# Multiple Size Service Disconnect Bonding Confusion



## Imwired (Aug 21, 2014)

Hey guys I could use a little clarification on bonding multiple service disconnects of different sizes.
I have a 2600 amp end line box/ copper detail, out of which a section of switchgear with a 1200 amp service disconnect is directly attached. I than have several conduits running underground from the end line box to two 400 service disconnects and three 200 amp service disconnects.

The 1200 amp disco is bonded through the buss work in the switchgear so no problems there. Since I have separate conduits for each additional service off the end line box can I size bonding wire accordingly based on each disco size? If so what size could I use for the 400 amp? Would a #2 copper be too small?

Also I believe I have to bond all the service switches together, last job the inspector had me add a #6 bond wire between each service disconnect, so I'm thinking it would be required on this job as well.

Any guidance would be much appreciated!


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## Imwired (Aug 21, 2014)

Just to clarify, I'm trying to size the bonding jumper to the Bonding locknuts on the conduits! Thanks


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## RIVETER (Sep 26, 2009)

Imwired said:


> Just to clarify, I'm trying to size the bonding jumper to the Bonding locknuts on the conduits! Thanks


I think # 6 is good but just size the bonding wire/jumper with enough metal mass to withstand the max current possible in a fault situation. It's in the book.


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## Imwired (Aug 21, 2014)

Thanks Riveter but 250.66 says to size bonding wire based on "largest ungrounded service conductor " which in my case I believe is the 3 sets of 600 mcm feeding the 1200 amp switchgear. 

So that is my question, am I required to use a bonding jumper sized for the 1200 amp gear, which seems to be copper 3/0, in the 200 amp and 400 amp service gear as well?


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## Dennis Alwon (May 9, 2009)

You are correct that the bonding jumper is to be sized the same as the grounding electrode conductor. However each disconnect that is fed with a different wire size may be bonded based on the size of its service conductors. 

If you had a 600 amp service with 3- 200 amp panels then your bonding jumper could be a #4 on each panel assume you use conductors that are sized appropriately and not larger than needed. T 250.66 is based on conductor size not overcurrent protective device.


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## Dennis Alwon (May 9, 2009)

BTW, there are 2 Tables in the 2014, one for the grounding electrode conductor and one for the bonding jumpers but they are basically the same until you get to the larger conductors


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## Imwired (Aug 21, 2014)

Thank you very much Dennis, your help is much appreciated!


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## Imwired (Aug 21, 2014)

Thanks Dennis!


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