1

Just found the setup in the photos below. This circuit was run with 3 wires + ground. White is neutral, Black and Red are on the same phase. There's a single pole 15 amps breaker feeding it. This is not a MWBC.

Each outlet has the neutral bridged between the two plugs, but each plug is fed by either the Red or black wire.

Why would someone install it this way ? Is there any upside I'm missing ?

The downsides I see are:

  • having two wires on the same screw connector.
  • using 3 wires were 2 would do.

The upside ?

  • Would this make it easier to separate this into two circuits in the future?

I'm looking for a rationale as to why the original installer might have done this, and whether there's any further downsides. If this is standard practice, I'd also be happy to learn about it.

Edit, from question:

  • neither the Red or Black are switched anywhere. Last point I see them they go into the wall and as far as I can tell they must simply be connected at the breaker panel.
  • they are indeed bridged on the neutral side and split on the hot side.

Edit:

  • breaker connection showing the red and black together at the breaker: (this setup was done twice by the same guy, only consider the top one. The bottom one goes to another room)

enter image description here

  • whole panel, although I fear the pros will have much to comment on:

enter image description here

original images: enter image description here enter image description here

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  • Have you checked whether there's a switch on the wall somewhere that turns power on and off to either the red or the black half of these receptacles?
    – Greg Hill
    Jan 4, 2022 at 21:33
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    It looks as if the outlets are only bridged on the neutral side. The doubling on the screws was apparently done to continue the circuit to another receptacle without using a pigtail or a wirenut. Go figure!
    – HoneyDo
    Jan 4, 2022 at 21:36
  • no switch for either red or black, and yes, bridged on the neutral side but split on the hot side
    – Jeffrey
    Jan 4, 2022 at 21:42
  • Does the single pole 15 amp breaker that this is fed from have both a red and a black wire connected to the single terminal?
    – Mark
    Jan 5, 2022 at 2:27
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    With a multi-meter or 120V/240V "twin probe tester" you can confirm whether the red and black at the receptacle are different phases. Red to black will be 0V or 240V.
    – P2000
    Jan 5, 2022 at 4:48

2 Answers 2

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The question is "why". I'm going to guess ... since that's all we can really do. Useless MWBCs that were poorly conceived, poorly executed, and never useful, were combined at the panel to gain back a couple of spaces.

Someone thought it would be cool to run two circuits to lots of outlets using MWBC. Just to have the capability all over the house to use one outlet for two big things. If it were done properly with pigtails this would be perfectly fine, even if I can't think of any great applications right now.

Later, someone needed space in the panel (the clue is, it's full) and realized having these twin-circuit outlets all over the house was not that useful after all. Maybe the couples hair drying sessions were fun but didn't need to be done in every room? Maybe as it turned out nobody ever needed to vacuum while microwaving in the kids bedroom? So they were combined onto one breaker as an easy way to gain back a couple of spaces without losing any functionality upstairs.

4

Just found the setup in the photos below. This circuit was run with 3 wires + ground. White is neutral, Black and Red are on the same phase. There's a single pole 15 amps breaker feeding it. This is not a MWBC.

Then they are both on the same breaker.

If they are different breakers then they are an MWBC which is dangerously misfired, and should be promptly placed on a 2-pole 240V breaker. (not a tandem).

Each outlet has the neutral bridged between the two plugs, but each plug is fed by either the Red or black wire.

Code requires a light switch in each room to operate a light. An exception allows a switched receptacle instead, presuming you'll plug in a floor lamp and that will be the room light.

Such wiring is typically done like this. Black is "always-hot" and red is "switched-hot". Each receptacle is connected either to black-only, or the tab is broken and one socket is connected to each, making one of the sockets switched with the switch.

The wiring in this socket is appropriate either for that, or a MWBC.

The deciding factor is -- Is there a switch in this room which seemingly does nothing? If so, most likely this is a switched circuit for the light, but some nitwit defeated the switch by wiring a receptacle just like the above but failing to "break off the tab". The improper tab is bypassing the switch, rendering it inoperative. Find that tab and break it.

Why would someone install it this way ? Is there any upside I'm missing ?

... having two wires on the same screw connector.

You can't ever do that. That's just amateur hour / "saving your way to the graveyard". 2 wires on a screw is just illegal and stupid. (unless the device's UL-approved instructions say otherwise). The right way to do this is either

  • Pigtail. Join the two to a third pigtail on a wire nut... then land the third on the screw.
  • Use receptacles listed for 2 wires per screw, and that means almost any "spec grade" receptacle (cost $3, come in a box instead of loose in a bin). Their instructions specify how to fit 2 wires per screw.

Note that if this is a multi-wire branch circuit (MWBC) then the neutral wire must be a pigtail -- it cannot cannot splice on the receptacle, because it must remain continuous if the receptacle is removed. (just like ground).

Would this make it easier to separate this into two circuits in the future?

No, installers never do things "for the future" unless Code requirements put a gun to their head (neutral in switch loops). They're generally wiring new houses by the dozen, profit margins are paper thin, they don't spare anything.

What you can use it for is entirely decided by where the /3 cables go right now. If to a switch, you can use it for switched receptacles. If to the panel, you can use it for a (corrected) MWBC.

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  • 2
    What you can use it for ... or replace the outlets with ones with intact bridges, cap the red wires in each box, use wire nuts and leave everything on a simple neutral-white and black-hot setup, right? There is a separate light fixture on the ceiling, so no, switched outlets have no value.
    – Jeffrey
    Jan 4, 2022 at 23:17
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    If the red and black wire are on different breakers, they should not use the same neutral wire either, it could get double the amps that the breakers are supposed to limit the system to.
    – Orbit
    Jan 5, 2022 at 12:00
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    Unless it's a proper MWBC setup, @Orbit.
    – FreeMan
    Jan 5, 2022 at 15:00
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    @FreeMan: Indeed, but then the powered lines would be on different phases.
    – Orbit
    Jan 5, 2022 at 15:08
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    Super useful info. Added the breaker panel pic after confirming they were indeed joined there.
    – Jeffrey
    Jan 5, 2022 at 19:04

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