Conductor Ampacity for a Resistance Welder

[codyab]

I am trying to size the conductors for this spot welder. My understanding according to 630.31(A)(1) is that I take the rated VA (25,000), and divide by the rated primary voltage (220v) to get the rated primary current (114 Amps). Then, since it's a manually operated welder, I take 50% of 114 to get my conductor ampacity (57 Amps). Does that sound right? My understanding is that the duty cycle multipliers in Table 630.31(A) only apply if your welder is used with the exact same settings/load every time, which sounds like something that would be the case for an automated setup, not manual.

Welder Manual

 

[Little Bill]

BUMP

 

[Eddie702]

@ 25kva is that already derated to 50%? Not sure myself

 

[hbiss]

From the instructions I'm seeing 45A time delay fuses and 10 mm² conductors which mean #6 CU here.

-Hal

 

[codyab]

If you're talking about this section, that is only for 400v and 50Hz.

Here is the specs for the model I'm working with.

 

[infinity]

What voltage are you supplying the welder with?

 

[codyab]

208v

 

[Julius Right]

According to Table 631(A) for 50% duty cycle you have to amplify the rated primary current
of 50% duty by 0.71. The rated primary current=25000VA/220V=113.64 A
Then 113.64*0.71=80.68 A . On the nameplate it is mentioned as Rated Current=81 A

 

[codyab]

Table 631(A) is only used in 630.31(A)(2). It doesn't use the rated primary current, it uses the actual primary current based on the current settings/configuration being used, and where the settings/configuration won't ever be changed. This makes me thing it's more of an automated setup, not a manual foot pedal like in my scenario. That's why I'm thinking we use 630.31(A)(1), which says to take 50% of the rated primary current for manually operated non-automatic welders.