Bonding for parallel conduits

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Blue Steel

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California
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Contractor/Inspector
The scenario; the site has a new 4000A main service (MS). The main service is only a main breaker that feeds the 4000A distribution (MSA) at a remote location. The feeders for MSA are fifteen sets of (4) 400Kcmil and a 500 G in 4" conduits made up of PVC and OCAL risers. At the risers of each end there will be bonding bushings on the OCAL. The question is what size bonding conductor is to be used to bond all the bonding bushings?
Article 310.10(H)(6) refers to 250.102 for parallel bonding.
250.102(C)(2) describes the bonding jumper for the supply side. These conductors are protected by the 4000A breaker at MSA which will make them load side.
250.102(D) says to refer to table 250.122 which would be a 500Kcmil. This size is larger than the lay-in lugs on the bonding bushings and visually seems excessive. Am I adding this up correctly? If this is all correct how would you attach the 500Kcmil to the bonding bushing knowing that the lay-in lug doesn't have this size wire in wire range?
 
Since you have a feeder you would base the bonding jumper on T250.122. For 4000 amps that's 500 kcmil copper as you've stated. Why do you need bonding bushings? If you use them you'll need to change the lugs on the bonding bushings.
 
infinity said:
Since you have a feeder you would base the bonding jumper on T250.122. For 4000 amps that's 500 kcmil copper as you've stated. Why do you need bonding bushings? If you use them you'll need to change the lugs on the bonding bushings.
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I believe the reason the contractor is bonding the bushings is due to 250.1(4). Are you saying that they may not have to?
 
Blue Steel said:
I believe the reason the contractor is bonding the bushings is due to 250.1(4). Are you saying that they may not have to?
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A feeder would only require them if there are concentric or eccentric knockouts and the voltage is over 250 volts to ground or if you had an open bottom switchboard. Depending on the particulars of the installation they may not be required at all.
 
With an open bottom switchboard they're required even if the system is less than 250.volts to ground.
 
This is an area where the code is screwed up....if these were supply side bonding jumpers and not EGCs, you would be able to use a smaller conductor. It makes no sense as the condition where a supply side bonding jumper is used typically is a case where the available fault current is greater than where an EGC is used.
 
don_resqcapt19 said:
This is an area where the code is screwed up....if these were supply side bonding jumpers and not EGCs, you would be able to use a smaller conductor. It makes no sense as the condition where a supply side bonding jumper is used typically is a case where the available fault current is greater than where an EGC is used.
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Do you have a PI crafted for 2026?
 
don_resqcapt19 said:
This is an area where the code is screwed up....if these were supply side bonding jumpers and not EGCs, you would be able to use a smaller conductor. It makes no sense as the condition where a supply side bonding jumper is used typically is a case where the available fault current is greater than where an EGC is used.
Click to expand...
I agree, I've been saying this for ever. Makes you wonder how some of this stuff ever got into the NEC in the first place.
 
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