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Today we're going to talk about box fill and
pull box calculations. In 314.16A
we talk about volume of a box. Now the volume
of the box just isn't what is inside the box as far as
the cubic inch. But if we put a device ring or an extension ring
on there and we add all that together. That will give us the total
volume of our box. That's 314.16A
In 314.16A1, it talks
about standard size boxes that are listed. And you'll see those
in table 314.16A
In 314.16A2 it
states that nonmetallic boxes shall have the volume marked by the
manufacturer inside the box. Take a look next
time and you'll see that. Inside the box
will be marked cubic inches. If you look inside of a two gang box
a lot of times you will see 36 cubic inches. And that's
how large the box is and that's what you use for your box fill calculation.
There are items that affect your box fill
and there are these. First...your conductors.
If we look at table 314.16B it gives
us standard size conductors and how many cubic inch they take up as
far as room inside of a box. Take a look at that table.
This code article also tells us that every
conductor counts as one conductor. Whether it comes
out of the box or it passes through the box.
Now if we do loop our conductors through the box, which you'll
see in a lot of commercial applications. If that
conductor is twice as long as the conductor length that's
rquired to meet code. Which we learned last time was six
inches of conductor from where it enters the box. So that would be
six inches times two inches we would have
twelve inches of conductor. If that is the case then you have to count it
as two conductors. So that is the time where it would
be a little more. In article B2 of
314.16. It tells us that cable clamps inside of a
box they count as one of the largest conductor.
So all of the cable clamps together only count as
one conductor. Remember that when you are doing your box fill
calculations. In 314.16B3
We see that fixture studs and hickeys....No not
the kind on your neck...but those are fixture supports that go
inside of a box. Those also count as only one
conductor. So don't forget that when you're doing a
calculation, that you have a support for a box that has a
a light fixture in it. In 314.16B4
There we talk about devices. and here's
one that I want to make sure that you understand well.
Every device counts as two conductors of the
size of conductor that is connected to it.
There are cases...especially in the kitchen where you're going to have a
number fourteen conductor in a box and number twelve conductor
in the same box. And if your
device has the number fourteens connected to it then that device
counts as two number fourteen wires.
your other device if it has the number twelves connected to it
counts as two number twelve conductors. So
remember that when you are doing your box fill calculations. Then
we go into 314.16B5 which talks
about our ground wires. Our ground wires all
count as one of the largest conductor in the box.
In the last example that
I gave you. Think about it, When you have number fourteens
and number twelves in the box. If I were to ask you
you the question. You have all these ground wires in the
box. How would you calculate those? What would your
answer be? Well hopefully that your answer
would be. They would all count as one number twelve
wire. Let's do some calculations
right now. And remember I would like for you to
when you first see the example pause the video
and try to do the calculation yourself first and see if you come up with the
same numbers I do. Let's do these calculations!!
Allright why don't you follow along with what I am doing on the screen.
Hopefully you guys looked at this
or you're going to look at this. Stop the video and then try to
do one of these examples on your own. Remember you guys will definitely
learn more when you do something on your own then if you just
listen to what I have to say and then don't follow through with
doing anything yourself. I would really appreciate it if you would at
least try one of these two on your own. So let's
get started. In this box I want to
know how large of a box I need. So I have
three fourteen two's with a ground, one device
and two cable clamps in this box.
Well lets remember that number fourteens from our table
number fourteens. They
equal two cubic
inches per conductor. So lets
get into out calculation. Follow along. You can do it however
you want. But I try to stay organized with my calculations
that way I don't lose something in the process. So
once again do it however you would like. I am just showing you how I do it
so I can keep everything straight. So what I look at
first is I have three fourteen
two with ground romex's. So I would start
like this. I have three cables
times two wires. That's what the two of the fourteen
two stands for is it has two conductors plus the ground and we'll deal
with the ground later. So three cables times two
wires...that equals
six wires for all my number fourteen
cables. I take that times
two cubic inch
and that equals twelve cubic
inch total for those three fourteen two's.
And then I cross it off. But since I don't have any
other cables to deal with I need to have my ground in there.
And we know that the code tells us that our ground counts as
one conductor of the largest conductor. So then I come down to
this column and I say I have one total conductor
times the largest size...which is two cubic inch a number fourteen.
Two cubic inch...so
now I have two cubic inch.
Now I cross that out. I am done with it. I have one
device. So we know that we have one device and
thats two wires of the size wire that's connected to it
So I have two wires total.
I take that times the size of wire connected to it which would be a
number fourteen in this case. So that's two cubic inches
and that equals four
cubic inches total for that device
Now I am completed with this device....I can cross it off.
Now look at our cable clamps. The code tells us that
all of our cable clamps together. Just like our ground count as
one of the largest conductors in the box.
We know that the largest conductor in the box is a number fourteen. So if I come
down here I have one wire times
two cubic inches
and that equals
two
cubic inch
So that's twelve
I guess I'm going to cross this off to. So I have twelve
fourteen, eighteen, twenty. So I have
twenty
that looks terrible...let me fix that.
I have twenty cubic
inch. Did you get that
answer? I hope so.
Lets move on to the next example. It's a little more complicated.
Since we did this last example.
Let me get this smaller. Since we did this last
example. I want you to try to do this on your own. So
stop the video and see if you can do this one on your own.
...................................................Well
welcome back for all of you that stopped the video. For you that didn't
chicken!!! Let's do
this one. Remember number
fourteens equal two cubic
inch....and now I have another size wire
number twelves. And if we look on our table we know that the number
twelves equal two point two five.
cubic inch. So lets start with this one.
We have three fourteen two's. So I know that I have three
cables....times two wires each...
that equals six
wires....times
two cubic inch because they are number fourteen
that equals twelve
...cubic inch
I can cross that one off because I have more wires to
deal with and we'll deal with our ground when we get to the larger one. So here I
have two cables times two wires
and that equals four wires
times two poin two five cubic inch
and that equals eight and
four times point two five would be one...so nine
cubic inch
Can I cross that off? No, I still have to do my gorund.
So I know I have one ground wire
and it's times the largest size conductor in the box. Which would be
a number twelve. So we take two point two five
cubic inches. So one times two point
two five is...two point two five
cubic inch. Now I can cross this one off. Let's
move on to cable clamps. Remember it's just like the ground
All the cable clamps count as one conductor of the largest
size. So lets just duplicate this formula right here.
One times two point two five
equals
two point two five cubic inches.
Now I can cross that one off.
Well here's where it gets a little more complicated. I
have two devices and each device is connected to a
different size wire. So lets deal with the fourteen device.
I have one device and we know it's two
wires...so that equals two wires
times the number fourteen
cubic inch which is two...
and that equals four
cubic inch. Am I done with that one?
Sure. Now I have a device
connected to number twelves. So I have one device
times two wires. That equals two wires
times two point two five
cubic inch which is four point
five...cubic inch,
So now I'm done with my devices.
Do we need to do anything else? I don't think
so. All right. So lets add all these
up. I know that
the two five and the two five and the five o is going to end up with
zero.
So I am going to add my one here and I have thirteen plus
nine is twenty two, twenty four, twenty six
thirty, thirty four.
So this box would be thirty four cubic
inches. How'd you do? Were you able
to get it on your own. I really hope so you know
try some of these on your own and see what you can come up with.
Now lets get on to our pull boxes.
Well I hope that you guys did good on those calculations
why don't you try a couple on your own, maybe use some real life
scenarios that you had at work and see how you do.
If we get into article 314.28 we start to talk about pull
boxes. And when we talk about sizing a pull box
we need to talk about straight pulls and then boxes with
angle, u-pulls and splices in them.
With the pull box and a straight pull you
have to figure eight times the size of the largest
raceway coming into that box. Well
if I have a box that has a two inch raceway
coming into it and I'm going to pull straight through that box
that is eight times that two inch would be
I would need sixteen inches to the opposite wall where
that conductor leaves the box.
Now think about that for a minute. I'm not saying that a sixteen by
sixteen box. I'm saying sixteen from
where the raceway enters to where the raceway
exits. The only width requirement would be
however wide you need that box to be for that raceway to attach
to it. That could really save a lot of money on a job
and there are a lot of electricians out there that don't know that, that's
part of this rule. So they go ahead and
order a box that's square when they could actually use a four
by four gutter that is however long they need it. Keep that in
mind next time you see somebody sizing a pull box and bring that up. You might
save a little money for your company on their job.
When we get into angle, u-pulls and splices
the rules change a little bit. The rules are
six times the largest conduit on a side
to the opposite side of the box plus
the addition of the conduits
that are also on that sided in the same row.
When you look at this graphic you'll
see that we have a two inch
and five one inch conduits. Well
six times that two inch is twelve inches and then
when you add the five one inch conduits which would be five inches
that box to the opposite side would have to be seventeen inches.
You don't have to count those other conduits in the second row
because the conduit in the last row
has more conduits in it and would require the box to be larger.
Keep that in mind.
Now when you get to another thing that we have to do
especially with angle pulls where you come in the box on
this side and you come out the box on the other
Then we have to maintain a spacing between
this conduit and that conduit of six times the size
of the conduit that enclose the same conductor.
So if I have a four inch conduit
coming in here and a four inch conduit going out of this
box. I then have to maintain a straight line
space between those two conduits of twenty four inches.
In this example you'll see a four inch and
two, two inchers in that box. And because
they come in sides that are ninety degrees to each other that
box ends up being square. And if you take six
times four plus the two, two inch conduits now I
have to have a twenty eight inch by twenty eight inch box to be able
to have an angle pull in there with those conduits involved.
And remember these rules....they are
only for wire that is number four and larger.
So this wouldn't apply to a number twelve j-box.
Keep that in mind as well.
Well I hope that you learned a lot today.
And as always: Take notes,
and I'll see you in class. Be Safe!!!