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Given that the following is true.
They are the same size.
They take the same amount of work to install.
They are twice as useful.
Double adapters are a thing.

So why do single power points 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.

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).


• 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).

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, (6' in most rooms, 2' on kitchen countertops). These special-purpose receptacles won't count, so you should find a normal receptacle nearby.

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.