Switch Box Fill Caculation's

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hurk27

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Portage, Indiana NEC: 2008
I have an inspector who by most is a very fair inspector as far as not calling things that are not in the NEC. But he has hit me with a box fill problem that just don't add up. And maybe I'm getting it wrong but I'd like to be sure before I talk to him.

Ok here's what it's about
I have a two-gain plastic switch box the listed size is 34.4 cubic inch's This should allow for 16 #14awg wires. we have 3-14/3 NM's and two 14/2 NM's entering the box. with two switch's one 3-way and one 4-way that will be mounted in this box.

ok from what I think I know is we have a total of 13 wires and one ground that can be counted. Now 314.16(B)(1) exception allows us to exempt the grounding conductor. now 314.16(B)(4) requires us to deduct 2 wires for each device yoke that will be mounted in the box from the allowed number of conductor's. this bring's us to 12 allowed wires. Now this is what is confussing:

314.16(B)(1)(last sentance) A conductor, no part of which leaves the box, shall not be counted.
Click to expand...
Does this mean that the wires that terminate on the 3-ways and 4-ways since they dont leave the box can be deducted from the count? Or is the inspector correct.
 
Re: Switch Box Fill Caculation's

You have 36 inches in your box...red-tag.

(3) 14-3's=9 conductors
(2) 14-2's=4 conductors
(1) EGC=1 conductor
(2) devices equals 4 conductors.

18 conductors at 2 inches each equals 36 cubic inches. Sorry :( .
 
Re: Switch Box Fill Caculation's

Wayne, look at it this way. You have 13 conductors entering the box. You have two yokes for a total of 4 more conductors. That makes 17, one over the limit. 314.16(B)(1) refers to conductors within the box such as pig tails that might be used to feed two switches from a single feed. Ain't gonna help you.

Now 314.16(B)(1) exception allows us to exempt the grounding conductor.

Not in this instance. That applies only to the ground wire entering the box from a fixture. No fixtuires here are there. So now that the ground wires count as another conductor you are over by two.

-Hal
 
Re: Switch Box Fill Caculation's

Thank's All.
I Thought that there has to be somthing that I was caculating wrong as two 4-ways could not be ever placed in a two gain box without using 14/2 for traveler's, I have seen it done and even heard some on this forum talking about it by center feeding/dead-end the light to the 4-ways. I know 14/2 can not be used for travelers.

4- 14/3 = 12 conductors
1 ground = 1 conductor
1 14/2 = 2 conductors
2 yokes = 4 conductors
Total = 19 ouch!

I knew this at one time just guess it got put in the back some where. LOL :roll:

Thank's again.

P.S. Guess I'll be rewiring those switch's tomarrow.

[ March 30, 2004, 12:18 AM: Message edited by: hurk27 ]
 
Re: Switch Box Fill Caculation's

Hurk, why no 14/2 for travelers? If you have nonmetallic boxes and sheath, you're allowed an exemption from having the grounded conductor run with the travelers. This is 300(b)(3)-99NEC. Has the '02NEC changed this?
 
Re: Switch Box Fill Caculation's

Stamcon if you have just have the travelers running between the two/three switches. it can cause all kinds of magnetic problems with TV's computer monitors Etc... While it not defined in the NEC It can cause some really big head ack's
Here's some earlyer thread's on the subject:

Two Wire Travelers

Or:

Two wire used in 3-way loops

[ March 30, 2004, 01:23 AM: Message edited by: hurk27 ]
 
Re: Switch Box Fill Caculation's

Would the EGC have an induced current on it, that would be drained at it's bonding point? Would the EGC act to lessen the single conductor issues?
Why does the NEC allow the exemption? :confused:
 
Re: Switch Box Fill Caculation's

Not the EGC but the grounded conductor or neutral. With a neutral and the travellers current flows both ways in the cable and the magnetic field cancels.

The NEC permits two wire travellers only with NM or other non-ferris jacketed cable and non-metallic boxes. This is because the NEC is only concerned with inductive heating and does not address EMF's.

-Hal
 
Re: Switch Box Fill Caculation's

I just wired a circuit today that could have used 2wire travelers, but I never do (for the next guy). It was a neutral issue.

I fed a box with 2 3ways and s/l out the other box.I had to have good power in the second box as well for a s/p s/l.

In a conduit, I would have no problem running only one neutral, four travlers and a hot between boxes. All power going out on all hots and s/legs comes back on the neutral keeping the EMF down which keeps heat down and wire within code temp ratings.

Using romex, I use 3 wire and isolated neutral from the first powered up 3way to the load keeping trouble shooting down to a min and back feed neutral problems history.

I had to use 3 neutrals from one box to the next but one for the feed one for each set of travelers. (costly) But so is conduit and labor.
I didnt have a romex 12-6 w/ground :)
 
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