Adding loads to an existing service

[olc]

Hypothetical Situation

Say you have a building with a 200A, 208V, 3Ph service.
And say the highest demand in the last 12 months per the utility is 80A.
So based on 220.87 you have 100A available for added loads.
However – the building has an infrequently used elevator. (95FLA, 195A start, 65.1A rated)
Say the building has three 5 ton 1 phase air conditioners (and maybe 6000W lighting).
Do you think the elevator shows up in the demand?

Bottom line - would you account for the elevator on top of the demand?

 

[charlie b]

I imagine that the elevator not only runs infrequently, but it also runs for very short periods of time. The utility metering would capture the energy it uses, but its impact on the average demand over (say) a 15 minute interval would be negligible. So I would not account for the elevator in my calculation of available capacity.

 

[Chamuit]

I agree with Charlie. As long as you follow the article, you should be fine and do not have to factor anything else in.

 

[steve66]

Code wise, I agree its allowed.

However, I'm always amazed at how low the demand metered loads are. I believe given the right combination of loads, the code may allow you to add enough load to an existing building to push the current up into the thermal mag trip of a main breaker. (Although I've never personally had this happen.)

You (or an engineer) should decide if that's a chance you are willing to take. Remember, the code isn't a design manual, and it doesn't guarantee that it will result in systems that operate as desired. Worst case is probably that the main breaker might occasionally trip, and someone may have to come back and upgrade the service later.

It might also be worthwhile to do a voltage drop calc. with everything running and the elevator starting just to make sure the voltage isn't dropping too much for the motor loads.

 

[kwired]

However, I'm always amazed at how low the demand metered loads are. I believe given the right combination of loads, the code may allow you to add enough load to an existing building to push the current up into the thermal mag trip of a main breaker. (Although I've never personally had this happen.)

I think that risk can possibly go up in some cases with a "cold start", like if the power had been off and many things are attempting to start at same time when power is restored.

 

[olc]

(Hypothetically speaking) I would not be adding enough load to the service to push the demand up past 100A.

Just looking at some numbers I would say that he elevator is not included in the demand.
The questions I have are:

How do the utility meters figure the demand? (I think it is a 30 min something - average?, peak RMS that lasts 30 minutes?)

If running the elevator actually pushed the service current above 200A (say 220A just for argument), would a run up two floors be long enough to trip a 200A circuit breaker?

If this were not hypothetical, I could go to the building on a hot day and put an amprobe on the service to see how it plays out when running the elevator.