balancing requirements for 3 phase

[curious george]

Just curious -

Is there any standard of parameters for balancing three phase panels? :-?

I have a situation where there are several three phase panels, between 20-32 circuits each, no motors on any circuits of the panels (lots of lighting and various fourplex receptacles for general use), but the volt-amps per phase are not even close. Is there a standard, say within 10%, or 20%, or whatever %, of each phasevfor balancing the load?

Existing has Phase A at 2250 VA, Phase B at 7500 VA, and Phase C at 8950 VA.

I have found nothing in the 2005 NEC, which is enforced here.


Thanks for your help!

George

 

[hurk27]

I think it is more of a design issue that a safety hazard which is why its not in the code and the fact it would be very hard to enforce since the amount of load at any given time in a building will change as loads are turned on and off, so unless there is an issue with voltage drop on the service or feeders, then it is usually not an issue.

 

[dbuckley]

Existing has Phase A at 2250 VA, Phase B at 7500 VA, and Phase C at 8950 VA.

At that loading, it falls into the "who cares" category, unless you're running off a 20KVA genset! There'll be another panel down the hallway (or next door) with a dissimilar load in a different combination.

Now if they were 2250 KVA, Phase B at 7500 KVA, and Phase C at 8950 KVA then we would all want to improve matters...

 

[mityeltu]

I would think that truly balancing 3-phase panels with 1-phase loads would be difficult, but the NEC gives some decen examples of how to estimate total 1-phase loads based on diversity factors for all types of equipment.

I would suggest that making a matrix of all loads accounted for on this panel and determine an appropriate diversity factor for each phase. Shift loads and recalculate the loading based on the new diversity factor. Sounds time consuming and I'm not sure of the real benefit given the types of loads your talking about, but that would get you closer to a balanced system.

 

[curious george]

Sorry it took me a while to get back online and thank you for the time and efforts put forth to help me. I do appreciate the responses!

George