Failed 50 amp Plug

I have a 6 gauge drop cord with 50 amp plug/receptacle I use to power my resistive electric furnace. The furnace is instrumented and at full power draws 33 amps. I figure 6ga is good for double that but with 4 conductors and 35ft of cord, sufficient margin. I do have a very small amount of instrument current in the neutral leg as I use one leg of the (US) 240vac for 120vac instrument and accessories.

During my timing cover melt, I moved the cord and shortly after I did I smelled hot/burning plastic and the plug was starting smoke. I briefly shut down, unplugged and inspected the plug and receptacle. It wasn't pretty. But I quickly cleaned the conductors, cooled it down with compressed air, and was able to continue and complete the melt and pour.



I checked a second such plug on the e-insert for my large furnace......also very bad.



The insulation on the individual conductors inside was cooked. I bought the plugs years ago. They were very inexpensive Amazon specials, like $6 each. The conductor tangs were actually quite robust but over time seem to oxidize heavily with use. I've been wire wheeling them clean before use. This time I didn't.

I suspect they are a less expensive copper alloy, have higher resistance in general, but especially so if oxidized. I pitched and replaced both of them. The replacements are of course Amazon special imports too. $17 each.



I'll keep an eye on them. Maybe I should apply some conductive grease. Any opinions on that?

Best,
Kelly

 

Even with the cord length and number of conductors I think 50 amp rating for the plugs is sufficient as long as the connections are clean. 6ga stranded conductor should be more than sufficient. I think those plugs I had were Sh!t. I know the furnace was drawing 33 amps. It would have been interesting to see current draw at the wall plug. FWIW, the plug on that end of the cord was/is pristine after years of use and no special care.

This was why I was dithering. If it wasn't a connection that was frequently separated and stored in open air, I wouldn't hesitate, but the likelihood it will attract dirt and eventually foul the connection versus isolate it from air and oxidation causes me to take pause.

Had same thought but they are not magnetic and scratching surface says not plated, but neither are the ones on the Sh!t plugs. Doesn't mean they are proper copper with that color, but not steel.

Best,
Kelly

 

It's stranded flexible cable. Even the lowest grade 6 gauge SO cord would be rated for 45 amps for that length 4-conductor cord both of which de-rate the standard ampacity. I think the cord is fine. It's the quality of the plug, not its NEMA configuration.



Best,
Kelly

 

I looked it over pretty good and they definitely were not loose. I broke each one loose and looked at the contacting surfaces. The type of binding terminal left something to be desired for 6ga cable. The small screw and stamped clip didn't result in a lot of contact area with the stranded conductor. The new plug and receptacle have large binding lugs with a screw that's almost .25"D.......much better. The blades aren't as thick as the failed ones but we'll see how the blades perform and age.

The previous ones did see 5yrs and ~300-400hrs of service so they didn't arrive at that condition in a day. As mentioned, the plug on the other end of the cord is pristine and the dimensions and appearance of the blades are identical to the new replacement plugs, so makes me more suspect of the old plugs design or materials.

True. The one on the end of the cord was molded so it couldn't be easily disassembled for inspection. I cut it apart on the band saw but couldn't tell much.

Also all made in China. Using industrial in a search is like using heavy duty....they all are.... Eaton is not even a US company. Doesn't mean they aren't a recognizable brand or cant make quality product, just sayin'.

Sort of funny you feel that way because you're a bit more invested in them than just a plug, it's the whole lift down in a hole in your floor for you........LMAO!.....and the plug blades aren't just plated, already covered that.

Best,
Kelly

 

For the old plugs, not likely. The new ones make some claims.



I liked the lugs and strain relief on the replacements. The strain relief was one of the few large enough to accommodate the 1" cord OD. And the add says it's super heavy duty.......so how can you go.....LoL.

I had been keeping an eye on the old ones. When I started to see signs of heat and oxidation on the blades, I'd clean them and feel the temp of the plug/receptacle. I just couldn't do anything about the receptacle and my guess is it degraded over time. I'll keep an eye on the new ones but if they are at least as good as the old ones, it may take 5 years for the next update.

Best,
Kelly

 

................or just plug'em in and see how they work. First couple hours were normal with no noticeable temp rise and still look like new......time will tell.

Best,
Kelly