Sharing an EGC

[bzzzt]

Can a 480v and a 120v circuit from separate panels fed by the same MDP share an EGC if it's installed in the same raceway and sized per 250.122?


obviously there's a transformer in between but it seems this might be paralleling EGC's

 

[mcclary's electrical]

Can a 480v and a 120v circuit from separate panels fed by the same MDP share an EGC if it's installed in the same raceway and sized per 250.122?


obviously there's a transformer in between but it seems this might be paralleling EGC's

Welcome to the forum.


IMO,,,If there fed from seperate panels, then one of them, would not be making its' way back to the source, Making it a violation of 250.6 (a), 250.4 (a) (5)



if they came from the same panel, 250.122 (c) allows it. IMO

 

[iwire]

Welcome to the forum.


IMO,,,If there fed from seperate panels, then one of them, would not be making its' way back to the source, Making it a violation of 250.6 (a), 250.4 (a) (5)



if they came from the same panel, 250.122 (c) allows it. IMO

Or if it split back to both directions once the circuit conductors split.

 

[mxslick]

Or if it split back to both directions once the circuit conductors split.

Huh?

If the circuits originate from different panels, wouldn't that still be a violation of 250.6 (a), 250.4 (a) (5)?

OOPS, re-read OP they are from the same MDP...

 

[pete m.]

Can a 480v and a 120v circuit from separate panels fed by the same MDP share an EGC if it's installed in the same raceway and sized per 250.122?


obviously there's a transformer in between but it seems this might be paralleling EGC's

Since there is a transformer involved (assuming a SDS) you would need a separate EGC for each circuit. If a ground fault were to happen on the secondary side of the transformer (the 120 volt circuit) the fault current would be looking for the grounded conductor of the transformer (X0) not the grounded conductor of the 277/480 system (assuming that the 480 volt system is grounded).

Pete

 

[iwire]

Huh?

If the circuits originate from different panels, wouldn't that still be a violation of 250.6 (a), 250.4 (a) (5)?

IMO no not at all.

Picture this

You leave a 480 panel and 208 panel with circuit conductors and an EGC each, they join together in a J-box, at that point you combine the EGCs and continue on in one raceway with all the circuit conductors and the combined EGC. Now when you get to the far end you split the circuits into different raceways each with an EGC.

I see no problem or violation, in fact we do it all the time. For instance if we had 408 site poles that have 125 vol receptacles on them. One EGC for both.

 

[iwire]

Since there is a transformer involved (assuming a SDS) you would need a separate EGC for each circuit.

No you do not need separate EGCs, you just need an EGC that goes back to all sources.

 

[pete m.]

I see no problem or violation, in fact we do it all the time. For instance if we had 408 site poles that have 125 vol receptacles on them. One EGC for both.

Didn't think about that scenario. That being said, I agree

Pete

(wasn't quick enough in eating that crow)

 

[iwire]

See attached pdf

 

[bzzzt]

I see no problem or violation, in fact we do it all the time. For instance if we had 408 site poles that have 125 vol receptacles on them. One EGC for both.

That is the same application I am questioning. Thanks for the help

Is there any reason not to size per the largest breaker or conductor of the two?

 

[mxslick]

IMO no not at all.

Picture this

You leave a 480 panel and 208 panel with circuit conductors and an EGC each, they join together in a J-box, at that point you combine the EGCs and continue on in one raceway with all the circuit conductors and the combined EGC. Now when you get to the far end you split the circuits into different raceways each with an EGC.

I see no problem or violation, in fact we do it all the time. For instance if we had 408 site poles that have 125 vol receptacles on them. One EGC for both.

Thanks Bob, that makes sense to me. :grin:

 

[LarryFine]

The same thing would happen with conduits that are electrically connected, which they would be when strapped to strut, for example.

 

[iwire]

The same thing would happen with conduits that are electrically connected, which they would be when strapped to strut, for example.

I agree, unless it's a wood structure with NM cable all EGCs are connected together a countless number of times.