Maximum length 14/2 lighting circuit run

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Old 03-31-13, 11:36 AM
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Maximum length 14/2 lighting circuit run

I am rewiring my 1906 home. For the second floor lighting circuit, I brought power to the closest 4" square switch box for the second floor foyer light. From there, I branched one way to the bedrooms and the other to the first 3-way for the stair lighting. The only way to run this involves a total of 4 runs up and down to the basement. So by the time the 3-way system is wired plus the foyer and the first bedroom light, the run is about 120 feet not including the neutral back to the panel. I am guessing that I have to stop the run there. Can anyone tell me if this is too long? Will the inspector have a problem with me using a breaker for only 3 lights even though a have a 40/80 panel. In Canada, code dictates use of only 14/2 for lighting circuits; maybe it has something to do with the ease of a changing light fixtures.
 
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Old 03-31-13, 12:00 PM
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Welcome to the forums.

It's not the length that dictates the circuit as much as it's the load. The inspector is concerned with overloading a circuit. You could have one light on each circuit if you wanted to.
 
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Old 03-31-13, 04:58 PM
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Does Canada use the same base version of the NEC we use here in the US? Our code doesn't provide any mandatory restrictions on legnth of a run, but it does recommend you have no more than a 3% drop in voltage along that run. (Longer the wire, the more resistance is has).

To calculate the voltage drop, use this formula:

Voltage drop = operating current (in amps) x conductor resistance (in Ω per thousand feet) x legnth. The length of conductor is the percent of 1000 feet and includes the distance to and from the load. If you have 120ft to the load, then double it to 240ft. For the equation, take your 240ft and divide by 1000ft and you get .24, or 24% of the 1000ft. The resistance of a specific size conductor is in chapter 9, table 8 of the code. The resistance of 1000 feet of solid strand 14awg is 3.07Ω

So, your voltage drop should be 15amps X 3.07Ω x .24 which is 11.05 volts.

To find out what percent this is of the total voltage, take the voltage drop and divide it by the nominal voltage being supplied. So 11.05V/120V = .09 or 9%.

So now your have a few things to consider. If you want to reduce voltage drop, you have to either shorten the legnth of run or increase size of the conductor since a larger conductor has less resistance. The other option is to leave it how you have it. If the load won't be affected by the variation in voltage and the local inspector won't allow a larger wire size, then leave it as is. Sensitive computer equipment may be affected by the voltage variation, but residential lighting is usually not be noticeably affected.
 
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Old 03-31-13, 07:41 PM
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As long as you're not putting a lot of load on the circuit (it sounds like you aren't), length isn't an issue.

But... maybe if you make a quick drawing of what you're trying to do, we may be able to help you save some wire. It doesn't sound like 4 runs up and down is the most efficient way, even though it may be code-compliant. And with the price of copper these days, you may want to try to limit the runs.

SolarEd:
Does Canada use the same base version of the NEC we use here in the US?
Canada uses the CEC, Canadian Electrical Code. The basics are largely similar, but there are a number of key differences in residential work. Similarly though, the CEC is only a recommendation, different provinces and cities adopt the code with or without additional amendments. So like here, it all depends.
 
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Old 03-31-13, 08:37 PM
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The only way to run this involves a total of 4 runs up and down to the basement.
Why so many? I would think one for the feed plus one for the traveler cable would do.
 
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Old 03-31-13, 09:00 PM
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Thanks for the help guys.

From what you're saying, I take it that this circuit is fine as long as it's limited to lights at this length.

From what others are saying on forums, is that NEC and CEC are very similar with minor differences. To name a few, here, the restricted use of conduit in some circumstances and also grounding techniques and the way voltage drop is calculated. No restrictions in length are noted for 14/2 or 12/2 in the Ontario Electrical Code Simplified book. It only 'recommends' limiting heavy appliance runs to 98ft, although longer runs could be acceptable. Also, in a heating circuit, the cable run to the first heater should not exceed 100ft. The one thing that both codes seem to have in common is the generous use of this word 'recommend'.
 
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Old 03-31-13, 09:37 PM
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I have several obstacles restricting where I can run the cable. As well, the exterior walls are masonry with embedded strapping which would mean rigmarole trying to run cables horizontally without damaging the jacket, securing, and protecting. Nashkat, home run to 2nd floor foyer light switch; branches to foyer light and bedroom with 14/3. The other branch goes back down, then up to 2nd floor 3 way for stairs. Then, 14/3 traveller down to first floor 3 way for stairs, then 14/2 back up to light on second floor ceiling ---that explains the 4 runs. I suppose if I were to run the cables on the masonry I could shorten the length quite a bit, I just wanted the installation to look as tidy as possible.
 
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Old 03-31-13, 09:54 PM
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Can you do one run for the bedroom and a seperate run from seperate break for the stair switches and lights? Keeping things that are physically closer on the same circuit may decrease your circuit length, though you will need to use more breakers in the box. I suggest this obviously without being able to see the floor plan for the house.
 
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Old 03-31-13, 11:57 PM
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Jer.....the Electrical Codes are a living thing. They are not etched in stone. The overuse of the word "recommend" is because they make recommendations but the final decision is left up to the AHJ...... the inspector.

It sounds like you have a bit of difficulty running wires......so you have chosen a way that makes sense based on the circumstances...... no problem. AS long as you aren't running heavy draw devices you should be just fine.
 
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Old 04-01-13, 09:47 AM
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You're right Ed, I can take the bedroom off the circuit but I have already added 14/3 to extend the branch to the bedroom from the foyer light. I would have to swap the wire with 14/2 to end at the foyer light. Not to mention, I have neatly stapled it place. Funny, you say that because originally, I accidentally ran 14/2 to the light not realizing that I was extending the circuit after the foyer light. Should have left it how it was and stopped the circuit there.
So from what you guys are saying, the inspector should be okay with this but shortening it wouldn't hurt to shorten the circuit.
This leaves me with one last question. For the run to the attic, should I use 12/2 to handle voltage drop better? I'm thinking, by the time I reach the attic, the length to the panel is already at 40 feet, let alone wiring in 8 receptacles. I'm trying to avoid running 20 ft directly up the masonry from the panel to the attic. It's so much easier to run the wire along the basement joist 20 feet, then up 20ft in the interior walls.
 
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Old 04-01-13, 12:34 PM
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For the run to the attic, should I use 12/2 to handle voltage drop better? I'm thinking, by the time I reach the attic, the length to the panel is already at 40 feet,
40 feet - 80 for voltage calculations - shouldn't be enough to require you to increase the conductor size.

let alone wiring in 8 receptacles.
If you're wiring the receptacles by splicing the cable conductors through and adding a pigtail for each function at each receptacle, then the number of receptacles should make no difference.

Quick question: It sounds like you're planning to run 14-2/G, protected by a 15A breaker, to feed receptacles. 12-2/G on s 20A circuit is better practice, especially with eight receptacles plus other loads.
 
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Old 04-01-13, 05:09 PM
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Nashkat, the number of receptacles dictates the length of the run. It's 40 feet(80 feet) just to the first receptacle, then all the extra length in between 8 receptacles. I think 8 receptacles on 14/2 is fine for an attic bedroom if voltage drop won't be an issue. The electrician I know says it's unnecessary to wire a house with 12/2, other than the kitchen. I've never tripped a breaker, other than in a garage. How often is a household circuit going to draw over 1800 watts. Regardless, i still wire my main floor with 12/2 just in case.
 
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Old 04-01-13, 10:27 PM
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I think 8 receptacles on 14/2 is fine for an attic bedroom if voltage drop won't be an issue... How often is a household circuit going to draw over 1800 watts.
Any time someone plugs in an 1800W space heater or hair dryer while some bedside clocks and lamps are on.

The electrician I know says it's unnecessary to wire a house with 12/2, other than the kitchen.
Oh? Ask him what he uses to wire the required small appliance branch circuits in the breakfast area and the dining room, or the GFCI circuit in a bathroom. Speaking of that, will any of the eight receptacles upstairs be in a bathroom?

Unless the requirements in Canada are different, #12 AWG conductors are needed in more locations than just the kitchen.

But it's your house. Wire it the way you want to.
 
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