Question on shared ground/neutral buss in breaker box

banyan · 06-26-2008, 02:32 PM

I have this old, small house, lived here for 30 years. Before my time, electrical service was upgraded a couple of times, apparently. There is currently 100A service to a circuit breaker box. Box contains 16 circuit breaker slots, two or which are labeled "do not install breaker here". There are no sub panels or fuses anywhere.

The house has never been remodeled nor had the overall circuitry upgraded other than what I've already described. I'd like to get at least one additional circuit to the kitchen. These old places were never designed for microwaves, electric teakettles and all those modern appliances, so basically there is just one 20A circuit to the kitchen receptacles. I looked in the breaker box and find there is one open slot for a new breaker.

But, when I look at the existing use of the box I see there is one buss for both ground and neutral. And it's pretty darn small. All terminal screws are in use, and in fact a couple of screws on the buss are hosting two wires - two bare ground wires on one buss slot, two white neutrals on another.

I asked an electrical contractor about an upgrade to the box but that quickly outstripped my budget. I need to consider an alternative.

First question - is it safe to have a single buss for both ground and neutral? I guess it was OK at one time but how about in today's world?

Second question - is it OK that a couple of 20A circuits share buss terminals as long as ground is with ground, and neutral is with neutral?

Third question - if all this OK, would it be OK to double up the neutral and ground of a new circuit with those of an existing circuit, as long as both circuits are the same amperage and approximate use? I was thinking the new kitchen 20a circuit could share ground and neutral buss terminals with the existing kitchen circuit since both are used only intermittently and for small appliances. The fridge is in a different room and is plugged into a different circuit than either the existing kitchen receptacle circuit or the proposed new circuit.

kok328 · 06-26-2008, 05:38 PM

What you are describing is a correct installation assuming that this is the main panel. If it were a sub-panel, then the ground buss bar and neutral buss bar must be kept separate.
You might consider install a sub-panel.

handyguys · 06-27-2008, 12:43 PM

The doubling up is OK at the main panel on the ground/neutral bar, not on the breaker. I curious why the empty slots are labeled "do not install breaker here". May be worth having your electrician make a determination as to why. Maybe way back when someone felt the panel was over loaded and it wouldn't be safe to add more breakers. Just a guess. Its my understanding that the amperage on the breakers does not need to add up to equal, or be less than, the the amperage on the main breaker.

banyan · 06-27-2008, 04:29 PM

It is the main panel.

The label on the inside of the panel (which is a General Electric, circa 1950's I think) is factory printed. Judging from the looks of things, this particular area was never designed to hold circuit breakers. The label has a little "GE" within a circle at the bottom right of the label.

Whatever the reason, that area is not in use. I can only guess how old the box is. Some of the old NMS cable is black plastic, with stranded bare copper wire for grounding. And some of the oldest cable (for the overhead lights) is probably all that was there originally in 1936 - fabric wrapped, no ground wire. An interesting box. The breaker box, which is exterior, sits on top of what I take to be the original fuse box, and the cabling exits through the bottom of the breaker box, into the old fuse box, and then is routed through the original holes drilled into the siding.

Depression era houses are so interesting. Apparently concrete was very expensive so they skimped on it, but good old heart redwood was cheap enough to use for framing and the floors are straight grain doug fir with no knots that people would kill for today. Go figure.

Thanks for your comments. I'll need to rethink this whole thing. Perhaps have an electrician install a sub-panel.

speedy petey · 06-28-2008, 08:58 AM

It is certainly NOT ok to "double up" neutral wires on the neutral bar.
Neutrals must be ONE to a hole. Depending on the panel you can have up to three grounds, or the same size, in one hole.

You can share a breaker with more than one circuit. The proper way to do this is to pigtail the circuits so a single wire terminated on the neutral and grounds and on the breaker.

A comment was made about the breakers adding up to a certain amount. This is a COMPLETELY non-issue. The sum of the breakers is a meaningless number.
It is not uncommon to have 5 to 6 times the main breaker rating in branch circuit breakers.
I have seen over 800 amps worth of branch breakers in a 200 amp panel, and it was NOT overloaded.

kok is correct about the neutral/ground bar.

The "Do not install breakers here" labels were common in some 100A panels. These stickers are typically installed opposite the main breaker since there is no buss stab to install a breaker to in that position. I can only assume they used the same cover for those main breaker panels as they did for their main-lug panels.

triple D · 06-29-2008, 02:39 AM

What you could do is take and add a ground bar to the panel, and remove all grounds from original panel ground neutral bar. Then see if you have enough holes for all your neutrals on the existing bar to have their own hole. And maybe a couple new ones. If there is not enough holes in bar to do this, you will need to make further modifications. Let us know what hapens, good luck.....