Unused outlets get warm when others under load

Question

When we run moderately high power devices (around 8-9 amps, e.g. vacuum cleaner, portable AC, small space heater), the other unused outlets on the same circuit get warm/hot after 15-30 minutes. The devices are plugged directly into the outlet, not through a power strip or extension cord. It's not so much the outlet the device is plugged in to as it is the other unused outlets, some of the outlets seem to get hotter than others. The breakers in question are all 15A.

So far we've tried to limit usage of the high power devices but for e.g. the AC we'd like to be able to run it longer. Is it safe for the outlets to be getting hot like this? Is this likely to be an issue with the wiring, outlets, breakers, or hard to say without further diagnosis?

Note: I see a lot of questions on here about hot outlets but they seem to all deal with the outlet getting used, not other outlets on the same circuit.

Answer 1

The appropriate response to a hot outlet is NOT "change usage patterns to reduce somewhat".

The appropriate response to a hot outlet is Kill It With Fire before it kills YOU with fire. This is a "get up out of your chair, trip the breaker off, and fix it Right Now PDQ" type deal.

2 things tend to cause this: backstab connections, and too-loose torque (or too-tight) on the side screws.

Get a $4-ish "Spec Grade" outlet (they come in a little box instead of loose in a bin, they are just better stuff, and they provide a good answer for 3+ wires on a side)... and swap that receptacle. Pay attention to the "tabs".

I want to say "get a torque screwdriver so you can set screw torque to spec", because science has shown screw torques really matter, even on the small stuff. ... and, master electricians can't set torques by feel. (neither can you). But I know no one will listen to that advice.

At the least, get a Robertson screwdriver that will fit the socket and really let you crank it down... because it's quite difficult to reach the specification torque with a Philips screwdriver.

I'm OK with the daisy-chaining method of having power go "through" each receptacle. It makes it easier to monitor it... you can put your hand on the receptacle and feel it. If it was pigtailed, the wire nut could be melting and you wouldn't feel much. A little warmth is to be expected.

While you're at it, double check that you don't have aluminum wire. If you do, relax... There are just two rules you need to follow. You already met the torque rule, equally important with aluminum. The other is use devices rated for aluminum wire (CO-ALR receps/switches, and Alumiconn splices).

Answer 2

If everything is properly installed and undamaged, ordinary connections (junctions between wires, between wires and receptacles, between wires and switches) should produce very, very little heat and definitely not feel noticeably warm to the touch.

Two key things to check, both easy enough to confirm/deny by opening up the receptacle boxes:

Back stab connections

There are four types of connections commonly found:

• Wires hooked around screws

This is the old standard. Make sure the wires are hooked around in the direction of the screw (i.e., clockwise) so that tightening the screw doesn't push the wire away. Make sure the bare part of the wire is fully under the screw with no insulation under the screw.

• Back stabs

These are single-use connections, normally designed for 14 AWG wire (but many circuits will have 12 AWG wire). They are fast and easy to install, but if (a) not inserted all the way, (b) not stripped properly, (c) removed and reinserted or (d) wrong size wire then they can result in bad connections = heat = fire.

• Screw-to-clamp

These are the best! You insert the stripped wire straight (like back stab, so no making a hook = fast and easy) and screw down to hold the wire(s) in place. Yes, wire(s) - you can usually have one wire on each side of the screw, which is an extra benefit. But the receptacles cost a little more than the cheapest ones - you get what you pay for. The same receptacles that include screw-to-clamp are also usually better designed in other ways. Well worth the cost, IMHO.

• Permanently attached wires

This is most common on smart switches, dimmers, etc. Instead of attaching wires in the box directly to terminals on the device, you use a wire nut to connect those wires to the device wires.

Any connection can go bad if repeatedly stressed or poorly installed. But back stabs seem to be most vulnerable to problems.

Aluminum Wiring

As Harper (and others) make clear, aluminum wiring is not inherently bad. However, aluminum branch circuit wiring, especially 15A and 20A wiring, has a very bad reputation that is well-deserved. Due to different expansion rates and poor installation practices, aluminum wiring installed with 15A and 20A receptacles, switches, etc. is a well-known problem. It can often lead to bad connections = heat = fire...

So open up the problem receptacle boxes and see what you've got.

If you have aluminum wiring then replacement of the receptacles with CO/ALR receptacles is highly recommended. If you have aluminum wiring, you should check every connection in each affected circuit, even if it does not feel warm. Any devices not rated CO/ALR should be replaced with CO/ALR, or add copper pigtails with AL/CU connectors (a.k.a., purple wire nuts).

If you don't have aluminum wiring but you have back stab connections, at a minimum move the wires to screw terminals. If any receptacle shows signs of melting, burning or arcing, replace it with a good quality screw-to-clamp receptacle.

If you find receptacles that are using screw terminals, redo the connections to make sure they are really solid (this is what torque requirements are all about). Again, if any receptacle shows signs of melting, burning or arcing, replace it with a good quality screw-to-clamp receptacle.

Answer 3

Nothing should make other outlets warm: you have a problem which should be fixed.

1. You may have hot wires. Hot wires cause fires.
2. You may have hot junctions. Hot junctions cause fires.

Hot wires are caused by undersized wires, or by bad junctions. You may have one junction that is so hot it is heating the whole wire, or you may have daisy-chained bad junctions in each of the outlets.

A junction that is not tightened properly can get so hot it can literally burn up, arc, and start a fire. A wire that is so hot that it is heating the outlets can -- well, probably weaken a junction, causing separation, arcing and fire.

You can measure the outlet voltage, to see how much voltage drop you are getting in the circuit. _{I'm not familar with 110V systems, so I can't say how much drop you should see, but you can compare it with other outlets}. And you can open each of the outlets and check for looseness and check for wire size and check for failed insulation and check for signs of burning.

Or you can get someone else to check it for you, which is what I'd probably do.