Isolation Transformer

Hello TVP45

I am unsure about the UK requirements for isolating transformers.

Here in NZ the secondary of the isolation transformer is TOTALLY isolated, there is no "Secondary Earth" whatsoever.

I'm sure it is the same in Australia, so maybe the UK is the same.

If the Isolating transformer has two secondary outlets, there may be a "bonding wire" run between the otherwise isolated "earth connections" of the outlet sockets.

Because of weight and size, Isolating transformers are now not generally used in homes or workshops, as the Earth Leakage Circuit Breaker = ELCB works extremely fast, preventing perceptible electric shock.

That's my thoughts, from New Zealand.

Kind Regards....

you could set it on a insulating board and it wouldn't be grounded I belive Great Briton is 220/380 volts and AU is 240/415 volts and it works the same as the USA, power only slower

If we consider Isolation transformer used to restrict upstream higher fault current to a lower value(e.g what we use 1:1 Lighting Dist board) the secondary side neutral must be earthed, so that ELCB can operate perfectly.

This can't be answered without knowing the application and the applicable regs. For example in the UK an SELV supply must not be earthed whereas the 110V supplies used on building sites must earth the centre tap to create a 55-0-55V supply (although the centre tap does not carry load current).

There are ways to implement earth fault detection without a hard earth to the system.

By corebalance CT.

I commonly run my Oscilloscope on an isolation transformer so nothing will happen if I inadvertently (or intentionally) connect the ground lead of the 'scope to a hot lead. Same for running unknown devices on my test bench, just in case.

No need to cut anything for this application: just tape or otherwise protect the end of the output ground lead and don't connect it to anything.

Yeah, that's what I've been doing for decades, but I don't know if it's exactly legit. You gotta remember to unhook the scope case from ground also (if it's metal) or you can get zapped pretty good.

Anyway, some time back, I worked at a place where the isolation transformers has 3 links: primary ground, shield ground, and secondary ground - and that worked great.

But, it sounds like you can get away with the same kind of thing in the UK. Thanks for all the good answers. My curiosity is satisfied.

You're right, of course. I usually work on a wooden bench with rubber-soled shoes. My 'scope that is on a cart has rubber wheels, but it would be necessary to avoid touching the cart to anything grounded while the 'scope ground is connected to anything that is not!

The main purpose of Ground is safety. Most loads (not all but most) are deigned to work with a differential voltage between two points and it does not matter if it is L-L or L-N. The ground is for safety; power conditioning equipment also uses the neutral to ground bond to reduce noise and line transients.