- Location
- New Jersey
- Occupation
- Journeyman Electrician
I'm not sure why you're still hung up on 40%. 3/8" FMT or FMC are limited to 6' in length and use the same table to determine the fill. There is no 40% factor involved.
3/8 F M T usage
- Thread starter BIG BIRD
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BIG BIRD
Member
- Location
- Birdland, San Diego
- Occupation
- Electrician
Good day Mr. Rob .
This is why I reference the percent fill :
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.
I read this as not exceeding percent fill in Table 1, Chapter 9 or
exceeding the permitted specified values in Table 348.22 or
exceeding metric designator 12 (trade size 3/8")
Don't do this or that or the other thing .
Don't exceed A .
Don't exceed B .
Don't exceed C .
page 695 in the 2020
page 696 in the 2020
page 208 in the 2020
For 3/8" FMT :
360 states that Table 348.22 is to be used for 3/8". { (I see that as only use Table 348.22) and don't use the wording of 348.22}
[ For FMC all of 348 applies ]
In 360 1/2" and 3/4" are mentioned purposefully with respective restrictions . [360.22A]
Then 3/8" is mentioned separately with instructions to use the Table . [360.22B]
What I gather is that the FMC and FMT have distinct qualities that make their respective usage limits different . [360.12(6)]
I came on the blog for help and being wrong is just a part of growth that is welcomed .
Finding out that my interpretation is erroneous is fine .
Another differentiating factor is the length limitations .
The venerable Mr. Hal helped me with that recently .
FMT has a 6 foot limit .
FMC does not have the same limit on use permitted .
348.10 Uses Permitted. FMC shall be permitted to be used in
exposed and concealed locations.
348.12 Uses Not Permitted. FMC shall not be used in the
following:
(1) In wet locations
(2) In hoistways, other than as permitted in 620.2l(A) (1)
(3) In storage battery rooms
(4) In any hazardous (classified) location except as permitted
by other articles in this Code
(5) VVhere exposed to materials having a deteriorating effect
on the installed conductors, such as oil or gasoline
(6) Underground or embedded in poured concrete or aggregate
(7) Where subject to physical damage
And with all of that, I'm fine with finding out this is all wrong .
Growth is worth it to me .
Be well .
Your efforts are appreciated .
- Location
- New Jersey
- Occupation
- Journeyman Electrician
3/8 FMC is limited to 6' just like FMT. You can use the table 348.22 for the maximum fill of either 3/8 FMT or 3/8 FMC. Forget the 40% it is not relevant.
BIG BIRD
Member
- Location
- Birdland, San Diego
- Occupation
- Electrician
Good day .
The limits I saw were :
FMC
348.10 Uses Permitted. FMC shall be permitted to be used in
exposed and concealed locations.
348.12 Uses Not Permitted. FMC shall not be used in the
following:
(1) In wet locations
(2) In hoistways, other than as permitted in 620.2l(A) (1)
(3) In storage battery rooms
(4) In any hazardous (classified) location except as permitted
by other articles in this Code
(5) Where exposed to materials having a deteriorating effect
on the installed conductors, such as oil or gasoline
(6) Underground or embedded in poured concrete or aggregate
(7) Where subject to physical damage
Nothing "FORBIDDING 6 FEET"
FMT
360.10 Uses Permitted. FMT shall be permitted Lo be used for
branch circuits as follows:
(I) In dry locations
(2) 'Where concealed
(3) In accessible locations
(4) For system voltages of 1000 volts maximum
360.12 Uses Not Permitted. FMT shall not be used as follows:
(I) In hoistways
(2) In storage battery rooms
(3) In hazardous (classified) locations unless otherwise
permitted under other articles in this Code
(4) Underground for direct earth burial, or embedded in
poured concrete or aggregate
(5) Where subject to physical damage
(6) In lengths over 1.8 m (6 ft)
"FORBIDDEN"
____________________________________________
I acknowledge :
348.20 Size.
(A) Minimum. FMC less than metric designator 16 ( trade
size ½) shall not be used unless permitted in 348.20(A) (1)
through (A) (5) for metric designator 12 (trade size 3/8).
(1) For enclosing the leads of motors as permitted in
430.245(B)
(2) In lengths not in excess of 1.8 m (6 ft) for any of the
following uses:
a. For utilization equipment
b. As part of a listed assembly
c. For tap connections to luminaires as permitted in
410.117(C)
The 6 foot limit is specific ..... and very common to the point that the "general rule" is 6 feet .
The NEC does not forbid going beyond 6 feet in FMC .
However, FMT beyond 6 feet is a use NOT PERMITTED .
According to the National Electrical Code (NEC), Flexible Metal Conduit (FMC) can be used in lengths greater than 6 feet, but only if a separate equipment grounding conductor is installed, as the length limitation of 6 feet primarily applies to using FMC as the sole grounding path; exceeding that length requires a dedicated grounding wire.
When using FMC in lengths over 6 feet, a separate grounding conductor must be run alongside the conductors within the conduit.
The 6-foot restriction mainly applies to situations where the FMC is used as the primary ground return path, like connecting to a lighting fixture.
That can reasonably satisfy the 6 feet limit point made .
The wording of 360 FMT and 348 FMC seem to show that percent fill applies to only one of them as mentioned .
This is just what I see .
Your efforts are appreciated .
- Location
- New Jersey
- Occupation
- Journeyman Electrician
The minimum size permitted for FMC is 1/2". It's right there in 348.20(A). If it meets the conditions in 348.20(A)(1) through (A)(5) then 3/8" can be used. One of those limits for 3/8" is no longer than 6'. Show us where in the NEC where field installed 3/8" FMC is permitted in lengths in excess of 6'.
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
BIG BIRD
Member
- Location
- Birdland, San Diego
- Occupation
- Electrician
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
Thanks
BIG BIRD
Member
- Location
- Birdland, San Diego
- Occupation
- Electrician
Good day to "us" .
Show us where in the NEC where field installed 3/8" FMC is permitted in lengths in excess of 6'.
one potential exception could be when used as part of a listed assembly for a specific piece of equipment where the manufacturer has designed it to be installed with longer lengths of 3/8" FMC, as long as it meets the requirements outlined in the listing and installation instructions.
Does the NEC Limit a Flexible Metal Conduit Run?
Four electrical experts offer their responses to this question.
www.ecmweb.com
According to the National Electrical Code (NEC), Flexible Metal Conduit (FMC) can be used in lengths greater than 6 feet, but only if a separate equipment grounding conductor is installed, as the length limitation of 6 feet primarily applies to using FMC as the sole grounding path; exceeding that length requires a dedicated grounding wire.
When using FMC in lengths over 6 feet, a separate grounding conductor must be run alongside the conductors within the conduit.
The 6-foot restriction mainly applies to situations where the FMC is used as the primary ground return path, like connecting to a lighting fixture.
A. The NEC does restrict the length of flexible metal conduit for lighting fixtures to 6 ft to limit the ground return path. Sec. 430-135(b) restricts the length of the motor leads between the motor and required junction box to a maximum of 6 ft, regardless of what type of conduit they are contained in — this pertains to the motor leads only. The length of flexible metal conduit for other uses isn’t restricted, while a grounding conductor is included with the circuit conductors. In response, the author may run any length of flexible conduit from the disconnect to the motor junction box, provided he also meets the requirements for support of the flexible conduit and location of the disconnecting means.
— E.C.G.
A. The limitation on the length of flexible conduit was removed from the Code several revisions ago. Before that, flex could only be a maximum 6 ft in length — in all cases. There are several references to 6 ft as a limitation on flexible conduit. However, here are the special cases noted.
Section 350-10 (a) states several rules for 3/8 flexible metal conduit only — one being that this flexible conduit isn’t longer than 6 ft in certain instances. Other trade sizes aren’t affected by this rule. The Code rule of 6 ft for lighting tap conductors [Sec. 410-67(c)] still limits all lighting fixture tap conductors to 6 ft. So all flexible conduit used from the last outlet box to a lighting fixture must be 6 ft or less. This applies to all trade sizes used as lighting fixture tap conductors.
You may use flexible metal conduit in any length as long as you follow the Code rules for support (Sec. 350-18) and grounding (Sec. 250-18).
Section 250-18 limits flexible metal conduit to 6 ft only for grounding. In lengths over 6 ft, you must install a separate grounding conductor.
Regarding the motor circuit in question, the equipment grounding conductor (EGC) must be terminated in accordance with Sec. 430-12(a) and Sec. 430-145.
—W.G.J.
A. The NEC allows a 7-ft extension of flexible metallic conduit (FMC) to a motor subject to the conditions in Art. 350. The primary restriction for lengths of FMC over 6 ft is it can’t be used for the ground fault return path. In general, if the overcurrent protective device is over 20A, you must install an equipment grounding conductor along with the circuit conductors. Flexible metallic conduit used in lengths over 6 ft must be supported within 12 in. of any conduit termination, at intervals not exceeding 4.5 ft.
—C.D.H.
A. The NEC permits longer runs of flexible metal conduit (FMC) with certain limitations. Per Sec. 250-9(b) (Grounding), a recognized equipment grounding conductor can be FMC where the conduit and fittings are listed for grounding. Both exceptions allowing FMC limit the length to 6 ft. If a grounding conductor is provided in the run, the armor is no longer acting as the grounding path, and the length isn’t limited under this section. For this, UL doesn’t test for the grounding ability of flexible metal conduit in lengths exceeding 6 ft, so there’s a possibility the Authority Having Jurisdiction (AHJ) wouldn’t approve an installation not providing a recognized grounding conductor. If the run were in excess of 6 ft, the added cost of a grounding conductor would be an inexpensive way to ensure NEC compliance.
—L.W.M.
TECHNICAL SERVICES DEPARTMENT
BULLETIN
No. 93
April 2006
(Reaffirmed 12/11)
(Rev 2/14)
(Reaffirmed 11/19)
Length Limitations for FMC and LFMC
The purpose of this Bulletin is to clarify the length limitations required by the National Electrical
Code on Flexible Metal Conduit (FMC) and Liquid Tight Flexible Metal Conduit (LFMC).
Articles 348 and 350 of The National Electrical Code cover the installation requirements for
FMC and LFMC. There is no length limitation specified for trade size 1/2 through 4 of either
FMC or LFMC. Lengths of both FMC and LFMC trade size 3/8 are limited due to their use in
specific installations specified in Section 348.20(A) and 350.20(A).
Some confusion exists on the permitted installed length of FMC and LFMC due to their use as an
equipment grounding path as covered by NEC Section 250.118. Both FMC and LFMC may be
used for equipment grounding under the specific conditions covered by NEC Section 250.118(5)
for FMC and 250.118(6) for LFMC. One of these conditions requires that the total length of the
ground path does not exceed 6 feet. However, this length limitation applies to the ground path,
not the conduit. Where the length of the conduit exceeds 6 feet, an equipment grounding
conductor must be used.
In summary, the only length limitation specified by the NEC on the installation of FMC and
LFMC is where trade size 3/8 is used for specific installations specified in NEC Sections
348.20(A) for FMC and 350.20(A) for LFMC. All other trade sizes have no length limitation.
Distribution List:
Standards and Conformity Assessment Policy Committee
Codes and Standards Committee
NEMA Technical Services Department
Disclaimer
The standards or guidelines presented in a NEMA standards publication are considered
technically sound at the time they are approved for publication. They are not a substitute for a
product seller’s or user’s own judgment with respect to the particular product referenced in the
standard or guideline, and NEMA does not undertake to guarantee the performance of any
individual manufacturer’s products by virtue of this standard or guide. Thus, NEMA expressly
disclaims any responsibility for damages arising from the use, application, or reliance by others
on the information contained in these standards or guidelines.
I had an original question that took these things into account .
Clarification of the 6 foot limits were established before I asked if 4 #12 THHN conductors are allowed in 3/8" FMT with outside fittings .
Are 4 #12 THHN conductors allowed in 3/8" FMT with outside fittings ?
I'd like to know why the "no words" comments made are not showing .
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I asked about field installed 3/8" FMC where the limit is 6' whether or not it's part of the EGC path. Most of your post hint at being generated by AI with code references from the 1990's.
One can only assume that a moderator felt that showing a dozen photos of cans was not relevant to that thread so it was removed.
BIG BIRD
Member
- Location
- Birdland, San Diego
- Occupation
- Electrician
Are 4 #12 THHN conductors allowed in 3/8" FMT with outside fittings ?
You have been given the answer more than once.
BIG BIRD
Member
- Location
- Birdland, San Diego
- Occupation
- Electrician
Are 4 #12 THHN conductors allowed in 3/8" FMC with outside fittings ?
- Status