Max conductors in box

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  #1  
Old 05-14-13, 06:53 AM
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Max conductors in box

Have a house from the 50's that has several device boxes that have one 12/2 going in and two 12/2 coming out with receptacles. Is the major concern with overloading a box the space issue or the heat issue? If the circuits are rarely used in the room does that effect the answer? Do I need to put some junction boxes outside the device box? Some are old and some look very newly done. Sorry for all the questions, but do not want to do the work if it is acceptable. Thank you for your response.
 
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Old 05-14-13, 08:35 AM
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Each 12AWG conductor takes 2.5 cubic inches. A device counts as 2 conductors. All ground conductors count as 1 conductor.
 
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Old 05-14-13, 02:43 PM
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I have done that calculation and am over by 1.5. I understand it is not code, but wonder if it is something I need to correct or if they are in there and working for now so do not worry. Or if over time it could become a problem, some look rather new. If it is a fire hazard, by all means, I would want to correct it. I am in Mississippi and the house passed the "home inspection".
 
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Old 05-14-13, 03:08 PM
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The reality of the NEC is that it is not barebones - like many systems, it is "padded". There's a large margin between "not completely adhering to the NEC" and "putting yourself in imminent danger".

You said that the house already passed local inspection. Unless you have any specific fears about the credibility/liability given by that inspection, then I would not be worried about it. The fact that you are examining the electrical system seems to indicate that you do indeed have your doubts. Is this true, or is there some other reason?
 
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Old 05-14-13, 06:42 PM
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If the box has clamps inside you may be over by more than you think. I would not consider it an imminent danger, but it is still a code violation. Clamps also count towards box fill.

A home inspector may not even know about box fill. They are not code inspectors.

The NEC is the minimum acceptable installation. It can be exceeded.
 
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Old 05-14-13, 10:02 PM
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Originally Posted by pcboss
The NEC is the minimum acceptable installation. It can be exceeded.
I'm going to interpret this to mean "You can have a box that's larger than you need but not one that's smaller."

Is the major concern with overloading a box the space issue or the heat issue?
The space is a concern because overheating is a concern. Possible damage to the insulation or conductors is also a concern.

If the circuits are rarely used in the room does that effect the answer?
No.

Do I need to put some junction boxes outside the device box?
I'm not sure what you mean by this. Just replace any box that's too small with a deep old-work box such a Raco 506.

do not want to do the work if it is acceptable.
Overfilling an electrical box is not acceptable because it creates a potential hazard.
 

Last edited by Nashkat1; 05-15-13 at 09:09 AM.
  #7  
Old 05-15-13, 06:23 AM
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Thank you for all the input. The box is 2X3X21/2 deep already. Like mentioned, when the calculations are done, I am over by at least 1.5 without looking in the box. for clamps. I had just noticed it this weekend when I was in the attic and wanted to make sure that it was not something I needed to address.
 
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Old 05-15-13, 07:34 AM
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The box is 2X3X21/2 deep already.
Not a deep box. A deep box is 2-1/4W x 4-5/16H x 3-3/4"D.

Example: DEEP SINGLE GANG OLD WORK BOX - HDSupplySolutions.com
 
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Old 05-15-13, 11:51 AM
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The box is 2X3X21/2 deep already. Like mentioned, when the calculations are done, I am over by at least 1.5 without looking in the box. for clamps.
My calculation shows that 18 in.[SUP]3[/SUP] are needed and that your box has 15 in.[SUP]3[/SUP]. You're right, the one I linked to earlier is no better.

Here is what I meant to link to: Steel City CXWLE - "Pre-galvanized steel gangable switch box, 3 inch x 2 inch x 3-1/2 inch, 18 cuin. Non-metallic cable clamps (C-5) and 1/2 inch knockouts. For use with non-metallic sheathed cable."

The plastic box that Ray linked to will work too.
 
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