Load Schedule

[Frank D]

We are working on a shop, it’s a large warehouse that has part of the area as a wood shop, the other half of the building is a metal shop. We are creating the load schedules and in some of the panels the loads will max out the feeder, or not have enough space for the 125% margin. According to the Shop Foreman, the maximum amount of equipment in use at any one time, is set at approximately 20%. Are there any exemptions where the load schedule, would be permitted to exceed the feeder rating of the panel.
Are there any demand factors, continuous usage, like less than 3 hours, or other contributing factors where the connected load would be higher than the breaker rating on the feeder?

 

[infinity]

There is no required 125% margin. If the load calculation is 100% of the available supply then that is code compliant.

 

[suemarkp]

About the only other out I know of is the non coincident load rule. For a 1 man shop, you can find the worst case load, e.g. a saw with a dust collector plus perhaps things that could come on by themselves like an air compressor. So if they have an employee limit of say 4 people in a shop at a time, then what are the 4 largest machines plus any that could come on by themselves or are used with others.

This may not fly with the AHJ. If not, you would need some sort of load management device that enforces the load limit.

Shops like this are a pain from the NEC calculation point of view because the machine nameplate values are rarely achieved. They need to be cutting wood or metal at full load to hit their nameplate. All tools get some rest as you move the workpiece around, and most people arent using them at full load for many cuts. But you get no NEC diversity factor for this in calcs.