Bonding an enclosure with multiple circuits.

electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
Occupation
Electrician
Say I have a metal box or wireway that has various circuits entering and exiting with PVC, so the box is not bonding by a raceway. Lets say I have 20 amp circuit and a 100A circuit passing thru. No splices. Can I bond the box with/to the EGC of the 100A circuit, and run the 20 amp EGC thru unmolested without bonding it to the box?
 
letgomywago said:
I'd say no it needs to hit the box also. If it were emt and an isolated ground this would be different.
Click to expand...
Code section? I was thinking 300.3 "all circuit conductors in same raceway or cable" , because if the smaller circuit faulted to the box then that fault current would be traveling on the EGC for the larger circuit which wouldn't be in the same raceway as the smaller circuit. Wanted to see if others agree or if there's another code section
 
Normally I just add a small bus bar and land all the grounds to it and then only one EGC back to panel at the largest circuit size.
 
Not sure what the code says but with different circuits in the same pie using just the largest EGC to bond the box is fine.

Multiple pipes the you need to use the largest EGC from each pipe.

In the OPs case what if the 100 amp circuit is later disconnected in the panel that would leave the box unbonded?
 
electrofelon said:
Code section? I was thinking 300.3 "all circuit conductors in same raceway or cable" , because if the smaller circuit faulted to the box then that fault current would be traveling on the EGC for the larger circuit which wouldn't be in the same raceway as the smaller circuit. Wanted to see if others agree or if there's another code section
Click to expand...
If you do not have a singular raceway for all the current carrying conductors, then it would be handled the same as any metal enclosure that has multiple circuits passing thru (like a typical 4x4), all grounds pigtailed to the enclosure. One issue is that all circuits need to come from the same panel for overcurrent protection other than a simple pass thru that has no splices and an insulated EGC.

250.144 Multiple Circuit Connections.
If equipment is required to be grounded and is supplied by more than one circuit containing an equipment grounding conductor, a means to terminate each equipment grounding conductor meeting the requirements of 250.8 shall be provided as specified in 250.134 and 250.138.
 
See 250.148. If the 20A circuit is passing straight through (no splices, no terminations), then it is not required to bond its EGC to the box.

Same nominally applies to the 100A circuit, but the box itself needs bonding. Not sure what section you could cite as a violation if you choose to use the 20A EGC to bond the box rather than the 100A EGC.

Cheers ,Wayne
 
Fred B said:
.

250.144 Multiple Circuit Connections.
If equipment is required to be grounded and is supplied by more than one circuit containing an equipment grounding conductor, a means to terminate each equipment grounding conductor meeting the requirements of 250.8 shall be provided as specified in 250.134 and 250.138.
Click to expand...


That section is strange. "A means to terminate shall be provided" but do I have to use it?
 
Logic tells me that the box itself may be bonded by just the largest EGC, but if any other circuits have joints in the box, their EGCs must also be bonded to the box.
 
electrofelon said:
So how do you respond to my idea in post number three that it is an all conductors in same raceway violation?
Click to expand...
250.148 is very explicit, it obviously controls. Just because in the corner case where the 20A circuit faults to the box the fault current will flow on the 100A circuit's EGC doesn't make the 100A circuit's EGC part of the 20A circuit. There's no 300.3(B) violation.

[Say you did bond both EGCs to the box, and there's a fault on the 20A circuit--most of the fault current will likely take the 100A circuit's EGC, as it will likely be a lower impedance path. Is that a 300.3(B) violation? No.]

Cheers, Wayne
 
So I guess my take is that 250.148 first paragraph requires interconnecting all the EGCs of all the circuits spliced or terminated in the box (and that interconnection may use the box if it is metal, e.g. via separate ground screws), and 250.148(C) requires that at least one EGC be connected to any metal box.

Cheers, Wayne
 
You must log in or register to reply here.
Top