ECN Forum Forums Code Related Discussion NEC & other Code issues isolating transformer

An isolation transformer has no electrical connection between the primary and secondary windings. A transformer that is electrically connected from primary to secondary is called an auto transformer.
There is such a thing as an isolated system where there is no ground on the secondary and that type of circuit is often used for specialized medical equipment.
In power distribution the secondary of an isolation transformer must be grounded. Even a delta-delta connection needs a ground to the non-current carrying components and ground detection lights.

Really?



If these outlets where intended for 'convenience' it sounds like both a violation and premise wiring.

Just because IBM was huge and did this does not make it right.

I took this thread to be about a audio system in a home, in that case the outlets must be supplied from a grounded system.

It was in no way connected to the building. How is it premise wiring? This is on the load side of the power plug of a U/L listed appliance. I got that same answer when I asked about other things they did that wouldn't meet NEC muster. It is like the 14ga wires inside a 50a range.
I bet on these studio setups they do the same thing. There is a power plug that feeds a U/L listed "appliance" and that feeds the amps and such.
I agree it would be easier to accept if it wasn't a 5-15 socket.
I suppose IBM would also say this was under the covers and unqualified people were not supposed to be using it.
I also do not see the hazard of not being grounded. This isolation transformer idea is also a very common thing on lab bench power supplies. They say it is safer, The first ground fault is free.

In the old days (30 yrs ago) totally isolated receptacles were used in many areas (particularly in lab benchs and computer rooms). These types of installations are no longer acceptable unless they are more than 150V to ground.

Recording studios offen have balanced supplies. A transformer with a 120 or 240 v primary will have a 120v secondary with a center tap grounded. There is 60v to ground. This is code permitted (have to get my code book to get the chapter) The balanced output reduces noise and hum in equipment. Robert

well i've solved(with some online research...thanks iwire) the isolating part(i think)
i relize now that since the studio is wood frame and my boxes are plastic (even floor boxes) i have essentially isolated my grounding ...since there isnt any metal and i have run all home runs to each and every required iso plug....for which i will install regular receptacles which will be isolated. the only metal will be my emt run to x-former(primary and seconday) and it will be bonded at x-former via bonding bushing (concentric knockout)but will not bond isolated groundbar to panel.
here is a question i have....
this designer will probably want to see those fancy orange iso ground recptacles, not believing that a regular plug is isolated.
but could that be a nec violaion(using orange recep) because lets say i decided to use a brass or stainless plate, it wouldnt be grounded since the yoke isnt(because plastic box)and in some rare and freak way could become energized posing a shock danger.
perhaps im out there and stretching on this one but somehow i feel i should ask, violation or not?
thanks,
H20

Loop the EGC through the yoke screw on the way to the IG screw. It's still isolated in a plastic box

Why use a metal wallplate? Wouldn't that cause some questions from knowledgeable people? As you mentioned, it could be misconstrued with an IG receptacle. What would be so bad with using a nylon plate, for example?

You are far better explaining to the customer why these are not IG receptacles and just use a good commercial/spec grade.
If they really think they got IG and you didn't do it they may come back at you.