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# Watts=Volt * Amp

#1
01-16-01, 11:47 AM
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how many lightbults I allow to install under this condition?

volt 120
amp 15A
light 100w

Thanks
T Ran

#2
01-16-01, 12:04 PM
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I get 18.

Each bulb draws 100 watts/120 volts = 5/6 amp.
15 amp/ 5/6 amp = 18 bulbs.

To check.

18 X 100 watts = 1800 watts

1800 watts / 120 volts = 15 amps.

#3
01-16-01, 06:00 PM
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I get 14.

You can only use 80% of the circuit capacity for lights.

#4
01-17-01, 06:25 AM
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I agree with you John. When I posted the response, I was only thinking about the pure circuitry. Yes, it must be down-graded by what you say, I was going to repost but didn't get around to doing it. Thanks for you correction.

#5
01-17-01, 08:57 AM
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Thank you pink and John.

#6
01-17-01, 06:46 PM
Wgoodrich
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Reducing the load to 80% is a good idea.

However if these lights are installed in a dwelling you are allowed to load that circuit to 100% by the NEC because they are general lighting.

These lights would be considered non contiuous loads, in the eyes of the NEC.

Wg

#7
01-17-01, 07:19 PM
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A matter of degree.

Hi,

I eagerly read these answers as a student of wiring, loosely speaking. I was excited to hear the 80 percent rule that I had learned before, thus good reinforcement in my DIY training! Then, I was even more wide-eyed as I read the 100 percent rule in the case of 'general lighting'! This is the kind of stuff I drool over to learn! Subtle, yet useful reasons behind the complexities of building codes.

Thanks everyone!

#8
01-17-01, 07:46 PM
Wgoodrich
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Mark please understand that everywhere is considered continuous except dwellings.

Single family dwellings, and inside apartments inside only, and inside hotel rooms for sleeping or living only, and inside motel rooms for sleeping or living only.

If you go out of a motel room then the lights in that hall is considered to be continuous.

Any wiring that runs more than 3 hours is considered as continuous.

The NEC states that inside the areas mentioned are for habatation and the general lighing is considered to be not continuous, even receptacles in these living areas are not considered to be continuous. However remember special receptacles such as laundry, kitchens, dinings, are nooks not considered as general lighting receptacles but special use receptacles. Everywhere else , not habitable areas, is considered to be continuous unless ruled by the "AUTHORITY HAVING JURISDICTION" is considered to be continuous.

The NEC says 100% of the non continuous and 80% of the continuous loads.

Hope this helps

Wg

#9
01-17-01, 09:35 PM
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Thanks Wg,

Your point is clear. And it was clear to me even before your last answer. I do appreciate your propensity for detail and clarity, and I understand the need for it. Rest very assured that I do indeed understand the difference between residential power needs verses non-residential needs. And if I did not understand it, you made the point crystal clear for everyone else reading this as well

In short, I'm on board with your meaning .

You are more exhaustive in explaination than anyone I can think of. That is a 'good thing'! That is why I proudly gave you the name of "professor" in another post. See

Thanks for the feedback doc!

#10
01-18-01, 09:03 PM
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How much difference would it be if we install a 400w, 500w 0r even a 1000w lightbulb? size of wire..ect

#11
01-19-01, 07:45 PM
Wgoodrich
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A 20 amp circuit would be good for 2400 watts @ 100%.

Hope that helped

Wg

#12
01-20-01, 09:06 PM
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Thanks for all the relies!!

would you recommend some of the good books, that may help me out?