Supply side bonding jumper

[hhsting]

Attached sketch shows 480/277V three phase 2 sets of 4#500 kcmil service conductors into trough. The service conductors are connected three times by 4#3/0 AWG which feed three main service disconnects fused at 200A.

Each main service disconnect inside has supply side bonding jumper which bonds the service metallic conduit. However at the other end of the conduit service trough side their is also supply side bonding jumper which bond metallic conduit to trough all sized #4 AWG.

The question is is the supply side bonding jumper from trough neutral conductor to the trough enclosure shown inside trough is still require or the supply side bonding jumper from each conduit to service trough sufficient ? It’s marked in sketch “Is this still needed?”

 

[infinity]

Yes, what's not needed is the bonding bushings in the wireway since the raceway is bonded at the disconnect.

 

[electrofelon]

Yes, what's not needed is the bonding bushings in the wireway since the raceway is bonded at the disconnect.

I would just add that it might be compliant without the trough to neutral bonding jumper if the code would address parallel bonding jumpers.

 

[PeterOven]

I would just add that it might be compliant without the trough to neutral bonding jumper if the code would address parallel bonding jumpers.

In NEC 2017 Table 250.102(C)(1), 1000 kcmil equivalent area copper requires a #2/0 bonding jumper. #4 is 41740 cmil, while #2/0 is 133100 cmils. Thus, three #4 in parallel (125220 cmil) will fall just shy of being equivalent to #2/0, so this would not be compliant even if parallel bonding jumpers were allowed.

Interestingly, the 2017 handbook has a very similar example in Exhibit 250.12, but without the extra bonding bushings in the trough.

 

[hhsting]

Yes, what's not needed is the bonding bushings in the wireway since the raceway is bonded at the disconnect.

Do you know is this in code NEC 2014 that only one side would need bonding bushings? I didn’t find it.

 

[electrofelon]

Do you know is this in code NEC 2014 that only one side would need bonding bushings? I didn’t find it.

No it is not in the code. Why would you need one on each side? One bonds the nipple.

 

[hhsting]

No it is not in the code. Why would you need one on each side? One bonds the nipple.

If a designer other than myself does this at both ends and I represent AHJ then in order for me to enforce you only need bonding jumper at only one end I would need code section otherwise if it’s not in code it is design issue. I cannot tell the designer what to do if not in code. As far as why would designer do this only he/she would know.

 

[electrofelon]

He can put one on each end, there is no code against it, it's just not necessary. Perhaps you could leave him a note saying "bonding at both ends is ok, but not required".