250.30(1) exception No.2

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Dsg319

Dsg319

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Wv Master “lectrician”
I cannot make sense of this exception. Can someone give me an example. Even if you had a non-metallic race way, if you were bonded at both places as it seems the exception allows. Wouldn’t there always be neutral current on the EGC?
 
That definitely seems odd. Maybe if you are suppling a 3 phase load only with the separately derived system. Where the neutral is not used, (IE, induction motors). Curious to see what others say.
 
This addresses a SDS outside. If you look at (A)(2) you will see the SSBJ is not installed so there is no "EGC"...
basically it's wired like a POCO service from the SDS transformer.
 
They said "as long as it does not create a parallel path".

They're talking about separate structures, where only earth is between the two bonding points, not an EGC between them.
 
augie47 said:
This addresses a SDS outside. If you look at (A)(2) you will see the SSBJ is not installed so there is no "EGC"...
basically it's wired like a POCO service from the SDS transformer.
Click to expand...
That makes sense compared to what I was thinking. Maybe I get time tonight I’ll read a little deeper into it.
 
Current path shown in the attached file. Since the earth is not considered a parallel path for this exception, you can see there is only one route for normal current to flow between secondary load and transformer.
 

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If I'm not mistaken, the reason no separate EGC is required is because there is no OCPD at the source end.

So, it's looked at similarly to a service, where the neutral itself is the conductive pathway for fault currents.
 
LarryFine said:
If I'm not mistaken, the reason no separate EGC is required is because there is no OCPD at the source end.

So, it's looked at similarly to a service, where the neutral itself is the conductive pathway for fault currents.
Click to expand...
Correct, if you did pull a SSBJ, then that would create a parallel path, so it wouldn't be to code.
 
lauraj said:
Current path shown in the attached file. Since the earth is not considered a parallel path for this exception, you can see there is only one route for normal current to flow between secondary load and transformer.
Click to expand...
Thanks for the image
 
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