Understanding Continuous Loads

[jdmz]

Does the continuous load factor of 125% apply to motor loads and AC equipment?

For example:
I have a panel with:
1x AC unit, using MCA and MOP on nameplate
1x 2 hp motor, using 1.25*FLC
1x combination motor (2 hp and 1 hp motor), using 1.25*FLC largest motor + FLC smaller motor

The three loads are continuous loads that can operate more than 3 hours. Do I add up all the loads and add 25% on top of it to size my feeder conductors and panel breaker?

Then going on to service loads feeding the panel.. add another 25% on top of what we added up so far? It seems like safety factor on top of safety factor.

Panel load = total continuous load*1.25
Service load = panel load*1.25

 

[davidbeach]

Motor loads are motor loads and get tracked independently of all other load categories, at least per the NEC.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[RRaghunath]

Motor kW is sized based on the driven equipment requirement and a margin over that. Hence, there is no need to add safety factor when you are already taking motor nameplate kW rating while calculating the load. If you have any motors that may be overloaded, it is a different aspect.
If you have any spare feeders in the panel which may serve some loads in future, you may want to factor that as well.
When it comes to sizing the cable, add margin only after adding all the loads as expected. No need to take safety factor while calculating the load.

 

[davidbeach]

If the NEC is the governing code, motor current comes from a table in the code based on motor horsepower and not from the actual driven load. All of those motors are carried at 100% of the code load. An additional 25% of the largest motor supplied beyond that point is also included. Is what it is.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[dpc]

At the risk of stating the obvious - this discussion is based on sizing protective devices and feeders based on the requirements of the NEC (US). The load that is calculated is extremely conservative in most cases and won't be predictive of what the actual load will be. But it is the law so we have to size equipment based on this.