SSBJ

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Wyeman94

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Hello everyone. Trying to understand the 2011 NEC handbook, article 250.30(A) for wye type services and would appreciate your insight:
Typically I would abide by 250.30(A)(1) exception 2 : allowing 4 wires, no ground in PVC between a padmounted transformer and the main disc -- leaving the X0-to-case connection from the factory & installing a MBJ at the main disc. No parallel path.

Now see 2011 NEC whereby they introduce SSBJ, requiring to include a "ground wire" between the transformer and the main disc regardless (if I understand it correctly). Conceivably a parallel path.

(1a) Is SSBJ intended for customer owned SDS (distribution), services, or both?
(1b) Would there be any difference if the padmount transformer feeding the main disc is customer or utility owned?

(2a) Since removing the factory installed X0-to-case is out of the question, are we now required to exclude the installation of a MBJ at the main disc?
(2b) If SSBJ applies to services, how can the term MBJ ever be relevant in a new installation?

(3) It seems to me that NFPA is effectively rendering 250.30(A)(1) exception 2 as worthless because a SSBJ is installed -- yet -- 250.30(A)(1) exception 2 has not been deleted from the code. Whats more, there are still graphs in the handbook depecting a service without any SSBJ (exhibit 250.5)

(4) Minor annoyance, but SSBJ is defined at the beginning of article 250 while SBJ and MBJ are defined in article 100.

Again, any insights would be greatly appreciated. Thanks for reading.
 
The rules for services and SDS are not the same. In general, the rules for services permit the grounded conductor to be bonded, both at the transformer and at the service disconnect. There is no need for a SSBJ on a service as the grounded conductor serves that purpose. Again, in general, the rules for a SDS only permit the grounded conductor to be bonded at one point and thus a SSBJ is required between the transformer and the first disconnect. The grounded conductor is not permitted to do both jobs, like it is for services.
 
I concur with Don's synopsis.

Just to add a little...

Do not confuse the purpose of an SSBJ with that of an MBJ or SBJ. An SSBJ is a specific-purpose equipment bonding jumper. An MBJ or SBJ connects the grounding system to the grounded conductor.
 
I agree with the OP in that I see a conflict between 250.30(A)(1) Exception 2 and 250.30(A)(2) when you have a customer owned SDS located outside of the building.
I have discussed it with a couple of Code gurus and they see the conflict. but I see no resolution as of now.
 
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augie47 said:
I agree with the OP in that I see a conflict between 250.30(A)(1) Exception 2 and 250.30(A)(2) when you have a customer owned SDS located outside of the building.
I have discussed it with a couple of Code gurus and they see the conflict. but I see no resolution as of now.
Click to expand...
There is no conflict, just a correlation "glitch". Upon implementing 250.30(A)(2) SSBJ requirement, 250.30(A)(1) Exception 2 is nothing more than superfluous text, as it states "if doing so does not establish a parallel path for the grounded conductor." With an SSBJ, such system bonding jumper at both points will always establish a parallel path.
 
augie47 said:
I agree with the OP in that I see a conflict between 250.30(A)(1) Exception 2 and 250.30(A)(2) when you have a customer owned SDS located outside of the building.
I have discussed it with a couple of Code gurus and they see the conflict. but I see no resolution as of now.
Click to expand...
No conflict...CMP5 knows that the electrons behave differently on the utility side of the service disconnect than they do on the load side of that disconnect.....:)
 
A tiny Maxwell's Demon sits in a tiny gate shack that is found only in SUSE equipment and hands them the Rules of Conduct.
A second Demon picks them up again on the return.
The two Demons trade places every half cycle.


Tapatalk...
 
augie47 said:
I agree with the OP in that I see a conflict between 250.30(A)(1) Exception 2 and 250.30(A)(2) when you have a customer owned SDS located outside of the building.
I have discussed it with a couple of Code gurus and they see the conflict. but I see no resolution as of now.
Click to expand...

That is precisely my predicament, because the customer owns the padmount transformer so I believe it would technically be a SDS. The "service" is ahead of a customer owned 15kV switch ahead of the transformer. I didn't see any differentiation in article 250.30(A)(2), but I agree with everything that has been said. Thanks for taking the time to look & reply!
 
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