Feed/Breaker for plasma cutter

[32Lateralus]

We have a plasma cutter, manual lists the following:

Input V - 480V
Input current (A) at rated output (21.9kW) - 31A
Input current (A) at arc stretch- 50A
Fuse, slow-blow (A)- 50A
Wire size- #8AWG power cord

Everything seems straightforward enough. Putting a disconnect at the unit with 50A time-delay fuses.

For the breaker in the upstream power panel and the feed to the disconnect, is that just 50A and #8 as well, or are there extra considerations with this being a plasma cutter? Will the input current at arc stretch trip that 50A breaker, or am I overthinking it?

 

[zbang]

I think you're overthinking it , the slow-blow takes care of the peak when the arc strikes/stretches, which takes very little time.

 

[kwired]

I think you're overthinking it , the slow-blow takes care of the peak when the arc strikes/stretches, which takes very little time.

Well the breaker needs to carry that same current no matter the duration, but with a typical thermal magnetic breaker you likely still fine.

 

[32Lateralus]

Well the breaker needs to carry that same current no matter the duration, but with a typical thermal magnetic breaker you likely still fine.

Yes, this was my concern. I didnt know if the 50A breaker in the power panel could handle that 50A max arc stretch, or if it needed to be upsized.

 

[kwired]

A 50 amp breaker should be able to hold 50 amps indefinitely.

I don't know typical trip curves, and they probably do vary some, but even a small overload level typically will hold for several minutes or even hours if right near the trip rating. The more you overload the faster it will trip though.