RAFCOL
Member
- Location
- Torrance, CA, USA
For example: for a wire AWG # 14, it is necessary to leave 2.00 square inches of free space, how they calculate this?
Thank you!
Thank you!
About table 314.16(B)
- Thread starter RAFCOL
- Start date
- Status
- Location
- New Jersey
- Occupation
- Journeyman Electrician
That is amount of physical room required in the box for each conductor of that size. So for example if the box were 10 cubic inches you could put 5-#14 conductors in it. {10 cu in/2 cu in=5}
Welcome to the Forum.
Welcome to the Forum.
RAFCOL
Member
- Location
- Torrance, CA, USA
new question...
new question...
Why 2 in3 to wire #14, 2,25 in3 to wire #12 and no another value in3, and then, How did they figure those values 2 or 2.25 in3?
thank you
new question...
Why 2 in3 to wire #14, 2,25 in3 to wire #12 and no another value in3, and then, How did they figure those values 2 or 2.25 in3?
thank you
Carultch
Senior Member
- Location
- Massachusetts
I'd like to know why there are no adjustments for the diameter of the wire. It is a lot more difficult to fit #12 RHH/RHW-2/USE-2 in a box, than it is to bend #12 THWN-2.
kwired
Electron manager
- Location
- NE Nebraska
If anyone can come up with a better system that does work in all situations then by all means submit it as a change for the future (2020 NEC I believe is soonest it would become code at this point in the game).
Otherwise with what we currently have and it has been relatively unchanged for a long time still leaves you wondering sometimes why we have what we have. You can have a box that is overfilled by the current rules that seems to have a lot of space in it in some instances and in other instances one that technically has room to spare it is about impossible to push a switch or receptacle into the box.
Examples: 4x4x1.5 box with 5.5 cubic inch mud ring = 26.5 cubic inches total of enclosure.
If I run all 12 AWG conductors I have an allowance of 11.77 conductors in this box - that is before deducting two conductors per device from what is allowed in the box. If I were to pull 9 conductors through the box plus an equipment grounding conductor with no extra conductor on any thing except two conductors that tap to a device in that box - it is overfilled according to 314.16 yet there is probably physically a lot of space in that box and is relatively easy to install the device in the box.
Now if I take same box and reduce to a number of conductors that is in compliance with 314.16 but also have a splice in every conductor I will not have many conductors and still have enough room to install the device, but it will seem much fuller then the first example is, or if I leave long pigtails on the conductors I do have it actually can be difficult to pack everything in that box though it still meets 314.16 requirements.
Otherwise with what we currently have and it has been relatively unchanged for a long time still leaves you wondering sometimes why we have what we have. You can have a box that is overfilled by the current rules that seems to have a lot of space in it in some instances and in other instances one that technically has room to spare it is about impossible to push a switch or receptacle into the box.
Examples: 4x4x1.5 box with 5.5 cubic inch mud ring = 26.5 cubic inches total of enclosure.
If I run all 12 AWG conductors I have an allowance of 11.77 conductors in this box - that is before deducting two conductors per device from what is allowed in the box. If I were to pull 9 conductors through the box plus an equipment grounding conductor with no extra conductor on any thing except two conductors that tap to a device in that box - it is overfilled according to 314.16 yet there is probably physically a lot of space in that box and is relatively easy to install the device in the box.
Now if I take same box and reduce to a number of conductors that is in compliance with 314.16 but also have a splice in every conductor I will not have many conductors and still have enough room to install the device, but it will seem much fuller then the first example is, or if I leave long pigtails on the conductors I do have it actually can be difficult to pack everything in that box though it still meets 314.16 requirements.
- Occupation
- Licensed Electrician
Like has been said, a line has to be drawn somewhere and box fill rules we have basically work. I overfill boxes on occasion. :ashamed1: Oh well.
What I marvel at is what those guys in the '50's and 60's did with those little gem boxes and tiny breaker panels.
What I marvel at is what those guys in the '50's and 60's did with those little gem boxes and tiny breaker panels.
RAFCOL
Member
- Location
- Torrance, CA, USA
My question is not How , why, where, or when to use
My question is not How , why, where, or when to use
So that someone could give a better suggestion, first, we should know how the values given in Table 314.16 (B) are calculated,
for now, that's what my question intends.:happyno:
Only: How they calculated the values set in the table, that is.
In some cases. if the box is a junction box, this will have much more space, whether this is for a regular switch it's fine,
but when you incorporate dimmers or electronic devices, this is more complicated, especially when we have to connect neutral and ground wires.
Now, I do not know if the wire diameter is associated with these calculations, if so, they should be proportional,
and if the insulation is smaller than years ago, these values in the table 314.16(B) should also be smaller. It's just a hypothesis.
For now, my only question is: How were the calculated values set in Table 314.16 (B) ?,:?
Thank you!
My question is not How , why, where, or when to use
So that someone could give a better suggestion, first, we should know how the values given in Table 314.16 (B) are calculated,
for now, that's what my question intends.:happyno:
Only: How they calculated the values set in the table, that is.
In some cases. if the box is a junction box, this will have much more space, whether this is for a regular switch it's fine,
but when you incorporate dimmers or electronic devices, this is more complicated, especially when we have to connect neutral and ground wires.
Now, I do not know if the wire diameter is associated with these calculations, if so, they should be proportional,
and if the insulation is smaller than years ago, these values in the table 314.16(B) should also be smaller. It's just a hypothesis.
For now, my only question is: How were the calculated values set in Table 314.16 (B) ?,:?
Thank you!
- Location
- New Jersey
- Occupation
- Journeyman Electrician
So that someone could give a better suggestion, first, we should know how the values given in Table 314.16 (B) are calculated,
for now, that's what my question intends.:happyno:
Only: How they calculated the values set in the table, that is.
In some cases. if the box is a junction box, this will have much more space, whether this is for a regular switch it's fine,
but when you incorporate dimmers or electronic devices, this is more complicated, especially when we have to connect neutral and ground wires.
Now, I do not know if the wire diameter is associated with these calculations, if so, they should be proportional,
and if the insulation is smaller than years ago, these values in the table 314.16(B) should also be smaller. It's just a hypothesis.
For now, my only question is: How were the calculated values set in Table 314.16 (B) ?,:?
Thank you!
This is a good question but I wonder why does it really matter? The code needs to establish some sort of guidance so that the boxes aren't overfilled to a point where the installation can damage the conductors. I kind of look this like why the staple needs to be within 12" of a box for NM cable and not 10" or 15".
Regarding larger devices the NEC already requires a two conductor deduction for a device, if you use a really small device, like a cheapo SP switch, you get some added bonus space in the box.
Carultch
Senior Member
- Location
- Massachusetts
That one I can kind of understand why 12" is the default stapling interval for NM cable. I can see that what likely happened is people attempted nice round numbers that are easy to find on the tape measure. 24" may be too far apart, and resulted in noticeable excessive slack. 12" would then be the next lower default interval, and it would take a few more attempts to figure out if it really should be 15" or 16", or somewhere in between 12" and 24".
And 12" seemed to be sufficient enough, for the cable to be secured with no excessive slack. No one really found it of significant value to hone in on whether or not it should be a few inches larger.
The volume allotments in box fill calculations, by contrast, are a lot more abstract. Intuitively, the same wire takes up more volume in a larger box. Not all splices and terminations of the same wire size are created equal. And even though you still need to fit them in the box, ground wires don't get counted, which makes no sense at all. And finally, it doesn't generalize it for working with all possible wire types, but relies only on you using default THWN-2 wire and similar.
I've never had experience working with boxes sized by this calculation, but when I see boxes my company built that are sized in excess of this rule, I'm surprised when I see just how much smaller the NEC calculation says that these boxes "could be". I believe that in practice, it can be a lot tighter than you really want to go. Selecting a box to meet the bare minimum NEC requirement can, in many cases, set you up for future trouble.
In my opinion, 314.28 calculations (the 6x and 8x trade size rules) are a lot more intuitive, and also give results that are much more practical for working with the wire.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Again we're talking about a guideline of cu inch minimum. There's nothing that says a maximum single conductor length. So if one used the 2.25 cu inches for #12 AWG conductors they still could have each conductor 18" long and try to stuff them into the box.
PetrosA
Senior Member
- Location
- Lancaster, Pennsylvania
GFCIs and dimmers are the main reason why I avoid metal wall cases anymore. I've damaged enough wires trying to get them folded back into the box without cutting them on a clamp or ground screw :rant:
I worked with a guy who insisted on using only metal boxes and leaving a MINIMUM of 12" spare on each conductor. Needless to say, those boxes were a nightmare to pack together. I asked him why he thought it was a good idea to leave all that "spare wire" and force it all into a sardine can that way since when you do hit something and burn your wire up (which you will...) it's going to happen 2" from where the wire enters the box. Butt crimp THAT, buddy
I worked with a guy who insisted on using only metal boxes and leaving a MINIMUM of 12" spare on each conductor. Needless to say, those boxes were a nightmare to pack together. I asked him why he thought it was a good idea to leave all that "spare wire" and force it all into a sardine can that way since when you do hit something and burn your wire up (which you will...) it's going to happen 2" from where the wire enters the box. Butt crimp THAT, buddy
kwired
Electron manager
- Location
- NE Nebraska
When I first learned this trade devices counted as 1 conductor for fill purposes, with GFCI's, dimmers, other large body devices being more common they eventually changed their fill volume to 2 conductors. (maybe about 1999 or 2001 code?)
How do you do the 6x or 8x rule with a box designed only for NM cable entries? Cubic inch method does make more sense for such applications, how to determine what the fill of a particular conductor or other object inside the box should be may not be quite so simple though.
They could require each device be marked with it's fill volume and that would just leave us with conductors as somewhat unknowns - then we possibly would need to watch what we replace in some existing situations.
You can add extensions to a box to gain necessary volume for what is contained - but nothing says you have to actually utilize that volume. How many times have you added an extension to a junction box so you would be code compliant on volume but yet the conductors inside are all left within (or very easily could be) the portion that was there before the extension was added?
How do you do the 6x or 8x rule with a box designed only for NM cable entries? Cubic inch method does make more sense for such applications, how to determine what the fill of a particular conductor or other object inside the box should be may not be quite so simple though.
They could require each device be marked with it's fill volume and that would just leave us with conductors as somewhat unknowns - then we possibly would need to watch what we replace in some existing situations.
You can add extensions to a box to gain necessary volume for what is contained - but nothing says you have to actually utilize that volume. How many times have you added an extension to a junction box so you would be code compliant on volume but yet the conductors inside are all left within (or very easily could be) the portion that was there before the extension was added?
MasterTheNEC
CEO and President of Electrical Code Academy, Inc.
- Location
- McKinney, Texas
- Occupation
- CEO
It is less about the difficulty and more about the space. The thermoset conductors you mentioned to have slightly thicker insulation but is negligible in terms of overall space. Here is an example :
THHN/THWN-2 - 12 AWG insulation thickness = .015in with an overall OD of 0.127*
RHH/RHW-2/USE-2 - 12 AWG insulation thickness = .045in with an overall OD of 0.179*
It may seem like a lot.....but in the scheme of box fill the differences in thickness of insulation is negligible.
Now that does not answer WHY something is not in the NEC....just kinda an example of why the insulation value does not really play that big of a factor.
* Allowing for UL 44 and 83 tolerances
RAFCOL
Member
- Location
- Torrance, CA, USA
One more time!
One more time!
Gentlemen, this is amazing, I understand that the values established for these types of wires on the table 314.16 (B) work for some cases for now, thanks to this, there is some control to guide electricians to not fill the boxes with too many wires and leave no space to add devices.:thumbsup:
Now, I ask you once more: this table is an axiom?:?
In other words, it should be taken as absolute true? and there is no method to calculate these values as set?:?
One more time!
Gentlemen, this is amazing, I understand that the values established for these types of wires on the table 314.16 (B) work for some cases for now, thanks to this, there is some control to guide electricians to not fill the boxes with too many wires and leave no space to add devices.:thumbsup:
Now, I ask you once more: this table is an axiom?:?
In other words, it should be taken as absolute true? and there is no method to calculate these values as set?:?
- Location
- New Jersey
- Occupation
- Journeyman Electrician
This table has been in the NEC since at least 1940 code cycle (the oldest book I currently have). I'm not sure if there is anyone still alive who would know the methodology that they used to determine the amount of space needed for each conductor at least 75 years ago. :roll:
RAFCOL
Member
- Location
- Torrance, CA, USA
Thanks
Thanks
Thanks for your answers! ... for now!!!
I think, I should continue to research over this topic, to see if I can know more about the table 314.16 (B).
Thanks
Thanks for your answers!
... for now!!!I think, I should continue to research over this topic, to see if I can know more about the table 314.16 (B).
kwired
Electron manager
- Location
- NE Nebraska
From things I have run into apparently nobody ever read that section until about 1995:roll:
- Location
- New Jersey
- Occupation
- Journeyman Electrician
LOL, I was surprised too as I started looking at the 1975 edition and kept working backwards all the way to 1940.
RAFCOL
Member
- Location
- Torrance, CA, USA
to know more
to know more
I arrived at this country in the year 2000, previously worked in Venezuela since 1986, in other words 29 years working as an electrician since I finished college
The electrical code of Venezuela (CEN) has a lot of similarity with the electrical code in the United States (NEC), it is always good to know: where did things go?, no matter if it is arbitrary, a rule dictated by field experience or calculations, the most important thing is to know where it came from, and then see if any of us can improve this, in order to improve the electric system and the safety of the people.:thumbsup:
if there is any other information on the table 314.16(B), it is welcome!
to know more
I arrived at this country in the year 2000, previously worked in Venezuela since 1986, in other words 29 years working as an electrician since I finished college
The electrical code of Venezuela (CEN) has a lot of similarity with the electrical code in the United States (NEC), it is always good to know: where did things go?, no matter if it is arbitrary, a rule dictated by field experience or calculations, the most important thing is to know where it came from, and then see if any of us can improve this, in order to improve the electric system and the safety of the people.:thumbsup:
if there is any other information on the table 314.16(B), it is welcome!
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