312.8 confusion!

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davedottcom

davedottcom

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312.8 Enclosures for switches or overcurrent devices shall not be used as junction boxes, auxiliary gutters, or raceways for conductors feeding through or tapping off to other switches or overcurrent devices, unless adequate space for this purpose is provided. The conductors shall not fill the wiring space at any cross section to more than 40 percent of the cross-sectional area of the space...

I have 9 conductors running through a 200 amp disconnect 30" x 14.5" x 6"

3 - 2/0
4 - #6's
2 - #12's

The Handbook Example:
If an enclosure has a wiring space of 4 in. wide by 3 in. deep, the cross-sectional area is 12 in. 2 Thus, the total conductor fill (see Chapter 9, Table 5 for dimensions of conductors) at any cross section cannot exceed 4.8 in. 2 (40 percent of 12 in. 2)...

so in my situation:
14.5" x 6" = 87" (squared)
87 x 40% = 34.8" (squared)

This can't be correct!? 34.8" squared is HUGE!

2/0 = 0.3505
2/0 = 0.3505
2/0 = 0.3505
#6 = 0.1041
#6 = 0.1041
#6 = 0.1041
#6 = 0.1041
#12 = 0.0353
#12 = 0.0353
-------------
Total: 1.7849 " (squared)


What am I doing wrong?:confused:

A little help would be GREATLY appreciated! :)
Thanks.
 
davedottcom said:
2/0 = 0.3505
2/0 = 0.3505
2/0 = 0.3505
#6 = 0.1041
#6 = 0.1041
#6 = 0.1041
#6 = 0.1041
#12 = 0.0353
#12 = 0.0353
-------------
Total: 1.7849 " (squared)


What am I doing wrong?:confused:

A little help would be GREATLY appreciated! :)
Thanks.
Click to expand...

I've got to think about this for a min.

First off:

2/0 .2223in2
#6 .0507in2
#12 .0133in2

We are talking THHN right?
 
Dave,
The complete enclosure is not the wiring space. The space you need to measure is between the side of the enclosure and the internal equipment at the point where you plan to install the conductors. In many disconnects the vertical wiring space is very limited at the point where the operating mechanism is installed.
Don
 
Dave,
Don, I thought the cross sectional area is the depth x the width.
Click to expand...
Yes, but only of the "wiring space", not the space occupied by the internal parts of the disconnect.
312.8 Enclosures for Switches or Overcurrent Devices
Enclosures for switches or overcurrent devices shall not be used as junction boxes, auxiliary gutters, or raceways for conductors feeding through or tapping off to other switches or overcurrent devices, unless adequate space for this purpose is provided. The conductors shall not fill the wiring spaceat any cross section to more than 40 percent of the cross-sectional area of the space, and the conductors, splices, and taps shall not fill the wiring space at any cross section to more than 75 percent of the cross-sectional area of that space.
Click to expand...
 
Whoops!

2/0 = 0.2223
2/0 = 0.2223
2/0 = 0.2223
#6 = 0.0507
#6 = 0.0507
#6 = 0.0507
#6 = 0.0507
#12 = 0.0133
#12 = 0.0133
-------------
Total: 0.8963 in2
 
"Yes, but only of the "wiring space", not the space occupied by the internal parts of the disconnect."

But I would have to add a 3rd dimension (Heigth)to account for that???
 
Dave,
But I would have to add a 3rd dimension (Heigth)to account for that???
Click to expand...
No, you use the measurement of the space between the side wall and the internal equipment multiplied by the depth of the enclosure.
Don
 
Don, the internal equipment is about 8" above where the conductors enter & exit the enclosure.

I entered the back of the disconnect (lower-right-back) with all 9 conductors. They exit out the lower, left side of the disco. The only conductors that actually just "pass through" are (3) #6's and (2) #12's.
The 2/0's and (1) #6 are terminated in the disco.

The Building Dept is requesting documentation supporting the cross-sectional area is not being exceeded per 312.8. I'm quite positive it is not, but I need a calculation to prove it.

So, you're saying to use the measurement from the entrance to the inside equipment (8") x 6" (depth)?

8" x 6" = 48in2

48 x 40% = 19.2in2

then...

2/0 = 0.2223
2/0 = 0.2223
2/0 = 0.2223
#6 = 0.0507
#6 = 0.0507
#6 = 0.0507
#6 = 0.0507
#12 = 0.0133
#12 = 0.0133
-------------
Total: 0.8963 in2
__________________

Not even close to exceeding it.
Does this sound right?
 
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davedottcom said:
Whoops!

2/0 = 0.2223
2/0 = 0.2223
2/0 = 0.2223
#6 = 0.0507
#6 = 0.0507
#6 = 0.0507
#6 = 0.0507
#12 = 0.0133
#12 = 0.0133
-------------
Total: 0.8963 in2
Click to expand...

Your 0.8963 is 40% of 2.24075, so I figure the space would have to be 2 1/4 by 2 1/4 or a little bigger than 5 sq inches.

0.8963 x 2.5 = 2.024075
2.024075 x 2.02475 = 5.0209605

I think I was wrong,
2.24075 should be squared = 1.4969134 so the space for your wire is about 1 1/2 inches.
I'm not the greatest mathematician in the world so if I messed up someone jump in.
 
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russ said:
I removed so I don't confuse things.
Click to expand...

LOL
I was already confused!;)

I guess I'm still confused about where exactly to measure from.
The "side" of the enclosure to the internal equipment
or
from the "Knock out" entrance to the equipment.

I came in the back and went out the side!?:confused:
 
I would measure from the side wall to the near edge of the equipment.
I doubt you want any wire in front of the equipment, or block access to it.
 
davedottcom said:
LOL
I was already confused!;)

I guess I'm still confused about where exactly to measure from.
The "side" of the enclosure to the internal equipment
or
from the "Knock out" entrance to the equipment.

I came in the back and went out the side!?:confused:
Click to expand...

here is a link of conversion of cubic feet to square feet. maybe that would help.

http://www.onlineconversion.com/faq_01.htm
 
davedottcom said:
The Building Dept is requesting documentation supporting the cross-sectional area is not being exceeded per 312.8. I'm quite positive it is not, but I need a calculation to prove it.
Click to expand...


This is where i have a 'problem' with this kind of thinking/action. Why should you HAVE TO PROVE you did NOT violate the code, isnt THEIR job to PROVE that you DID violate the code?? Otherwise there is no reason for them to question(not pass) your installation!! Your GUILTY till proven innocent???

If they (Building Dept) feels you violated 312.8 THEY should have to SHOW YOU (let them do the calculation) that you did; NOT you showing them that you did not!! I would challenge them on this practice/thinking.
 
brother said:
This is where i have a 'problem' with this kind of thinking/action. Why should you HAVE TO PROVE you did NOT violate the code, isnt THEIR job to PROVE that you DID violate the code?? Otherwise there is no reason for them to question(not pass) your installation!! Your GUILTY till proven innocent???

If they (Building Dept) feels you violated 312.8 THEY should have to SHOW YOU (let them do the calculation) that you did; NOT you showing them that you did not!! I would challenge them on this practice/thinking.
Click to expand...
I would say it's best, if possible, to be certain before challenging :grin:
 
Smart $ said:
I didn't visit the link... because there is no such thing as conversion from cubic feet to square feet. The former is volume measure and the latter is area measure. They cannot be converted one to the other.
Click to expand...


For goodness sake maybe the 'title' (cubic ft to sq ft) is misleading but you can at least check out just to see what info is there that might help!! Why you would prejudge/dismiss something before even having a look at it?? do whatvever you want to do but i do believe you are making a mistake. Hopefully the OP has more sense than that.
 
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