15 A circuit limit, what is it?
I need someone with a little more knowledge of the electrical code than me.
In remodeling a client’s entry way, mostly cosmetic stuff, I need to relocate a couple of electrical outlets on the living room side of a wall. No problem there, not adding or subtracting anything. Then today, they asked me if they could add a couple of wall sconces and a couple of low-voltage lights. If the circuit has room, it would be easy to do. If the circuit does not have room, it’s a nightmare to add a circuit.
It’s a 15 A circuit with both lights and receptacles. The only circuit in the room. There are currently 9 duplex receptacles and 4 – 6″ recessed can lights with par 38 75W bulbs on the circuit. They want to add 2 sconces (1 – 100W max bulb in ea.) and some low voltage lighting yet to be determined
Here in Seattle, the IRC is the code. My book says that for residential lighting and convenience receptacle loads to calculate 3VA per square foot. The floor area is 18 x 20 so 360 S.F. x 3VA = 1080 VA. That is well within 1500 VA for the circuit (80% of max on a 15A circuit that my electrician told me as a rule of thumb years ago).
My understanding from the code is that there is no limit on the number of receptacles per circuit in the residential code, just the S.F. calculation on the area served. However, it seems rare to find much more than 10 – 12 receptacles max on a circuit. In commercial work, it seems I remember hearing from my electrician that each duplex receptacle or light fixture count as 180 VA which would account for about 10 per 15A circuit. If that were the case here, they would be well over the limit.
Are they O.K. in adding the two new lights and some low voltage under these circumstances?
Normally I would just phone up my electrician who is also a friend, but he is in Mexico for the next two weeks on vacation. So, if anyone can help out and set me straight, I appreciate it.
thanks,
Brad
Replies
No limit.
The 180VA is for load calculations. It isn't a limit even though some have incorrectly taken it as such.
There are rules of thumb. Mostly used for new construction but even then they are flexible and just custom.
How many receptacles can be, be on a particular circuit in actual usage, will vary with the users and their use patterns. No law or physical restraint on a HO plugging in a blow drier in a bedroom. Daughter does it in the other bedroom on the same circuit and the breaker will trip. No problem. HOs think it is a disaster for a breaker to trip even though it is doing its job as designed.
Actually beneficial for breakers to be turned off, preferably not under load, and reset every year or so. Redistributes the grease at the pivot points. Keeps them from seizing up.
Most receptacles, particularly in bedrooms, will typically carry small to insignificant loads. A clock-radio draws essentially nothing. Seldom, if ever discounting a HO that is wildly wasteful, will most loads that are plugged in be active at the same time.
Even then the breakers can operate for minutes at considerably greater load than what they are rated at. Given the two blow drier example as long as they are only on at the same time for a minute or two will the breaker trip.
Hook it up. If it trips reset the breaker. If it happens again come back and divide the circuit or reassign the active load to a less used circuit.
Thanks.Really, so there is no rule for the number of outlets on a circuit? We're all just relying on the breaker to let us know if the circuit is overloaded? What is the reason then for 12 and 14 gauge wire and 20 and 15 amp circuits? Is it just that on a 20A circuit you can run a bigger single load without tripping the breaker?
12 gauge versus 14 gauge? Like any other wire size constraint, that is about heating of the wire to a dangerous level (and sometimes about excessive voltage drop).If you have only one receptacle on a 20A circuit, what is to stop someone from plugging in two hair dryers, at 12A each? Run that 24 amps for 4-5 minutes and the C/B will trip.In a room (the kitchen) with lots of potentially high-amperage appliances (toaster, countertop microwave, coffe maker, etc) you are required to run two 20A circuits. That situation doesn't normally arise in other rooms. but if it might (shop, home office) then run extra circuits. I like alternating A - B - A - B etc. And, in a shop, I label them accordingly.
David Thomas Overlooking Cook Inlet in Kenai, Alaska
Dave Thomas has it right. Its about bigger loads and more headroom.Just make sure that the circuit with #14 wire gets attached to a 15 amp breaker. Nothing larger in the way of breaker or fuse. The #12 gets a 20A breaker or fuse. You could go with #12 wire on a 15A breaker. Sometimes temporarily I will do this if I don't have a 20A breaker handy and come back with the proper breaker.Recently I had a service call, unrelated, at a house I had installed a 15A breaker on a #12 wire circuit I had added and had forgotten to get back with the 20A breaker. Years had gone by and no problems. I changed it out to what it should have been while I was there. Better to avoid confusion.Sometimes you may see a 15A breaker connected to #12 wire. A couple of good reasons, beyond not having a 20A breaker handy, can explain this. Either the equipment on a dedicated circuit demands a 15A breaker, some AC units used to recommend this, or somewhere on the circuit is a run of #14 wire and the breaker is being properly sized for the weakest link.Just because you find #12 wire in a panel hooked onto a 15A breaker don't assume it was just because the electrician didn't have the right breaker. There may be a good, but hidden, reason for it being that way.
Thanks again for the help. I've got the basics (very basic) of wiring gauge, resistance, voltage drop, etc., I just wasn't aware there were no limits of the number of outlets. On the other hand, if you were in a situation where you found a series of fixed loads on a given circuit, say a bunch of lights, then you would have to calculate the load before deternining if you could add any more since it would be reasonable to assume that all of the lights will be running at the same time. right? Outlets, on the other hand, there is no rule since it is not likely that all outlets will be used at the same time and if that were to happen, then you are relying on the breaker to save you. right?
you are doing it wrong. square feet has nothing to do with the equation. Add up all the watts on the cicuit and the total cannot be more than total of 1440 watts. you can have a 100 recptacles has long as the power used is no more than 1440 watts. then the wire start overheating.
Its 80% of the 14 gauge wire. 4lorn would be a better advicer on this subject than me.
Edited 1/21/2005 7:50 am ET by BROWNBAGG
Note, some locals do limit the number of receptacles on a circuit. but that is not in the national code.Another consideration for specific loads is that if a single load takes more than 50% of the capacity then you can't have anything else on that circuit.Typically comes into play with things like window AC and permanate kitch appliances (refierator, DW, garbage disposal).
"you would have to calculate the load before determining if you could add any more since it would be reasonable to assume that all of the lights will be running at the same time. right?"Your beyond the scope of what you need to be into with this. Such things are better left to electricians who should already know or those willing to go through extensive and in-depth study and preparation necessary to understand the theoretical aspects of electricity, the requirements of codes, the underlying reasoning and logic behind the NEC and the practical application of these aspects. Anything but a fully rounded understanding is going to leave you with a lot of misconceptions that will work against you in other cases. The complete understanding of these things is beyond the scope of this forum.
I appreciate the help. thanks. But, one question leads to another and it doesn't take me long to be in over my head on electrical theory. There's always more to learn.
Another factor in considering the "headroom" for the circuit capacity
and the raetd draw is distance from the panel. We have rerun #12Ga with a 15A breaker to avoid the higher voltage drop on the #14 Ga. Good example is the 1200W clothing iron in the oppositie end of the house
from the panel. Supposed to be no gretater than 5% voltage drop at load
around here.
"Sometimes you may see a 15A breaker connected to #12 wire. . . . or somewhere on the circuit is a run of #14 wire and the breaker is being properly sized for the weakest link."I do that sometimes. Especially if running 3-way switches, I like to use 14-3 because two 12-3's are so stiff in a switch or 4" round box. This has got me thinking that I should label the 12-2 in the distribution panel "14 gauge wire downstream" so, in the future, someone else doesn't see the 15A C/B and 12-2 and replace with a 20A C/B.David Thomas Overlooking Cook Inlet in Kenai, Alaska
Sounds like a good idea. A tag on the hot lead near the breaker might be good. Something obvious and very permanent being ideal.Better still would be to go with the 12/3. A little more trouble but no chance of a tag falling off. marker fading or someone missing or not understanding what the situation is. You probably know this but I'll go over it for the other, and future, readers who are not as knowledgeable. A regular mistake I see with inexperienced electricians is that they try to make the wires fit by cutting them short, don't remove the jacket far enough or fail to 'dress' the conductors. Often a combination of longer wires 'dressed' with jackets cut back properly is a lot easier to work with.Dressing: Bring the cable into the box. Leave the cable long. 12" measured from the back of the box is about right. Larger multi-gang boxes, especially 4 to 6 gang, take more. Always easier to cut what you don't need than stretch what you don't have. Cutting is faster than splicing. The jacket on each cable has to continue into the box but anything beyond an ideal of 1/2" or so gets into the way. Once the jacket and paper filler is removed from all the cables the conductors get sorted and grouped. The conductors run independently along the back of the box to the grouping. Typically on a receptacle all the grounds go into the lower left corner. Neutrals upper left and blacks upper right.Once grouped in the far back corner of the box the bundle of wires comes out straight. I use the older, IMHO better, standard of 6" free conductor from front face of the box. Grouping the conductors that will be connected all the way from the back of the box forward prevents 'tripoding', the stiffening effect of wires held apart being harder to bend. The same gauge and number of wires tightly bundled together are a lot easier to fold into the box.Also longer conductors widely looped or neatly and gently folded are easier to manipulate than short lengths sharply kinked. Having a full 6" outside the box makes stripping and connections easy.Third thing is that the more conductors are manipulated the stiffer they get. Work hardening. Metal fatigue, in extreme cases, can make the wires so stiff that they snap where they are bent to mate with the screws or at any scratch or nicks. Using pliers to strip the wires can lead to shallow nicks that make this even more an issue.
"Having a full 6" outside the box makes stripping and connections easy."I think of having of 9" from the (back) entry to the box - same thing, near enough.Agreed, strip all you can from the romex jacket (1/2" min). I usually do that BEFORE inserting into the box because it is easier to work in the open.I also pre-fold the groups of wires accordian-fashion to make receptacle insertion much easier.David Thomas Overlooking Cook Inlet in Kenai, Alaska
"...I like to use 14-3 because two 12-3's are so stiff in a switch or 4" round box. This has got me thinking that I should label the 12-2 in the distribution panel..."
Why not just use 14ga all the way so there is no confusion? It's a lot easier to work with when doing multigang switches, as well as 3 ways.
"Why not just use 14ga all the way"That would be good. I usually have no 14-2, stock only 12-2 and decent outlets. But 14-2 for those runs with three-way lighting on them would be a good option.David Thomas Overlooking Cook Inlet in Kenai, Alaska
I don' tknow how many people that I have run into thing that if you have a 15 amp breaker and load it to 15.1 amps that it should trip in a second. My house was built in 79 and only has the 2 20 amp kitchen circuits for everything. That includes the refigerator and builtins (DW, instant hot water dispenser, garbage disposal, and trash compactor). And the counter top microwave and toaster.In 25 years of living here never once trick a breaker in the kitchen.Never bothered to map out exactly which was on which circuit.But I know that the trash compactor is on the circuit with the microwave.When the TC does it reverse cycle and the MW is on you will see the light dim. But that point where the motor stalls and reverse only last a couple of seconds.The refigerator and DW are typically the only things that run for more than a few minutes at a time.
Edited 1/21/2005 11:24 am ET by Bill Hartmann
I thought that there is a maximum limit to the number of "openings" allowed in a single circuit. I recall on a job (that I designed the HVAC system) that the electrician had to do some recicuiting because that number exceeded 30, though I can't be certain. Is there, or was there, such a limit in either outlets or openings in single residential circuit?