Using a thermal camera (coolest thing in the world, by the way), I discovered that a GFCI outlet in my bathroom is hotter then the surrounding wall when nothing's plugged into it:

enter image description here

It's not boiling hot; just slightly warm to the touch. I never noticed it before I had a thermal camera. This is probably bad, but what does it mean? Should I replace it? Is my house about to burn down?

Update to answer several people's questions:

  • The GFCI is on an interior wall covered with cementboard.
  • The wiring is copper.
  • All other non-GFCI electrical receptacles--including those on exterior walls--are any different from the surrounding wall in terms of temperature. Here's one on an exterior wall: enter image description here
  • I don't believe there are any downstream connections.
  • The heat is emanating from the right side of the unit itself: enter image description here
  • The box is quite small; the sides of the GFCI are about 4mm away from the sides of the box. Not a lot of room for it to dissipate heat.
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    The surface is cementboard, and the wall is an interior wall. There's another bathroom on the other side of it. – iLikeDirt May 13 '14 at 19:21
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    If it had been an exterior wall on a warm day, that alone can explain it -- as the electrical box means there's less insulation in that location. – Joe May 13 '14 at 20:16
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    Probably normal for powered up electronic devices, which a GFCI is... Find a wall wart you've got plugged in and powering something, it will likely be brighter. – Fiasco Labs May 13 '14 at 20:53
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    Heh, we live in such a neat time for this kind of thing. Was at the dentist a while back and the assistant didn't like the looks of something, whipped out this thing that was the approximate size of a screwdriver with a thick plastic shank, stuffed it in my mouth and made a comment, "as I figured, the amalgam filling swelled and is trying to crack your tooth, let me take a picture of that to show Doctor". – Fiasco Labs May 14 '14 at 4:03
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    Is it possible that this receptacle is feeding other devices that might be consuming power? – Tester101 May 14 '14 at 10:29

As mentioned in several places, GFCIs use a little bit of power even when nothing is plugged in or energized downstream.

The heat distribution sure looks like it is coming from the GFCI electronics, but it could also be heat seeping from the other side of the wall, especially if that room has higher air pressure than this one—like if the exhaust fan were running in this room and someone took a hot shower in the other room. Presumably there is another outlet on the other side of the wall close to this one.

You could try turning off this circuit for 15–30 minutes and see if it completely cools. That would also rule out whether there is anything downstream causing a current to flow through it.

Or you could measure its power consumption and see if it is more than 100 mW or so. If it is more than 1.0 watts, I'd replace it.

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    Due to the electronics, GFCIs will be slightly warm to the touch, IR imaging like this can blow all out of proportion what is going on as they're built to detect heat envelope flaws and are quite sensitive to minimal IR levels. – Fiasco Labs May 13 '14 at 20:52
  • Indeed! Other GFCI outlets in other houses I looked at with my gizmo today exhibited the same thing. You learn something every day. – iLikeDirt May 14 '14 at 1:06
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    It seems odd that the electronics in a GFCI receptacle would raise the temperature of the device 15°F above ambient. I'd suspect there's current flowing through the device, just not through the receptacles on the device. – Tester101 May 14 '14 at 10:36

I wouldn't suspect the electronics in a GFCI receptacle would raise the temperature of the device 15°F above the ambient temperature. I've read a lot of technical documents about GFCI receptacles, and I couldn't find any mention of heating while not under load. I don't ever remember feeling a warm GFCI receptacle (not under load), and after measuring every GFCI receptacle in the house with an IR thermometer, I wasn't able to find any that were noticeably above ambient.

If the house wiring is aluminium, you'll want to inspect the connections. Make sure they're all tight, and not corroded/damaged in any way.

If it's copper wiring, you'll want to determine if there's anything downstream from this device (either on the LOAD terminals, or pig tailed off the feed). If there is, unplug/disconnect it, wait an hour or so, then take a new reading. You'll also want to verify the box is not overfilled (which would reduce heat dissipation).

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Way cool toy.

There are a variety of possible causes. The actual hole in the wallboard reduces the insulation value of the wall: thus if the inside of your walls are warm, you could see hot spot even with a blank cover plate. A matching outlet hole on the other side could lead to a interior wall. For exterior walls insulation is rarely "fluffed" properly around an outlet, leading to a hot spot on a hot day.

That said, GFCI outlets and breakers do use power 24/7 (this is called parasitic or vampire power). And as of this writing, Murray and Seimens at least don't even specify how much. Bench measurements show at least 5mA for GFCI's and 20 mA for AFCI's (600 to 2400 milliwatt). Compare that to the latest technology Apple Computer products (http://www.apple.com/battery-charger/ ) at less than 30 milliwatt. So basically each outlet is a mini electrical resistance heater. It's known that an electrical panel full of GFCI/AFCI breakers can have heat problems. For people on solar systems this is level of loss 24/7 is a deal breaker, for most people on grid power it's mostly not noticed.

But to narrow it down in your case: Do regular outlets show the same thing? Other GFCI outlets in the house? Is this repeatable at night as well as during the day?

If your GFCI is drawing more than the average, it should be replaced.

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  • This outlet is on an interior wall. All other outlets and electrical receptacles--even those on exterior walls--show no temperature difference compares to the surrounding wall. This is the only GFCI in the house (others in other houses have shown the same thing though). It's repeatable at night as well as during the day. How should I measure its electrical usage? My Kill-A-Watt registers nothing through the sockets. – iLikeDirt May 15 '14 at 18:38
  • Zero current will register through the socket. To measure the GFCI's internal use with a Kill-A-Watt would be hard (it can only measure small currents over a long time average). Better is to take out the GFCI, place an meter inline to the hot lead, then use an Ohm's law calculator to get Watts. Any common volt/amp meter can do this, set to AC Amps. – Bryce May 15 '14 at 19:11

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