View Full Version : help with subpannel

05-05-2009, 08:40 AM
We recently bought a 1950's house that had an addition done in 2004. At that time the electrical service was relocated and upgraded to 200A. It seems as if the old main pannel located in the attached garage was converted to a subpannel fed off a 100A breaker in the main pannel. There was also another subpannel in the garage for the air handler fed off a 60A breaker in the main pannel. When we moved in an electrician added 2 new circuits for the kitchen. He added them to the air handler subpannel becuase access to the attic to get to the main pannel would have been very difficult. I then added one more circuit to that pannel for a garage receptacle and 2 exterior lights. From my reading, it seems as if subpannels in attached garages should have neutrals and grounds separated and be fed by a 4 wire feed from the main pannel. In my pannel there is only a 3 wire feed and the grounds and neutral share the same bar. I could move these circuits to the main pannel, but the access to the attic is terrible, although I will probably have to do that eventually. My question is- Is this a dangerous situation and why?

Thanks for your advice,

Main pannel:


Air handler sub pannel with kitchen and garage circuits:

Old main, now sub pannel for old part of house, dryer, water heater, range.

Bill Arden
05-05-2009, 03:50 PM
It looks like your subpanels have two hots, a bare ground wire and no neutral.

That would be fine if all they were supplying were 240 volt loads.

The real danger here is if that ground wire corrodes or gets loose you will have both a floating neutral and potently dangerous voltages on the grounds/cases of devices.

The reason they want two wires going back to the main panel is that if one(or both) open up there is no way that you end up with a neutral connected to a floating ground/case of a device.

1. It is not necessary dangerous right now... but the problem occurs over time when connections loosen and things corrode.

FYI: I've done this for temporary/testing wiring since it does not matter in my case since it's going to get destroyed anyway. (destructive testing)

2. It's not up to code and would not pass the type of inspection you need to sell a place.

05-05-2009, 06:33 PM
The danger comes if you somehow "lose" the neutral that feeds the sub.

Where is the 120 "returning" current going to go?

It will go thru the grounds and thru everything grounded that is plugged in.

05-21-2009, 03:42 AM
Thanks for the replies. You are correct the HVAC subpannel is fed by 2 hots and a ground. If I move all the 110 volt circuits to the main pannel and leave the 60 amp breaker in the HVAC pannel will that be acceptable as the air handler disconnect? The air handler is about 4 feet away from the pannel connected by flexible conduit. Will this then be up to code?


05-21-2009, 06:30 AM
It appears that they used "entrance cable" to wire the subpanel, and that wire uses the exterior sheathing for the neutral by twisting it together into a cable. Your ground and neutral in the main panel are interconnected so the entrance cable is a "neutral" even though it is attached on the ground side. But, you do not have a dedicated ground wire for the sub panel circuits.

05-21-2009, 01:34 PM
The HVAC panel feed will be fine if it only has 240V loads.

The laundry sub appears to have a 4 wire feed and, although it's ugly, the feed is compliant.