2 circuits to one receptacle?

From time to time, I do some small jobs for sellers getting ready to put their house on the market. A lady wants GFCI’s installed in the bathroom and kitchen of a mid 70’s Split Level. The kitchen receptacles went great.

When I got to the bath, I plugged a shop vac in the receptacle (so I can hear it from the basement) and found the breaker. I returned to the bath, start clipping the wires off the receptacle and ZAP!-it bites the crap out of me! My bad, I know to always use my meter! After 1/2 dozen trips back and forth, I found the “other” breaker that feeds the receptacle. I found, thru testing, that there are two wires that are only “hot” when the lite switch is on, even when disconnected from the receptacle, both black and white are “hot”. The other two feed the vent fan and heater. Yet they are on separate breakers. I checked, the tabs are not broken on the receptacle. It’s wired “normally”, but I can’t understand how it could even work.

I tried just installing the GFCI, wiring it like the old receptacle, but it won’t work. As soon as I turn the light switch (on or off), it trips.

After playing with it back and forth for about 3 hours, I gave up and re-installed the original receptacle.

Anybody ever seen this type of scenario before? I really hate admitting I don’t know hot to fix it!

I think it’s very dangerous to have two separate breakers “feeding” one receptacle. Seems there is a potential for miswiring and creating 220 volts there?

It sounds like either you missed the tabs being removed on the hot side of the receptacle or you got some wires mixed up which were feeding the fan or light separately. What you’re describing doesn’t sound possible.

As for multiple circuits in a single receptacle, it’s common and not an issue. MWBCs are common for sumps and sewage ejectors around here. Often the receptacle is just being used as a junction box for the circuit when multiple circuits are present.

Nope, the tabs are definitely in place. It didn’t make sense to me either. I guess I should have checked continuity to verify, but the tabs were not removed. What confused me was the receptacle was not “feeding” power to anything. Both circuits were "hot’ with the breaker on, disconnected from the receptacle.

Then it has to be the wires got mixed up. There’s no scenario where two ungrounded(hot) conductors could be connected to a 120 v receptacle(tabs intact) without tripping the circuits or frying some 120 volt equipment.

Not true

How about if both are on the same phase .
Regardless it is wrong .
An electrician would have no trouble figuring out this instantly.

Hmmm, I stand corrected. I guess that wouldn’t trip the circuit/s would it?

There’s still the problem that it tripped when Mike connected them up to the receptacle which may indicate they are on opposite phase. Keep us updated, this is an interesting one, glad you didn’t get bit badly.

I see two circuits to one outlet now and then in my area. Usually on a switch controlled outlet so if the power trips on one, the light plugged into the other will still work. Tabs on the outlets are usually cut. As for not tripping , like stated above if they are the same phase it will not trip as there is no difference in potential. We’ll Chalk this one up to a DYIer getting lucky and forgetting to cut the tabs and it just happened to be two circuits, same phase…

I am fairly confident that you got zapped by the return current on the neutral. That outlet is sharing the neutral with that other circuit that you found later (a multi-wire branch circuit, MWBC, that another poster referred to). Please do a google search on how MWBCs work. It’s confusing at first, but you’ll figure it out. These circuits were originally wired wrong in this instance. The two breakers feeding this circuit should have been connected by a breaker tie, that way when you kill power to one, you kill power to both, and the neutral current won’t zap you.

that’s kind of where I was heading. The main breaker never tripped, but the GFCI tripped.

That makes sense.

My good friend and former employee is a Master Electrician. He’s stumped as well. Either I didn’t explain it right, or I am mistaken about the broken tab.

Both breakers are on the same phase

If the hots did not feed through to other devices or if only one did, abandoned one in the box and install the GFCI.

If they go to feed other devices you could bypass the outlet for that circuit.

That’s how I see it. Connect the non-switch controlled hot to GFI and switch controlled to the correct outlet (light, heater, fan). Or cap and abandoned hot that is not needed.

Thanx guys. Slap myself on the forehead. That 's too easy.

Tomorrow I shall call and give my electrician buddy a lesson.

I am curious…

Why are you doing electrical work?

You are not qualified.
You are not licensed.
You do not have the proper experience.
You have no insurance or bond for such work.
It is illegal.

You are putting yourself, your client and the rest of the community at risk for safety and legal issues. Not to mention it is a conflict of interest for you to do so. It also invalidates your company slogan that is at the bottom of your posts.

You are mistaken

Actually, finding the answer and completing the work validates the slogan, thanks for the HELPFUL brothers here

Actually, it is for you:
§29-3B-8. Effect of noncompliance with article; failure to obtain license.
Any person, firm, corporation or employee thereof, or any representative, member or officer of such firm or corporation, individually, entering upon or engaging in the business of performing any electrical work as defined in this article, without obtaining the required license or otherwise complying with this article, is for the first offense guilty of a misdemeanor, and, upon conviction thereof, shall be fined not less than one hundred dollars, nor more than five hundred dollars. For a second and each subsequent offense, the penalty and punishment is a fine of not less than five hundred dollars nor more than one thousand dollars. Each day during which such electrical work is performed without the required license or while in noncompliance with any of the provisions of this article, after official notice that such work is unlawful, is a separate offense.

Be careful with your insurance: it won’t pay off if you are doing work you are not licensed for.

You are mistaken. Again. Read the entire article. Here’s the link.