Warm Outlets: How Warm is Too Warm?

[forrestc]

A time before that, I had built a small shed to be an electronics workshop and ham shack. It is a good 50' from my house and double that from the main panel. I had dug a 2' deep ditch for the conduit from the house to the shed. I told the guy I wanted 40 amps to a subpanel in the shed and I'd take it from there. Too much work for a an hour or two and $300 and not enough for a longer period. I think he wanted to bill all the time for the wiring in the walls and outlets. He also didn't want to work with PVC, even underground, even though it is perfectly legal in this jurisdiction. (Must be sch 80 above ground). In the end he didn't bid or even return calls.

I wonder if part of the problem was that where you put a subpanel in you must (in many localities) feed the outbuilding with a 60A feed, and 40A wouldn't be permitted.   This of course varies from location to location thanks to lack of clarity in the code in relation to this. 

Still, if was me, I'd say 'PVC, great, I love PVC, but we need to put a 60A panel and feed in to meet electrical code.  this means 6AWG, or a bit larger to avoid drop so we need to size the conduit and cable appropriately".   But again, I'm not a sparky, just someone who has had to deal with the code a lot.

-forrest

[forrestc]

Hey all,


Basic question. Running a light off a 20 amp circuit. Light draws 14-16 amps continuous. The area surrounding very near to the wall plug (like within a couple inches at most of where I plug the light in) gets slightly warm after running the light for 30-60 minutes. Warm as in, warm enough to feel a difference when I put my hand up a few more inches, but not hot by any means. Is this normal? Or does it mean that the wires inside the wall are dangerously hot and I'm only slightly feeling it on the outside?

Thanks!

Just my $0.02, adding and repeating what others have said:

Whenever I get heating of any part of the electrical system of the house, I worry.   A lot.

Something is higher resistance than it should be.   Assuming correct wire sizing in the house (i.e. 12GA wire on a 20A circuit), the most likely cause is either a bad plug or poor quality connections in that outlet box.  It could also be a poor quality connection between the plug and the cable.  Does the plug itself get warm?

At a minimum, I'd pull the plug out and investigate.  And while I had it out, I'd replace it with a good quality specification or commercial grade plug.   I prefer the ones which are 'backwire', not to be confused with 'back stab' or as I like to call them 'poke and pray'.  The backwire ones use a screw and plate to hold down the wire, and not some hokey compression fitting.  I also would ensure that the circuit did *not* go through the plug - instead a pigtail should come from the wiring in the back of the box to the plug.   That way a plug failure does not cause a circuit failure.

[rrinker]

My old house, I replaced all the outlets, most of them wouldn't even hold a plug. I used the more expensive ones as replacements. This house - I have to do the same thing. One of the ones in the master bedroom literally fell apart, the surround of the top half came right off. And others are of similar dubious quality. So, next project, start replacing outlets around the house. Such a fun job - not.

Wow, that's a lot of work. How old were the two houses and their respective electrical systems before you did the work? My house is only around 10 years old so it should be fairly up to snuff.

 The previous one was not that old at all - was built around 1990 and I was living there in 2004. The previous owners were definitely the type of people who didn't take care of anything, so most of the really loose ones were almost certainly caused by abuse, not poor quality. Others in the same room that hardly got used were fine, but I just replaced them all - took a while, it was a rather large house.  This house was built in 73 or 74, and as far as I can tell these are the original outlets and are mostly just worn out. Shouldn't be as big a deal since this is a much smaller house, and the kitchen already has new outlets since I redid it when I moved in, also updating to GFCI on the counters, not required because of grandfathering but I'm not going to skimp on that sort of thing. The bigger project here will be doing the basement, I want to require everything but the appliances to support my planned model railroad, with a single switch shutting off everything but the overhead lights (too much for one switch, so it will have to be some sort of low voltage switch operating a contactor in the box). That way there's no danger of equipment failing while unattended, or quitting working on something and leaving a soldering iron plugged it for days.

[TimFox]

Quick question:  is the outlet near a heating duct?  I had a similar problem with a wall switch for a 100 W ceiling fixture, where the switch box was very close to the forced-air duct in the wall.

[djacobow]

I wonder if part of the problem was that where you put a subpanel in you must (in many localities) feed the outbuilding with a 60A feed, and 40A wouldn't be permitted.   This of course varies from location to location thanks to lack of clarity in the code in relation to this. 

Could be. I think, though, he wanted to do just the opposite. I believe it is legal to feed an out-building that is within a certain distance of the main house (eg, freestanding garage) with a simple branch circuit and no subpanel (or local ground), so that seemed the easiest to him. He could not understand why I wanted 40A. Maybe he thought I was building a grow house? In the end, I don't think I'll ever draw 40A from that building, but it's nice to know I could. (starting large tools that I don't own but maybe one day?)  IIRC, I did use #6. 300' of that wire was most the expensive part of that project. #8 has the required ampacity, but the full-load voltage drop would have been unacceptable.

Still, if was me, I'd say 'PVC, great, I love PVC, but we need to put a 60A panel and feed in to meet electrical code.  this means 6AWG, or a bit larger to avoid drop so we need to size the conduit and cable appropriately".   But again, I'm not a sparky, just someone who has had to deal with the code a lot.

Yes, and code is a funny thing. There is the NEC, there is the local code which may adopt the NEC in total or as a "base" and then there are the local inspectors who seem to have their own ideas. A neighbor of mine is a newish GC. He has lots of stories of inspectors both making up little requirements that can't be found written anywhere, or letting other things slide because they "do not really matter." I suspect being a successful contractor in part is about knowing the local variation, formal and informal. We just got a new roof on our house and the city inspector made his assessment from the street...

[djacobow]

Quick question:  is the outlet near a heating duct?  I had a similar problem with a wall switch for a 100 W ceiling fixture, where the switch box was very close to the forced-air duct in the wall.

Wow, that is a good question! When you're an on EE website, everything looks like an EE problem ... but maybe it's not!

[Cubdriver]

At a minimum, I'd pull the plug out and investigate.  And while I had it out, I'd replace it with a good quality specification or commercial grade plug.   I prefer the ones which are 'backwire', not to be confused with 'back stab' or as I like to call them 'poke and pray'.  The backwire ones use a screw and plate to hold down the wire, and not some hokey compression fitting.  I also would ensure that the circuit did *not* go through the plug - instead a pigtail should come from the wiring in the back of the box to the plug.   That way a plug failure does not cause a circuit failure.

I much prefer the back wired ones with the clamping plates too - far simpler to install without the need to loop the wire and get it wrapped around the screw head and down into the little recess.  Doing that is especially fun on things like 4 way switches with 4 terminals with connections that need to wrap one way on one side and the opposite on the other.

Pigtailing too is definitely the way to go IMO.  Not only does it prevent a poor connection at a receptacle terminal from taking out everything downstream of it, it also means that the receptacle terminals need only carry the current being drawn from that particular receptacle.  If they're daisy chained, the first connection passes ALL the current for that receptacle and everything beyond it (the worst case); each subsequent one downstream carries all the current not drawn off before it (less total current, but still more than it needs to carry).  When they're pigtailed, the main current goes through a (hopefully) nice tight splice.  Fewer screw connections and less chance of something coming loose.

-Pat

[IanB]

Pigtailing too is definitely the way to go IMO.  Not only does it prevent a poor connection at a receptacle terminal from taking out everything downstream of it, it also means that the receptacle terminals need only carry the current being drawn from that particular receptacle.  If they're daisy chained, the first connection passes ALL the current for that receptacle and everything beyond it (the worst case); each subsequent one downstream carries all the current not drawn off before it (less total current, but still more than it needs to carry).  When they're pigtailed, the main current goes through a (hopefully) nice tight splice.  Fewer screw connections and less chance of something coming loose.

I get the reasoning for this, but when I replaced all the sockets in my house there were about 100 of them to do and it took ages to complete as it was. I used the back wired sockets and yes, there was lots of daisy chaining. However, I observed the sockets had a brass bus bar for continuity that was at least the same cross section as the wire, and with the back wired sockets it is possible to insert two wires into one screw terminal which minimizes the current path between the wires in any case.

If I had attempted to pigtail them all it would have taken forever. There are times when pragmatism wins out over ideals.

[Audioguru]

I agree that the "push the wire in the hole and hope it makes a good contact" is Mickey Mouse and is asking for a fire.
Amateurs and newbie electricians screw down a wire the wrong way around then it becomes loose.
I have never seen a cheapo Chinese copy of an American electrical receptacle.

[tommygdawg]

Just an update: pulled the socket out and ran the light for close to an hour with the socket out of the wall. Flipped off the breaker and then felt up the wires leading out of the socket. They were marginally warm but not hot by any means, but would that not be expected for a constant 14-16 amp draw after running for nearly an hour?

It was really stiff wire, unlabeled but around the same thickness #12.

[IanB]

The place to look for warmth is junctions and contact points. For example, where the wires are connected to the outlet, the outlet itself (where the plug pins contact the internal spring contacts), and where the appliance flex is joined to the plug inside the molded casing. These are places where high resistance can occur.

[tommygdawg]

The place to look for warmth is junctions and contact points. For example, where the wires are connected to the outlet, the outlet itself (where the plug pins contact the internal spring contacts), and where the appliance flex is joined to the plug inside the molded casing. These are places where high resistance can occur.

Those places felt about as warm as the wires themselves. It was basically an even distribution of heat throughout. The main pos/neg wires out of the socket were also twisted with plastic caps on top to the wires proceeding down into the wall. Those caps felt about as warm, if not a slight bit more warm than the rest. Good or bad? Indifferent?

I didn't remove the wars from the socket itself, they were in fact screwed down to the inside of the socket.

[IanB]

The main pos/neg wires out of the socket were also twisted with plastic caps on top to the wires proceeding down into the wall. Those caps felt about as warm, if not a slight bit more warm than the rest. Good or bad? Indifferent?

Those are wire nuts. They are a common source of poor connections. It wouldn't hurt to redo them.

If you unscrew the wire nuts you will find the wires twisted together underneath. Make sure they are twisted together well (use pliers for this). Then screw the plastic wire nut back on top until you feel resistance. Then keep on screwing it down really hard until the wires underneath twist right down to the insulation. A common fault is failing to twist on the wire nut hard enough. You should twist it until it hurts your fingers.

[Ian.M]

Plug in a short 20A rated extension lead, in good condition with clean pins and plug the appliance into that.  If the excess heat problem follows the appliance plug, its the plug or appliance lead that's bad.  If it stays at the socket, and you've eliminated loose connections, the socket's gone bad - change it.

[forrestc]

If you unscrew the wire nuts you will find the wires twisted together underneath. Make sure they are twisted together well (use pliers for this). Then screw the plastic wire nut back on top until you feel resistance. Then keep on screwing it down really hard until the wires underneath twist right down to the insulation. A common fault is failing to twist on the wire nut hard enough. You should twist it until it hurts your fingers.

One of the best things I've ever bought is the ratcheting version of one of these:



(See about 1:30 in the video if you're impatient).

Getting a nut tight enough isn't a problem anymore with this.

They also have drill attachments.  That seems like overkill.

[necessaryevil]

This sounds very bad to me, assuming that the heat is caused by the electricity and not by the lamp itself. Wire or outlets shouldn't get warm, or, at least, you shouldn't be able to notice it by touching it.

By the way, do you live in a lighthouse ;-)? 20 amps at 120v, that's a whopping 2400w. What kind of lamp is that?

[uncle_bob]

The place to look for warmth is junctions and contact points. For example, where the wires are connected to the outlet, the outlet itself (where the plug pins contact the internal spring contacts), and where the appliance flex is joined to the plug inside the molded casing. These are places where high resistance can occur.

Those places felt about as warm as the wires themselves. It was basically an even distribution of heat throughout. The main pos/neg wires out of the socket were also twisted with plastic caps on top to the wires proceeding down into the wall. Those caps felt about as warm, if not a slight bit more warm than the rest. Good or bad? Indifferent?

I didn't remove the wars from the socket itself, they were in fact screwed down to the inside of the socket.

Hi

Connectors carry current. They have contact resistance. They way you get a current rating is to define a maximum temperature. You then work back from there through the temperature rise on the connector to figure out if it is ok or not. The tables you see of "this connector does this" are generally done for a specific temperature rise (10,20,40C). There are other things (wet contact issues) that also get into it. If you don't plug in the light with it turned on, they aren't an issue.

It is not at all uncommon to see a connector that is "rated for 20A" in a catalog, running fine for years and years at 5X that. The rating is at 10C rise. The particular application is fine with a 50C rise. Connectors "die" when the insulation goes over temperature. That's rarely going to happen below 105C. Connectors with 200C or higher insulation do exist.

So, is 10C "warm"? If you are in a 20C room, the connector did not get to body temperature. That may or may not be warm. IR thermometers are made because most people are not very good at the "touch it and see" approach for exact temperature measurement. Indeed there are some who can come very close. Don't place bets on this sort of thing.

The standard advice on any electrical issue is always the same. If it worries you, replace it or have it looked at by a pro. We're talking about an outlet that costs less than $3 around here.

Bob

[tooki]

I have never seen a cheapo Chinese copy of an American electrical receptacle.

Of course not, cuz that's what most receptacles in USA already are! When you buy a pack of 10 outlets for $4.99 at Lowe's, you know damned well they're not a quality Made in USA product. But even a (supposedly made in USA) Leviton industrial grade receptacle is just $6.

When I first moved to Switzerland (from USA) I was absolutely shocked (no pun intended) at how expensive light switches and outlets here are. Now, in all fairness, part of explanation is due to lack of economies of scale, since Switzerland uses its own outlet (Type J) — for a country with a population just below that of New York City! 

Consequently, a standard 3-socket wall receptacle here cannot be had for under $20 (and that's for the Chinese-made one), and a European-made one can be double. (And don't even ask what a GFCI outlet or wall dimmer costs. Just don't go there.)

But even in the rest of Europe where the common Schuko outlet does have massive economies of scale, they're still far more expensive than American ones.

[DivineChaos]

Well, my US vacuum cleaner is a 10a 1200w type and after 15 minutes or so of cleaning, the cord and the outlet are quite warm, no matter which plug I put it into, even the GFCI one in the bathroom.

Honestly, it does worry me, but it seems normal and safe, because after years and years of using a vacuum to clean my house, nothing has ever happened.

[tommygdawg]

Well, my US vacuum cleaner is a 10a 1200w type and after 15 minutes or so of cleaning, the cord and the outlet are quite warm, no matter which plug I put it into, even the GFCI one in the bathroom.

Honestly, it does worry me, but it seems normal and safe, because after years and years of using a vacuum to clean my house, nothing has ever happened.

I've noticed this as well with vacuum cleaners. I guess the question is how long is it safe to run such equipment?

Also fun fact after doing some research. GFCI's tend to always be a little bit warm. I noticed that even when nothing is plugged into mine they always feel warm. I got the thermometer out and measured about a consistent 5 degree higher temperature than the surrounding wall on all my GFCIs. I googled this and apparently it's a common phenomenon due to their electronics on the inside.

[uncle_bob]

Well, my US vacuum cleaner is a 10a 1200w type and after 15 minutes or so of cleaning, the cord and the outlet are quite warm, no matter which plug I put it into, even the GFCI one in the bathroom.

Honestly, it does worry me, but it seems normal and safe, because after years and years of using a vacuum to clean my house, nothing has ever happened.

I've noticed this as well with vacuum cleaners. I guess the question is how long is it safe to run such equipment?

Also fun fact after doing some research. GFCI's tend to always be a little bit warm. I noticed that even when nothing is plugged into mine they always feel warm. I got the thermometer out and measured about a consistent 5 degree higher temperature than the surrounding wall on all my GFCIs. I googled this and apparently it's a common phenomenon due to their electronics on the inside.

Hi

If a 5F rise counts as warm, then yes, all your electrical gear will feel warm.

The insulators in there are rated for at least 180F. That's a lot more than warm. To get that hot, something needs to be very wrong. In the context of outlets, 100F (in a normal 70F room) is "warm".

Bob

[Xplode]

I'm an electrician by trade and going back to some of the earlier posts, I agree that not all electricians are smart.   Construction/Installation electricians aren't as generally well versed with the problems and fixes as a service electrician would be.   I work more in the service end of things, and often in commercial and industrial settings.   

That said, the guys that decline a job because they're not sure (ie that generator) are smart.  They know their limits, and are willing to admit it.  Be afraid of the cowboy who just does it anyway.  never ends well.
The other guy that turned down the job even though you'd dug and laid the pipe, probably just wasn't interested because the job was now too small.   I can't make money if I have to field calls, drive out, look at it, bid on it, then pickup materials and go back and install it for only a couple hundred bucks.     Its just not worth it unfortuanately, can't keep the machine turning so to speak.   However, in my jurisdiction at least, a homeowner is allowed to pull a permit and do their own electrical work so long as the follow the codes.

Now back to the original topic - the warm plug.

There are several reasons, and fixes, to get to the bottom of this.    Most suggestions have already been covered, so this is just confirming and agreeing.
1) turn off the power and pull out the receptacle.   Ensure the wires are in fact large enough (should be #12 awg copper).  Make sure they're under the screws and not stabbed in to the holes in the back (I've received so much easy money from this one)
2) Check for signs of heat on the wire where it connects to the receptacle, and where any splices are made in the box.   Discoloration and added or reduced "shininess" compared to the rest of the wiring is a sign of trouble.  Cracking or flaking insulation is a sign of long term heat damage as well.  Copper being a bit darker and not shiny is NOT an issue.  natural copper oxidization is ok, so long as it isn't combined with signs of heat damage in the insulation.
3) Replace the receptacle.   Go to a proper electrical supplier and buy a good quality plug from a large manufacturer.   Ask for "commercial grade" or "spec grade" or "hospital grade" (local terms might be different than here).   It will cost $6 instead of $.89.  But will have a nice metal back strap, feel absolutely solid, and the internals will be significantly stronger.
4) Check your cord end - does it look good?   Old cord ends with metal fatigued pins can cause grief as well showing signs of heating in the receptacle that aren't the receptacle's fault.   If in doubt, buy a good cord end (again, not dollar store.  go to an electrical supplier, and buy a proper 20A cord end).    Sometimes 15A cord ends show up on manufactured devices due to the regulations for manufacturing being quite different than the regulations for electrical installers (ie your vacuum cord being warm - its anticipated that the duty cycle is so low on the vacuum cleaner that it will be ok. - commercial units don't warm up quite the same)

That should get you fixed up.    If you replace any receptacles/cord ends/etc make sure you re-connect it correctly.    The "Neutral" side and the "Hot" side can not be safely interchanged on the receptacle or cord ends.   (swapping ends could energize the light socket so you get a good wake-up blast when changing bulbs)

Hope that helped!

[Cubdriver]

Xplode -

re your #4 suggestion about buying a 20A cord end - by that are you suggesting a replacement plug for the cord?  If so, wouldn't a 20A unit (here in North America) be a NEMA 5-20P, with the neutral blade at 90 degrees relative to the hot (the 'winking' plug) to prevent it being plugged in to a 15A receptacle?  If replacing the plug is what you're suggesting, I'd think he'd be better off with a good quality 15A one, otherwise unless he has 20A receptacles he won't be able to plug it in anywhere.

Everything else I wholeheartedly agree with, especially about not cheaping out on the receptacles.  Spend a few bucks each and get good ones - this is not the place to use things from the 99 cent store!

-Pat

[uncle_bob]

Xplode -

re your #4 suggestion about buying a 20A cord end - by that are you suggesting a replacement plug for the cord?  If so, wouldn't a 20A unit (here in North America) be a NEMA 5-20P, with the neutral blade at 90 degrees relative to the hot (the 'winking' plug) to prevent it being plugged in to a 15A receptacle?  If replacing the plug is what you're suggesting, I'd think he'd be better off with a good quality 15A one, otherwise unless he has 20A receptacles he won't be able to plug it in anywhere.

Everything else I wholeheartedly agree with, especially about not cheaping out on the receptacles.  Spend a few bucks each and get good ones - this is not the place to use things from the 99 cent store!

-Pat

Hi

According to the original post, the light pulls up to 16A continuous. If it does not already have a 20A plug on it, that raises some significant questions about the basic design of the light.

Bob

[bitslice]

I also would ensure that the circuit did *not* go through the plug - instead a pigtail should come from the wiring in the back of the box to the plug.   That way a plug failure does not cause a circuit failure.

I've just watched a US video on 'pigtailing' because I wasn't sure what was involved (I'm in the UK), and the problem seems to be the odd way of designing the sockets.

You are kind of forced to use those bulky cable nuts to terminate wires instead of terminating them into the socket because they are screw-downs that can only carry one wire.
Then having to wrap electrical tape around the outside just in case?
Then having to work out if I still need a ground wire by guessing if the wiring is running in metal conduit or not. Eeek

In the UK I can just strip back the insulation from a single cable, bend it over and screw down into the socket.
I don't need to cut a wire at all so the cable can carry its rated amps regardless of how many terminations I make.

If I do need to make a termination we have heavily over-engineered termination boxes that isolate everything. I've not seen the same item in the USA?

I like a lot about America, but the electrical system is a teeny bit scary.