208Y/120V Lighting Panel sizing 1

[ksavoie]

I’m trying to figure general Lighting Load on an office building that is 11,400ft2. Using table 220.12 I will multiply 11400ft2*3.5VA/ft2 =39,900VA.

The part I’m confused about is how to calculate the amperage to size the 208Y/120V panel. Would it be calculated as 39,900VA/208*1.73?

I think I'm confusing my self becasue I will be using single phase 120v lighting.

 

[rbulsara]

Yes. That will be "calculated" current in each phase assuming you have balanced 120V lights among three phases.

Also attempt to caluclate current per phase this way:
Find load on each phase if you have 3 phase service.
Divide the per phase load with per phase voltage.
Compare the answer to that you got using what you posted. Hope that will help diffuse the confusion.

I am only answering your question on face value. There is more to it to size a service or a panelboard, if that is what you are after. Consult your senior staff as well.

 

[Senselessticker]

For what its worth: Don't get too caught up in the NEC... and use your actual lighting loads to figure the power requirements for the panel(s).

 

[SteveFehr]

If you're using 120V (Wye), you can simply add up the 1-phase line currents. But it works out the same either way you calculate it:

39,900VA/(208*1.73) = 39,900VA/(120*3) = 111A/phase.

This may be a good value for scoping, but if you know the actual load, it's best to use it instead.

 

[BJC]

KSAVOIE
The 3.5 Va/sq ft may not be enough. You have to add any specific loads that you know of. Typically refridgerators and mircowaves in a break room, copiers, etc.
The 3 Va/sq ft covers what use to be in an office ( the NEC may be a little behind.).
i have seen office layout where every cube had it's own circuit. Some people had two computers two or three monitors, their own printer, a coffee warmer, a heater under their desk etc. etc.
Your up to a 225 amp panel which is good a good match for a 75 Kva transformer. IMO a 250 amp panel and a 75 kva panel are better.
In my experience you run out of circuts pretty fast and you may want to use two panels ( a main breaker panel with feed thru lugs and a main lug only panel down stream from that.
Depending on the layout of the building you can seperate the panels to shorten branch circuit runs.
OR
you can use two 30 KVA transformers and 125 amp panels depending on the building layout.
Talk with your client and if possible vist an office where they are now located.
Good Luck.

 

[ksavoie]

BJC,

I am only using 3.5VA/sq ft to determine the "Minimum Lighting Load" as shown on table 220.12. I'm actually going to have 1 lighting panel, 2 power panels (one for each floor, 1 equipement panel and 1 computer panel. For the power panels I estimated 180AV per receptical plus the VA for all known appliances.

 

[EEJaime]

I don't know your location, but using 3.5 VA/sf will give you quite a large factor of safety as most current energy codes restrict office lighting to below 1.5 VA/sf.

 

[DonPhillips]

For office occupancy, the 2006 IECC limits the lighting to 1 W/sf.

Don Phillips

http://worthingtonengineering.com