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250.32(B)(1) Exception #2

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R

Revous

Member
Location
NJ
Occupation
Design Engineer
david luchini said:
Or to put it another way.

The main section of 250.30(A)(1) REQUIRES you to have a single system bonding jumper.

The exception #2 to 250.30(A)(1) PERMITS you to have TWO system bonding jumpers, one at each end.

250.30(A)(2) REQUIRES you to have a supply side bonding jumper between the source enclosure and disconnect enclosure.

The exception to 250.30(A)(2) says the SSBJ is not required when you have installed the TWO system bonding jumpers permitted by 250.30(A)(1) exception #2.
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I agree with everything except the last line, that the SSBJ is not required between the enclosures if you are in compliance with 250.30(A)(1). But 250.30(A)(1) does not require you to have two system bonding jumpers. Only installing one system bonding jumper is still in compliance with 250.30(A)(1).

(The exact wording) 250.30(A)(1)Exception: A supply-side bonding jumper shall not be required between enclosures for installations made in compliance with 250.32(A)(1), Exception No. 2.


The key difference is that 250.30(A)(1) Exception #2 only kicks in for "a building or structure supplied by feeder from an outdoor separately derived system..."
 
david luchini

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
Revous said:
(The exact wording) 250.30(A)(1)Exception: A supply-side bonding jumper shall not be required between enclosures for installations made in compliance with 250.32(A)(1), Exception No. 2.
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Sorry, but if you don't install the TWO system bonding jumpers permitted by the exception, your installation is in compliance with the MAIN TEXT of 250.30(A)(1). The Exception then has NOTHING to do with your installation.
 
R

Revous

Member
Location
NJ
Occupation
Design Engineer
david luchini said:
Sorry, but if you don't install the TWO system bonding jumpers permitted by the exception, your installation is in compliance with the MAIN TEXT of 250.30(A)(1). The Exception then has NOTHING to do with your installation.
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I see where you are coming from, and as I re-read it more I lean more toward agreeing with you.
But what do you think about the two sections being in conflict with each other? If you install 2 system bonding jumpers and follow the exception above for a new 480V feeder into the building, wouldn't that mean that these sections are in conflict with each other?

If you connect the equipment ground of an incoming feeder to the grounding electrode system in compliance with 250.30(A)(1) wouldn't that mean you are creating a parallels path for between the neutrals?
 
david luchini

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
Revous said:
I see where you are coming from, and as I re-read it more I lean more toward agreeing with you.
But what do you think about the two sections being in conflict with each other? If you install 2 system bonding jumpers and follow the exception above for a new 480V feeder into the building, wouldn't that mean that these sections are in conflict with each other?

If you connect the equipment ground of an incoming feeder to the grounding electrode system in compliance with 250.30(A)(1) wouldn't that mean you are creating a parallels path for between the neutrals?
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It seems that you are trying to use the exception to avoid repulling the conductors to the 208V switchboard. If you can't do that in a way that complies with all of the NEC requirements, then repulling those conductors with an SSBJ is probably your only solution.
 
D

david

Senior Member
Location
Pennsylvania
Revous said:
I agree with you on that, back to the drawing board I suppose.

@david & @david luchini I appreciate you guys taking the time to go back and forth on this.
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I hope not to confuse you,
Let's back up and look at two points closely.

The first one is pretty clear.
250.30 (C)

Your neutral at the outside source has to be earthed, (a grounding electrode condoctor bonding the transformer neutral to a grounding electrode at the transformer location)

The second point 250.30 (A) (1) but just the last sentence where it starts with

" if the source is located outside"

You have options with an inside transformer that you do not have with an outside source.

" a system bonding conductor [shall] be installed at the grounding electrode conection in compliance with 250.30 (C)

Since the equipment grounding hasn't been established for the building at the outside transformer, the system bonding jumper must bond the neutral to the supply side bonding jumper out at the transformer.

It's not an eather or situation the system bonding jumper has to be out at the transformer

When the system bonding jumper comes into the building from the outside transformer and bonds to the buildings equipment grounding and the buildings grounding electrode system the buildings neutral must remain unbounded (must float).


Once that is clear and understood you can apply exception # 2.

Remove the supply side bonding jumper between the outside transformer and add a second system bonding jumper at the building

But as you noted the exception can only be used if earth and the derived neutral is the only current path from the transformer neutral to the building
 
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