Box Fill

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Also remember that cable clamps within the box count as one conductor as per table 314.16B.So if you have cable clamps in a box and the largest conductor is #12 you have to add an additional conductor @2.25 along with the actual number of conductors entering the box.Connectors originating from outside the box do not count..ie..MC conns,EMT fittings etc.I don't know if someone has already stated that "Pig tails"also don't count.Also when you get to condutors #4 or larger this all changes.Then you size the box by the raceways entering the box.But, that's another post. Don't let your 4 Sq. box runneth over! lol
 
Karl,

Can you site the code for your thought on equipment grounding conductor "Pig tails"? According to my findings Post 18 they do count.

Right-on on the 4 sq box statement, it sure is nice to see um done right especially if your the "shmoe" entering the box later!
 
Karl H said:
Yes read ART. 314.16(b)(1) A conductor,no part of which leaves the box, shall not be counted.
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Looks like your right but I wonder how 314-16(B)(5) applies: "a single allowance...shall be made based on...equipment bonding jumper present in the box." :-? (B)(5) Seems contradictory to (B)(1). Maybe it means "Where...equipment bonding jumpers ENTER a box, a single volume allowance..." how does an equipment bonding jumper enter a box??

I still hate hany boxes!
 
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I agree "Jumper" is confusing and should be re-worded.314.16(B)(5) is saying One or more equipment (grounds) really Bonding conductors are counted as one conductor using the volume of the LARGEST Bonding conductor.So in my understanding that means if you have 3 12/2's in a box you only count 7 conductors instead of 9. The combined "Grounds" would be three but you only count for one.Because it's #12 that would be 2.25.Now if you had one 12/2 and one 14/2 there would be two "ground" wires but you only count the largest so once again it would be 2.25. The box "bonding jumper would not count neither would the wire nuts ,MC connectors, etc.
 
Okay then,
A 110V 20A metal conduit circuit with one receptacle would be:
  1. 4.5 in sq (2 conductors, hot, neutral & equipment ground as per 250-118(2)-(8))
  2. 4.5 in sq (2 conductors for the device)
9 in sq total, I think most handy boxes are 10 cu in (3x2x2). In this example you would need a box larger than 9 cu in

--And--​

A 110V 20A NM cable circuit with one receptacle would be:
  1. 6.75 in sq (2 conductors, hot, neutral & 1 equipment ground)
  2. 4.5 in sq (2 conductors for the device)
  3. 0.0 in sq for 2-screw cable connector
11.25 in sq total. In this example you would need a box larger than 11.25 cu in
 
You're trying too hard. A 3x2x2 box is.... do the math.... 12 cu in. Though usually handy boxes are 4 x 1-7/8 x 1-1/2 which is 11.25 cu in, I prefer the 2-1/8 deep myself for 15.9 cu in space
 
yursparky said:
You're trying too hard. A 3x2x2 box is.... do the math.... 12 cu in. Though usually handy boxes are 4 x 1-7/8 x 1-1/2 which is 11.25 cu in, I prefer the 2-1/8 deep myself for 15.9 cu in space
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See 314-16(A)(1), and I like math :)
 
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Wow, haven't seen that before, maybe because all my boxes are stamped with their volume.

Maybe it's the Trade Size 3x2x2 is not the actual size, and they are underestimating to be safe. Anyhow, 314.16A(2) requires boxes 100 cu in and less to be marked with volume by the manufacturer. So what could be the "other" boxes described in Table 314.16A?

Anyone seen one not have volume stamped?
 
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The funny thing is I don't think I've ever seen an inspector check box fill. They have always just opened boxes to check to see if you "Bonded" them . lol Eventually the box fill will sadly become a lost art form. :grin:
 
Karl H said:
I don't think I've ever seen an inspector check box fill
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I've gotten caught once - ONCE - overfilling. Total negligence on my part, completely unintentional. I count wires almost always since, became a habit.
 
While you all do the math, I'll just install a bigger box and get on with my day. :smile:

Never been called on box fill....

Tip: If the stuff don't fit, it's too small. (mabey that's how the code should be written).
 
frizbeedog said:
If the stuff don't fit, it's too small.
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Here's a story for ya: first time I did floor heating mats - think second year apprentice now, we dropped the leads into the crawl space to tie them in with 12/2 in j-boxes to run back to the contactor. So there I am in the dark with my pair of kleins, the JW can't hear me, never seen the steel wrapped heatpad leads before, I strip the ends, tie the outer steel to the ground, make up the others, STUFF the whole 5' of the heating cable into the 2 gang carlon box, cover it up and repeat three times. Box fill, what's that?

That was not the time I got caught.... :grin:
 
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Electrical circuitry needs heat dissipation this is extremely important. With conduit fill heat dissipation is the main reason but also included are tensile/conductor damage as reasons, box fill mirrors these reasons but it also includes respecting wire bending.

I wish inspectors would make a habit to check box fill! I also wish electricians would honor box fill capacities like they do breaker size, wire size and conduit fill.
 
frizbeedog said:
Tip: If the stuff don't fit, it's too small. (mabey that's how the code should be written).
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I would go for that. A plain english version of the code. Article 250 could be reduced to one sentence. "Connect all the metal parts together ";)
 
electricman2 said:
I would go for that. A plain english version of the code. Article 250 could be reduced to one sentence. "Connect all the metal parts together ";)
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Gee, you think if they did that, the cost of a Codebook would go down? :grin:
 
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