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Max. Number Can Lights on Circuit?

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  • Max. Number Can Lights on Circuit?

    I find it perplexing that I'd be allowed to put a thousand duplex receptacles on a circuit per code. I have read a FHB article where they guy suggested 13 might be a good stopping point. Same article showed about 10 can lights, 2 bath fans, 2 ceiling fans, Smokes, 2 Bath light bars ALL ON ONE 15AMP 14-2 Circuit! Doesn't that seem like a hec of a lot on that?

    How many cans would you figure is too many if say 75 watt bulb was the most allowed per can?

    I plan on all 12-2WG wire just because I'm too lazy to figure out a bunch of 14 gage seperate circuits.

    Any easy "rule of thumb" way to figure this?

  • #2
    Re: Max. Number Can Lights on Circuit?

    The code says you should only design circuits to draw about 80% of the breaker value. So if you have a 20 AMP circuit, you only want to load it fully to about 16 amps. 16 amps at 120v is 1920 watts so How many 75 watt bulbs? simple 1920/75= about 26 bulbs would be the limit if they would be on all at the same time. As I recall the code calls for a single outlet to be considered for so many watts so it is not a infinite amount allowed. Usually its about 13 for 20A and about 10 for 15A. Not a good idea to overload circuits. Stay safe and plan your loads carefully. Lou

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    • #3
      Re: Max. Number Can Lights on Circuit?

      'Stormin,
      You can pick up the book "Wiring Simplified" by HP Richter, WC Schwan, and FP Hartwell for about $12. Based on the NEC code. Invaluable for just about any electrical projects you might do. Also the formula V X A = W (Which QROKING referenced in his post)
      (V = volts, A = amps, and W= watts) will be real helpful. Like your 15 amp circuit: 120 V x 15 A (based on your 14-2 w ground) = 1,800. Then take your 80% of that so you don't exceed the ampacity of your wire. Then all the variations of that equation are listed HERE:

      http://www.powerstream.com/Amps-Watts.htm

      Hope that helps somewhat. If not, ask some more questions. Lots of people here that will jump in and help.

      Jim Don
      Last edited by JimDon; 12-19-2007, 03:31 PM. Reason: Wanted to add clarifier and give credit

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      • #4
        Re: Max. Number Can Lights on Circuit?

        For dwellings receptacles are calculated as having no load, so yes the number is infinite. Non dwellings do have specific values.

        Load calculations are based off the concept of circuit diversity. It is assumes all circuits it a structure will never be used at maximum at the same time. You can read up on service calculations in the code book. It is an interesting read but in the end no one truly uses it and bases their services on rules of thumb and past experiences.

        When we do a new home we generally will do 1 or 2 15 amp circuits for each floors main lighting. Bedrooms are done with on a single 15amp circuit for the lights and outlets. Master bedrooms have a 15amp circuit for each. 1 20 amp circuit for each floors bathroom GFI's 2 20amp circuits and at the kitchen counter. Kitchen and dinning room each get there own 20 amp outlet circuit and each other room gets a 15 amp circuit for outlets. Each major appliance gets an appropriate dedicated circuit.

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        • #5
          Re: Max. Number Can Lights on Circuit?

          Thanks to all for great info. I plan on putting a 2 gang box (2 duplex receptacles) on either side of most likely bed position for clocks, lamps etc etc.(In addition to a receptacle every 6 feet) The MAIN idea is to NOT have to use extension cords isn't it? Anyway - I'll use 15AMP AFCI breakers with 12-2 wire for extra safety. thanks again.

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          • #6
            Re: Max. Number Can Lights on Circuit?

            If you're going 12g all the way I see no reason to not just go for a 20A breaker. Might as well take advantage of capacity.

            Comment


            • #7
              Re: Max. Number Can Lights on Circuit?

              When it comes to how many lighting fixtures per circuit, look at the ratings of the actual fixture.

              Example: The fixture is rated at 100 Watts max. You are only going with a 60 Watt light bulb so you figure on it. Later someone changes the light bulb to a 100 Watt. You can overload the circuit if you aren't careful. Also, you do need to use the 80% max load so you have a safety factor. On a 15 Amp circuit you can run up to 1440 Watts and on a 20 Amp circuit 1920 Watts. Be sure all switches are commercial or industrial specification grade and rated at or above the breaker or fuse rating. The cheapo home use switches can't withstand the inrush current.

              Normally other than in commercial-industrial applications the use of #14 copper wire is fine for a lighting only circuit as long as you use a 15 Amp breaker or fuse. Please do not connect receptacles to a lighting circuit. You need to think about what will happen if you plug in too heavy a load or a defective load. The breaker trips or fuse blows and you are in darkness. Please wire receptacles on their own circuit and if in a bedroom area do use the new arc fault type breakers unless they are in an area where a GFCI breaker is required.

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              • #8
                Re: Max. Number Can Lights on Circuit?

                AS Woousko says, it is a good idea to have outlets separate from lighting, however, this is NOT a code and they can be joined, but it is a BETTER job to keep them separate. I would not go overboard and not connect a closet light to a outlet circuit, but I would keep most other lighting separate. This is why there are such big differences in estimates on electrical work. 9 time out of 10 the more expensive estimate will do things like have separate circuits for outlets and lights, the cheaper ones may run it all together. Of course in certain instances you can not do it, but in bedrooms and the like it is done alot. Lou

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                • #9
                  Re: Max. Number Can Lights on Circuit?

                  Really apreciate the advice guys. Luckly while I was waiting 7 months for my permit I had time to install a new 200 AMP 40 space panel so I can have lots of circuits. Only downside of that is those $35 a pop AFCI breakers.

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                  • #10
                    Re: Max. Number Can Lights on Circuit?

                    This is a great thread.

                    >You can pick up the book "Wiring Simplified" by HP Richter, WC Schwan, <
                    This is the book I stared with a few years back. Although it was very informative it was a little terse in reading. In addition it covered topics which I suspect are not very common such as farm wiring. Probably better for the student. I picked one up from Black and Decker a while back which was excellent. Can't remember the title. Very well written and illustrated. Included a lot of why you do something this way along with a section with pics showing code violations which was my favorite.

                    >I plan on putting a 2 gang box (2 duplex receptacles) on either side of most likely bed position for clocks, lamps etc.<
                    I did the same thing and never regretted it.

                    <(In addition to a receptacle every 6 feet)<
                    You sure you will like the look of an outlet every 6 feet in a bedroom for example. It might look a bit commercial but up to you. I believe code is any point on the wall has to be within 6 feet of an outlet. Thus Outlets can be spaced twelve feet a part.

                    <12-2 wire for extra safety.<
                    I used to use 12-2 for everything but 14-2 is much easier to work with especially when wiring in Light fixtures and bathroom ceiling fans. Your space can be so limited at times I think 14-2 can even be safer without having to cram large wires into a tiny space.

                    >The fixture is rated at 100 Watts max. You are only going with a 60 Watt light bulb so you figure on it. Later someone changes the light bulb to a 100 Watt. <
                    I bet the norm now is a reduction in wattage. Those new Florissant bulbs are less than 20 Watts. I wonder if there will be any changes in the code because of this.

                    Bob

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                    • #11
                      Re: Max. Number Can Lights on Circuit?

                      Originally posted by QROKING View Post
                      The code says you should only design circuits to draw about 80% of the breaker value.
                      Do you have an art. number for this?

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                      • #12
                        Re: Max. Number Can Lights on Circuit?

                        Originally posted by GilBeQuick View Post
                        Do you have an art. number for this?
                        Unless I am mistaken, he is probably refering to 210.23(A)(1). Which would be incorrect though as that article refers to any one piece of utilization equipment not exceeding 80% of the branch circuit ampere rating.

                        210.23 is the only article I can think of of the top of my head that limits branch circuit ampacity to 80%. I have heard many others state you can't go over 80% as well, and most point to 210.23, but that article is specifically for one piece of utilization equipment.

                        210.23 also states that: In no case shall the load exceed the branch circuit ampere rating. This is the general statement, the (A), (B), and (C) get specific about the one piece of utilization equipment and 80%.

                        Jeff

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                        • #13
                          Re: Max. Number Can Lights on Circuit?

                          Originally posted by piette View Post
                          Unless I am mistaken, he is probably refering to 210.23(A)(1). Which would be incorrect though as that article refers to any one piece of utilization equipment not exceeding 80% of the branch circuit ampere rating.
                          Exactly, thank you Jeff! I see the "80% rule" thrown around all the time but no one seems to realize that it's for ONE thing. Just because there's "10 can lights, 2 bath fans, 2 ceiling fans, Smokes, 2 Bath light bars" doesn't mean you're going to overload a 15a circuit. Is it good practice to put all that on one 15a circuit....no, but the odds are greatly in your favor that each one of those things aren't going to be turned on at the same time.

                          Point is, just because that amount of things is pushing the limits of the 15a circuit, it doesn't mean it's not code compliant, and you CAN load a circuit past 80% as long as it's not one item doing so..

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                          • #14
                            Re: Max. Number Can Lights on Circuit?

                            Originally posted by 'Stormin View Post
                            Thanks to all for great info. I plan on putting a 2 I'll use 15AMP AFCI breakers with 12-2 wire for extra safety. thanks again.
                            I wouldn't bother with 12-2 on a 15A circuit for "extra safety". 14-2 is plenty safe on a 15A circuit and it is a whole lot easier to work with.

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