Number of outlets or lights per 20 amp CB

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Old 08-27-07, 03:01 PM
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Number of outlets or lights per 20 amp CB

Is there a standared rule of thumb for the # of outlets or # of can lights per 20 amp CB. Most of the outlets won't be used all the time or at once. The lights are a seperate question.

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Old 08-27-07, 03:55 PM
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If all you have on a circuit are lights, then base the number of lights on the circuit size and the maximum wattage bulb that can be installed in the light. For safety, do not exceed 80 percent of the circuit rating, in this case 80 percent of 20 amps, or 16 amps. Use the formula power (wattage) equals volts (120) * amps. So do not exceed 1920 watts.

For receptacles, the answer depends on what the receptacles will be serving and where they are located.
 
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Old 08-27-07, 06:38 PM
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You don't post a location. In Canada the limit is 12 outlets on a 15 or 20 amp circuit.
 
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Old 08-27-07, 07:17 PM
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Thanks guys. Location is in Indiana. I'm finishing a basement so a lot of the outlets are placed as possible periodic use. I think thus far the most I've planned is 9 on one circuit.
 
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Old 08-27-07, 07:24 PM
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Racraft,

So what you're saying is if I use 100watt bulbs (which I doubt I'll go that high) I can put approximately 19 lights on one 20 amp CB?

Thanks,
 
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Old 08-27-07, 07:38 PM
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Originally Posted by fieldsmr View Post
Racraft,

So what you're saying is if I use 100watt bulbs (which I doubt I'll go that high) I can put approximately 19 lights on one 20 amp CB?

Thanks,

Breakers are rated for 100% use, so if you want put 2400 watts worth on one 20a CB if you want... to answer your original question, there is no maximum # of receptacles on a circuit, they are included in the general lighting load.
 
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Old 08-27-07, 08:14 PM
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Originally Posted by Chris75 View Post
Breakers are rated for 100% use, so if you want put 2400 watts worth on one 20a CB if you want... to answer your original question, there is no maximum # of receptacles on a circuit, they are included in the general lighting load.

for continuous use (3 or more hours) , breakers are rated for 80%. Lighting is generally considered continuous use although if it is in multiple rooms, it often is not all used at the same time.

It is generally better to be safe that PO;d.

Not sure what you mean by the receps are included in the general lighting but in load calcs, they are not. As well, most folks will recommend to keep lights on a light circuit and receps on a recep circuit. I agree with them.
 
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Old 08-27-07, 09:13 PM
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Yes, if you used 100 watt bulbs you could us 19 of them and be within the 1920 watts. However, you would likely burn your house down. Most can lights are not rated for 100 watt lights. Look at the rating of the lights.

You are finishing your basement. Planning on a computer setup? Run a dedicated circuit for the computer.

Planning on a home entertainment setup (TV, DVD Player, stereo, etc.)? Run a dedicated circuit for that.

Need a dehumidifier? Run a dedicated circuit for that.

Any other significant loads? Run them a dedicated circuit as well.
 
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Old 08-27-07, 09:20 PM
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Originally Posted by nap View Post
for continuous use (3 or more hours) , breakers are rated for 80%. Lighting is generally considered continuous use although if it is in multiple rooms, it often is not all used at the same time.

It is generally better to be safe that PO;d.

Not sure what you mean by the receps are included in the general lighting but in load calcs, they are not. As well, most folks will recommend to keep lights on a light circuit and receps on a recep circuit. I agree with them.

What code section says breakers are to be used at 80%? and if receptacles are not in the general lighting load, what do you rate each one at? and I disagree with the lighting is generally considered a continuous load... read the definition of a continuous load...
 
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Old 08-28-07, 06:21 AM
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In a residence, there are cases where breakers are used at 80 percent of their rating. However, lights are not considered one of these. That being said, it is a good idea to limit a lighting circuit to 80 percent of the circuit breaker rating if it serves a single room and it is likely that the lights will be on for extended periods of time.
 
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Old 08-28-07, 03:52 PM
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article 100 definitions

continuous load: a load where the max current is expected to continue for 3 hours or more.

So, depending on what the lighting is, it may be considered continuous.

My mistake about the receps in the lighting load calc but truly that is not the issue here. That is for branch circuit LOAD CALCULATIONS. Calculations are not a practical method of designing a specific circuit.

Now, I do work commercial where many things are continuous so that does change things in my head a bit BUT a breaker is designed to be loaded to 80% capacity for continuous loads. If you want nuisance trips, go ahead and load it to 100% if you want. I did not say it was a code requirement, just good design. As well, if you use your ideas, you load the breaker to 100% with lights and then toss on some receps. Guess what happens on cleaning day when all the lights are turned on and the vacuum and the carpet cleaner are all running at the same time.

If you notice I did say that depending on how the light circuit is laid out, you could load it heavier.



btw; when I do calcs, a recep is rated at 180 va. but like I said, that is non-residential.

bottom line; you can design a system that is right on the edge and wait until somebody gets po'd because the used it a bit more than you figured or you can design a system that is not overly taxed and allows for something you may not have known.

It's the diff between a cheap job and a good job.

as far as the lights, I always try to keep lighting and power seperate. Not only is it often spec'd that way in jobs I do but it is just common sense. The lights are a consistant given. Generally the load does not change so you can load it a bit heavier. Receps are an unknown. If you trip a breaker and the lights are on the same circuit, you are now in the dark.

which customer will be happier?
 
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Old 08-30-07, 12:59 PM
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Nap,

Hey thanks for your input. The lights I'm fine with. 19 lights is plenty with 60 watt bulbs. Lights and outlets are on seperate CB. The outlets I'm still a little confused. About 70% will be used at any one given time. There's mosly just household stuff that will be plugged in lamps, clock maybe some exercise equip., that sorta stuff so in your opinion how many would you put on a 20 amp CB? So far I've spected out 10 at the most on one and about 60% of those will be used at any one given time. Thanks again!!!
 
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Old 08-30-07, 01:48 PM
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Exercie equipment? Some of those units require a dedicated 20 amp circuit. Check the specs on the euipment and wire a dedicated receptacle.
 
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Old 08-30-07, 01:58 PM
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The issue is not how many receptacles.

You talk about exercise equipment. How much power do each of these pieces of equipment need?

Something like a treadmill may need quite a bit of power.
 
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Old 08-30-07, 07:02 PM
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I would suggest 1 20 amp circuit for general purpose outlets and you can put as many as you want on that circuit. For larger equiptment, you should calculate the loads and have a seperate circuit(s) for that. I recommend that lighting always be kept on seperate circuits because some outlet loads will cause a voltage drop that dims the lights. Also, if you trip a breaker due to an overload caused by something you plugged in, you won't be left standing in the dark. Another suggestion, is that if you plan on putting in a dimmer switch, you watch the wattage. I may be corrected by someone else, but all the dimmer switches that I've seen at the hardware store are only rated at 600 watts. If you go over that rating they'll overheat. So if you want a dimmer and you have more than 600 watts, you'll probably have to go to an electrical wholesale house to get a higher rated one.
 
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Old 08-30-07, 07:48 PM
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Dimmers are available at many different wattages, even at the hardware stores.
 
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Old 08-30-07, 08:29 PM
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Originally Posted by brewcityc View Post
Another suggestion, is that if you plan on putting in a dimmer switch, you watch the wattage. I may be corrected by someone else, but all the dimmer switches that I've seen at the hardware store are only rated at 600 watts. If you go over that rating they'll overheat. So if you want a dimmer and you have more than 600 watts, you'll probably have to go to an electrical wholesale house to get a higher rated one.

Installed one yesterday that was 1500 watts. 600 watts is the standard youget at most big box stores.
 
 

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