Working out which plug is on which half of a handle tied circuit

Question

In a house built in the early 1980s in California, USA.

My kitchen and dining room are (mostly) on a single pair of 20 amp circuits - excepting the dishwasher and garbage disposal, which each get a 15A circuit, and a "Microwave" circuit which is entirely inappropriately located above the oven (maybe they planned to have a Microwave/range hood) in a spot only the range hood can utilize. The pair of circuits are handle tied, so my guess is they are most likely a multi-wire branch circuit. (And yes, I know this is nowhere near current code - it's a rental, unfortunately, so limited options for changing things.)

Unfortunately, due to the inaccessible "Microwave" circuit, I have to attach both my microwave and toaster oven to the main set of circuits (but have some choice over which outlet to use for each, as I can move them around). Is it possible to determine which outlet is on which circuit of the pair, without opening the wall or doing anything significant to the panel? And if I determine that, say, these outlets are on "5" and these outlets are on "6" (the numbering in the panel), am I correct that it would work to have the two appliances on one each, and wouldn't trip (assuming other things weren't utilizing the circuits), since each would be on a different hot leg?

Ideally I'd either temporarily un-tie the two circuits and intentionally trip one, and then see what works and what doesn't, or have some way of telling which is which using the multimeter. (I'm also considering running an extension cord to the microwave plug, as ugly as that looks, because it certainly isn't a good idea to have two 1200+W appliances that often will be run at the same time on one circuit; but hoping there's a way to have one on each hot leg.)

Here’s a pic:

Answer 1

You can tell by how the panel is phased.

Service panels have their 2 phases (poles, really) laid out in a very particular way.

You have a GE panel. It's a little odd, but still decipherable. Let me stripe it for you like in the link.

Yup, 5 and 6 are on opposite poles. Note how GE does double-stuffing a bit different. Note also the Code violations; the empty holes at breaker 0 and 6-1/4 need to be filled with GE approved blank plates. The easiest-to-find models of blank plate are THQP115 and THQP120, which are also breakers LOL.

Now, watch Technology Connections' video on how we use 120V and 240V, and particulary his measurements on how breakers are phased. I cued it up for you. Notice how breakers on opposite poles are 240V from each other. Don't open your panel; you don't own that house.

So now it's a simple affair. If you can just measure voltage from the hot terminal of the microwave from the hot terminal of any other candidate socket... if the voltage difference is around 0 volts, it's on the same pole of the MWBC. If it's around 240V, it's on the opposite pole. Mark your receptacles in some manner.

To measure at a socket, just insert the UL listed and 600V rated voltmeter probe into the hot terminal. On a NEMA 5-15 or 5-20 socket, you already know ground... neutral is the taller one (or T-shaped one). The other one is hot.

Answer 2

If these receptacles truly are wired in MWBC there's no need to remove the covers or disconnect anything. Just use your volt meter to measure AC volts between the hot/line terminal of one receptacle and that of another receptacle. Doesn't matter which meter lead (red or black) goes to which. Use an extension cord if necessary to get everything within arm's reach.

If you measure approximately 0 volts then the pair of receptacles are on the same leg of power. Mark them both with a colored tape or other tag. If, on the other hand, you measured approximately 240 volts then the two receptacles are on opposite legs of power. Mark them with differently-colored tape or other tag. By "approximately" I mean that if it's a few volts or less that's close enough to 0; if it's 220-250 or so that's close enough to 240.

Repeat the process, always measuring between one previously-marked receptacle and one unknown receptacle. When you measure 0 volts mark the unknown with the same mark as the known one; when you measure 240 apply the opposite mark.

If for some reason you still want to know which half of the handle-tied breaker each set goes to, try these steps:

1. turn off the breaker
2. remove the dead front from the panel
3. disconnect the wire from one of the breakers
4. turn the breakers back on
5. go see which set of outlets has power
6. turn off the breaker and restore everything as it was

Answer 3

Great question and good thinking!

• Flip the two breakers off.
• Open each of the outlets that are now dead.
  • Plug a lamp or something similar into each outlet before taking the cover plate off, just to be 100% sure. You don't want to end up dead from this little experiment.
• You should note that some of the outlets are wired to the black wire and some to the red wire.
  • This presumes that the house was wired with NM-B cable, not conduit in which case the hots could be any color but green, white and grey.
  • If you are on conduit, then you'll find some outlets on "Color A" and others on "Color B".
• It's possible that you'll see a red wire on the top outlet and a black on the bottom outlet of the same device.
  • This means the top outlet is one one breaker and the bottom on the other. Perfectly legal and acceptable.
  • Make 100% certain that the metal tab is broken off between the screws. If not, that means that the two circuits will both be energized when either breaker is on (should the handle tie ever be removed).

The ones on the black wire are on one of the handle tied breakers and the ones on the red wire are on the other breaker. It doesn't really matter which is which for your purposes, you just need to know "A" and "B" circuits so you can distribute your loads appropriately.

Answer 4

FreeMan's answer is the standard way to do this. There is one other option, which involves removing the front panel of the breaker panel (which you may or may not feel comfortable doing) but does not involve disconnecting any wires.

• Remove the front panel. This is usually pretty easy as it needs to be done any time a breaker is added or changed. **Be careful. Keep metal (rings, watches, tools) away and stay away from the feeder (usually at the top or bottom, and usually connected directly to a big breaker).
• Get a clamp meter:

• Get a helper
• Unplug everything from all 5/6 receptacles.
• Have the helper plug a reasonably high powered device (e.g., a lamp with incandescent bulbs - remember those?) into each receptacle
• Measure the current on the hot wire going into each breaker (5 & 6) to determine which receptacles are on each breaker