Lighting Demand Factor

curious101

Member
Regarding commercial buildings, lighting branch circuits: we add up the lighting fixture wattages and always use 125% for demand factor for the load because lighting is continuous load. Is this wrong? I'm trying to have it proved that it's right by NEC, but....Looking into NEC 2014 210.20(A), 125 percent is required for the overcurrent protection and not for load. NEC 2014 table 220.42 shows the lighting load demand factors, where for a commercial office building the demand factor would be 100%. Is there any other section of the NEC which tells us that commercial office building lighting load demand should be at 125%? Thank you!

david luchini

Moderator
Staff member
The lighting demand factor for an office is 100%. The 125% for continuous load is not a demand factor.

curious101

Member
The lighting demand factor for an office is 100%. The 125% for continuous load is not a demand factor.
Thank you!

electrofelon

Senior Member
Regarding commercial buildings, lighting branch circuits: we add up the lighting fixture wattages and always use 125% for demand factor for the load because lighting is continuous load. Is this wrong? I'm trying to have it proved that it's right by NEC, but....Looking into NEC 2014 210.20(A), 125 percent is required for the overcurrent protection and not for load. NEC 2014 table 220.42 shows the lighting load demand factors, where for a commercial office building the demand factor would be 100%. Is there any other section of the NEC which tells us that commercial office building lighting load demand should be at 125%? Thank you!
I think you have to use the VA per square foot values in the table, unless your actual fixtures draw more than that value.

WA_Sparky

Member
Looking for some clarification... So lighting demand factor is 100%. Continuous loads are 125%. Lighting fixtures that are used in everyday operation are considered continuous loads so essentially get a 125% demand factor applied right? So the only 100% demand factor for lighting would be like lamps or plug in fixtures?

I'm trying to piece these two threads together. https://forums.mikeholt.com/forum/active-forums/electrical-calculations-engineering/724-general-lighting-load-demand-factor-in-nec?t=52496

david luchini

Moderator
Staff member
Looking for some clarification... So lighting demand factor is 100%. Continuous loads are 125%. Lighting fixtures that are used in everyday operation are considered continuous loads so essentially get a 125% demand factor applied right? So the only 100% demand factor for lighting would be like lamps or plug in fixtures?

I'm trying to piece these two threads together. https://forums.mikeholt.com/forum/active-forums/electrical-calculations-engineering/724-general-lighting-load-demand-factor-in-nec?t=52496
The 125% is not a "demand factor." See 220.40 - The calculated load of a feeder or service shall not be less than the sum of the loads on the branch circuits supplied...after any applicable demand factors permitted by Part III or IV or required by Part V have been applied. There is nothing in Part III, IV or V regarding 125%