According to the table for lighting loads in the NEC, I have to allow 2 volt-amps per square foot for a commercial building. Doesn't volt-amp mean the same thing as Watt? If so does that mean that a 400 watt bult covers 400 square feet? If not, how do you calculate lighting? Thanks!
NEC wants you to multiple Volts x Amps to get VAs. For lighting, Volts and Watts are pretty much identical, but since NEC is talking VA, you don't need to worry about power factor at all, it makes your job much easier.
That is really the calculation for the general lighting load including receptacles and it is a monimum number. Occupancy can and usually will raise what you actually need. Lighting is really calculated by lumens per square foot and each industry has different recomendations.
[This message has been edited by gfretwell (edited 02-19-2007).]
I don’t mean to be rude, and part of me would love to wax on enthusiastically about what this means and how to apply it, but if you are asking this question then I sincerely hope you are not actually doing electrical work.
Perhaps you should consider taking a code study class, it would explain this and all the basics behind it, which you really should have under your belt to be an electrical contractor in the first place.
Again this is not intended to be mean or rude, and is meant in complete sincerity.
This is a forum where electricians, contractors, apprentices, and others, all with different levels of experience and knowledge post here to get or give advice and pick the brains of others. Everyone has their strengths and weaknesses, and in my opinion, shouldn't be shot down for asking an honest question. Just my 2 cents.
"Will it be cheaper if I drill the holes for you?"
I agree Sixer. Lighting can be as simple or as complicated as the occupancy requires. The table in 220 can be misleading. That is not a lighting plan, it is just the minimum calculated load you can use for service computations. I'm sure we could go on for days about what light you need in various situations.
Thank you for your responses. I have worked with electrical contractors who just placed lights all over the place and if the inspector said anything, they would move them or add more lights. But, I want to actually know how to do it right. When a commercial building calls for 2 volt-amps per square foot does that mean for example that I take the voltage of the fixture (120 volts) times the amperage (.50) which gives me 60VA. Then if I divide that by 2VA (per square foot), that gives me an area of roughly 30 square feet that this fixture will cover. This is probably way off, someone help me please! : )
Again this is with complete sincerity; if you are asking if VA is the same as W, then you really should be looking into a code study class instead of asking people you don’t really know on the internet to explain the difference between a load calculation and whether a 400W lamp is adequate for 400sf based on reading T220.12.
I am not shooting anyone down, but there are some fundamentals here that can not be adequately taught on a message board, and the original poster is asking questions that would be thoroughly covered in a code study class, or even a structured apprenticeship through a local union.
This is what I feel is offering the correct advice for this question.