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I'm replacing 15 amp outlet receptacles in my home and I came across an outlet that had me confused.

The receptacle has two hot wires (a black wire and red wire) with the hot tab broken. The receptacle has one neutral wire with the neutral tab broken.

What has me concerned is that the neutral tab is broken and there's only one neutral wire. What scenario would call for that wiring configuration?

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    Does that half of the receptacle supply power if you plug something in? Do you have a ground wire going into the receptacle? – Niall C. Nov 14 '16 at 15:49
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    In that configuration 1/2 the outlet would never work. – Tyson Nov 14 '16 at 16:07
  • What is the voltage across the two hot wires 120 V or 240 V? – Jim Stewart Nov 14 '16 at 16:10
  • What is the voltage from each 'hot' wire to the neutral? – Jim Stewart Nov 14 '16 at 16:19
  • There is a ground wire going into the receptacle. I'll try to provide more information tonight once I have the outlet in front of me. Thanks for the input so far! – Justin Helgerson Nov 14 '16 at 19:14
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Let me guess, the room with that outlet, most likely a bedroom, doesn't have a ceiling light fixture. That or a ceiling light was added later on. And one of those outlets never worked.

The setup you described is typical of bedrooms in many homes where the primary light source is a plug in lamp. Since the lamp only needs one outlet, the other outlet can be left hot at all times instead of switched. So the electrician runs a three conductor cable from the light switch: white is neutral, black is constant hot, and red is the switched lamp socket. This way you can plug in an alarm clock or phone charger and not have it controlled by the switch.

My guess is the electrician was inexperienced and broke off both tabs without realizing they only needed to break off the hot tab. Probably a new guy tasked with doing the grunt work of wiring the receptacles and fixtures. No one ever bothered to check both sockets and the rest is history.

  • Mister Tea, your explanation sounds much more reasonable to me. Presumably we will hear whether there is a switch box and what is in it, and if one single- pole breaker controls both hots. – Jim Stewart Nov 14 '16 at 22:16
  • I tested the outlet and the bottom socket didn't work. Even with the nearby switch on there was no power. I replaced the receptacle and kept the tab for the neutral in tact and now the bottom socket receives power when the switch is on. I'm guessing the previous owners didn't know or didn't care about the bottom socket not working. FYI, this was the living room. I thought it was a mistake at first, but then wondered if something else was going on that I didn't understand. I probably should have tested both sockets from the beginning! – Justin Helgerson Nov 15 '16 at 3:57
  • @JustinHelgerson I have seen this setup outside of bedrooms but rarely. Glad you got it fixed. – Mister Tea Nov 15 '16 at 12:54
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One scenario is that this duplex receptacle was originally split wired almost correctly with the neutral tab intact, and the tab on the hot side removed. Originally the two hots went to two separate single pole breakers on different legs so that the current in the neutral was the difference in the currents in the hots. Later at least one of the breakers was moved and the breakers then connected to the same leg. The current in the neutral was now the sum of the currents in the two hots. This caused problems and someone removed the tab on the neutral to stop overloading the neutral even though that disabled one of the receptacles.

According to this article* in a dwelling a single two-pole breaker should have been used rather than two single pole breakers. This is to prevent the condition described above and to prevent someone from being able to switch off only one hot in the box.

*Duplex Receptacles And Break-off Tabs

  • I sort of doubt that. The likely scenario is an inexperienced electrician broke both tabs off when it should have only been the hot tab. One outlet worked which was enough to pass the install and no one though to check the other. That box is most likely fed from a switch, the black is a pass through for the constant hot and the red wire is switched. – Mister Tea Nov 14 '16 at 18:16
  • It's possible the reason for a broken tab is not to use two circuits, but to switch half the outlet using the same circuit. – Tyson Nov 14 '16 at 18:18
  • It would be nice to confirm that the two hots in the receptacle are on the same leg (and presumably on the same circuit and breaker), but at this point it is 99.99 % certain that Mister Tea and Tyson figured this one out. (In my house I just put in a whole house surge protector with a 50-A double-pole breaker and I had double-pole breakers 'on the brain'). So the voltage across the two hots should be zero and one single-pole breaker should control both plugs. The original poster could look in the switch box, but it may not be worth it. – Jim Stewart Nov 15 '16 at 12:06

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