sub panel wiring

csoc64

Senior Member
Location
northeast
Installing solar pv into existing sub-panel. Sub-panel is wired with seu, so no ground wire (do not know when panel was installed). All grounds and neutrals landed on the isolated neutral bar, which is NOT bonded to the panel, (measuring 54 volts to ground...green bond screw was sitting in the bottom of the can. This has been installed.). My question is this; since I am adding circuits, am I obligated to provide an isolated neutral and separate the grounds. I would obviously need to re-feed the panel to provide grounding.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Installing solar pv into existing sub-panel. Sub-panel is wired with seu, so no ground wire (do not know when panel was installed). All grounds and neutrals landed on the isolated neutral bar, which is NOT bonded to the panel, (measuring 54 volts to ground...green bond screw was sitting in the bottom of the can. This has been installed.). My question is this; since I am adding circuits, am I obligated to provide an isolated neutral and separate the grounds. I would obviously need to re-feed the panel to provide grounding.
is this at a separate building? if not, this would never have been allowed.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Sub-panel is right next to main panel in basement. What specifically would not be allowed?
you would never have been allowed to run three wires from the main panel to this subpanel. it would always have required 4 wires, unless it was installed in the dark ages.

in any case, since they are adjacent to each other it should not be real hard to run the required 4 wires.

I don't understand why someone would have used service cable anyway for this. seems odd.
 

csoc64

Senior Member
Location
northeast
you would never have been allowed to run three wires from the main panel to this subpanel. it would always have required 4 wires, unless it was installed in the dark ages.

in any case, since they are adjacent to each other it should not be real hard to run the required 4 wires.

I don't understand why someone would have used service cable anyway for this. seems odd.
I suspect it's a homeowner job. Thanks for your input. So, if I throw in a 6/3 romex, I'm good to go?
 
Last edited:

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I suspect it's a homeowner job. Thanks for your input. So, if I throw in a 6/3 romex, I'm good to go?
depends on the feeder breaker size and the calculated load on the subpanel.

I think you mentioned in a previous post you plan to tie a PV system into this subpanel. There are some odd rules about such installations I am not real familiar with that have to be observed as well.
 

csoc64

Senior Member
Location
northeast
depends on the feeder breaker size and the calculated load on the subpanel.

I think you mentioned in a previous post you plan to tie a PV system into this subpanel. There are some odd rules about such installations I am not real familiar with that have to be observed as well.
Breaker feeding the sub-panel is 60A. Loads appear to be minimal, but I still need to verify. I am not concerned with the addition of the PV, as the 60A breaker, combined with the bus bar rating is sufficient for this particular application.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Breaker feeding the sub-panel is 60A. Loads appear to be minimal, but I still need to verify. I am not concerned with the addition of the PV, as the 60A breaker, combined with the bus bar rating is sufficient for this particular application.
I don't recall off the top of my head but I think 6/3 romex is good for 55A. so as long as the calculated load is less than 55A, a 60A feeder Cb would seem to be OK.
 

csoc64

Senior Member
Location
northeast
I don't recall off the top of my head but I think 6/3 romex is good for 55A. so as long as the calculated load is less than 55A, a 60A feeder Cb would seem to be OK.
According to 310.`5(B)(16), #6 good for 65A at 75C; 55A @ 60C. Do I need to size based on 60C?
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
Stick a short PVC nipple between the panel and the sub panel and used thhn wire. Now you can install a 70 amp breaker if the calculated load is 65 amps or less
 

jaggedben

Senior Member
I suspect it's a homeowner job. Thanks for your input. So, if I throw in a 6/3 romex, I'm good to go?
You're still gonna need a #8 GEC for your solar. I don't install enough 6/3 romex to remember what size the ground is, but I would guess it's only #10.

With that said, you can bring your solar GEC to the GES by some other route, if you prefer.
 
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