Multiple 3Ph Welders load calc.

[IanO3]

Trying to load calc. (14) Welders to be added in a commercial building. Want to ensure I'm doing my calculations correctly. The gist of the question is when to multiply by 1.732, (If the nameplate gives values for 3ph amperes , both Imax & Ieff, do I still multiply by 1.732?)

(14) 3Ph welders (using 630.11b for demand factors)
Nameplate shows - 3PH @208V , Imax - 34A , Ieff - 18A
Lets assume 100% duty cycle for this exercise.


What do yall get for a service size?

 

[tortuga]

Item​	Ieff​	Qty​	Extended​	Factor​	Amps​	VA​
Welder 1​	18​	1​	18​	100.00%​	18​	​
Welder 2​	18​	1​	18​	100.00%​	18​	​
Welder 3​	18​	1​	18​	85.00%​	15.3​	​
Welder 4​	18​	1​	18​	70.00%​	12.6​	​
Welder 5 – 14​	18​	10​	180​	60.00%​	108​	​
Total​	​	​	​	​	172​	61920​

 

[tjdilly]

Agreed with Tortuga. Here's an excel snip from a recent job.



Going from Amps to VA for any 3-phase load always requires the 1.732 factor, otherwise you would be calculating the single-phase wattage.

By the way, speaking from experience with many manufacturing facilities, be VERY conscious of what breaker size you use. Read the owner's manuals, not the cutsheets, for the breaker sizing.