Wye-Wye

[winnie]

Sounds correct to me.

 

[ggunn]

Seems ok to me. I believe you still need a grounding electrode system for the SDS, there will just not be a SBJ.

How can an ungrounded system have a GES? The inverters and enclosures have EGCs back to the service.

 

[electrofelon]

How can an ungrounded system have a GES? The inverters and enclosures have EGCs back to the service.

The same thing can be said of grounded separately derived systems. You'll have to ask the code gods why the EGC supplying an SDS is not sufficient, I doubt anyone really knows. Although the system is ungrounded, the equipment still needs to be connected to Earth via a GEC.

 

[ggunn]

The same thing can be said of grounded separately derived systems. You'll have to ask the code gods why the EGC supplying an SDS is not sufficient, I doubt anyone really knows. Although the system is ungrounded, the equipment still needs to be connected to Earth via a GEC.

I have always connected the GEC at the N-G bonding point either at the xfmr secondary or in the PV AC disco. If there is no neutral to bond to, can it still be a GEC?

 

[wwhitney]

I have always connected the GEC at the N-G bonding point either at the xfmr secondary or in the PV AC disco. If there is no neutral to bond to, can it still be a GEC?

(2017) NEC 250.30(B) covers ungrounded SDSs, and subsection (1) says "A grounding electrode conductor, sized in accordance with 250.66 for the largest derived ungrounded conductor(s) or set of derived ungrounded conductors, shall be used to connect the metal enclosures of the derived system to the grounding electrode . . ."

Cheers, Wayne

 

[ggunn]

(2017) NEC 250.30(B) covers ungrounded SDSs, and subsection (1) says "A grounding electrode conductor, sized in accordance with 250.66 for the largest derived ungrounded conductor(s) or set of derived ungrounded conductors, shall be used to connect the metal enclosures of the derived system to the grounding electrode . . ."

Cheers, Wayne

Thanks for the reference, although the language is a bit confusing to me. 250.30(B)(1) says to size the GEC to 250.66, but it also points to 250.30(A)(3) and section (c) says that for 3P3W delta system, which this is, the grounded conductor "shall have an ampacity not less than that of the ungrounded conductors", which I take to mean the ampacity of one of the phase conductors when there is not a parallel set. It says "grounded", though, not "grounding", so is it talking only about corner grounded systems?

In this case the CCCs are 3/0 copper. so does the GEC need to be #4 per 250.66 or 3/0 per 250.30(A)(3)(c)? I'm thinking #4.

My other question is can it be a combination GEC/EGC and can it connect to the transformer enclosure rather than back to the service electrode? The transformer has a #2 grounded conductor back to the service, which is correct for an EGC (450A fuses) but does it need to be sized per 250.66 for 2 sets of 4/0, which would, I believe, be 1/0?

If not, should I remove the #4 that is currently between the transformer and the switch on the 480V side?

Grounding is Black Magic...

 

[don_resqcapt19]

How can an ungrounded system have a GES? The inverters and enclosures have EGCs back to the service.

The only difference in the grounding and bonding rules between a grounded system and an ungrounded one, is that the grounded system has a main bonding jumper and the ungrounded one does not. Everything else is the same.