SDS Bonding dilemma

augie47

augie47

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Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
I have a situation that I can't resolve.
SDS system with outside pad transformer supplying a panel at separate building.
Transformer secondary circuit consist of 3 phases and a neutral with no wire type SSBJ.
Conduit system from the transformer to the panel is rigid conduit which I understand can be used as the SSBJ however the contractor installed a section of LFMC for the last few feet of the run and the LFMC is not an adequate grounding means for the current involved.
I can't use the exceptions in 250.30 to omit the SSBJ as I have a parallel path even though it has limited ampacity based on 250.118
To add to the dilemma the panel is connected to a UFER and ground ring at the building and the grounding electrode conductor extends direct buried to the pad transformer so essentially it is serving as a SSBJ although it's not run with the power conductors.
Plus, 250.102 requires the conduit be bonded which can be accomplished at the transformer but the LFMC will then be an objectionable path albeit limited by 250.118.
Any input on the steps necessary to mike the install Code compliant would be appreciated.
 
Last edited:
augie47 said:
Conduit system from the transformer to the panel is rigid conduit which I understand can be used as the SSBJ however the contractor installed a section of LFMC for the last few feet of the run and the LFMC is not an adequate grounding means for the current involved.
Click to expand...
How long is the LFMC?

250.102(E)(2) allows a bonding jumper on the outside of the LFMC if it is less than 6'. Not clear on whether that would resolve all of the issues raised.

Cheers, Wayne
 
I don't see a requirement that the supply side bonding jumper must be of one material or without splices. I would suggest changing to a wire type supply side bonding jumper at the end of the RMC.
 
don_resqcapt19 said:
I don't see a requirement that the supply side bonding jumper must be of one material or without splices. I would suggest changing to a wire type supply side bonding jumper at the end of the RMC.
Click to expand...
That was my suggestion....a jumper around the section of LFMC.
Do you see any problem with the parallel path thru the GES ??
 
Not sure (I'm getting the question 2nd hand) but with the SSBJ installed as you suggest,, it (the neutral) would only be bonded at the transformer.
 
augie47 said:
Not sure (I'm getting the question 2nd hand) but with the SSBJ installed as you suggest,, it (the neutral) would only be bonded at the transformer.
Click to expand...
It could be at either end with the supply side bonding jumper only connected to the neutral at the location of the system bonding jumper.
Unless there is more than one connection between the grounding system and the neutral, I don't see an issue with a parallel path.
 
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