Burnt the immersion heater cord receptacle up:

[Rob]

Decided last evening to plug my R-612ST as it was going to be well below zero. Turned out it only got to minus five degrees. When it was minus two degrees this morning I jumped up in the truck, turned the key and it roared to life as if it were 90 degrees outside. Deciding to let it run for a few minutes to warm, I went to the front of the truck to unplug the cord and noticed smoke coming from the receptacle in the headlamp panel. A good heavy 12ga power cord too. No damage to the truck but if it would have went much longer, it could have been a problem. The cord was plugged into a GFIC which did not trip so not a direct short for certain. I'll get a photo of the cord receptacle when back out to the shop as didn't have my phone with me at the time.

I'll have to meter that heater element as it's never been a problem in the past but this could have been catastrophic had I not noticed it.

 

[h67st]

I worked for a fleet in the 80's, we ran into a lot of dirty plugs or receptacles that would burn up the connectors. We'd put in a new plug and receptacle, no more trouble. Drawing 1500 watts all night will test the quality of any connection.

[Freightrain]

Yup, dirt and corrosion will create high resistance and can burn up the plug with no real electrical issue otherwise.

[Rob]

I had wired brushed the innards of this receptacle with a purpose brush before plugging in the cord. It was clean but I've not checked the wire terminations on the rear yet. That is probably the compromise really. Here is from the front of the truck:

Headlamp panel receptacle:

Innards after the melt down of the female plug:

Female end of the extension cord:

I'll pull the assembly out of the hood this afternoon and address whatever is needed. I don't have a female extension cord end small enough to insert into the cavity so will need to purchase something. The burnt up end was the only one I had to fit this application so will get it addressed fairly quickly.

[mrsmackpaul]

A couple of things, as already stated, it is most likely a crook connection between the lead and the truck and most likely the lead (99.9% guaranteed) 

A crook connection causes heat, the heat will cause the spring loaded parts of the plug on the lead end to become softer and put less pressure on the lead, this inturn creates even more heat and the cycle repeats itself until the plug melts off or the breaker trips

Now irony of this is the GFCI (ground fault current interrupter) or as we call them in Australia a RCD (residual current device) measures the power going in the positive and out the negitive and as long as those two are the same it wont trip

So you can have a dead short between positive and negative and it wont trip as the load is equal on those two wires, so when these values dont match (the values I'll quote are the ones we use in Australia or NewZealand and maybe different were you live but I doubt it) by anymore than 30 milli amps or 30 milli volts the GFIC trips as the power is no longer balanced and is going elsewhere, ie thru a person and these GFCI should trip before you can even feel it 

So when we test these we check for how many amps and volts it takes to trip and also how long it took to trip  once that value was reached, it is no good if it trips but it happens after your dead

I didn't go into this to try and sound smart but rather to try and give you a good understanding of what has happened

 

So your problem wouldn't of been the truck or the socket fitted on the truck and would of been the plug on the lead

 

Paul 

 

[Rob]

Thanks Paul. Most likely the compression type crimp applied to the wire terminations prior to being encapsulated in the molding. I cut the end off the cord and will replace it with a quality receptacle and be done with it. The wire terminations looked good on the back side of the hood but those are properly tinned and environmentally sealed which I'd done years ago. I did not see any degradation to the terminations but it's nice to rule that out.

Measuring from spade to spade in the connector on the truck is right at 9.5 ohms which computes to 1.5kw resistive closely with 120VAC applied. A 12AWG extension cord at 25' should be more than adequate to support this amperage draw. I have several cord grip receptacle ends in the shop being "Hubble", and "Woodhead", but both are too large in circumference to fit into the recess of the heater receptacle, (go figure) so I must purchase additional.....

Edited February 21, 2021 by Rob

[mowerman]

We have a lot of problems with those sockets at work as well as the power cards burning out ... bob