# burn marks on outlet



## LMHmedchem (May 21, 2021)

Hello,

I have an outlet where an oil space heater is plugged in. I removed the cord since I am putting the heater away for the summer and noticed that there are burn marks on the outlet. There was a 20 foot 12/3 gauge outdoor extension cord connecting the heater to the outlet and the plug from the heater was partially melted into the jack on the extension cord. There was nothing else plugged into the outlet. There is an air filter in the room on a different outlet, but likely on the same circuit.

I am wondering where the fault is here.

Is the appliance faulty?

Is there a problem with the outlet or the feed to the outlet?

The extension cord seems to work, but I guess that could be the issue as well.

At some point, I will be pluggin an air conditioner into this outlet so I need to get this sorted before I do that.

*LMHmedchem*


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## bud16415 (May 21, 2021)

It could be a number of things but it boils down to current and current produces heat. For things to start melting together is not good nor are burn marks.



The end result is fire.



Go back to the power source and is the outlet on a fuse or circuit breaker and what is the rating of that device?



What size wire is running from the panel to the outlet?



Before something got that hot the safety device should have opened.

Is there a current rating on the heater?


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## LMHmedchem (May 21, 2021)

bud16415 said:


> Go back to the power source and is the outlet on a fuse or circuit breaker and what is the rating of that device?


The house is on circuit breakers. Do you mean the rating of the circuit breaker? It's probably a 20 amp but I will check.



bud16415 said:


> What size wire is running from the panel to the outlet?


I am not sure, I will look.



bud16415 said:


> Before something got that hot the safety device should have opened.


I would have expected the breaker to trip, but the heater has been operating all winter with no issues.



bud16415 said:


> Is there a current rating on the heater?


I will check.

There was definitely a problem with the extension cord. I used it to trim the hedge and the breaker for that circuit was tripped. I looked at the cord and all of the insulation had melted off of the cord near the outlet end. One of the wires was bare as well as the ground. It wasn't like that when I disconnected the heater.

I don't know if a damaged extension cord caused the issue with the heater, or some wiring issue caused the damage to the cord. I am not willing to say it was just the cord and move on.

*LMHmedchem*


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## bud16415 (May 22, 2021)

I never 100% trust what these extension cords say on the package. Plus the length of the cord plays a part as adding resistance along with each time there is a plug there is a chance for a poor connection and high resistance. There could have been some arcing in the plug by the sound of it that would cause the heat and the discoloration at the outlet.



I would check the above stuff and make sure the circuit is rated at what you have plugged in and then replace the outlet. If it is 20a make sure you buy a good 20a rated outlet. Also work the breaker on and off a few times and make sure nothing is sticking there.

Maybe some of the electrical pros will drop in and comment.


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## oldognewtrick (May 22, 2021)

I have a couple space heaters I use in my garage and they're marked to not use with an extension cord. Check yours and see if yours is not intended to be used with an extension cord.


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## afjes_2016 (May 22, 2021)

.

First of all any type of space heater even oil filled are a fire hazard in my book.
I can't remember how many receptacles (outlets) I have had to replace because the space heater plugged in melted it or caused it to heat up that it actually started burning.

Space heaters are dangerous and I don't care what anyone says about if you use them carefully then they are fine. The issue is that the plug of the heater gets so hot that it melts the plug and the receptacle at that point and the breaker does not even know about it because it is not the pull of current that is over heating the wires in the circuit (which should then trip the breaker) but the heat generated right at the receptacle and this is usually due to the fact that the plug fits loosely into the receptacle causing even a slight bit of arcing which in turn causes heat and then of course then to fire. 

Using a space heater on an extension cord makes it even worse of a scenario. Just like Bud mentioned above the length of the extension  cord will even play a factor in generating heat.

Rules for using a space heater if needed.
#1 Always make sure that the connection of the plug to the receptacle is tight and not loose. Meaning that if the receptacle does not have a tight fit on the plug this will cause over heating in possible arcing.
#2 Every 10 to 20 minutes feel the plug of the heater to see if heat is being generated. Even with a good connection of the plug to the receptacle heat can still be generated at the plug which can cause melting or even a fire.
#3 Never, never, never leave a space heater plugged into anything when someone is not in the room to monitor the heater such as checking to see if the plug or receptacle is hot or even warm.
#4 Never, never, never leave a space heater plugged in while sleeping even in that same room or area that the space heater is plugged into. If you can't be awake to test the plug for heat then it is the same thing as leaving the heater plugged in while no one is in the room.
#5 If a space heater is going to be used it should really be the only device on the circuit running at that time. Most space heaters use 1500 watts and this is about the peak of what most circuits are rated for receptacles (15 or 20amps). considered a continuous load-yes in my book so rate it at 120% and basically nothing else can run on this circuit with the heater without tripping the breaker all the time (which means the breaker is doing its job).

Any of my customers who were landlords/property owners I always warned them about allowing their tenants to use space heaters because of the dangers. They ended up putting into the leases prohibiting the use of space heaters by their tenants. 

.


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## ajaynejr (May 28, 2021)

The exact cause will remain unknown until you find it, perhaps by X-raying some of the applicable materials.
1.  The cord wires were not properly connected to the plug prongs* or said connections were damaged by rough handling.
2.  The plug prongs did not make good contact with the contacts in the receptacle.
3.  Internal metal parts in the receptacle, notably riveted parts, were improperly manufactured and/or become oxidized so as not to make good contact.
4.  Wires of in-wall cables were not tightly connected to the internal parts of the receptacle, this problem being more likely with push-in rear connections (back stab; quick-wire) but not totally ruled out using screw terminals or screw clamps..

I have used extension cords that, after a failure and post mortem, were found to have flimsy contacts in their (typically molded) female ends so as to give a good chance of a poor contact.

Occasionally an extension cord has an amperes rating embossed in the plug or receptacle that applies only to that respective part and not the wire in between.

If a stretched out extension cord wiring is overloaded, overheating would be uniform over its entire length except the first and last 12 inches could be warmer due to added resistance at the plug and/or receptacle..

* In an earlier lifetime I had a space heater in a hotel overheat and melt the receptacle. My own inspection revealed that the plug was not assembled properly. The cord wires screwed onto the plug prongs and were loose. The plug itself looked okay and I fixed the problem and tested the heater and plug in a different receptacle for proper operation. Then I moved the heater (which seemed otherwise brand new) to the other side of the room so it would not be discarded.


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## bud16415 (May 28, 2021)

For the first 25 of my 43 years working in an industrial setting we made our own extension cords. Rubber coated flexible #12 or #10 cable with industrial grade yellow plugs on one end and a 2x4 box clamped on the other end with a 20a outlet and metal cover plate. I don’t ever remember a failure with these and after a few years they found a few with the knockouts out so safety started making us weld the knockouts in place. Then OSHA came along and we had a big safety group of people come in and the first thing they did was outlaw DIY extensions cords. We got industrial grade cords and they worked ok also. Over time the rule changed again and they threw all them out and the new ones were GFCI also. They also worked pretty good except we would get a lot of trips from tools that we couldn’t find anything wrong with. Over time the cords they would get for the shop seemed to be made cheaper and lighter despite the ratings. They started wearing out faster and running hotter.



IMO ratings on home appliances often say no extension cords for the reason they have the liability and they have no control over what the user decides is a proper extension cord. People plug these heaters into cords intended for lamps or some junk cord that claims a high rating.

Everything or a lot of things today are intended to take the thought process and knowledge out of the picture. The last push mower I bought was so safe I couldn’t mow my grass.


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## WasVilla (Jun 19, 2021)

Your heater was overloading your receptacle.  Do this:  (1) change out your receptacle to a new heavy duty version.  (2) change out the breaker on that circuit to ensure protection in the future.  (3) Do NOT use an extension cord, particularly if it is under-rated.  If you must have a cord, make up your own using no less than #12 wire (#10 is better).  How to Replace an Electrical Outlet – Replace Burnt Out Electrical Outlet and Old Damaged Socket - YouTube


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## Eddie_T (Jun 19, 2021)

Back when twin tube quartz heaters first came out we had a Presto. It was a true infrared heater in that it had a simmerstat instead of an off/on thermostat. My wife kept it pointed at her adjusted for comfort level of radiant heat. With time I noticed that the plug and receptacle were quite warm. I unplugged it finding the receptacle had lost its spring tension. So I did the math, 20A breaker, 15A receptacle, 1500W heater (max), 117V input yielding 12.8A. There was also a table lamp plugged into the receptacle. The heater alone on a colder day could be placing the receptacle at 85% capacity (continuous) so the heat gradually diminished the spring tension of the receptacle increasing resistance and adding to the problem. I replaced the receptacle with a better grade and the problem didn't recur.

Nowadays the simmerstat heaters aren't available but I bought a twin rube heater (off-season sale) for $15 and added a Chinese 10KW voltage controller. I spliced it into a cheap extension cord as I am the only user and never turn it higher than a dull glow for radiant heat. I laugh at the so called infrared heaters that are in reality fan forced space heaters.


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