# Determine if two outlets are on the same circuit without breaker access [closed]

I live in an apartment and do not have access to the circuit breaker panel. In the summer I run two AC units, and have inadvertently tripped the breaker before while running my vacuum cleaner. This caused a big hassle, as I had to wait for the super to get home so he could go down and flip the breaker back. I'd like to avoid this ever happening again, as 1/3 of my apartment was without power for about 6 hours that day.

When it happened, I made note of which outlets went out, so I now know all the outlets on that circuit. I'd like to be able to differentiate between the outlets on the remaining two circuits, so that I can space my high-draw appliances out evenly and avoid future issues.

What I'm looking for is a device (or pair of devices) I can purchase that will allow me to check two outlets and see if they are on the same circuit. I've seen circuit breaker testers that come with one device which you plug into an outlet, but the other end requires that you have breaker access and wand the device over the breaker or something similar to check. As I mentioned, I do not have access to the breaker, so this is not an option. Ideally there would be a pair that I can plug into two separate outlets, and have one of them tell me whether they are connected or not. My searches online haven't yielded any results on a device like this, so I'm curious if there's any way to do it from within the apartment, without breaker access and definitely without tripping any breakers.

Not accepting answers that say "turn off your AC before running the vacuum" or any such thing. Obviously in the future I will make sure that I turn them off, but this is more a question of load-balancing my devices which do have to run simultaneously.

## closed as off-topic by Brian Carlton, PeterJ, Bimpelrekkie, Rev1.0, Daniel GrilloApr 4 '16 at 11:40

This question appears to be off-topic. The users who voted to close gave these specific reasons:

• "Questions seeking recommendations for specific products or places to purchase them are off-topic as they are rarely useful to others and quickly obsolete. Instead, describe your situation and the specific problem you're trying to solve." – PeterJ, Bimpelrekkie, Daniel Grillo
• "Questions on the use of electronic devices are off-topic as this site is intended specifically for questions on electronics design." – Brian Carlton, Rev1.0
If this question can be reworded to fit the rules in the help center, please edit the question.

• Don't run stuff on the same circuit that is over 20A, or even better, give yourself some margin and don't run more than 18A on the same circuit. – Voltage Spike Apr 1 '16 at 23:33
• Plug the AC and the vacuum into one of the remaining outlets? Basically, there's no way to do this without turning off one of the breakers. Why don't you just get together with the superintendent and work it out once and for all? (And in any case, product recommendations are off-topic on this site.) – Dave Tweed Apr 1 '16 at 23:34
• @laptop2d - That would be helpful advice, if I knew which circuit was which :P – carbide20 Apr 1 '16 at 23:34
• @DaveTweed I generally don't like working with my super, and avoid it at all costs. He's not been the most helpful, and I'm not the type to let people into my apartment when there's a way to do/fix something myself. Last time he wanted to call my electric company for no reason, and started bugging me about my apartment instead of just flipping the breaker. Plus there's a language barrier, so it's hard to convey what I need. At any rate, I'm curious if a device exists to do this. Not looking for a name/brand/sales pitch on a specific one, just what you would call the thing if it does exist. – carbide20 Apr 1 '16 at 23:38
• I have not tried the sensor that is used at the breaker on other outlets, but I think there is a good possibility it will work. You might also consider what local codes require. In the USA National Electrical Code, two or more 20 amp circuits are supposed to supply only kitchen counter outlets and one 20 amp circuit must supply only bathroom counter outlets. Older construction will not meet current code requirements. You should try the Home Improvement Stack Exchange. – Charles Cowie Apr 2 '16 at 0:35

## 2 Answers

There are a few ways. Let's assume you've already mapped circuit 1 and exclude that from these tests.

This method will work if there's a long wiring run back to the service panel (breaker box). Remove every big load from every circuit in the house. Nothing in the house but wall-warts, vampire loads, and clocks.

Now pick any receptacle, designate this circuit 2. Plug a power strip into one outlet, and your biggest load in the other. Put even more stuff on the power strip until you've loaded that circuit as much as you dare. Measure the voltage between hot and neutral as you add loads; ideally it is starting to sag a volt or two.

Now measure the voltage between neutral and ground on every outlet. We're looking for a small difference of less than 1 volt. Those are all on the same circuit - the one you loaded to max. You will notice that some outlets have slightly higher voltage than others because they are at different places along the cable. What they will have in common is their voltage will restore to normal when the circuit is unloaded.

Now turn your loads off ASAP. Breakers can take up to 20 minutes to trip if they are only slightly overloaded.

Why does this work? If you load a circuit heavily, its voltage will sag very slightly, due to our dear friend Mr. Ohm. But hot and neutral wires are the same size. That means both of them will sag about equally - hot will drop in voltage and neutral will rise in voltage. Ground isn't sagging: like the unloaded indicator beam on a torque wrench, it's a reference point. If ground tracks precisely with neutral, you may have a bootlegged ground.

This method will work only if the two remaining circuits are on -opposite- poles in the service panel (assuming the usual 120/240 split phase service common to North America). All things being equal there's a 50/50 chance this is true.

Pick any outlet, designate this circuit 2. Plug a long extension cord into it. Bring the extension cord near every other outlet, and measure the voltage between hot (on the extension cord) and hot (on the outlet). Some will be 0 volts. Others MAY be 240 volts. If they are, you have identified your third circuit. If you get 120 volts, something is wrong - e.g. hot and neutral reversed. If you get 0 volts the two outlets are on the same circuit.

• This answer is perfect, as I own a multimeter already and this will save me from purchasing a circuit tracer (assuming that the stipulations that your methods require are satisfied, of course). Thank you! – carbide20 Apr 2 '16 at 4:43
• One question: for method 2 when you say compare the hot on the outlet with the hot on the extension cord - Do you mean plug one lead of the multimeter into one hot, and one into the other hot at the same time? Just want to make sure before I try this. – carbide20 Apr 2 '16 at 4:59
• Yup, that's what I mean, and be careful because there may be 240v across them. Or not. 240v hits a lot harder than 120v. – Harper Apr 2 '16 at 7:48

You can use a sensitive magnetic field sensor to pick up the field around the heavily loaded wires to accomplish what you intended to do.

As it is suggested in the other answer, unload all loads from all outlets. Pick one of the outlet and load it as heavy as possible with the heaviest load you have, perhaps with a 2kW electric kettle.

Now use the field tracer to track the wires and follow it to all the other outlets it is connected to.

If you don't have a field tracer, you actually can make one cheaply. I did mine by modifying a old, junked portable audio cassette player, classically known as the walkman. Rip off its playback head and replace it with the motor solenoid of the wall clock. Stick the solenoid on the walkman and solder its leads to the lead wires which originally connected to the playback head.

After plugging in two AA batteries and the 3.5 mm stereo headphone to the walkman, you will have a perfect portable field sensor. After few experiment with solenoid placement and orientation over the current carrying wires, the field tracer's sensitivity can be well recognized and be used in very predictive manner. Just listen to the loudest mains frequency noise, 50 or 60 Hertz depends on where you live.

edit

The walkman starts to act as the AC magnetic field tracer when it's PLAY button is depressed, but during this time it's internal motor mechanism starts to run too. This motor leads must be cut in order to avoid this motor noise from being picked up by the sensor solenoid.