334.15B Romex in pipe question...

Status
Not open for further replies.
wrobotronic

wrobotronic

Senior Member
Location
Colorado
Hello All,
From what I can tell 334.15B allows for romex to be protected by pipe. I want to run a 10-2 and 12-2 in 3/4in. EMT. Would I size the pipe based on my conductors like I would for THHN etc or is there a different method?

Thank you all very much,
WROBO
 
roger said:
See Chapter 9, Notes to Tables (9)

Roger
Click to expand...
From 2014 NEC
(9) A multiconductor cable, optical fiber cable, or flexible
cord of two or more conductors shall be treated as a
single conductor for calculating percentage conduit fill
area. For cables that have elliptical cross sections, the
cross-sectional area calculation shall be based on using
the major diameter of the ellipse as a circle diameter.
Click to expand...

Southwire reports their Simpull NM 10-2 is 494 x 210 mils and their 12-2 is 410 x 179 mils. For those that don't know, a mil is one thousandth of an inch. So it's...
pi × (.494" ÷ 2)² + pi × (.410" ÷ 2)² = 0.642 in²​
This cannot occupy more than 31% of a single conduit so the conduit internal area must be...
0.642 in² ÷ 31% = 2.07 in²​
Looking at a 1-1/2" EMT to run both down the same pipe.

To run just the 10-2, looking at...
pi × (.494" ÷ 2)² = .192 in²​
Cannot occupy more than 53% so...
.192 in² ÷ 53% = .362 in²​
Looks like 3/4" EMT can accommodate the 10-2.

A 1/2" EMT will accommodate 12-2.
 
Note 4 allows 60% if it is 24" or less between boxes and furthermore Table 9 does not apply to sleeves used for protection. Note 1
 
Dennis Alwon said:
Note 4 allows 60% if it is 24" or less between boxes and furthermore Table 9 does not apply to sleeves used for protection. Note 1
Click to expand...
0.642 in² ÷ 60% = 1.07 in²
1-1/4" EMT sleeve not greater than 24" would be required for a 10-2 and 12-2.

My bad earlier in that 0.642 in² ÷ 60% = 2.07 in² is greater than the internal area of 1-1/2" EMT at 2.036 in². A 2" EMT would be required for a sleeve greater than 24" in length.
 
Smart $ said:
Southwire reports their Simpull NM 10-2 is 494 x 210 mils and their 12-2 is 410 x 179 mils. For those that don't know, a mil is one thousandth of an inch. So it's...
pi × (.494" ÷ 2)² + pi × (.410" ÷ 2)² = 0.642 in²​
Click to expand...
Umm, I get

pi × (.494" ÷ 2)² + pi × (.410" ÷ 2)² = 0.192 + 0.132 in² = 0.324 in^2​

I think you may have divided by 2 after squaring instead of before?

Cheers, Wayne
 
wwhitney said:
Umm, I get
pi × (.494" ÷ 2)² + pi × (.410" ÷ 2)² = 0.192 + 0.132 in² = 0.324 in^2​

I think you may have divided by 2 after squaring instead of before?

Cheers, Wayne
Click to expand...
Ahhhhhh, Baloney!

I tried retracing my steps but I don't know what I did. Regardless, it wasn't correct, that's for sure. :ashamed1::rant:

Anyway, at .324 in², he is good to go with 3/4" EMT.

Thanks, Wayne.

My apologies, wrobotronic.
 
wrobotronic said:
Hello All,
From what I can tell 334.15B allows for romex to be protected by pipe. I want to run a 10-2 and 12-2 in 3/4in. EMT. Would I size the pipe based on my conductors like I would for THHN etc or is there a different method?

Thank you all very much,
WROBO
Click to expand...

If you look at the section Roger posted it will tell you that flat cables are calculated as if they were round using it's widest dimension.

(9) A multiconductor cable, optical fiber cable, or flexiblecord of two or more conductors shall be treated as asingle conductor for calculating percentage conduit fillarea. For cables that have elliptical cross sections, thecross-sectional area calculation shall be based on usingthe major diameter of the ellipse as a circle diameter.
Click to expand...
 
Status
Not open for further replies.
Top