burned out dryer outlet

[Stevenfyeager]

A customer showed me a photo of an overheated dryer outlet (one phase wire has melted insulation). Is there a test I can take on the dryer plug to tell if the dryer is bad ? (which I suspect) Thank you.

 

[ptonsparky]

Replace the cord and the outlet. The dryer is probably still good.
Take your current and voltage readings after that is done.
Improper torque at receptacle from day, one IMO.

 

[Fred B]

A customer showed me a photo of an overheated dryer outlet (one phase wire has melted insulation). Is there a test I can take on the dryer plug to tell if the dryer is bad ? (which I suspect) Thank you.

Don't rule out a bad installation of the receptacle, an improperly torqued termination will heat up enough to cause a meltdown on one side as you indicated. The looser the connection the quicker it will meltdown.

 

[Stevenfyeager]

I was thinking a test could be run on the dryer before I use the new parts. I can see me plugging it in and ruining the new parts...the way my luck goes. Thanks.

 

[Buck Parrish]

I was thinking a test could be run on the dryer before I use the new parts. I can see me plugging it in and ruining the new parts...the way my luck goes. Thanks.

If the wire is already melted then the metal conductor be it copper or aluminum has started to break down. It will not conduct electricity properly causing heat .
So you couldn't get an accurate test with out first fixing the wire. That loose connection is most likely the problem.

 

[Fred B]

I was thinking a test could be run on the dryer before I use the new parts. I can see me plugging it in and ruining the new parts...the way my luck goes. Thanks.

Check with mfg for specifics of line resistances, you have multiple conditions that wouldn't recommend a megger, also you likely have different resistance between lines as most of control circuitry is on one leg thus altering resistance on one side also not sure if drive motor is 240v or 120v, and the heating load usually 240v and that specific resistance would need to get from mfg. A lot of parameters to consider to diagnose a potential problem that is most likely not there.

 

[growler]

I was thinking a test could be run on the dryer before I use the new parts. I can see me plugging it in and ruining the new parts...the way my luck goes. Thanks.

Even if a dryer totally locks up all it should do is trip the breaker.

I have replaced a lot of dryer receptacles over the years and that's normally the only problem. If the dryer cord is also burned then replace that to.

 

[Stevenfyeager]

Thank you all. I'm scheduled to go tomorrow morning, so I will replace both parts and see if those do the job. Thanks again.

 

[WasGSOHM]

With new parts and the (25A?) dryer running, check the voltage drop across the connection.

Leaving the plug slightly out gives you voltmeter access to the plug but getting access to the socket side may be a problem.

Treat each connection and screw fastener and bond as a component of questionable resistance.

The bad connection with 20w(?) dissipated and with 25a through it
should have given you almost a volt and so a contact resistance of 30 mOhms.

The new one should measure much less than this.

 

[kwired]

Receptacles typically used on dryers can likely carry 100 amps for quite some time without being heated too much, if in good condition.

Chances are your failed receptacle had poor contact in either the supply terminals, receptacle to cord cap connection, or something in the cord cap.

If you replaced all components that were heat stressed, it should carry pretty significant overcurrent without damage for long enough to tell if something is wrong in the dryer itself. If on 30 amp OCPD it should trip well before there is any damage also.

 

[WasGSOHM]

Receptacles typically used on dryers can likely carry 100 amps for quite some time without being heated too much, if in good condition.

10w worth of heating a bulky plug and socket at 100A gives 1 mOhm resistance. Sounds reasonable.

A regular plug and socket for me came in at 4 & 7 mOhms. But this is a low sample size.

 

[kwired]

10w worth of heating a bulky plug and socket at 100A gives 1 mOhm resistance. Sounds reasonable.

A regular plug and socket for me came in at 4 & 7 mOhms. But this is a low sample size.

Well I based my answer on the likelihood that many 30 and 50 amp receptacles I have seen probably have same components other than the neutral in the 30 amp version has a notch in the receptacle contact to accept the L shaped plug. Then on top of that I have seen many 50 amp receptacles mis applied and carrying more than 50 amps at times. They still seem to hold up pretty well though.

 

[ptonsparky]

Well I based my answer on the likelihood that many 30 and 50 amp receptacles I have seen probably have same components other than the neutral in the 30 amp version has a notch in the receptacle contact to accept the L shaped plug. Then on top of that I have seen many 50 amp receptacles mis applied and carrying more than 50 amps at times. They still seem to hold up pretty well though.

I agree. I‘ve even seen four wire range receptacles used at 480 volts. Properly torqued those receptacle can handle anything a dryer or range can throw at them.

 

[WasGSOHM]

Properly torqued

That leaves installation errors and MTBF problems due to day/night temperature cycling and other environmental abuse.

My reasoning:
a 25w bulb with the same surface area as a dryer plug and dissipating 25w would be pretty hot.
So a good dryer plug only getting warm must be dissipating less than 25w.
Temperature rise above ambient may be directly proportional to surface area and wattage, but this relationship leaves out "emissivity".

 

[winnie]

Your reasoning is correct. A dryer cord and receptacle should dissipate far less than 25W on a continuous basis.

It is possible that something wrong in the dryer is drawing more than 30A and causing damage to the receptacle. The receptacle will easily survive this overload long enough to take measurements to diagnose this and shut things down.

Pulling 100A through a 30A receptacle with 5mOhm resistance will toast it eventually. But it will be fine for seconds to minutes without damage.

-Jon

 

[WasGSOHM]

Pulling 100A through a 30A receptacle with 5mOhm resistance will toast it eventually. But it will be fine for seconds to minutes without damage.

-Jon

Thermal inertia at work!

I'm assuming only "the smell test" alerts female HOs to a problem. It sure does with mine.

 

[Fred B]

With new parts and the (25A?) dryer running, check the voltage drop across the connection.

Leaving the plug slightly out gives you voltmeter access to the plug but getting access to the socket side may be a problem.
.......................

Why not test at panel rather than leaving plug slightly out? Leaving plug slightly out can actually induce the problem you are trying to correct and are checking for, and not tell you of problem in the dryer.

 

[retirede]

Why not test at panel rather than leaving plug slightly out?

Because you can’t see if there’s a problem with the receptacle by measuring at the panel.

 

[Little Bill]

Because you can’t see if there’s a problem with the receptacle by measuring at the panel.

You can take the plate off the connection point on the dryer and measure there, while also observing the receptacle. I think everyone is going way beyond basics here. 99% of all burnt dryer or range receptacles or plug ends that I have come across have been from loose/worn connections.

 

[augie47]

You can take the plate off the connection point on the dryer and measure there, while also observing the receptacle. I think everyone is going way beyond basics here. 99% of all burnt dryer or range receptacles or plug ends that I have come across have been from loose/worn connections.

Replaced a bunch of them over the years.. loose connections or poor contact.
Replace receptacle, check plug for burn or pitted & replace if necessary... Drive off ,., end of story
No rocket science needed.