Please check my work

[eager2learn]

Okay so another welder calculation. I'm second guessing myself, so any info you have will be greatly appreciated . I'm working in a machine shop that is installing new equipment and welders. My question is in regards to a group of welders.

1. - 13 amps at input with a duty cycle of 100% = 13 amps @ sum of 100% = 13 amps
2. - 11.4 amps at input w/ a duty cycle of 100% = 11.4 amps @ sum of 100% = 11.4 amps
3. - 11.4 amps at input w/ a duty cycle of 100% = 11.4 amps @ sum of 85% = 9.69 amps

4. - Sum of Amps added together = 34.09 amps or 35 amps total = #10 wire @ 75 degree

5. - OCPD = 35 amps @ 200% = 70 amp

6. - All in all I have #10 wire on a 70 amp OCPD that will be energizing the circuit

7. - Is this correct? It looks weird to me

8. - Art. 630.11 & 630.12 reference

Thanks again

 

[eager2learn]

Sorry, everything is at 480v

 

[Little Bill]

Bump

 

[JFletcher]

1-4 are correct, however I do not think you can round up to 35A at that point to arrive at 70A OCPD. Max is 200% welder ampacity(-ies), no 65A breaker so istm that a 60A would be more apropos. You do not have to go to 200%, that's just max allowed. Istm to be unlikely that all 3 units would be at a 100% duty cycle simultaneously too.

Just curious, why not separate circuits for the 3? At 480V, 3 sets of #12 in 3/4" EMT on 25A breakers would suffice.

It looks weird to me too since one welder, the largest, is just 13A @ 480V. Putting that on a 70A breaker doesnt look right tho I admittedly dont do "multiple welders on same circuits" calcs often; closer to the "never" end of the spectrum.

eta: just saw the nameplates in the 2nd pic, which list larger I_1max values than your initial post calculations. Which are correct? They are different enough to possible affect both wire and breaker sizes. Are they 1 or 3 phase (I assumed 3)?

 

[eager2learn]

The welders are all 3 phase 480. The shop has existing lathes and cnc's that are installed now, but will be relocated. The existing 480 panel is in the immediate area and has limited space available.