Main bonding Jumpers, and neutral sizing

[SPLandry]

As I understand it, the maximum size grounding electrode conductor is 3/0, but bonding jumpers on the supply side of services or seperately derived systems are required to be 12.5% of the size of the service-entrance phase conductors when the equivalent size exceeds 1100 kcmil copper. So for example when you install a 2000 amp (120Y/208) service with 5 sets of 600 Kcmil copper conductors your main bonding jumper would need to be 375 kcmil (400 kcmil). This size conductor is required at the service entrance equipment to connect (bond) between the grounded conductor, and the equipment grounding bus, and any place you would need to provide for the bonding of raceways or enclosures of service entrance conductors. My question is why would not also be the required minimum size for the grounded service conductor, unless I am missing something you could derate the grounded service conductor down to 1/0 unless you had a large phase to neutral load. I also would feel like if you agree with the logic that equipment grounding conductors of the correct size needs to be provided in all conduits of a multiple run circuit (which I do)you would also need to have that minimum size grounded conductor in all conduits of the serive entrance. The reason I brought up the 3/0 as maximum size for a grounding electrode condcutor, is because I have had inspectors tell me that the grounding electrode conductor also needs to be no less than 12.5% of the service entrance conductors. Thank you for pushing all thre way through this.

 

[jumper]

Welcome to the forum. I hope you do not mind but I broke our post into smaller segments, which I think make it easier to read.

As I understand it, the maximum size grounding electrode conductor is 3/0, but bonding jumpers on the supply side of services or separately derived systems are required to be 12.5% of the size of the service-entrance phase conductors when the equivalent size exceeds 1100 kcmil copper.

So for example when you install a 2000 amp (120Y/208) service with 5 sets of 600 Kcmil copper conductors your main bonding jumper would need to be 375 kcmil (400 kcmil).

This size conductor is required at the service entrance equipment to connect (bond) between the grounded conductor, and the equipment grounding bus, and any place you would need to provide for the bonding of raceways or enclosures of service entrance conductors.

My question is why would not also be the required minimum size for the grounded service conductor, unless I am missing something you could derate the grounded service conductor down to 1/0 unless you had a large phase to neutral load.

I also would feel like if you agree with the logic that equipment grounding conductors of the correct size needs to be provided in all conduits of a multiple run circuit (which I do)you would also need to have that minimum size grounded conductor in all conduits of the service entrance.

The reason I brought up the 3/0 as maximum size for a grounding electrode conductor, is because I have had inspectors tell me that the grounding electrode conductor also needs to be no less than 12.5% of the service entrance conductors.

Thank you for pushing all the way through this.

 

[Dennis Alwon]

Your grounded conductor can never be smaller than your grounding electrode conductor. 250.24(C)(1) if that is what you are getting at. The same rule applies for grounded conductor as it does for bonding jumper and gec-- 250.28(D)(1). Maybe I am missing your question.

 

[augie47]

Take a look at 250.24(C).
The 12-1/2% applies to your grounded conductor, but the "parallel conduit" rule will dictate the size per conduit.