First – I do follow box fill maximums.
But –
Was wondering – how are those numbers generated?
The best I could figure that it was determined by the maximum permissable heat rise, given x total inches of conductor at maximum rated amperage.
??
Anyone got the real answer? Bill?
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Replies
They did time trials at the NEC proving grounds. They set up boxes of various sizes and put a bunch of wire in them. Professional electricians took turns using the blunt ends of their lineman's dykes to shove wire into the back of the box. When >50% of the testers said 'uncle' they determined that too much wire was in the box, and made out the box fill table accordingly.
Along that same vein, I've found that if I transition the 12ga to lampwire prior to the wires going into the box, I can get more wires in the box.
Why not just wire the house with 18/2 zipcord? So much cheaper and easier.
Gee--18/2 is getting really hard to find. All my local orange box had was that oversized 16/2 stuff. But the nice young man said that oversizing the house wiring would not hurt. Of course, I had to wait a few minutes before he was done watering the plants in the garden center.
Ha, Ha, Ha! I hope you folks know that there are some reading this that won't pick up on the sarcasm. I can hear the sirens from the fire trucks already.
Randy
I've never installed any of that 18/2 or 16/2 - but I have taken a bunch of it out!
My favorite installation was 18/2 brought out of a wall switch box (channelled the plaster under the edge of the switch cover - so it would fit nice), office-type stapled to the edge of a door case molding, down to the bottom of the door opening, through the opening and along the baseboard in the next room - terminated in one of those old plastic two outlet splitters which was screwed to the baseboard. All painted neatly to match!
On a positive note - it did work and it was removed before anything burned.
I have no idea how the box fill tables were derived - I just know that I like even more space than the tables provide especially with all the GFCI's and dimmers around. I never heard anybody say, "Geez, I wish this box was smaller! Look at all this wasted space."
Jim
Never underestimate the value of a sharp pencil or good light.
Reminds me of when I bought my first apartment building. It had lamp cord wiring running around the base board feeding outlets that clipped onto the wire. Splices were held together with scotch tape and the tenant was running electric heaters off of this. In some places the wire had gotten so hot it had melted off all the insulation. Oh, did I mention that it was held on to the base with tacks nailed thru the wire between the conductors.
The tenant got upset when the first thing I did when I saw this was rip it all out.
For you and Link, similar line:
My neighbor had a ceiling fan, which had been installed by previous owner. The previous owner had run the lamp cord down a joint or groove in the wall paneling, then wallpapered over it. It was then plugged into a wall receptacle.
Can you imagine hanging a picture right in the wrong place? "Yep, I think I'll put a nail in the wall right HERE." ZZZZZZZZZAAAAPPPPPPP
A few years after my neighbor told me this story, he said he found out that the previous owner had died recently. No lie, he said he was electrocuted.
Go figure.
Pete Duffy, Handyman
The 16-2 is for 20A
:-0
Forrest - not to be taken seriously
thats a great idea,but you should follow up with a 8 amp breaker at the panel. sometimes hard to find,but if you use a 15 amp you can run 2 lampcords off the same breaker. saves room in the box also.hand me the chainsaw, i need to trim the casing just a hair.
You guys use breakers?I've discovered that by using paper clips to attach the lamp cord directly to the buss bar, I don't have to waste any more money on breakers.An added plus? With the lamp cord giving off a bit of heat, I'm using less oil to heat the house this winter.It ain't easy being a genius.
I'm not sure how they're generated, but they do track fairly well with the maximum number of wires you can jam into a box without using a hammer.
My assumption would be that they're a rough attempt to keep folks from jamming things together so tight that they're damaging the wires in the process.
David's explenation is probably as close a I know.
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
IIRC
Count each wire entering box... not pigtails for outlets/switches.
Add ONE to the total for the ground.
If 14ga, multiply by 2 = minimum box volume
If 12ga, multiply by 2.25 = minimum box volume
Example:
2 each 12/2 w/gnd entering junction, 2 ea 12/2 w/gnd exiting junction = 8+1=9
9(2.25)= 20.25 cu in minimum junction box volume.
Don't hold me to it, though. I ain't the electrimical guy.
Troy Sprout
Socialism in general has a record of failure so blatant that only an intellectual could ignore or evade it."
-- Thomas Sowell
We have started using IR Wireless outlets, very safe , put them anywhere.
You have to count the device too. Usually, it counts for 2 (a typical switch or outlet). Actually, you are counting conductors.But I'm not crazy about how they count things. Like you said, pigtails don't count, but wire nuts sure take up space!
I, too, hate the count if you include pigtails and 'nurts. It gets mighty crowded in there if you intend to wire it for later repairs.
I like fewer wires and more junction boxes. Sometimes, though....
Ya gotta bend things around a bit.Troy Sprout
Socialism in general has a record of failure so blatant that only an intellectual could ignore or evade it."-- Thomas Sowell