50 Amp Breakers and 12 AWG Tool Cords

[[memphis]]

So... I'm electrical tarded

I have a Lincoln Mig Pak 15 240v welder... max input amps on the machine is 22-23 amps and it has a 12 AWG power cord attached to it.
For almost 20 years I have used a 10 AWG extension cord I made for it and for 15 of those years I powered it off a 30 amp dryer circuit with another adapter... zero issues zero problems never tripped a breaker, no melt downs

The Lincoln comes with a 6-50p on it we all know that can handle 50 amps... recently bought the Yeswelder $150 chiner plasma... also has this style of plug... the machine says 55 amps is the max cut amperage but again it has a wimpy 12 AWG cord on it suggesting it can only safely pull ~20 amps

I know duty cycle is not 100% on either machine but if I am truly pulling 55 amps with the plasma (I have my doubts) shouldn't the power cord be melting? If not... why?

I am questioning my 10 AWG extension cord I made while using the plasma...

 

[PAE]

Whats the reading when you use a clamp on amp meter ?

 

[[memphis]]

Whats the reading when you use a clamp on amp meter ?

I am but a mere mortal peasant… my hand based thermal gauge does not tell me “ne touche pas!”

I’ve been looking for an excuse to purchase one so… I guess this is it

 

[u2slow]

I know duty cycle is not 100% on either machine but if I am truly pulling 55 amps with the plasma (I have my doubts) shouldn't the power cord be melting? If not... why?

Because duty cycle. It takes a time for the higher current to heat up the smaller wire to a failure point. Your welder enforces the duty cycle by an internal thermal cut-out.

So... ignore the fact the machine has a 50A plug on it. Size your cord on the machine's primary current rating and duty cyxle. The owners manual very likely has it dumbed to down to say "use X gauge cord for up to Y feet long."

NEC/CEC has a welder section that helps you do the calculation.

 

[[memphis]]

Because duty cycle. It takes a time for the higher current to heat up the smaller wire to a failure point. Your welder enforces the duty cycle by an internal thermal cut-out.

So... ignore the fact the machine has a 50A plug on it. Size your cord on the machine's primary current rating and duty cyxle. The owners manual very likely has it dumbed to down to say "use X gauge cord for up to Y feet long."

NEC/CEC has a welder section that helps you do the calculation.

Unfortunately the plasma didn’t come with any sort of “proper” instructions which is par for the course when it comes to stuff ordered off the jungle site.

When I read about my Lincoln that’s how I decided on 10awg

 

[bad zuki]

G00gle found This Owners Manual. 20A max, NEC says that should have 125% Over current protection, or max breaker size of 30A and #10 wire. It also has an internal breaker. So nothing to worry about on the welder.

Since China really doesn't care about electrical requirements or rating selling what they actually put out, I found the 2012 code (60974-1) that the "55 amp plasma on amazon" cites for the codes.

U1, Voltage in,
U2, Voltage out,
I2, Max value of the welding current that be obtained at the welding power source at its max setting. IE what I'd size it for/ In-rush.
Ignore the red/yellow. I don't feel like re-clipping that.

I don't know what cords they use on these, They can't be over #10 wire, but for ratings sake, Id go 50A plug with #8 cord. Thats what I did for mine.

Also, voltage drop rates are nothing under 100' on a 30A. I have the charts, but Southwire's website is what we use now. It's spot on. NEC says no more than 3% drop over a run on 1 circut. We try and stay under 2-2.5%. Now keep in mind that this is 100' from the panel, not 100' from the plug.

 

[u2slow]

Welders are a special case and general purpose circuit wire sizing is usually overkill, and breakers can be larger than normal.
If you know the duty cycle at whatever primary current, you apply the appropriate muitiplier

Electric Welders | UpCodes

Explore a searchable database of US construction and building code. Code regulations are consolidated by state and city for easier navigation.

up.codes

 

[PAE]

When it comes to wiring be it on a house or a truck / car always go larger than called for or required and you will be ahead of the game.

 

[bad zuki]

Welders are a special case and general purpose circuit wire sizing is usually overkill, and breakers can be larger than normal.
If you know the duty cycle at whatever primary current, you apply the appropriate muitiplier

Electric Welders | UpCodes

Explore a searchable database of US construction and building code. Code regulations are consolidated by state and city for easier navigation.

up.codes

Yep, this is to prevent the insulation cooking off over time from In rush amperage. Or in case someone runs 200’ of extension cord out then runs the welder all day.

630.11-A Lists the I-eff value as the absolute maximum seen or inrush amps… most equipment is clearly spelled out exactly what the full load, breaker, and/or inrush is. I started highlighting it, but didn’t feel like bothering everyone with a formula. The yellow line is from a similar plasma’s advertisement. I-max is the inrush and I would rate the plasma with the highest listed number for that doing a ballpark calc.

So taking the 33.7, you would multiply that by 125% (per NEC to get MOCP or breaker sizing) you get 42 amps rounded up to a 45 or 50 amp breaker. I’d go to a 50a incase you ever upgrade your welder, you will have the capacity in the cord/plug.

If you use the 26.1 number it still comes out above 30 amps and you would still need to step up from a #10 to a #8.

This a plasma cutter and shouldn’t fall under the welder section of code. It would probably fall under general appliance section and use I’ll review that when I get back into the office.

I think they have some kind of different, non NEC code, that allows aluminum #12 wire that rated for 42 amps. But that just a theory.

 

[[memphis]]

Something else I didn’t think about but it plays a factor. The thickest material I’ll be cutting is 1/4” which is at the lower end of the machines capacity but I still believe you are right in upgrading the cord

 

[SomeGuyFromOlympia]

Something else I didn’t think about but it plays a factor. The thickest material I’ll be cutting is 1/4” which is at the lower end of the machines capacity but I still believe you are right in upgrading the cord

that isn't what matters in this situation, you are looking at power being used by the machine

 

[sdmuleman]

Check voltage at the machine with it running at max power you'll use and compare to unloaded voltage. As long as it's above about 200V under load you're probably fine.

It's important to keep in mind that the NEC is a bureaucratic one size fits all thing that has more to do with CYA and idiotproofing than safety in many cases. Consequently, while code is a good guide, violating it is frequently no where near the instant death sentence that some try to convince you it will be. For instance, 'suicide plugs', generator transfer switches, ground wire for outbuilding subpanels - all portrayed as horribly dangerous to not follow, but with a tiny bit of common sense are perfectly safe in reality.

In this case, max amperage of wiring is based on heating and assumptions about cooling or lack thereof - specifically, that the wire is inside a wall, conduit, part of a bundle, etc. This is a conservative assumption, and probably reasonable for house wiring. Also, it's assumed that it's a constant steady state load, and temperatures are limited by what is guaranteed safe for being in contact with wood/flammables and not damaging the wiring.

An extension cord is most likely exposed to air for cooling, likely intermittently loaded, and most likely on a concrete floor, which means better cooling and lower risk of fire if it does gets hot. Further, being in the open and near a person, if it does start to get hot it's likely to be noticed in time to do something. Again, very different than a wire buried within the wall getting hot in the middle of the night.

End of the day, I bet 12ga cord and 10 ga extension will work perfectly fine. I've got plenty of 10ga cords in my shop and have never had them get noticeably hot under 40-50a loads.

This same logic is why power lines are far smaller than the equivalent house wiring - better cooling and lower impact of heating.

 

[kf4zht]

G00gle found This Owners Manual. 20A max, NEC says that should have 125% Over current protection, or max breaker size of 30A and #10 wire. It also has an internal breaker. So nothing to worry about on the welder.

Since China really doesn't care about electrical requirements or rating selling what they actually put out, I found the 2012 code (60974-1) that the "55 amp plasma on amazon" cites for the codes.

U1, Voltage in,
U2, Voltage out,
I2, Max value of the welding current that be obtained at the welding power source at its max setting. IE what I'd size it for/ In-rush.
Ignore the red/yellow. I don't feel like re-clipping that.

I don't know what cords they use on these, They can't be over #10 wire, but for ratings sake, Id go 50A plug with #8 cord. Thats what I did for mine.

Also, voltage drop rates are nothing under 100' on a 30A. I have the charts, but Southwire's website is what we use now. It's spot on. NEC says no more than 3% drop over a run on 1 circut. We try and stay under 2-2.5%. Now keep in mind that this is 100' from the panel, not 100' from the plug.

Per that chart at 220v the max inrush is 33.7a and effective is 26.1a. it should be fine with a 30a breaker and 10ga wire. Might pop a breaker on absolute max, but probably not.

That is assuming you aren't a huge distance from the panel

The 55a rating is output, at a lower voltage.

 

[GLTHFJ60]

Regarding breakers and wire size, just remember that the wire is sized to the load, and the breaker is there to protect the wire, end of story. In a dead short situation, the 50a breaker wouldn't trip before the 12awg wire melted all of its insulation off and burned your building down.

Food for thought.

 

[bad zuki]

All I'm saying is that the NEC is actually in the National Fire Prevention Code.

I bet it will run okay on the #10 cord, but I'm not gonna do it.

 

[u2slow]

Regarding breakers and wire size, just remember that the wire is sized to the load, and the breaker is there to protect the wire, end of story. In a dead short situation, the 50a breaker wouldn't trip before the 12awg wire melted all of its insulation off and burned your building down.

Food for thought.

Breaker protecting the wire is a general default for receptacles, heating/lighting, and general power distribution.

Motors and welders are special cases - the breakers providing magnetic-trip protection (trip fast on a high and hard fault.) Thermal overloads take care of protecting the wiring and machine from overheating.

 

[300sniper]

Everyone is ignoring the OP’s question. His #10 EXTENSION CORD is fine.
10/3 SO is rated for 30a,

The machine max draw (not in rush) is 23a @ 220v, which will be 21a @ 240v.

I’ve got hundreds of hours of time on my Millermatic 251 with 150’+ of 10/3 SO. I’d not lose a second of sleep in the OP’s situation.

Edit to add: the the “55 amps is the max cut amperage” is likely at a much lower voltage than the input voltage (has to be). I’m not sure what output voltages plasma cutters use, and honestly don’t know if it’s AC or DC. Not something I’ve ever looked into, nor had any curiosity, until now…

 

[GLTHFJ60]

Breaker protecting the wire is a general default for receptacles, heating/lighting, and general power distribution.

Motors and welders are special cases - the breakers providing magnetic-trip protection (trip fast on a high and hard fault.) Thermal overloads take care of protecting the wiring and machine from overheating.

My welders don't have mag starters. Thermal overload due to overcurrent within the breaker does the tripping.

 

[u2slow]

My welders don't have mag starters. Thermal overload due to overcurrent within the breaker does the tripping.

It is internal to the machine. That is how they can get away with a #12 cord on a 50A plug.

Household panel circuit breakers are dual action - magnetic trip and thermal trip. Thermal trip takes time to build heat from the current draw. A momentary spike to 55-60A isn't going to trip anything.

 

[GLTHFJ60]

It is internal to the machine. That is how they can get away with a #12 cord on a 50A plug.

Household panel circuit breakers are dual action - magnetic trip and thermal trip. Thermal trip takes time to build heat from the current draw. A momentary spike to 55-60A isn't going to trip anything.

TIL, I understood household breakers to be just thermal.

Time to hit the books, thank you.

 

[M92PV4U]

This same logic is why power lines are far smaller than the equivalent house wiring - better cooling and lower impact of heating.

Higher voltage, lower amps.

 

[subybaja]

I am but a mere mortal peasant… my hand based thermal gauge does not tell me “ne touche pas!”

I’ve been looking for an excuse to purchase one so… I guess this is it

Got this from the Deals thread. Seems ok.

Amazon.com

 

[sdmuleman]

Higher voltage, lower amps.

Even for the same voltage they're allowed far higher ampicity. Look at the overhead line going to your house - same voltage on either side of the peckerhead, but power co side is something like a #4 whereas house side is #2/0+. Same exact current, but 2 different sets of rules.

 

[M92PV4U]

Even for the same voltage they're allowed far higher ampicity. Look at the overhead line going to your house - same voltage on either side of the peckerhead, but power co side is something like a #4 whereas house side is #2/0+. Same exact current, but 2 different sets of rules.

Over head is in free air not conduit .

 

[Muckin_Slusher]

Even for the same voltage they're allowed far higher ampicity. Look at the overhead line going to your house - same voltage on either side of the peckerhead, but power co side is something like a #4 whereas house side is #2/0+. Same exact current, but 2 different sets of rules.

One is swinging in the breeze, other is stuffed in a pipe.
Much difference in cooling capacity.

 

[sdmuleman]

Over head is in free air not conduit .

One is swinging in the breeze, other is stuffed in a pipe.
Much difference in cooling capacity.

And not near anything combustible either.

Which is exactly the point. An extension cord in open air on a concrete garage floor has much better cooling and very likely low risk of causing a fire even if it does get hot.

NEC rules are based on the most conservative possible situation, with a healthy dose of margin and idiot proofing. Yes, it is wise to follow them, but there are many cases where there's little to no risk real if you don't.

Running a 50A load on a #10 wire buried in your wall is really dumb idea. 50A on a #10 across your garage floor is only going to be a problem if you really try hard to make it one.