Transformer Installation 5

[Ripcord13]

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?

 

[resqcapt19]

apowerengr,

How (by code) can you not ground the wye-connected neutral point on the secondary of the proposed transformer? NEC 250.21?

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

 

[apowerengr]

resqcapt19,

I am curious how you would propose to meet NEC 250.4 B with this ungrounded system?

 

[davidbeach]

While I wouldn't recommend leaving it ungrounded, I don't see any problem meeting 250.4 B. Where do you see a problem with 250.4 B?

 

[resqcapt19]

apowerengr,
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

 

[apowerengr]

davidbeach and resqcapt19 - I agree, you are required to have a grounding electrode system and equipment grounding conductors. That's 250.4 B(1). B 2&3 require a permanent, low impedance path for ground fault current to flow. Since this transformer is wye on the 460 volt side, the path for ground fault current has to be back to the Xo bushing. Therefore to meet subs 2&3 it would seem you need a conductor back to the Xo bushing, and it has to be connected to conductive equipment enclosures (same as the grounding system) which will render the system grounded as I see it.

Do you agree?