General lighting loads

[mego6000]

Hi everyone
Firstly, Could any one explain for which type of lamp the general lighting loads by occupancy table (220.3(b))has been derived.
secondly, if it is not the filament lamp but (say) Fluorescent lamp then which power factor has been used in the table (the corrected or the uncorrected)one.
Finally, if you are using fluorescent luminaires with individual power factor correction to 0.95, which power factor should you use in load estimation? is it the original PF ~ 0.5 or the corrected one ~0.95 or an average value in between (say) 0.7 and why?

Many Thanks,
Amged

 

[websparky]

Re: General lighting loads

Amged,

A unit load of not less than that specified in Table 220.3(A) for occupancies specified therein shall constitute the minimum lighting load.

This section has to do with the load (VA or WATTS) not the amount of light (lumens) in the structure. In other words, the type of fixture or lamp is not a part of the calculation.

 

[mego6000]

Re: General lighting loads

Thanks dave
I know that but this doesn't mean that these values have no lux basis.

 

[nvcape]

Re: General lighting loads

Maybe someone (Charlie?) knows the history of the General Lighting Loads table. I looked in an 81 book and found the same values. For dwellings, it includes general receptacle loads, not just lighting. So, don't try to justify lighting energy compliance with NEC! When you run the loads for a large apartment complex or hotel, and use the 23% demand factor, it is impressive that this system, which seems obsolete works so well.

 

[charlie]

Re: General lighting loads

Some of the rules, I know the history. However, this one . . . I do not.

I will tell you that some of the numbers get into the Code by someone making a proposal to permit something with an arbitrary number like 100 feet. The CMP agrees that it is great idea and puts it into the code at 100 feet. The next cycle, several problems are encountered and proposals are made to reduce it to 25 feet. Again, the CMP agrees somewhat and changes it to 30 feet. After that cycle, a lot of proposals are mad to increase it to 50 feet because 30 feet is too restrictive. One more time the number is changed and this time very few proposals are made to change it and it stays as a Code rule.

Sometimes a rule is made to 'fix' a problem with an arbitrary number. After time, no one knows where it came from. If you know the cycle, that information is available from the NFPA archives at a cost for research, copying, and faxing.

 

[charlie b]

Re: General lighting loads

Originally posted by mego6000: I know that but this doesn't mean that these values have no lux basis.

Yes it does. The function of that table, and while we?re at it the entire calculation section, is to ensure the end user has enough power coming in at the service entrance to meet a minimum set of needs. It does not mean that the end user will be happy with the builder?s selection of light fixtures, nor with any other aspect of the design. The NEC is not a design manual, and has no interest in customer satisfaction.

If the results of your calculation are that you need a minimum of 3000 watts (e.g., 3 watts per square foot times 1000 square feet), and if you choose to install 9000 watts of general power and lighting, the NEC will let you do that. (ASIDE: State energy codes might throw a flag on the play, but not the NEC.) This is the point in time where you look at the types of fixtures, and deal with their power factor issues. It may cause you to upgrade the service from the minimum calculated per Article 220, but here again that is a design decision.

To answer you last question, if a device has integral power factor correction, so that within the device the 0.5 power factor is corrected to 0.95, then for calculation purposes you use the 0.95 value. The electrical distribution system never sees the 0.5 number, so it does not come into the calculations.

 

[mego6000]

Re: General lighting loads

Thanks charlie for you reply and I agree with most of what you have said but in the last point what if some Fluorescent luminaire capacitors fail to work don't you see with me that the load of these luninaires will come back to its uncorrected value? so is it better to take that into account by taking an average value let (PF=0.7)?

Many thanks,

Amged

 

[charlie b]

Re: General lighting loads

I would not, but once again it?s a design decision.

The NEC calculation process does not address what happens to load if some component were to fail. That would be similar to saying that you need four parallel 1/0 conductors, but you choose to install 3/0 conductors, so that if one conductor fails the other three are large enough to handle the load.

 

[mego6000]

Re: General lighting loads

Thanks Charlie for your valuable reply, which I really respect however, I have some comments not for the sake of argument but to increase the benefits that we can get from this discussion.

quote:

Originally posted by charlie b: - If a device has integral power factor correction, so that within the device the 0.5 power factor is corrected to 0.95, then for calculation purposes you use the 0.95 value. The electrical distribution system never sees the 0.5 number, so it does not come into the calculations.

My comment
With all my respect but this is not absolutely true because in case of capacitor operation failure, the load will come back to its uncorrected value and the electrical distribution system does see the 0.5 number. Hence I see to take the 0.95 value as you said for the calculation of the OCPD rating and an average value as I said before for the branch circuit conductor rating.
Please, note that I know 100% that this is not NEC problem but a design decision which may vary from person to person.

quote:


Originally posted by charlie b: The NEC calculation process does not address what happens to load if some component were to fail.

My Comment
Again I see that is not absolutely true because if it is so, then why in 460.9 the effect of the capacitor has been disregarded in determining the motor circuit conductor rating? And why generally the same effect (of capacitors) is not mentioned in determining the Main circuit breaker and conductors of a main switchboard with central power factor correction?!
Finally I like to express my appreciation to all replies I?ve got.

Many Thanks,

Amged El-Wakeel

 

[steve66]

Re: General lighting loads

Deleted double post.

Steve

[ June 02, 2004, 09:20 AM: Message edited by: steve66 ]

 

[steve66]

Re: General lighting loads

With regard to 460.9, one could argue that the capactiors effect is ignored because the capacitor could easily be removed or disconnected even if it was still working. Also, the full motor current could still flow on the branch circuit conductors between the capacitor and the motor.

At any rate, it seems very unlikely that enough ballasts could fail in the same manner to cause an overloaded circuit. Even if they did, the circuit breaker should protect the wiring.

That said, for other reasons, I seldom fully load a lighting circuit. I like to leave room for a couple of extra lights to be added later. It often seems easier to minimize voltage drop by limiting load than by increasing wire sizes. And it is possible that ballasts will be replaced as they go bad with ones that have a poorer PF. In my designs, the lights that are actually installed are the lowest biders' brand, so I usually don't know exact ballast specs. when I lay out a circuit.

Steve