630.12 over current protection for welders

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Dsg319

Dsg319

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Wv Master “lectrician”
630.12 over current protection- Overcurrent protection for arc welders shall be as provided in 630.12(A) and (B). Where the values as determined by this section do not correspond to the standard ampere ratings provided in 240.6 or where the rating or setting specified results in unnecessary opening of the overcurrent device, the next higher standard rating or setting shall be permitted.

With that being said if I have a non-motor welder with an input current of 50amps and a 20% duty cycle. Calculation comes out to 22.5 conductor ampacity. So with NM cable limited to 60degree conductor ampacity one would have to use #10awg conductors. Than would I be limited to a 30amp OCPD BUT than I read 630.12b which allowed OCPD up to 200% of conductor ampacity. So with all that said I could get by with #10awg and a 50amp OCPD correct?

Before I learned about conductor ampacity and duty cycles of welders I would have just assumed slap a 50amp OCPD and some #6awg.
 
ActionDave said:
You have it correct. Many folks don't like these provisions in the code because they never got past chapter three and don't take the time to understand why such installs are safe.
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Yep I never would have thought it to be correct before either until I learned about duty cycle and if used correctly it makes more sense.
I know with 20%duty cycle you can only use 2 min out of 10minutes right? But is that at maximum welding output or does that go for any setting.
 
Dsg319 said:
I know with 20%duty cycle you can only use 2 min out of 10minutes right? But is that at maximum welding output or does that go for any setting.
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Varies with the unit. Most are 100% to some output, falling to some (20% and 30% are common for portable units) linearly. Some PURELY A MADE-UP EXAMPLE, 200 amp @ 20%, 100 amp @ 100% might be a specification. I'm not accustomed to tabulation of INPUT currents, however. I believe if you size for the 100% load, 20% duty cycle, you are covered for all settings.
 
ActionDave said:
You have it correct. Many folks don't like these provisions in the code because they never got past chapter three and don't take the time to understand why such installs are safe.
Click to expand...
Were discussing 50A breaker on 10 AWG wire to 6-50 recept? (years ago this would have been the 10-50)
Consider a residential garage, someone installs a NEMA 6-50 with 10's and a 50A breaker. Per the code for welders.
HO moves new owner plugs in something else like a large shop heater or a EV charger.
Or say in a metal shop, they unplug 50 A welder and plug in large break press or compressor with a 6-50.
 
tortuga said:
Were discussing 50A breaker on 10 AWG wire to 6-50 recept? (years ago this would have been the 10-50)
Consider a residential garage, someone installs a NEMA 6-50 with 10's and a 50A breaker. Per the code for welders.
HO moves new owner plugs in something else like a large shop heater or a EV charger.
Or say in a metal shop, they unplug 50 A welder and plug in large break press or compressor with a 6-50.
Click to expand...
That could be a bad scenario, I believe in doing such good labeling is a must.
 
A comment only on duty cycle:

Though 20% duty cycle is still a typical USE scenario, many welding machines that I encounter are rated at 40% to 60% duty cycle at nameplate current.

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