6-50 extension cord with 8 ga. cable and 6 ga. plug

[LikeABigFriedEgg]

Hi all.

I see people selling extension cords for welders and (I guess) dryers, those cords being made of 8 ga. cable, but the plug and receptacle being 6-50. How is this considered good practice? I thought the idea of the 6-50 plug and receptacle was that if the plug fits, then it can handle 50 amps.

Also I read the schematic of an old Lincoln welder having a 6-50 power plug, the schematic calling for 60-amp fuses. Again I don't see how this is supposed to be safe.

Edited: cords for welders and dryers, not welders and ranges as I previously wrote.

 

[Stuff]

8 gauge copper NM is only rated for 40 amps but most other 8 cu wire is rated for 50 amps. Extension cords are also supposed to be for short term use only.

Welders and several other special applications can be fused at higher ampacities than you would expect.

 

[Sponsor]

 

[LikeABigFriedEgg]

Extension cords are also supposed to be for short term use only.

I guess you mean they assume a lower duty cycle for extension cords.

 

[WorthFlorida]

You’re kinda looking at it backwards. The circuit breaker is determined by the wire gauge to the outlet. Just because the plug is rated at 50 amps does not mean that the wire of the extension cord is rated at 50 amps or the wire feeding the outlet.

Tools and appliances have breaker ratings to prevent false tripping on the occasional surge. Stuff is correct on his statements.

Therefore, a 40 amp breaker with 8 ga wire with an outlet rated at least 40 amps is what is required. The outlet, cord, plug can be rated at 50 amp or higher but it is still a 40 amp circuit. On the Lincoln welder, if the cord was attached from the factory, it falls under UL requirements, not NEC.

I hope this was clear.

 

[Jadnashua]

For whatever reason, they use a 50A socket for many dryers, but often put that on a 40A circuit breaker. This means that you could try to pull that full 50A, but it should trip the breaker. In most circumstances, the codes require the socket to not allow a bigger load than the supply, like you can't put a 20A receptacle on a 14g, 15A circuit, but can use either a 15 or 20A one on a 20A circuit since neither one, by itself, would overload things. THat logic does not continue as you go larger, probably because they were trying to save some money and many of the older devices didn't need the full power.

Funky, but that's the way it is.

FWIW, you can buy cheap extension cords with say 18g wire with 15A plugs and sockets on them...work fine for a lamp, but not for a heater. They're cheaper, though.

 

[LikeABigFriedEgg]

Thanks, Stuff, Worth, and jad. I think I pretty much understood what you wrote. I was stuck on the idea that the receptacle used was supposed to guarantee an ampacity according to code.

Safe anyway if the fuse capacity doesn't exceed the capacity of the lowest-ampacity component.

And I'm thinking that people can use a welder on a 40-amp circuit when the duty cycle of the welder is low, for example, just 20% on those classic Lincoln AC-225's, even though the peak ampactiy of the welder is 50 amps.

 

[Jadnashua]

FWIW, most circuit breakers and some fuses, actually require either a sustained over current or a significantly higher peak to trip. As a result, say on a 15A circuit, a sustained 15.2A load would likely eventually trip a breaker, but say a 30A one might trip it almost immediately or a short delay (depending on the peak). Some fuses are referred to as slow-blow, and work similarly. Those that are simple wire strips will blow quickly with an overload. You can read the specs for the breakers to get the actual trip curves. They do make different ones, for example, you might want to use a special one for a well pump verses say a lighting circuit...there is often a big surge when a pump wants to start, but its run-time current could be relatively low...you wouldn't want the breaker tripping every time the pump started (or with your welder example), thus the delays built into most of them. Sustained use, though, tends to trip when right at or near the maximum of the device if used continuously. This is one reason why some circuits must be derated to 80%. For example, my EVSE (the device I use to recharge my EV) is limited to 32A on my 40A circuit because it could be on for more than 3-hours at a time. You usually have the same situation for water heaters. This keeps things from overheating.

Licensed electricians spend years of study and apprenticeships to learn all of the intricacies and rules. I'm a long ways from there, but have a background in physics, which helps! IOW, still learning...keeps things interesting.

 

[LikeABigFriedEgg]

but have a background in physics, which helps! IOW, still learning...keeps things interesting.

I also have some physics behind me, and same here: it helps. Also agree that the devil is in the details, so to speak.