50 Amp Main

1967 home with 50 amp main…when I through the upper left 50 amp it killed the whole house. Original home did not have AC, now it has a 3 1/2 ton unit and gas furnance for HVAC.

The meter is behind the box outside and no external breaker. SO the 50 amp uper left is it.

Already going to recommend Electricain, have false grounds, polarity issues, one outlet puts out 50 volts only, so its got some issues.

Question for the electricians what should I know about the picture, please explain what you see. It would be greatly apprciated.


Hi Curt,

Looks like you have a split bus panel, the conductors attached to the top lugs are the supply, and the 50amp breaker supplies the lower 1/2 of the panel, no primary disconnect is required as throwing the top 6 breakers shuts down all the power to the home.

In reality that is probably a 100amp supply which may be a little small for a home with AC these days, an electrician would need to do a load calculation to determine what size service would be needed.



That’s exactly what that is. It is an older Square D split buss panel. The top four two-pole breakers are the mains. The 50 is the “house” or lighting main.

top left was 50 amp right side was 30 amp still think its 100 amp service? I would like to know more if you have a minute to post something about the box and its grounds ect…

I concur with my fellow HIs.
Another concern is: it appears that the branch wiring may be undersized on the bottom right 40 AMP 240 breaker .

That was another call out I had and why I deferred to a electrician. Can’t figure out how Garry and Pete think its a 100 amp service. There is only one 50 amp breaker in the whole box.


That’s got nothing to do with it. Even if that 50 was the only breaker at the top it would still be a 100A service.

What size are the service entrance conductors? THAT is likely your weakest link. Looks like #2 to me. Even if they are #2AL that is good for a 100A service.

Like I said, ALL FOUR two-pole breakers at the top are mains.

Could very well be for an A/C unit and be completely legal and safe.

It’s probably for that 3.5 ton unit outside.

Nailed it it was a 3 1/2 ton unit


It sounds like you are not familiar with how a split bus panel works. The NEC requires that the main panel be shut down with 6 or fewer breaker throws. In the 70’s, it was popular for panels to not have a single main breaker, but instead to have essencially 6 main breakers in the upper half of the panel, one of which shut down the lower half of the panel. Often times the upper and lower sections of a split bus panel are visually set appart, but not always and not so with this panel. The 50 amp breaker at the top left feeds the lower breakers in the panel. Only the top 4 or 6 two-pole breakers are supplied by the mains. The lower half of the panel is supplied from the 50 amp breaker. When you turn the 50 amp breaker off, the upper two-pole breakers are still live.

BTW, why are you flipping off breakers during a home inspection?

When determining the service capacity of a home with a split bus panel, you take the lowest of the panel rating (you have to read the panel sticker to get this), the main conductor rating, and the meter box rating. You do not reduce the service capacity if the sum up the upper section breakers is less than the panel rating. This may limit the actual current draw at the home, but this is different from service capacity.

This was real helpful, Thanks.

The house was vacant so flipping a breaker to gain a better insight on what was it was doing seemed warranted, very rare event for me personally. The house had outlets with only 50VAC so there where other issues. I did not clutter the post all of them.

My concern in this box was the largest breaker was 50 Amps, home originally had no AC and the appliances had been upgraded. So if the 3 1/2 ton unit on start up draws so many amps and just so happened to coincide with Oven on and a separate stove on might it not be to much load for the current breaker set up…regardless of service capacity?

Service capacity could be what ever but if the breaker configuration is not adequate to the conditions the house presents, its a problem. Therefore I referred it to a electrician for a load capacity and some other issues in my final report.


Watch my video…not specifically on Split Buss Panels but it explains sizing a service rather well…I think anyway.


Very helpful, Thanks Paul

Some new thoughts that make me feel good I asked on this board.

I could not tell what size the service lines in where and only wires visible is what you see in the above…hold that thought I will do a clip of the wires in. See in this post a close up.

thats 4 cu going to the 50amp but the main wires in are not much bigger and no labeling, So I did not guess (see in video) I asked.

Now I label the post 50 amp main and that may have been misleading but I really did not see how this could be a 100 amp or better service with the information that I could “see”. No label on meter, painted panel dead front. So until I knew otherwise I called it as high as I could see and that was 50 amps. I thought it may be 70 amp box but I wasn’t sure, so I posted and asked for help. I kept thinking 1967 no ac may have been a small box and in my mind call it smaller and have a electrician open it up and do a true load capacity for the home.

Some of these older boxes are tight and seeing everything is difficult. I’d rather ask and have a few of you think I was a ninny than get it wrong. However most of the members are very helpful and teach rather than preach.

Again Paul thank you,


NO problem my brother…if all else fails never guess and you did the right thing in asking…