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how many lights on 1 circuit??

how many lights can be installed on a single (1) 15 amp circuit?


i am planning on having multiple fluorescent shop lights along the wall in the workshop. the specs on the light states 32W each and nothing about amps. since i am building the workshop space, i am planning ahead for the electrical needs.


if i can get 10 lights on a single 15 amp circuit, that is fine. but i would like to see what the maximum number of lights can be safely installed.




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Posted 2012-03-02T17:05:12+0000  by wazzzy wazzzy

Hello wazzzy.  Welcome to the community!


Power (watts) = Current (amps) x Voltage (volts)


So a theoretical maximum load on a 15 amp circuit would be 15 amps x 120 volts = 1800 watts.


The NEC limits on lighting is based on watts per square footage. This is not a big help in your case.

The common rules of thumb on circuits (15amp ones anyway) is no more than 10 loads per circuit, and no more than 80% of available current is to be anticipated.


Even accounting for ballast losses, 10 single 32 watt bulb strip lights will pull no more than 400 watts.


How many can be safely installed?  Well, if the load gets too high then a breaker trips.

The more heavily loaded a circuit, and the longer the wire runs, the more power is lost due to resistance in the form of heat.  Be conservative here rather than trying to push the envelope.

This issue is more important for outlets, where the circuit load can vary widely depending on what you plug into any outlet. 


So since you are building this project yourself.  Take into account the loads you expect to see at any particular outlet and plan your circuits so you have no unwelcome surprises.  Give items like an air compressor or even a garage door opener their own breaker.  It's easy to do and very inexpensive when done now.


Lastly, local electrical codes can vary widely.  Give your local building inspector a call to find out if there are any limitations beyond the NEC for your area.  Often there are.


I hope this helps,





Posted 2012-03-02T21:41:36+0000  by Chris_HD_CHI

the lights will be on a dedicated circuit. i'm trying to figure out how many of the lights (posted in the original post) can i safely put on one circuit. lights will be separate from outlets and the 'light circuit' will not have anything else plugged into it.


watts = amps X volts


80% of 15 amps is 12 amps


X watts = 12 amps X 120 volts


X watts = 1440


1400 / 32 = 45


with a 32 watt light, i could put 45 of these lights on one dedicated circuit. please check my math. my plan will have NO MORE THAN 16 lights on each circuit. i should be safely within the limits.


i agree with electrical codes being there for reasons in the pursuit of safety and i will follow the local codes.


thanks again,


Posted 2012-03-03T01:32:03+0000  by wazzzy

Hey wazzzy,


I just wanted to follow-up on your last comment. Your math is pretty much dead-on, and following all national and local codes is key to making sure you'll have an efficient ligthing system.


The only extra item I was going to add is that most people tend to be conservative with wiring their circuits so as to allow for any future expansion on the lines. Also, long lengths require higher amperage wire so as not allow for overheating and failure on the circuit.


In other words, you can split the circuits in order to lessen the load IF you you plan on ever adding on anything extra, such it more fixtures.


Just something to consider, but it sounds like you are well on your way to getting in the right circuit for your lights.




Posted 2012-03-03T17:16:11+0000  by Joseph_HD_ATL

Hey wazzzy.


Your math is fine.


Your conclusion that 16 lights will not overload a single circuit is also correct.


One thing to keep in mind is that you have 16 other loads on this circuit.  The ballast that drives each of these lights consumes a small amount of power.  Usually they are rated as a % of efficiency to the lamps being driven.

Taking this into account won't change your conclusion to use 16 lights, but I bring it up only to make you think in terms of circuit loads rather than just light bulbs or outlet quantities.


wazzzy wrote:

i agree with electrical codes being there for reasons in the pursuit of safety and i will follow the local codes.


That's the most important point of this thread...




Posted 2012-03-06T14:11:01+0000  by Chris_HD_CHI
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