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The situation is the following: We had a microwave and a toaster oven connected to the same receptacle in the kitchen – actually, even to the same socket of that 2-plug receptacle, using one of these extender things:

3 outlet extender

Now, I know that’s not necessarily a good idea, but we weren’t planning to use both at the same time. Of course, predictably, at some point we forgot not to do that and ran both the microwave and toaster ovens simultaneously. After a few minutes of that, they both turned off and the top half of the receptacle didn’t work anymore. However, the bottom one still did, so we just used that one instead and I assumed that something in the top part had fried, making a note to replace the receptacle at some point.

Before I got to that, it unfortunately happened again (yes, I know it’s stupid). And here’s the problem: Even after replacing the receptacle, it still doesn’t work! (Tested directly without without the extender, of course.) While replacing it, I couldn’t find any signs of damage (neither on the receptacle nor on the wires), and as far as I can tell, none of the fuses blew and all other receptacles are still working (I can’t really be sure, though).

So it seems clear that the second time around, something different must have happened than the first time, since initially only half of the receptacle stopped working, i. e. the rest of the circuit must’ve been completely unaffected. What are the possibilities here?

  • Blown fuse. Possible, but as I said, everything else in the house still seems to be working, and as far as I can tell I tried replacing each of them individually (house is from the 1980s with old fuses, so it’s not necessarily straightforward to tell if any have triggered.)
  • Damage to the wiring. This answer has some good information, but since there’s no visible damage and the wiring is different, I’m not sure how much applies here. And also, I would think that the fuses should prevent damage if the load becomes too large?
  • Something else?

Wiring: There’s one black and one red (hot) wire, one white neutral, and a bare ground connected to the receptacle.

This is in Ontario, Canada.

Socob
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2 Answers2

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You describe a typical multiwire branch circuit (MWBC) as is normal for kitchen receptacles in the USA & Canada. Each half of the receptacle (red wire-black wire) would be protected by a separate fuse.

You blew the fuse (Egads, really? Still? Fuses? How...quaint) serving one half of it, and then you blew the fuse serving the other half of it.

Unclear if your replacement fuses were already blown before you installed them, or what the issue is there. If you have a multimeter you can check them for continuity to see if they are blown or not.

If you did the usual "person not familiar with MWBCs" trick of not breaking the tab between the hots when you replaced the receptacle, the new fuses would have blown instantly, so it's probably that. The original receptacle is probably fine.

If you either break the hot tab or put back the original receptacle, and install two good fuses, you can plug both devices into the receptacle, top and bottom, and run them without overloading, since top and bottom are two separate circuits. Using the extender to put them both on one of the two circuits was your error, here. Save that for something trivial like a can opener, not a heavy load.

Ecnerwal
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You overloaded the circuit. Hopefully the repair problem so far is not finding the fuses, not worse. You need to find the fuses and if you cannot you need to trace it back, if it connects to another plug or junction box which I expect it could have burnt the wire off there.

Gil
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