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Given that the following are true.

  • They are the same size.
  • They take the same amount of work to install.
  • Doubles are twice as useful.
  • Double adapters are a thing.

Why do single electrical receptacles even exist? I was looking at the plans for a house and some of the power points were specified to be singles. Is it a code/standards compliance issue? It can't be to make a house $2 cheaper, they wouldn't be worth manufacturing if that were the case.

Someone edited this to say "Receptacles". I assume that's an Americanism? Sounds very odd to me.

enter image description hereenter image description here

Standard Australian power points. They're the same size, fit in the same hole, and have the socket in almost the same point. I've seen singles mostly in older houses. I thought maybe doubles used to be more expensive, or maybe they just ran out and put a single in. But then I saw the building's wiring overlay and somebody decided - in the planning stage - that for some reason that point needed to be a single. I know it's of no real importance, but this has been bugging me for years. This is just an average room in an average suburban house. No basement pump. (Cultural note: Australian houses don't have basements. Until recently, we tended to spread out horizontally, not vertically.) There's nothing that would be damaged if the power failed. Except the fridge, and I've never seen a fridge with it's own circuit.

We live in a world where these exist.enter image description here So if single power points are supposed to be the solution to stop people plugging in two devices, someone should rethink that.

enter image description here

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    Also the receptacle for an electric dryer. – Barry Feb 21 at 23:12
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    How old are we talking? I remember houses where there was exactly one power socket per room, and that was considered normal. Back then there simply wasn't the dearth of powered devices. – Criggie Feb 22 at 5:37
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    Single-socket wall boxes are common in many other countries where they are more compact than a double or triple-outlet: e.g. Single: diy.com/departments/267075_BQ.prd vs Double: diy.com/departments/173672_BQ.prd – Dai Feb 22 at 6:53
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    @Criggie - I think you meant there wasn't the breadth of powered devices; there was a dearth. – AndyT Feb 22 at 14:33
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    Not sure where you are but, in the UK and continental Europe, a single receptacle is, as one would expect, about half the size of a double. – David Richerby Feb 22 at 15:26
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There are quite a few reasons to use a single receptacle instead of a duplex receptacle. A few that I know of:

  • Recessed for clock or behind a TV. In this case, it is sometimes easier to use with one centered receptacle instead of top or bottom of a duplex receptacle.
  • Air conditioning, range, dryer or other larger-than-usual circuit (in the US, this means anything > 120V or > 20A). I believe in at least some cases this is a code requirement.
  • Refrigerator or freezer in a GFCI-required area in order to avoid GFCI requirements (subject to local code and AHJ). In this case a second receptacle would be indication of intent to plug in additional devices rather than using a single receptacle for a specific exemption.
  • Cooktop ignition. I have this in my own house. My electrician installed a single receptacle as (a) there is no reason to ever plug in anything else inside the cabinet under the cooktop and (b) he installed it "upside down" - ground pin on top - instead of the more typical (for the US) orientation, for an extra little bit of safety (which would be awkward/confusing elsewhere but for the seldom unplugged cooktop is perfectly fine). The same logic would apply for a single receptacle for a garbage disposal.
  • Specialized sensitive equipment - e.g., medical or computer - to minimize interference from other equipment on the same circuit (e.g., there are devices that will reboot due to voltage drop if a laser printer starts printing on the same circuit, but which will be fine as long as they are on separate circuits - and any time you have an open receptacle it becomes "available" for a printer or vacuum cleaner or whatever).
  • Backup power - if you have a generator or battery backup with limited power then using single receptacles is a way to make sure that only the specified loads are on the automatically transferred circuits.

I am sure there are more reasons - if anyone has any good ones, feel free to add to this list (or make your own answer if you prefer).

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    They actually all sound like pretty good reasons. None of them apply in the case I'm looking at though. It's just sitting in the corner of the room on the same circuit as the one in the other corner and about a third of the house. – Spike Feb 22 at 0:43
  • @Spike Weird, what did he have a surplus of those? They're worth real money.) I would map your circuits, i.e. find out which breaker powers which outlets. (I'm fond of labeling them with a labelmaker with codewords, Thor, Sif, Odin, Loki, Cap, Widow, Stark, Hulk, Etc. Whatever.) Shrug, maybe he's in a locale where you're only allowed so many receptacles per circuit and he was "over" and that was his answer. – Harper Feb 22 at 3:57
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    @Spike They don't happen to be on toggle-switches in the room, do they? Being in corners, I could see them using single-receptacles for wall-plug outlets on a light-switch to avoid confusion about which outlets in the room are on the switch and which are not. – Der Kommissar Feb 22 at 16:50
  • @Harper I always assumed there should be a limit, but when electricians here wire in new power points I've never seen them check anything. They just grab the first cable they see and get cutting. They definitely don't go and count how many points are on the circuit first. – Spike Feb 23 at 0:32
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    Also add dedicated switched outlets, such as for plugged in (rather than direct wired) garbage disposals. – simpleuser Feb 23 at 18:20
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enter image description here

Single receptacles are used for reasons

Nobody installs one of these by mistake - they're a lot more expensive, to start with! When you find one, it has a specific purpose for being there because of a Code requirement for its application.

  • It may be in a place where GFCI protection is required, but it is appropriate for this individual load to not be GFCI protected. An example is a refrigerator or freezer in a basement or garage.
  • It may be effectively a dedicated circuit, provisioning power to a single large appliance that needs the entire circuit's capacity. An example might be a large window air conditioner, dishwasher, or built-in microwave oven.

In these cases, providing only one socket is on purpose. It is to prevent you from using the circuit for anything else.

Now, you may know that every room is supposed to have receptacles at certain intervals, (12' in most rooms, 4' on kitchen countertops). These special-purpose receptacles won't count, so you should find a normal receptacle nearby.

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    Distance from a receptacle is 2' & 6" or 4 ' & 12' between. I know you know this but interval would be 4' in kitchens and 12' in other rooms. – Ed Beal Feb 22 at 15:10
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    @spike that is keying. The vertical part allows common NEMA 5-15 plugs. The horizontal part lets in NEMA 5-20 plugs, which have different keying so you cannot plug em into 15A sockets. – Harper Feb 23 at 1:00
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    This answer is incorrect for NZ/Aus at least. – Someone Somewhere Feb 23 at 2:23
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    @SomeoneSomewhere OP didn't specify. Long after I wrote my answer, he added localization. I couldn't have known. Edits which alter the question so basically are discouraged on SE for obvious reasons. Anyway the "cost" thing is correct, they spent extra to use singles. Has to be a reason. – Harper Feb 23 at 11:42
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    @Spike by the way, Australia has the same deal with differently keyed plugs and sockets. On your 20A sockets and plugs, the power pins are taller. So a 10/15A plug will fit in a 20A socket, but not the other way 'round. . North America couldn't do "taller" because we use that for hot/neutral keying. – Harper Feb 23 at 11:55
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Sometimes a single receptacle is installed to ensure that the circuit is dedicated to a single appliance. For example, you might install a single receptacle for a sump pump in the basement. If you install a regular duplex receptacle, someone might use that second receptacle and trip the breaker. Nobody notices and the basement floods because the pump is offline. Other examples where a single receptacle might be a good idea: refrigerator or storage freezer.

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    Basement toilet pumps, also called sewage ejector pumps, too. – whiskeychief Feb 24 at 1:06

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