase to ground. This suggests that the outputs are still earth referenced , is that correct even although there is not galvanic coupling? But how can I have a potential difference to the mains earth reference from the primary, is this due to capacitive coupling via the transformer ? is that the answer that allows the secondary to still be referenced to ground or is it through the magnetic core. I thought isolation would mean the ground could not be referenced to the secondary outputs?. Appreciate an explanation of this. I hope my question makes sense. I thought there would be no relation from either of the separate outputs to earth. Perhaps its wired differently internally , its a sealed unit, possible centre tapped on secondary to ground , that may possibly explain it as you show on this video...... Many thanks
Capacitive coupling through the transformer windings. Connect a 100K resistor between the multimeter probes and measure again - the voltage will disappear.
Excellent John, thanks for the quick reply , that makes sense now. Best Regards
How are airplane electrical systems set up without earth grounds? Thanks.
i thought it was 120/240v? is this just britain specific ? i live in Canada
Britain has 240V only, there is no 120V supply and nothing to connect to 120V either - all appliances, lighting and everything else is 240V.
These 55-0-55 transformers are used on construction sites only, where power tools are made as 110V specifically for use with these transformers.
I bought a 220v to 60v toroidal transformer when I hook the wires to 240 it just pops my breaker? It has 2 red and 2 yellow. Am I hooking it up wrong?
Toroidal transformers have a very large inrush current, which will trip many circuit breakers. You will need to use a larger rating of circuit breaker or a type which can handle large starting currents without tripping - however it will still need to be suitable for the circuit wiring and available fault current.
John Ward I found I had it hooked up backwards, Chinese told me wrong. But it still trips the breaker sometimes. Your exactly right. So I have fused it after the breaker and will use a slightly larger breaker! Thank you sir for your knowledge
Could you please make video with subtitles
Assuming that the building site transformer has a plastic case, I'm assuming that disconnecting the earth connection to the transformer would achieve the result of creating a 110v isolated transformer but may not be the best idea. :). I guess an internal fault in the transformer could cause the earth pin on the output to become live.
I believe they have earth connections to the transformer for safety too, you would end up with an isolation transformer but if one side of the output became grounded (under single fault condition) the other side will be at 110v WRT earth.
+cumberland1234 so if you disconnect the earth from the mains input, it would be isolated unless one side of the primary became shorted to earth internal to the transformer I think. I have absolutely no plans to try this as I realise it's a stupid idea but I'm just playing with theories. :)
Apab