Supply Side Bonding Jumper

M

myntz

Member
Location
New Jersey
Occupation
Engineer
I have an outdoor MV transformer (Delta - Wye) that feeds an indoor MV switchgear with a main disconnect. It will have (5) parallel feeds from the transformer to the SWGR. Am I right to do the following:

1. Tie X0 to the grounding electrode outdoor. Tie X0 to indoor SWGR Neutral. Indoor Neutral will be completely isolated from the MV SWGR chassis/ground.
2. Tie indoor MV Chassis/Ground to the grounding electrode system. I am under the impression that under 250.102(E)(2), I can run a single supply side bonding jumper outside of the raceways as long as it is limited to 6 feet. I have a 500MCM tied to the grounding electrode and it is about 30 feet in length which will stubup inside the indoor MV swgr. Will this entire length 500MCM be considered as grounding electrode or supply side bonding jumper? If it is considered as supply side bonding jumper, then I would have to run the bonding jump in the same raceways as my current carry conductors?

Any comments are appreciated.
 
If the raceways are not metallic, you need a supply side bonding jumper IN each of the raceways. If the raceways are non-flexible, metallic and correctly bonded no wire type supply side bonding jumper is needed.
 
don, if the raceways are non-metallic, could he not apply the exception to 250.30(A)(2) ??
 
don_resqcapt19 said:
If the raceways are not metallic, you need a supply side bonding jumper IN each of the raceways. If the raceways are non-flexible, metallic and correctly bonded no wire type supply side bonding jumper is needed.
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Thank you for the quick response. The conduit is rigid metal and bonded on both end via ground bushing. I assume the bonding between the conduit ground bushing to the swgr ground has to be sized per table in 250.102(c)?

Can you direct me to the NEC section that talks about not need supply side bonding jumper if raceway is nonflexible, and metallic?
 
myntz said:
Thank you for the quick response. The conduit is rigid metal and bonded on both end via ground bushing. I assume the bonding between the conduit ground bushing to the swgr ground has to be sized per table in 250.102(c)?

Can you direct me to the NEC section that talks about not need supply side bonding jumper if raceway is nonflexible, and metallic?
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The last sentence of the parent text of 250.30(A)(2).
Yes the bonding of the metallic raceway would be sized per table 250.102(C)(1).
 
don_resqcapt19 said:
The last sentence of the parent text of 250.30(A)(2).
Yes the bonding of the metallic raceway would be sized per table 250.102(C)(1).
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Wow, I completely missed that! Thank you! Out of curiosity, does it hurt anything if additional ssbj is provided outside of the conduit in parallel to the metallic conduit?
 
myntz said:
Wow, I completely missed that! Thank you! Out of curiosity, does it hurt anything if additional ssbj is provided outside of the conduit in parallel to the metallic conduit?
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It would not hurt anything other than the pocketbook. Because of the ferrous conduit between the circuit conductors and external supply side bonding jumper, it would not play much of a part in the effective fault clearing path. The inductive reactance would limit the current flow. Even with an internal supply side bonding jumper the vast majority of any fault current will flow on the conduit and not on the wire type supply side bonding jumpers. in the conduits.
 
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