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Just curious. Is there a maximum number of junction boxes (and then branches coming off of those junction boxes) that one circuit is allowed by code to have?

Could you theoretically just continue to add junction boxes to one main line of power and split that power into new branches over and over?

example main circuit line with lots of junction boxes and branches Off of those boxes

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    This appears to be locale specific, and you have neither tagged the question nor have a location in your profile. – Pete Kirkham Apr 4 '20 at 13:26
  • I'm thinking there are code limits on the number of outlets or fixtures on a single breaker. – Hot Licks Apr 4 '20 at 15:09
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    NEC: Only for commercial occupancy, where you have to calculate outlets as 180VA each, limiting you to 13 outlets (no limit on junctions) on a 20A circuit. Residential, if you want 57 outlets on one circuit, code does not care. There are reasons not to do that, but code is not one of them, barring an ignorant inspector making stuff up (too common) or a local rule. – Ecnerwal Apr 4 '20 at 18:48
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No, and also, no. But perhaps a qualified yes.

No limit on number of junctions/branches per circuit, unless it's been added at the local level. And even then, reports I've seen here of inspectors with some number of end-use boxes in mind as a limit don't care if the boxes are all in a line or madly branched every which way.

But you will soon run out of available power to run devices at the same time; Or you won't meet required VA per square foot requirements; Or, you will be lacking adequate overcurrent protection.

Of course, if you care to modify your interpretation to include the breaker boxes along the way that DO provide the current limiting, "adding breaker boxes and junction boxes to one main line of power" is exactly what your house and even neighborhood power system looks like. There just happen to be a larger number of branches at a few breaker boxes to deal with the overcurrent protection.

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  • Please add to your answer which country you are talking about. – Mads Skjern Apr 5 '20 at 22:25
  • I think you mean short circuit protection, not over current protection. Anyway, the number of branches is not relevant when considering short circuit protection. That depends only on the total resistance in the short circuit path, which is defined by the distance and wire gauges from the point of supply to the point of consumption. – Mads Skjern Apr 5 '20 at 22:35
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Wiring must be tree topology. No loop-back or balloons, no current going out one cable and back another. Other than that, there's no limit. You can have as many T's as you want.

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    Except in the UK where they love ring mains... – Ecnerwal Apr 4 '20 at 14:38
  • This site basically has an unstated assumption that posters are in the USA, unless there is evidence to the contary :/ – Peter Green Apr 4 '20 at 15:27
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    @PeterGreen no, it's an unstated assumption that OP's facts and choices of phrasing reveal their locality. If OP had dropped "ring main" and "consumer unit" I'd have written a UK answer. – Harper - Reinstate Monica Apr 4 '20 at 15:34
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    Here in the UK, we don't have "code". We have "Building Regulations" and "Wiring Regulations", only the former of which is actually legal regulations. – Simon B Apr 4 '20 at 20:47
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Reliability is the main concern... Nothing prevents you from adding boxes but the more you add the less the reliable the ckt. Safety and reliability should always be considered in your electrical design. Nothing is more reliable than a solid wire. The more you splice the less the circuit will last. My approach is always to try and avoid splices. They fail and that is never a good thing.

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  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably take our tour so you'll know the details of contributing here. – Daniel Griscom Apr 6 '20 at 14:05
  • A properly made splice is not unreliable. A typical house requires dozens to hundreds of them. – Ecnerwal Apr 6 '20 at 20:08
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USA answer: In conformance with NFPA 70 (Electrical Code) you are allowed 1920va on a 20 ampere 120 volt circuit. There are no limits on the number of junction boxes (without devices) in any particular circuit. Each piece of 'utilization equipment' reduces the maximum allowable load by it nameplate rating, 180va for each receptacle, and each light fixture at its maximum labeled lamp wattage.

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    180VA/yoke (220.14(I)) only applies when 220.14(J) (dwelling unit receptacles) and 220.14(K) (office building receptacles) do not apply.... – ThreePhaseEel Apr 5 '20 at 5:18
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Well, you can have as many junction boxes you want, technically, because the code limits the terminals, not the path to the terminal. Ad I recall, a circuit should have a typical load of 80% of the breaker max, so:

A 12 ga/20 Amp line can run .8 x 2400 = 1920w

A 14 ga/15 Amp line can run .8 x 1800 = 1440w

Then it depends on what's on it. There are rules/guidelines for appliances, including that you need a dedicated line for some.

You're supposed to use 180w (1.5a) for each standard outlet, giving you a max of 10 on a 12 ga line if all you are doing is running branches to random general outlets. I forget how you are supposed to count an overhead light, and technically you're supposed to count an outlet that may have certain things (like an air conditioner) differently.

But to your question, it's not based on junction boxes or number of branches per se, but practically speaking I have a hard time seeing you with many more than 10 if you're limited to 10 outlets.

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Yes there is a limit the easy way to figure it out so you won't pop the breaker . The formula is volts times amps = watts or watts divided volts = amps or watts divided by amps = volts example you have 120 volts you have a 10 amp breaker 120 x 10 1200 watts meaning you can run a maximum of (12) 100 watt light bulbs . Always know approximately what you may be running if the circuit and wattage at any time run the formula the only thing that you can change is the ampsof the fuse or breaker from 10,15,20,30,40 amps be certain to have the appropriate gauge wire. Always turn of the main breaker to the box and check with volt meter before servicing.

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    Hello, and welcome to Home Improvement. Please take our tour so you'll know how best to participate here. – Ack Apr 5 '20 at 19:01

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