CodeQuandary
Member
- Location
- Washington DC
Here's a funny one.
Existing subpanel, single family residence. Run at 240V 30A with older (but apparently fine) 3-wire no ground MC cable. No additional ground lead in the cable.
The ground and neutral are tied together in the panel.
This is a no-no.
In the absence of being able to run a new ground (long difficult run: the client probably won't do it), it would be possible to put the entire subpanel on a GFCI back at the Main.
a. This is actually arguably safer than running a ground and not adding a GFCI to the circuit, I think... (change my mind!)
b. The only way this works is to disconnect the neutral from the box & all the grounds, I believe. Given old house wiring: then (I think) connect all grounds to the box, in case any of them (or the cable) get back to a real ground.
c. An unpredictable downside is nuisance trips, but the house got a whole bunch of GFCI's and AFCIs during some recent work, and doesn't seem to be having any problem with nuisance trips.
Not ideal, but (as inferred above) probably safer than a proper ground but no GFCI. Definitely better than as-is.
Another idea would be to put the (6) circuits each on their own GFCI, but I think that might be less safe than more (the box and cable are no longer protected) and it's definitely more expensive.
Other thoughts?
Existing subpanel, single family residence. Run at 240V 30A with older (but apparently fine) 3-wire no ground MC cable. No additional ground lead in the cable.
The ground and neutral are tied together in the panel.
This is a no-no.
In the absence of being able to run a new ground (long difficult run: the client probably won't do it), it would be possible to put the entire subpanel on a GFCI back at the Main.
a. This is actually arguably safer than running a ground and not adding a GFCI to the circuit, I think... (change my mind!)
b. The only way this works is to disconnect the neutral from the box & all the grounds, I believe. Given old house wiring: then (I think) connect all grounds to the box, in case any of them (or the cable) get back to a real ground.
c. An unpredictable downside is nuisance trips, but the house got a whole bunch of GFCI's and AFCIs during some recent work, and doesn't seem to be having any problem with nuisance trips.
Not ideal, but (as inferred above) probably safer than a proper ground but no GFCI. Definitely better than as-is.
Another idea would be to put the (6) circuits each on their own GFCI, but I think that might be less safe than more (the box and cable are no longer protected) and it's definitely more expensive.
Other thoughts?