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Re: Lighting Question #75247 02/20/07 11:30 AM
Joined: Jan 2005
Posts: 5,316
renosteinke Offline
Cat Servant
K, I think you're using the table wrong. That table has absolutely nothing to do with actual lighting you ought to install.

The table is in the part of the code that discussed "load calculations." This same area also defines panels as one of two types (power or lighting). By "lighting load" they are referring to the basic minimum electrical service that ought to be supplied to an area. The different occupancies listed are more of a guide, than actual code distinctions; a wise designer will likely break up an area into several different 'occupancies' for these calculations - even if there are no walls!

This "lighting load" is but a starting point. The same section of the code includes methods to calculate loads for receptacles and specific appliances or areas. These figures, added to the 'per sq. ft.' figures, gives you the minimum service size.

This is completely different from calculating how much light you need, and where that light should be located. For example, you'll want a lot more light over a work bench or aisle, than over the tops of the pallet racks. In those calculations, you will typically be using lumens, or candlepower .... not watts.

As for watts vs. volt-amps, for all intents and purposes they are the same thing. The difference only becomes relevant in discussions of power quality. Simply put, loads with large impedances (motors, transformers) or lots of electronics (ballasts, frequency drives) change the waveform from a nice, smooth sine wave to something else ... fooling you meter into thinking they are using less power than they really are.

Load calculations are a basic part of traditional electrical apprentice training programs. They are not, generally speaking, ever mentioned in the training of an industrial electrician. The industrial guy's training is focused on the equipment, rather than the building. It is certain that the industrial guy deals a great deal with motors and controls - but he can still go his entire career without ever seeing a GFCI or pulling a meter.

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Re: Lighting Question #75248 02/20/07 12:23 PM
Joined: Aug 2005
Posts: 64
kyelectric Offline OP
renosteinke, thanks for the great explanation! That is what I thought this forum was for. I misunderstood the table. I understand now that it is for load calculations and not for instucting on how much light to provide. Yes, you are correct. I have been an industrial electrican for 12 years now and have not had to deal a whole lot with lighting. I have read the code book through and study it when I have questions about different situations. I have mostly been doing small jobs on the side for several years. Over the last year, my jobs have been getting a little bit bigger as the area that I live in is experiencing heavy economic developement. I have wired several houses and have helped wire several commercial buildings in the last few years. But, like I said, no one that I have worked with has actually showed me how to determine how much light to provide. They just seem to put up enought light that either the inspector likes it or he does not. Again, thanks for giving a positive response. I'll try to read the book and understand a little better next time before I post the question.

Re: Lighting Question #75249 02/20/07 03:02 PM
Joined: Jul 2004
Posts: 9,605
gfretwell Offline
Don't worry about it. This is supposed to be the place where you can ask "dumb" questions, among friends. This trade is so varied from job to job that there are no dumb questions, only questions about parts of the job we don't see every day.
I have said some dumb things here and been corrected. It was just part of the learning experience. In the volatile job market we are in it is wise to know a little about a lot of things you never thought you would ever need to know. Knowlege is power.
You also have energy laws and new products coming on the scene that make a lot of old "rules of thumb" obsolete. That is particularly true of lighting. That 2va/sqft may actually be very generous in California.
The next generation of LED (or other solid state lights) may make office space capable of being lighted with a fraction of a watt per foot.

Greg Fretwell
Re: Lighting Question #75250 02/20/07 03:50 PM
Joined: Apr 2002
Posts: 7,254
HotLine1 Offline
I was out of town for a few days, hence I could not respond promptly.

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