# How Many Lights on a 15 amp Circuit?



## ctsmiths

A 15 amp circuit can handle 1440 watts, or equal to 24-60 watt lamps. Add up the wattage and do not exceed 1440 watts and you will be fine. This is for non- residential installations, but is widely used as a good guide, because the 1440 is really the max a 15 amp circuit is allowed to be loaded.

The code takes into consideration that it would be very unlikely most homeowners will not, and should not need to, worry about how much load is on a circuit. 

Residential lighting circuits are size according to the square foot, using 3 watts per square feet of livable space , so a 1200 Sq ft home has an estimated 3600 watts of general lighting load. Next 3600 / 120 volts = 30 amps. The home would be wired with at least 2-15 amp circuits. 

Even though you are using the less wattage ones, you need to size it for normal load that someone, other than you, might use the circut for.


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## Speedy Petey

ctsmiths said:


> This is for non- residential installations, but is widely used as a good guide, because the 1440 is really the max a 15 amp circuit is allowed to be loaded.


Actually a 15A circuit can be loaded to 15A, or 1800 watts for a 120v circuit. 
The 1440 watt number is for continuous loads, and like was mentioned, residential lighting loads are not typically considered continuous loads. 

You really can't say a 15A circuit is only supposed to be loaded to 80% period. It all depends on the load and the type of circuit.

See NEC Table 210.24 and section 210.23(A)


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## Scuba_Dave

In a residential home I've always loaded a 15a circuit to 1800 watts based on the MAX bulb allowed by the fixture
So 18 100 watts fixtures

Residential lighting is not considered continuous & can be loaded to the allowed wattage of the circuit. I use almost all CFL's, so loading to 1800 watts by the fixture I still only use about 1200w if every light was on at the same time. I'm lucky to have 300w of lights on at any given time

As stated it doesn't matter what bulb you are using
It depends upon the Max wattage bulb that could be installed according to the fixture. IE my cans usually have a rating of 100w, but I only use the 23w CFL's


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## jerryh3

ctsmiths said:


> A 15 amp circuit can handle 1440 watts, or equal to 24-60 watt lamps. Add up the wattage and do not exceed 1440 watts and you will be fine. This is for non- residential installations, but is widely used as a good guide, because the 1440 is really the max a 15 amp circuit is allowed to be loaded.
> 
> The code takes into consideration that it would be very unlikely most homeowners will not, and should not need to, worry about how much load is on a circuit.
> 
> Residential lighting circuits are size according to the square foot, using 3 watts per square feet of livable space , so a 1200 Sq ft home has an estimated 3600 watts of general lighting load. Next 3600 / 120 volts = 30 amps. The home would be wired with at least 2-15 amp circuits.
> 
> Even though you are using the less wattage ones, you need to size it for normal load that someone, other than you, might use the circut for.


Here we go again. The old 80% rule...


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## Scuba_Dave

Which begs the question

If the breaker is rated for 15a, the wire is rated higher
Then why can't you run it at Max capacity - or very close to it ?


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## micromind

The answer is mainly because of manufacturing tolerances. 

No two breakers will trip at exactly the same amperage. Some 15's will hold 15 forever, others might trip at 14. The 80% rule is to minimize nuisance tripping. This is why it generally applies only to continuous loads. 

Certainly, there are other factors, but this one makes the most sense.

Rob

P.S. Some large industrial breaker are listed for 100% continuous, and code allows their use at full rating.


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## Scuba_Dave

I guess they can only go so far in codes
But its quite possible to load any 15a or 20a circuit to near capacity & leave it that way. The only time I ever unplugged anything from a circuit ( as a kid/young adult) was if I kicked the breaker out :laughing:

I guess I just find it weird that they would regulate lights commercially when they can't regulate what will be plugged into the outlets. You just know if a business has a choice between paying an electrician to come in & add a circuit VS loading outlet circuits to close to 100% they will in most cases just load the circuits up

One place I worked they only ran new circuits when the breakers kept tripping - too many computers added


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## Speedy Petey

With commercial lighting the key is the word "expected" in the definition of "continuous load". 
Commercial lighting _IS_ expected to be on for three hours or more.


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## Steelhead

ctsmiths said:


> A 15 amp circuit can handle 1440 watts, or equal to 24-60 watt lamps. Add up the wattage and do not exceed 1440 watts and you will be fine. This is for non- residential installations, but is widely used as a good guide, because the 1440 is really the max a 15 amp circuit is allowed to be loaded.
> 
> The code takes into consideration that it would be very unlikely most homeowners will not, and should not need to, worry about how much load is on a circuit.
> 
> Residential lighting circuits are size according to the square foot, using 3 watts per square feet of livable space , so a 1200 Sq ft home has an estimated 3600 watts of general lighting load. Next 3600 / 120 volts = 30 amps. The home would be wired with at least 2-15 amp circuits.
> quote]
> 
> 
> Even though you are using the less wattage ones, you need to size it for normal load that someone, other than you, might use the circut for.[/
> 
> 
> I was looking at a book about home wiring the other day and when I got to the chapter about sizing the load the author used the same example about residential lighting. He continued on with all the other required calculations for the laundry circuit, appliance circuit and so on and so forth. I got to wondering though what about the other general use receptacle load.
> 
> I happened to look at another book that I had and it stated that the general receptacle load was included in the lighting load calculation. Is this correct? Is this usually sufficient for todays homes?


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## ctsmiths

Bill_in_NY said:


> Thanks in advance for taking the time to answer my question. :thumbup:
> 
> I have a 15 amp circuit that goes into the attic and I want to install a series of screw-in type lightbulb fixtures.
> 
> I am planning to run those new 27-watt CF bulbs.
> 
> How many outlets could I feed on that one circuit?


 Any receptacles going on this circut as well, or other things such as ceiling fans or a whole house fan?


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## Speedy Petey

Steelhead said:


> I happened to look at another book that I had and it stated that the general receptacle load was included in the lighting load calculation. Is this correct? Is this usually sufficient for todays homes?


Sure it is. Keep in mind this is for load calculation purposes. 

Sure it could be used as a BARE bones unrealistic minimum of circuits to run, but the real world is much different.


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## ctsmiths

jerryh3 said:


> Here we go again. The old 80% rule...


 Well it does apply if you are going to supply other equiptment on this circut, thats why I asked later if he was going to be feeding any thing else with this circut.:boxing:


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## Speedy Petey

ctsmiths said:


> Well it does apply if you are going to supply other equiptment on this circut, thats why I asked later if he was going to be feeding any thing else with this circut.:boxing:


You are misreading 210.23(A)(1). The 80% rule in this case is for any ONE piece of equipment. NOT for the whole circuit.

_*(1) Cord-and-Plug-Connected Equipment Not Fastened in Place.* The rating of any one cord-and-plug-connected utilization equipment not fastened in place shall not exceed 80 percent of the branch-circuit ampere rating.
_


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## ctsmiths

Speedy Petey said:


> You are misreading 210.23(A)(1). The 80% rule in this case is for any ONE piece of equipment. NOT for the whole circuit.
> 
> _*(1) Cord-and-Plug-Connected Equipment Not Fastened in Place.* The rating of any one cord-and-plug-connected utilization equipment not fastened in place shall not exceed 80 percent of the branch-circuit ampere rating._


 You misunderstand me, I am talking about the other equiptment. I was wondering if anything else was going on the circut and if so what it was. I dont dispute that the 80% rule is a rule of thumb for lighting for res work, not a hard and fast NEC rule. :detective:


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## Bill_in_NY

ctsmiths said:


> Any receptacles going on this circut as well, or other things such as ceiling fans or a whole house fan?


No ceiling fans. Maybe 1 plug in fan if it gets too hot in there in the summer. I don't know what you would actually call these light fixtures. It's just a single socket receptacle that you screw a lightbulb into (like you might see in the closet of an old house). I just plan to run several of them along the same wire controlled by a single light switch.

I think the wire is connected to a ceiling light downstairs, so I am taking that into consideration.

I may just go with a couple track lights, not sure yet.

I just didn't want to install 10 lights in the attic to find out that it would keep tripping the breaker. They might be on for 3 to 4 hours at a time, as I am setting up a small workshop in there. Any electrical needs other than the lights would be on a seperate outlet.

Thanks for the help! :thumbsup:


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## DIY_JC

ctsmiths said:


> Any receptacles going on this circut as well, or other things such as ceiling fans or a whole house fan?



What max wattage value is used for receptacles & ceiling fans... when performing the calculations?

also- bathroom exhaust fan (no lights)


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## Scuba_Dave

DIY_JC said:


> What max wattage value is used for receptacles & ceiling fans... when performing the calculations?
> 
> also- bathroom exhaust fan (no lights)


Ceiling fan can vary depending upon the fan
You need to find out the model & look it up
I don't mix receptacles with lights/fans
There isn't a real calculation for receptacles
But considering a bathroom outlet could have a 1600w hair dryer plugged in that doesn't leave a lot of extra power for lights & fans


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## DIY_JC

Scuba_Dave said:


> Ceiling fan can vary depending upon the fan
> You need to find out the model & look it up
> I don't mix receptacles with lights/fans
> There isn't a real calculation for receptacles
> But considering a bathroom outlet could have a 1600w hair dryer plugged in that doesn't leave a lot of extra power for lights & fans


There isn't a standard used? What if it is being done before the lights/appliances are purchased by the builder? As for my particular fan, I can't get to it as the ceilings are too high (and I don't have a way to get to it safely).


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## Scuba_Dave

My existing fan light is rated for a 100w light bulb
My replacement light fixture is rated for (2) 60w bulbs
I think that would be MAX - 120w
My fan I don't know

Actually I just checked & the new one uses 2 candelabra lights
So its going back, I want to use 2 13w CFL's


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## jogr

ctsmiths said:


> Even though you are using the less wattage ones, you need to size it for normal load that someone, other than you, might use the circut for.


Brings up an interesting Friday afternoon question. Since incandescent bulbs between 40 and 150 watts won't be manufactured after 2014 does this or will this affect your approach to designing residential lighting circuits? 

Many fixtures are currently rated for 60 watt bulbs based upon incandescent. I guess for now you still assume the use of 60 watt incandescent. Come 2014 the fixture manufacturers will probably still be putting out the same fixtures rated at 60 watts so do you assume that customers will be putting in a high wattage CFL (say 27 or 42) to get increased brightness or do you assume they will put in 14 watt cfls to get equivalent brightness? Or maybe it just doesn't matter cause you probably don't max out too many residential lighting circuits.


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## Scuba_Dave

Actually they are coming out with new energy saver incandescent bulbs. Lower wattage use, same lumens. Only took 100+ years to make a better light bulb

Due out "By 2010"

http://news.cnet.com/8301-10784_3-6162567-7.html

You have to go by the fixture rating, not by the bulb

13w CFL = 60w reg
23w CFL = 100w reg

We have put in larger wattage CFL's to make rooms brighter
If your fixture is rated for 60w, its not based on incandescent
So it seems you can put a 23w CFL (100w equiv) into a 60w fixture. Since it is the same bulb base & it is not using the 60w rating


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## Scuba_Dave

Oops, maybe not:

Looks like the anticipated bans have caused GE to dump all research :furious:
That's too bad since CFL's have Mercury
Instead they are concentrating on LED's
After cutting hundreds of jobs 

http://cleantechnica.com/2008/12/02...descent-bulbs-focuses-on-leds/comment-page-2/


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