> >
>

# How to measure octagonal j-boxes

#1
12-29-07, 04:10 PM
Member
Join Date: Nov 2007
Location: Seattle, WA
Posts: 157
How to measure octagonal j-boxes

I have an "octagonal" j-box... at least I think it is... it is basically square w/ rounded corners... anyway, assuming this is the definition of octagonal... the NEC lists standard box sizes and mine here is 3.5" across side to side x 1.5" deep. But it is not stamped w/ volume and it is UL listed, so I am wondering if by 4 x 1.5" in NEC do they mean measuring from octagonal corner to octagonal corner? That is 4" on my box.

Thanks!

#2
12-29-07, 10:46 PM
Member
Join Date: Jul 2003
Location: NE Ohio
Posts: 32
from table 314.16(A) - for 4" x 1.5" octagonal box is 15.5 cu. inches

#3
12-30-07, 11:14 AM
Member
Join Date: Nov 2007
Location: Seattle, WA
Posts: 157
Originally Posted by bob100
from table 314.16(A) - for 4" x 1.5" octagonal box is 15.5 cu. inches
Granted, but is the box I am looking at a 4" x 1.5" box? That's what I don't know! If I were stating the size of the octagonal box I'd say it was 3.5 x 3.5 x 1.5--but that would make it a nonstandard size box and that would imply that it should have the volume stamped on it; which it does not. So... are the box sizes stated in the NEC and given as (for example) 4 x 1.5 meaning 4" diagonal (for an octagonal)?

#4
12-30-07, 11:21 AM
Member
Join Date: Feb 2006
Location: USA
Posts: 6,604
Box Size

The "diagonal" measurement of 4 in. is correct.

#5
12-30-07, 11:38 AM
Member
Join Date: Nov 2007
Posts: 160
It sounds like you have a 3 1/2" round box to me. octagon boxes are measured and calculated like round boxes are.

Check 3 1/2 x 1 1/2 octagon box in this T&B steel city cat for volumes

http://www.tnb.com/contractor/docs/sc_indoorboxes.pdf

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Pingbacks are Off
Refbacks are Off