Too many junction boxes?

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  #1  
Old 01-04-06, 02:38 PM
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Post Too many junction boxes?

Hello,
I am starting to rewire my 1927 home which contains k&T wiring. Most of the upstairs and part of the downstairs is on one circuit so I get dimming lights throughtout the house when running an iron or vacuum. I have run new 12/2 cable into the attic (unfinished attic with easy access to walls and floor joists) to split off the upstairs into seperate circuits for each bedroom. In the first BR I am working on I am adding 2 new receptacles and will be rewiring the existing 2 receptacles to the same 20amp circuit. Since I am not removing the existing plaster walls in the BR, I will be running the wires from above in the attic. This means I will not wire each receptacle to each other but instead will be running the wires to a junction box above each receptacle in the attic. My question is there a limit to how many junction boxes I can use on one circuit? I guess I could run a second wire down to each receptacle and connect it up and over to the next receptacle but it seems like a waste of wire and it would be easier using juction boxes. I figure I will end up using 4 junction boxes for this room. Thank you for your help.
-Bill
 
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  #2  
Old 01-04-06, 03:12 PM
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Personally I would use one large junction box and branch off that box to each receptacle. Actually, I would use no junction box and go receptacle to receptacle, but you seem against that idea.

Remember AFCI protection, and remember that you need proper receptacle spacing. Four per bedroom may not be enough receptacles.
 
  #3  
Old 01-04-06, 03:19 PM
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Originally Posted by slukster
will be running the wires to a junction box above each receptacle in the attic. My question is there a limit to how many junction boxes I can use on one circuit?
-Bill
This is what I did in many places. My attic has a "ring" of interconnected EMT and aluminum flexible conduit between many boxes that in turn have flex dropped down to the first floor boxes. At two points the conduit system descends to the basement for the feeds from the load center. It passed under the 1999 NEC and WI & local codes.

I used conduit to cut down on the number of splices, which with 12 AWG can be an issue. (The WI code also waives the NEC limitation on the number of circuits that can share a conduit.) Also if you daisy-chain with #12 and you are using remodeler boxes, you may have box fill issues. I reused the existing metal boxes and tapped them for grounding screws. I would not have had room to daisy-chain.

You could check with your local authority but I can't think of a reason your idea would be a problem, although you might want to use 12/3 so you can provide a switched lighting recep in each room, if that's being updated too.

Just make sure you calculate box fill, do the grounding and pigtailing (if any) properly and follow the usual procedures outlined in _Wiring Simplified_ by Richter and _Electrical Wiring Residential_ by Mullin, as well as your state and local codes. Whew.
 

Last edited by ArgMeMatey; 01-04-06 at 04:37 PM. Reason: box fill
  #4  
Old 01-04-06, 07:58 PM
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You need more than one circuit fed, you should have one feed per room.
 
  #5  
Old 01-05-06, 02:38 PM
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Thank you all for the advice!
 
  #6  
Old 01-08-06, 07:23 PM
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Originally Posted by ArgMeMatey
Just make sure you calculate box fill,
What is box fill?
 
  #7  
Old 01-08-06, 07:39 PM
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Originally Posted by FairwayFatty
What is box fill?
See NEC 370-16.

It's a volume in cubic inches representing the amount of space taken up by devices, wiring and fittings in a junction box. That number must be less than or equal to the rating (in cubic inches) of the junction box and any extension rings and mud rings.

For example, each 14 AWG wire coming into the box takes up 2 cu. in. Each #12 takes 2.25 in. A yoke (for a receptacle or switch) takes up two volumes of the largest wire size in the box, if memory serves. So if the wiring is all #14, the yoke counts for 4 cu. in. But if there is some #12, the yoke counts for 4.5 cu. in.

My example is incomplete, though, as there are specific rules in NEC 370-16. I would guess there is a helpful guide somewhere online.
 
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