Transformer Installation
Transformer Installation
(OP)
I have a 175 KVA transformer to step up the voltage from 208 to 460. The nameplate reads Primary 208 Delta H1 H2 H3
Secondary 460/266 X0 X1 X2 X3 We have a 208/120 3 Phase Y system. I do not need a neutral on the secondary side. Will this transformer suffice?
Secondary 460/266 X0 X1 X2 X3 We have a 208/120 3 Phase Y system. I do not need a neutral on the secondary side. Will this transformer suffice?






RE: Transformer Installation
RE: Transformer Installation
RE: Transformer Installation
RE: Transformer Installation
RE: Transformer Installation
I read this as you mean that you do not need neutral on the 460/266V side and it is OK. But you must ground the neutral (X0) at the transformer. You need not take it out to the load. The transformer is fine as is.
You still need the ground conductor as wareagle said.
RE: Transformer Installation
RE: Transformer Installation
You don't need the neutral.
RE: Transformer Installation
Why does he need to ground XO? It is not required by the NEC.
Don
RE: Transformer Installation
Why would you not ground it? What do you gain? NEC is not a design manual. NEC does not require most of things we do.
RE: Transformer Installation
RE: Transformer Installation
I read your post as saying it must be grounded. I agree that it is a good design practice to ground the sytem in most cases, but it is a design issue and not a code requirement.
Don
RE: Transformer Installation
Great, we agree. Why would we advise someone other than a what is a good practice/design?
RE: Transformer Installation
I just work under the assumption that anytime someone says that we "must" do something, it is because there is a code that requires it.
Don
RE: Transformer Installation
With all due respect, firstly you are hung up in semantics.
Secondly, NEC does require the system to be grounded to keep the L-G voltage not to exceed 150V for systems rated less than 1000V. See NEC 250.20 (B). Where it is permitted to be ungrounded, there are many other requirements that need to be met, see NEC 250.21.
RE: Transformer Installation
How do we get a voltage to ground of less than 150 volts for a 480 volt system? The question is about the grounding of the secondary of a step-up transformer.
Don
RE: Transformer Installation
It seems that Ripcord had it correct in the posting dated August 16th.?
RE: Transformer Installation
RE: Transformer Installation
Still I would stand by my recommendations. I would not advise a ungrounded system, unless there is a dire need for it for some reason.
RE: Transformer Installation
I hope that others may find similar rules in the NEC,
and,
I am several thousand miles away from my copy of the NEC just now.
I believe that if a system may be grounded so that the maximum voltage to ground will be not more than 150 volts to ground, it must be grounded.
If the maximum voltages will be more than 150 volts to ground it may be grounded.
If the system has a neutral, it must be grounded. (I am not sure if your transformer will be considered a system and require a ground under this clause.)
If the system is ungrounded it must be equiped with suitable ground detection devices.
Grounding is often cheaper than ground detection devices.
respectfully
RE: Transformer Installation
250.21(4)permits this system to be an ungrounded system. I agree that in almost all cases it should be a grounded system, but as I said earlier, it is not requried by the NEC.
rbulsara,
You are correct that the 2005 NEC requires the use of a ground detector system for most ungrounded systems. This was a change to 250.21 for the 2005.
Don
RE: Transformer Installation
I am curious how you would propose to meet NEC 250.4 B with this ungrounded system?
RE: Transformer Installation
RE: Transformer Installation
With an ungrounded system all 250.4(B) requires is a grounding electrode system and equipment grounding conductors. The only real difference from a grounded system is the lack of a main bonding jumper. Don't get me wrong here, there a number of safety issues with using an ungrounded system, but at this point in time the code still permits such systems.
Don
RE: Transformer Installation
Do you agree?