Electricians - Load Center Ques...
 

I'm doing some remodeling in a 30-year old garage and looking at the hodge-podge of electrical problems. There are many problems that I can immediately identify as "wrong" but there is one that I am just not sure about.

One of the previous owners added on a office to the garage. He pulled #10-3/g wire from a 220v breaker to the office, where he used it to feed a sub-panel (load center) which consists of 2 15a breakers. Each hot leg to a lug, and the neutral and ground wires to the grounding rail.

It works, and #10 wire is rated at 30a, so it seems safe.
But is it legal (to code)?

Hope you have several fire extinguishers handy.... it sounds hokey...

Looking at various Google results, it sounds like it is common, and acceptable.
http://www.homerepairforum.com/forum...ervice-sub.jpg

Mounting And Wiring A New Sub-Panel - Old House Electrical Update

Sub-Panel Electrical Wiring for the Home

Joe - about half of the electrical in the place had no ground wiring at all. That portion that does have grounding has the conduit wired as the ground. I've been told this was a standard practice, but I don't like it for some reason.

We are rewiring that old stuff, putting in 3-prong outlets, and will be installing GFCI outles as necessary.
Sure, the old way worked. We're just trying to make it a little safer.

As far as I understand, the ground on the sub-panel should go to a separate ground stake at that location (NOT back to the main service panel) and the neutral bus should not be bonded. The other question is what is the amperage of the feed breaker in the main service panel? With 2x 15A breakers on each of the hot rails in the sub-panel, you have a 60A draw possible. I am pretty sure the 10-3/g is not sufficient for that load. 8-3/g or even 6-3/g is needed.

How would 2x 15a breakers allow a 60a draw?
Wouldn't 2x 15 = 30?

10-3/g is adequate for 30a, but certainly not for 60a.
60a would require #6 wire.

your problem is going to be with the lugs in the sub-panel. i have never seen them rated for a size smaller than #6. there is your potential hot-spot. as far as the breaker in the panel, it must be a 2 pole 30amp breaker with a handle connecting the two. you don't need a second breaker in the sub-panel because the wire you are protecting is the one running from the main panel to the sub panel. does this make sense?

Agree with Arcsine. The neutral assembly should NOT be bonded to ground in a sub panel if the ground is originating in the main panel. You should bond the neutral if the panel is grounded with a ground rod as it is then treated as a seperate service.. Supply breaker in the house should be a 30A double pole with a tie handle.

I read the original post as the sub-panel having two 15A breakers on each side of the hot rails for a total of four 15A breakers.

What's the feeder breaker size? Also, what is the secondary panel rating? 100A, 200A???? The panel rating also determines the legal feeder wire size, not whether you only have two 15A breakers in it. Another thing to think about is how far away the secondary panel is from the main. You have to de-rate for length and then also if it's run in conduit, jacketed 3 conductor vs individual wires....

Just on what info you've provided, I'd be making some changes....

Yes... it does.

Based on the above, some changes are in order.
The feeder breaker is 100a.
The sub-panel is a 70a box.
The wire feeding it was 10ga.
The run was 40 feet.
The neutral bonding was incorrect according to NEC links I found, and according to the above advice.

I'll be making a trip to the hardware store later today.
I'll use the same box, but will rewire it with #4.

What do you intend to power in the garage/office? With number 10 x2 you have a 220volt 30 amp subservice. This is probably plenty.
I have 60 amps directed to my garage and use number 6 with a 60 Amp feeder breaker. The garage panel is a 100 Amp rated panel with 12 spaces for breakers. I use 1 -15 circuit for lights ,2 15A circuits for plugs,a double 30A for my compressor,a 15A circuit for my garage gas furnace . Several spaces still available.

This is the best pictorial description of things that I have found. Sounds like you are on the right track.

http://forums.pelicanparts.com/uploa...1293730462.jpg

The old sub-panel does not have a separate neutral bar and equipment grounding bar, and no room in the little panel to install one safely.... so it has to be changed. That, coupled with running the heavy feeder wire, and other problems, has led us to decide to just strip everything out and start from scratch at the main panel.

It's been a very unproductive day, but sometimes you have to take a step backward before you can go forward. I'd rather this all be up to code and safe, and not have to deal with an inspector breaking my balls over something stupid.