10 Welders in Educational Welding Shop

[tiffytommy]

I am working on a school that is increasing it's welding training area from 7 welding stations to 10 welding stations. The instructor says that all 10 may be in use simultaneously. We are upgrading the existing ventilation also. I am looking for some provisions, in the 2002 NEC, that will allow me to prove a non-continuous load. I guess I am looking for a clarification of Article 630.11 (B)

Example: Welders have an input of 45.5 amp

Using Article 630.11 (B), does this mean...

45.5 x2 (100% of the 2 largest welders)= 91
45.5 x.85 (85% of the 3rd largest welder)= 38.7
45.5 x.70 (70% of the 4th largest welder)= 31.9
45.5 x.60 x6 (60% of all remaining weldes)= 163.8

Then 10 welders would yield a total of 325.4 amps?

Thank you for your help,

- Randy

 

[charlie b]

Re: 10 Welders in Educational Welding Shop

I concur with your math, and with your interpretation of the code. That?s the ?good news.?

But let me now invite your attention to 90.1(B). Compliance with the code will give you an installation that is ?essentially free from hazard by not necessarily efficient, convenient, or adequate for good service . . . .?

Since this is a training situation, and since they stated that all of the welders would be in use at the same time, and since they are adding welders (i.e., they expect to have 10 students at a time), I recommend going beyond the code minimums. I would size this for 455 amps (i.e., 10 times the 45.5 amps per machine). Anything less, any use of the allowable demand factors, would give them a system that would not perform in an acceptable manner.

Make sure they understand this: The code is minimum. It does not guarantee customer satisfaction.

 

[tiffytommy]

Re: 10 Welders in Educational Welding Shop

Wouldn't you take into consideration the duty cycle?

For instance, these welders have a 20% duty cycle over a 10 minute period.

Thanks,

- Randy

 

[charlie b]

Re: 10 Welders in Educational Welding Shop

I would have a chat with the instructor (or other owner's representative). Tell them what the code says. Ask how they intend to use the equipment. Work out a configuration that gives them what they need, and for which they would find the price acceptable.