Diversity Factor on Distribution Panel 1

[Golestan]

Hi,
Is there any standard or accepted practice for a diversity factor value for loads connected to a distribution panel?
Also is there an NFPA, IEEE or NEC rule pertaining to the percent overload on a distribution panel.
regards,

 

[wareagle]

The NEC gives factors in section 220 to use when
calculating the panel load. Other than that it may be
an engineering decision. You can use a demand recording meter to establish the panel loading.

 

[saladhawks]

I assume by diversity factor you mean the ratio of the sum of the individual peak demands in a system to the peak demand of the whole system. This is the reciprocal of the coincident factor, which is the more common factor I use when estimating electrical loads.

Coincident Factor = Peak Demand of System / Sum of Individual Peak Demands

The coincident factor will vary based on the type of load (residential, commercial, or industrial), the geographic location, and the season. I would say it is more an "art" than "science" that is gained from years of experience.

If you can give more details as to the type of loads connected, I can let you know the factors that I most commonly use for your type of application.

 

[Golestan]

My situation pertains to he followig:
-commercial/industrial building
-loads are HAVC pumps/fans;
-electrical motors connected to various rotating equipment
run about 15 hours per day
-the usual receps/lights in common areas

thanks,

 

[waross]

This sounds more like demand factors for a single building rather than the coincident factor of a system. The demand factor is the amount of reduction allowed for sizing of feeders based on diversity of loading. For example, it is not expected that all the electric ranges in an apartment building will be drawing their full rated wattage at the same time. The code allows a reduction in that part of the total calculated load that supplies the ranges. Look up demand factors in the code. If it is possible for all the motors to run at once you won't get much of a demand factor reduction. Many load centers are not allowed to be loaded above 80% of their rating.
respectfully

 

[saladhawks]

Don't bother looking up the demand factors in the NEC Code, as for non-residential applications these factors are appliable only to lighting and receptacle loads. Most of your load is motor based and the NEC Code is silent on the specific demand factors to use for motors. Thus, this is now an engineeering judgement based on the duty cycle and operating sequence (i.e. how many of the motors will operate at the same time).

For quick "sanity checks", I have seen the following demand factors used. Note that these factors should only be used to check the results of a thorough design completed by a competent professional engineer:

Industrial - 0.8
Commercial - 0.6

Thus, if you have an commercial application with 3500A of 120/208VAC, 3-Phase, 4-Wire loads connected, it would be common to see a 2000A panel specified.

 

[BJC]

Beamans book "Industrial Power Systems" had load or demand factors. It's so old now a lot of them are for equipment and processes that don't exist any more ( at least in the US). Thereis a new edition out, but I don't know whats in it.