No equipment ground pulled to sub-panel

[jaggedben]

Ok you have 3 wires from a wye grounded source. Now you pull a noodle off the zig zag for your 240 volt servers. Do you or do you not grounded the neutral?

Let's say you ground it.

 

[mbrooke]

Let's say you ground it.

Ok- now neutral current goes up to the zig-zag, and some goes back to the source via EGC.

 

[jaggedben]

Ok you have 3 wires from a wye grounded source. Now you pull a noodle off the zig zag for your 240 volt servers. Do you or do you not grounded the neutral?

Wait, back up.

Why do you have a zig-zag if you already have a wye grounded source?

 

[mbrooke]

Wait, back up.

Why do you have a zig-zag if you already have a wye grounded source?

To save on the N conductor and eliminate neutral shift.

 

[jaggedben]

To save on the N conductor and eliminate neutral shift.

Thanks for finally educating me.

I gather this is the system you're talking about?
Interesting comments there about how that system is not or may not be allowed by the NEC!

 

[mbrooke]

Thanks for finally educating me.

I gather this is the system you're talking about?
Interesting comments there about how that system is not or may not be allowed by the NEC!

Yup- you got it. Thats two of several variants.


There is debate, but as far as I know nothing explicitly prohibits it and has been put into service without issue.

 

[jaggedben]

Well, to relate it to 250.32 as best I can... This seems like something the CMP will eventually decide to ban. :lol::roll: Or at least they might require one to run a neutral to the neutral point, not a GEC to building steel. (Note: it's not an SDS, or at least the second variant isn't.)

 

[mbrooke]

Well, to relate it to 250.32 as best I can... This seems like something the CMP will eventually decide to ban. :lol::roll: Or at least they might require one to run a neutral to the neutral point, not a GEC to building steel. (Note: it's not an SDS, or at least the second variant isn't.)

It is not something the code has thought about to be honest. Stuff like this are becoming more common as applications like solar and technology proliferate where things get really, really bizarre.

 

[kwired]

Wait, back up.

Why do you have a zig-zag if you already have a wye grounded source?

good question.

Well, to relate it to 250.32 as best I can... This seems like something the CMP will eventually decide to ban. :lol::roll: Or at least they might require one to run a neutral to the neutral point, not a GEC to building steel. (Note: it's not an SDS, or at least the second variant isn't.)

Neither one is a SDS, NEC that applies is titled autotransformers.

450.5 allows such setup from 3 phase 3 wire ungrounded supply. I have to chew on what the exception that follows is saying for a while to understand what it is saying, it may apply to what mbrooke is talking about.