3/8 F M T usage

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BIG BIRD

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Birdland, San Diego
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Electrician
Good day .

Happy New Year !

For this question, I need some assistance on Code intent :

Are 4 #12 THHN conductors allowed in 3/8" FMT with outside fittings ?

I came up with yes .

The cross-sectional area of 4 exceeds percent fill .

FMT does not reference percent fill in 360 .

It seems to intentionally leave it out .

Maximum of 4 because TABLE 348.22 says 3 + 1 with no limit imposed by Chapter 9 ,

In 360.22(A), 1/2 inch and 3/4 inch are specifically written to refence Chapter 9 Table 1 .

Then in 360.22(B), 3/8 says Table 348.22

A reason I think that 40% fill was intentionally left out is the short run .
360.12 Uses Not Permitted. FMT shall not be used as follows:
(6) In lengths over 1.8 m (6 ft),

360.22 Number of Conductors.
(A) FMT - Metric Designators 16 and 21 (Trade Sizes ½ and ¾). The number of conductors in metric designators 16 (trade size ½) and 21 (trade size¾) shall not exceed that permitted by the percentage fill specified in Table 1, Chapter 9.
Cables shall be permitted to be installed where such use is not prohibited by the respective cable articles. The number of
cables shall not exceed the allowable percentage fill specified in Table 1, Chapter 9.
page 70-178
(B) FMT Metric Designator 12 (Trade Size3/8). The number of conductors in metric designator 12 (trade size 3/8) shall not exceed that permitted in Table 348.22.

I see that as saying specifically to use TABLE 348.22 . (ONLY)

If using words of 348.22 was the intention, stating 348.22 would be easier .
page 70- xxx
Table 348.22 Maximum Number of Insulated Conductors in Metric Designator 12 (Trade Size3/8) Flexible Metal Conduit (FMC)

The TABLE says the answer is "4"
3 + 1 ( with no limit imposed by percent fill )

page 70-xxx Chapter 9 Table 348 percent Fill For FMC
Page 70-xxx 348.22
Page 70-xxx Table 348.22
Page 70-xxx Chapter 9 Table 5 for Area
page 70-xxx
FMT uses FMC Table
The asterisk denotes adding one more CONDUCTOR
3 + 1= 4
FMT SAYS USE TABLE 348.22, SO USE THE TABLE MAX IT OUT .
ARTICLE 360
Flexible Metallic Tubing: Type FMT

#12 x 4 is
0.0133in^2 x 4 =
0.0532in^2 which is over the 0.046in^2 for 3/8" FMC



The percent fill looks like it was intentionally left out by saying that FMT
follows Table 348.22 and not words of 348.22 .

If "percent fill" is needed, the diction that leaves out 348.22 should change .

348.22 Number of Conductors. The number of conductors
shall not exceed that permitted by the percentage fill specified in
Table 1, Chapter 9, or as permitted in Table 348.22, or for metric
designator 12 (trade size3/8).
Cables shall be permitted to be installed where such use is
not prohibited by the respective cable articles. The number of
cables shall not exceed the allowable percentage fill specified in
Table 1, Chapter 9.


0.0532sqin - 0.046sqin = 0.0072sqin

Right is right and wrong is wrong .

Chapter 9 Table 1 note (7) is nonapplicable .

I'd like to figure out if the principle of 0.8 rounding from Chapter 9 Table 1 (7) can apply for 72 ten thousandths of an in^2 per Code as written .

Table 1 Percent of Cross Section of Conduit and Tubing
for Conductors and Cables
Notes to tables
(7) ·when calculating the maximum number of conductors or
cables permitted in a conduit or tubing, all of the same
size (total cross-sectional area including insulation), the
next higher whole number shall be used to determine the
maximum number of conductors permitted when the calculation
results in a decimal greater than or equal to 0.8.
When calculating the size for conduit or tubing permitted
for a single conductor, one conductor shall be permitted
when the calculation results in a decimal greater than or
equal to 0.8.

Page number xxx because the information is "steady" for different years .


0.0532in^2 - 0.046in^2 = 0.0072in^2

Since a little bit of knowledge is dangerous, I'm trying to be safer .
 
Please update your profile to include an accurate location.
 
Just a heads up, long posts are hard to follow and it's not unusual to see them ignored, not to mention that FMT is and has always been a rarely used item.
 
hbiss said:
Don't know what your problem is. Table 348.22 says that three #12 THHNs are allowed along with one EGC. Is that what you have??

-Hal
Click to expand...
Good day .
I have the 3 plus one more .
*

Table 348.22 Maximum Number of Insulated Conductors in Metric Designator 12 (Trade Size3/8) Flexible Metal Conduit (FMC)*

*In addition, one insulated, covered, or bare equipment grounding conductor of the same size shall be permitted .

That is what I have .

The total area of 4 conductors is over 40% fill of 3/8 FMT .

Is that a problem ?

Your efforts are appreciated .
 
BIG BIRD said:
The total area of 4 conductors is over 40% fill of 3/8 FMT .
Click to expand...
Why are you using 40%? That is for 1/2" and 3/4" FMT {360.22(A)}. Table 348.22 is where you'll find the answer based on the conductor insulation and whether the fitting is on the outside or the inside {360.22(B)}.

Table 348.22:
#12 THHN w/Outside Connector=3*
*In addition, one insulated, covered, or bare equipment grounding conductor of the same size shall be permitted.

Answer is 4.
Fitting on the inside answer is 3.
 
infinity said:
Why are you using 40%? That is for 1/2" and 3/4" FMT {360.22(A)}. Table 348.22 is where you'll find the answer based on the conductor insulation and whether the fitting is on the outside or the inside {360.22(B)}.

Table 348.22:
#12 THHN w/Outside Connector=3*
*In addition, one insulated, covered, or bare equipment grounding conductor of the same size shall be permitted.

Answer is 4.
Fitting on the inside answer is 3.
Click to expand...
Perfect .
I was thinking that .
Not using FMT a lot made me less confident .

So if it was FMC it would be 3 correct ?
 
hbiss said:
You can have 4 as long as only three are current carrying conductors and the fourth is an EGC.

-Hal
Click to expand...
Good day .

If it were FMC, would be 3 correct ?

Does the EGC count toward percent fill in FMC ?

348.22 Number of Conductors. The number of conductors shall not exceed that permitted by the percentage fill specified in Table 1, Chapter 9, or as permitted in Table 348.22, or for metric designator 12 (trade size3/8). Cables shall be permitted to be installed where such use is not prohibited by the respective cable articles. The number of cables shall not exceed the allowable percentage fill specified in Table 1, Chapter 9.

#12 THHN x 4 is
0.0133in^2 x 4 =
0.0532in^2 which is over the 0.046in^2 for 3/8"

0.0532in^2 - 0.046in^2 = 0.0072in^2
a little bit over by 0.0072in^2
 
infinity said:
It's the same table so why would FMC be different?
Click to expand...
Good day .
That was my problem .
FMT is low usage in some places .
FMT 360
FMC 348
348.22 Number of Conductors. The number of conductors shall not exceed that permitted by the percentage fill specified in Table 1, Chapter 9, or as permitted in Table 348.22, or for metric designator 12 (trade size3/8). Cables shall be permitted to be installed where such use is not prohibited by the respective cable articles. The number of cables shall not exceed the allowable percentage fill specified in Table 1, Chapter 9.

#12 THHN x 4 is
0.0133in^2 x 4 =
0.0532in^2 which is over the 0.046in^2 for 3/8"

0.0532in^2 - 0.046in^2 = 0.0072in^2
a little bit over by 0.0072in^2

FMT is just TABLE 348.22 .
FMC is all of 348 including the wording that states use Ch9 Tbl 1

With that 0.046in^2 limit for 40%
It looks like 3 for FMC .
Do you see it differently ?
Mr. Hal mentioned the comment I made about the short run .
It seems that may be the reason why it would be different .



"A reason I think that 40% fill was intentionally left out is the short run .
360.12 Uses Not Permitted. FMT shall not be used as follows:
(6) In lengths over 1.8 m (6 ft), "
 
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