...and a wonderfully dry sense of humour to match.

I remember many years ago when I was carrying out PAT testing at an aircraft factory near Gloucester. I found an oscilloscope that had no earth continuity because someone had foolishly disconnected the earth conductor in the mains plug. They were not happy when I reconnected it. I had no alternative other than to submit a formal report to the firm's safety officer.

You mean this type of isolation transformer ? kzfaq.info/get/bejne/a7maidBe16yXaXU.html

+istoreit Yes it would. The RCD might trip, depending on how much current passed via the test lead.

Neutral (blue or black ) is connected to 'the earth' and transformer windings, Earth (green or green and yellow) is only connected to the 'earth' but NOT the transformer so protects you by providing a preferential 'path to earth'.

kzfaq.info/get/bejne/jqijhJakv5qZdp8.html

+IrishHitman79 Yes, double pole MCB should be used on the output. Larger transformers with multiple outlets such as those used on building sites usually have DP MCBs fitted as standard.

An RCD there would only work if the output was referenced to Earth - which would make the isolating transformer pointless.

John , figured it out I think. The fault passes through the man, through the ground to the Neutral of the primary winding, to the Live of the primary winding but the loop is broken here - no physical link between the primary Live winding and the secondary Live winding - so no complete circuit. This may help others if I'm correct.

+Simon Howroyd Yes it is redundant and some standards specifically require that the earth on isolation transformer outputs must not be connected. Depending on the situation the earth after an isolation transformer can increase or decrease safety in case of a fault, so this is a contentious point.

Yes, in Finland Isolating transformers do not provide any earth connection as one use is to use an unearthed device in an earthed room. www.trafox.fi/wp-content/uploads/2015/12/KLT2000_230.jpg

+TornTech This has been asked before by "sbusweb" amongst others, hope John Ward will answer that original question eventually =)

@Darren Tipple In Finland isolating transformers actually have an unearthed socket on the output. The only legal way to use an unearthed class 0 equipment in a room with earthed sockets is actually an isolating transformer. www.trafox.fi/wp-content/uploads/2015/12/KLT2000_230.jpg If course most people just take a knife and cut the plug to fit a schuko socket. Nothing is more comfortable than using a computer resting your feet on the grounded case and operating an old hot chassis radio with your left hand.

Connecting multiple items will compromise safety, as it's far more likely to have multiple faults when multiple items are connected. One item with a fault to the case = no danger as you can only touch one of the connections. Two items both with faults = 50% chance of 240V on exposed parts between the two items. Three or more just makes it even more likely.

A little late, but yes it should, there should be no connection to mains Earth at the output socket.

+sbusweb +John Ward (bump!) -- Please answer above comment John - lots of people seem to be asking similar/related questions in this videos' comments ... NB: I also notice some confusion happening between isolation transformers and CTE 110v transformers, too, have to be careful to segregate the concepts...

+sbusweb New video covers the earth connections on both types of transformer: kzfaq.info/get/bejne/nLiYosmUst-lqZ8.html

The output is still isolated regardless of whether the earth is connected or not. For many things it doesn't matter if the earth is connected, but it may be relevant in some situations, all depends on the equipment connected to it. Could be useful to have earth connected for some types of electronics to cover ESD issues, and older items such as radios or televisions may need the earth reference to operate correctly. However caution is required as connecting an item that contained a fault to earth would then result in the isolated output being referenced to earth, defeating the isolated aspect of it.

@@jwflame Thanks very much for the detailed response. I think I will leave the earth connected for now. Somebody on WhatsApp scares me a bit by saying that mains filters on the item under test could be an issue if I disconnected the earth. Thanks again for helping. All the best.

some houses still have an earth rod where for various reasons the network operator cannot supply an earth. but in most cases now new supplies have the house earth tapped off the neutral in the service head, since the neutral itself is earthed at the substation. there are several situations where this is undesirable for example petrol stations, where outdoor machinery and metal pipework is used, animal barns, garden sheds. this is because there can be a difference between the ground potential on the neutral wire and the local ground potential, so it is inadvisable to use an exported earth outdoors. in these cases a local earth rod should be installed and tested and the network earth abandoned for the outdoor installation.

+Steve Craft Where you from steve ? Here in Belgium it's either a rod into the ground in renovation work. And in new buildings we have a earth loop around the house few meters deep.

+Brian Boterman Sorry i should have made it clear, I'm from the uk.

+Brian Boterman Is that TN-C-S with auxiliary earth or TT system?

Sounds like TT to me.

Theoretically yes, however in reality this would require modifications to one of the transformers, as if using it in reverse the output would be the exposed plug pins and the input a socket. There may also be other problems if the two transformers are not exactly matched, output voltage may not be what you expect and there could be further issues with inrush current.

Get a 3kVA or 3.3kVA one, they are the most common and usually cheaper. In theory a 2kVA one would do but in reality it won't because that assumes 2000W = 2000VA, plus the smaller transformers are usually advertised with the intermittent rating rather than the continuous one.

🤯💥

Ebay. They don't show up very often, so it's just a matter of looking until you find one. They are often described incorrectly, as many people either don't know what they are, or think they are the building site 240-110 types. Here is one which ended for £10 in Feb 2018 - www.ebay.co.uk/itm/222827715513 - wrongly described as 240-110, but is actually 240-240. Others from Jan 2018: www.ebay.co.uk/itm/292377020720 - more money at £39 but seller had several of them and they were high power 3kW versions as well. Also worth checking local places such as real auction houses, where all kinds of things can be had for very little, particularly if you are willing to buy a large lot of assorted stuff.

Here's another one which only ended a few days ago - www.ebay.co.uk/itm//162954628060 £50, but it's a massive one and seller was willing to deliver for a reasonable amount extra. Only 1 bid.

You can, provided the maximum rating of the transformers is not exceeded.

***** I will have 3.3 amps 160VA/48V. I will buy a 4 amp auto transformer and fuse both sides, in and out at 3 amps. Thank you.

It's 3.3A only at 48V. On the 240V output, the maximum current is only 0.6A

The reason for that is somewhat complicated but I will try to explain my take on it. In the case of GFCI outlets (other countries call them other names) all of the power goes from the live and into the neutral, and in theory, the current measured through each terminal should be the same. However, if current leaks from live to ground, such as a faulty motor winding or a wet piece of equipment, the RCD will notice that more current is going through the live terminal than the neutral (because live is leaking to earth) and disconnect that piece of equipment. The earth helps to make damn sure that someone didn't mix the live and neutral around, because if there was just live and neutral and the chassis was connected to neutral instead of earth, if someone jams the plug in backwards or the electrician had too many drinks, all of the sudden the appliance becomes live. Here in america, we had non polarized sockets where you can mix the live and neutral around without any difficulty, these were mainly used for older lamps and stuff. I know this is not a great explanation, but I hope it helps :D

Thank you that helps.

+Colin Herbert A single connection for earth and neutral used to be common in many places, the building where I work is still wired that way. You need to provide local GFI/RCD protection as needed like Luke described. As you say it is now only common on a distribution level, and split up where the power enters the house. This way you can still have a lower earth resistance and better lightning protection without the associated danger of unreliable connections in your house wiring.

+Colin Herbert Here in Belgium we still run 3phase 230VAC (3X230VAC) in some places and so that means that there is no neutral whatsoever. These are the older lines, and are replaced on street level with 3x400+N, with each domestic house tapping into one phase randomly or controlled, to spread the load. But in the case of 3x230 you obviously need a separate earth tap. Also in some cases the power companies fuckup hard and your voltage will be higher between phase and PE than phase and N. This means that your own earth will protect you more than the N. It all stacks up. And i do have a question for some people here. In Belgium we require the PE tap to be below 30ohms for domestic purpose. What is value in some other places ?

In the UK there is a supply system called TN-CS which in essence only has the two wires entering the premises, the line and the combined earth/neutral. The reason we then separate the earth and neutral, apart from RCD issues, is reliability. If you have a combined earth and neutral in your final circuits and the combined e+n became detached then you can end up with full mains voltage on the exposed metalwork on anything downstream. It is an illegal practice in the UK for a consumer to combine the earth and neutral in the same conductor. For a similar reason, the TN-CS earthing system is banned in caravan sites and marinas as the risk is of an open circuit neutral and earth from the supply is considered too great.

They can be purchased new, or used cheaper ones can be obtained from the usual suspects on ebay, local Facebook groups, auctions and similar.

In Finland a transformer can serve hundreds of houses. I think it is same in the UK and other 400 volt countries.

Everything in the UK and Europe is 240, there is no center tap, and no appliances or anything else that uses 120V. All appliances are designed for 240V, including lighting. Two wires from the transformer with 240V between them, one of those is grounded and becomes the neutral.

Yes all our lighting and power sockets is 240. All our appliances are designed for 240.

That is normal - the core is earthed so that if a fault occurs between the winding and the core, it will trip the circuit breaker or fuse. The 180 volts is due to capacitance between the core and the windings. If you connect the 60W lamp and then measure the voltage, it will be zero. Only appears with a high impedance connection such as a multimeter. The outlet is usually earthed as well, although it's not referenced to the isolated output.

No, it's only the UK which is obsessed with having transformers and useless shaver outlets in bathrooms. Everyone else has normal outlets. Bathroom may have been on a different circuit, or the voltage changed between measuring the various outlets - 2V is insignificant.

No, it is just a normal earthed socket. The different voltage could be for example that it gets a different phase. In several European counties the standard used to be that on wet rooms sockets were earthed and on dry rooms unearthed. On modern installations everything is earthed. This also means that you cannot plug in an unearthed lamp that you inherited from your grand mother. AN isolating transformer is the only way to connect it legally and safely unless you have an electrician earth it. My bathroom socket says: "Only for a washing machine". Probably so that nobody puts a radio or something like that on it.

@@okaro6595 "This also means that you cannot plug in an unearthed lamp that you inherited from your grand mother. " Nonsense, even today new lamps aren't earthed. That's a classic example of a double insulated device, of which there are millions of sold every year.

@@kyle8952 Unearthed (class 0) and double insulated (class II) are different things. An unearthed device has no extra layer of protection. The safety is based on the idea that there is no ground potential nearby. In Finland unearthed lamps were sold still in the 90s (which is idiotic, they should have been banned a long ago). I think they were only banned in 1997 when grounding in all rooms became mandatory. They still are a problem when people move to new homes. Many have incentive to cut the plug or even change it. That is strictly prohibited. 3.bp.blogspot.com/-5r8ISaXrPTY/WhFmIIM3WTI/AAAAAAAANp8/kbOs6HlQoDAsIV6OkyKwQsMHAzfeakJ2gCLcBGAs/s1600/pistotulpat.JPG In the 70s we had tile floor on the TV corner. That mandated a grounded socket. TVs at the time were class 0 (they became double insulated in the late 70s). That is the plug did not fit. One of my parents solved this by making an extension cord that had a grounded pug and an ungrounded socket (strictly illegal, in fact any wiring as banned at the time). Many others did the same. When the cord became unnecessary they removed it and later reused it as a normal extension cord without realizing how dangerous it was. Such cords have caused fatalities. The general attitude was that grounding was a hindrance.

+RICHARD SALE In some circumstances yes - all depends on the particular generator.