# flex question



## zen (Jun 15, 2009)

if im running a 8/3 in a plenum cieling" i think i said that right",i call it a "return air" and my cieling is complete sheet rock can i use flexable metal conduit,,"flex" i call it with thhn or will i need to use 8/3 m.c. my length is 75 ft. and my ceiling in the vanetian plaster...so cutting hole for pipe my not work..thanks


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## kbsparky (Sep 20, 2007)

You should be able to use it, provided you install an EGC, it is properly supported, and the total number of bends in the flex do not exceed 360 degrees.


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## Nephi (Mar 20, 2010)

i would run mc then the 360 rule doesnt apply, also you can run romex through return air bays as long as it passes through perpendicular, if you planning on running it parrallel in a return bay then its not permitted


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## zen (Jun 15, 2009)

thanks, i am the new go to guy for code questions,,so i can learn for my journeyman lisc. test,, of coarse im only a helper now,,,i looked under 360. in the code book but didnt find the right answer,, i found ``1.8 meters or 6 ft. any tips what i missed will help,,and thanks either way:thumbup:


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## Nephi (Mar 20, 2010)

in any run of conduit you cannot exceed 360 degrees per pull without hitting a pull box or conduit body ex. L B.


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## B4T (Feb 10, 2009)

Flex can't be over 6ft... so run MC cable


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## Nephi (Mar 20, 2010)

flex cant go more than 6' without being strapped but you can most certainly run more than 6' of it


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## zen (Jun 15, 2009)

im confussed..i was under the impression that 6ft. was my max length w/o a e.g.c or "ground" as i call it..if any one has the answer with the code section that may help..


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## B4T (Feb 10, 2009)

Not sure what your using it for...
*348.20 Size.
(A) Minimum. ​*​​​​FMC less than metric designator 16 (trade
size 1⁄2) 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)
(3) For manufactured wiring systems as permitted in
604.6(A)
(4) In hoistways as permitted in 620.21(A)(1)
(5) As part of a listed assembly to connect wired luminaire​
sections as permitted in 410.137(C)


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## zen (Jun 15, 2009)

Nephi said:


> i would run mc then the 360 rule doesnt apply, also you can run romex through return air bays as long as it passes through perpendicular, if you planning on running it parrallel in a return bay then its not permitted


 i dont think ive ever seen a green tag where we ran romex through any section of a return or stud bay no matter what direction...n,s,e,or w


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## zen (Jun 15, 2009)

Black4Truck said:


> Not sure what your using it for...
> *348.20 Size.*​
> 
> *(A) Minimum. *
> ...



its for a shower steamer,,specs given to us by plumber{the wire size} its in a high rise residential home with a plenum ceiling..​


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## Bob Badger (Apr 19, 2009)

3/8" FMC is limited to 6' 

Larger FMC can be run as long as you want.

FMC longer then 6' requires a wire EGC along with it.


Zen I would use MC.


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## B4T (Feb 10, 2009)

Can't be more than 6'.. IMO you need to run MC cable


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## Bob Badger (Apr 19, 2009)

Black4Truck said:


> Can't be more than 6'.. IMO you need to run MC cable


I can run 1/2 to 4"" FMC 250' as long as I pull a ground and keep it under 360 degrees of bend.


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## Nephi (Mar 20, 2010)

fmc yes but that was never specified, the stuff is useless and is miserable to pull through but for lfmc or nmfc the 6 ft rule does not apply and ill find the plenum rule for you in an minute


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## Bob Badger (Apr 19, 2009)

Nephi said:


> the stuff is useless and is miserable to pull through


I agree




> but for lfmc or nmfc the 6 ft rule does not apply and ill find the plenum rule for you in an minute


What 6' rule are you talking about? I can run LFMC as long as I want as well. I do not know about LFNC.


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## zen (Jun 15, 2009)

Bob Badger said:


> 3/8" FMC is limited to 6'
> 
> Larger FMC can be run as long as you want.
> 
> ...


 is the price difference gonna cause anyone to have a nervous break down,,,im asking because i m thinking flex and thhn is a lot less than 8/3 mc.we have a shop guy who will get the flex / thhn ready so the cost for that labor would mostly be on the install..


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## Nephi (Mar 20, 2010)

im sorry in your original post you did call it flexible metal cinduit...sorry


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## RIVETER (Sep 26, 2009)

zen said:


> is the price difference gonna cause anyone to have a nervous break down,,,im asking because i m thinking flex and thhn is a lot less than 8/3 mc.we have a shop guy who will get the flex / thhn ready so the cost for that labor would mostly be on the install..


Now that we have all this figured out, how do you plan to support whatever you use along the 75 foot path?


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## zen (Jun 15, 2009)

sorry im trying to use the correct names for what i mean that why i put " i call it" after them,,,and thanks for every ones patience.


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## zen (Jun 15, 2009)

RIVETER said:


> Now that we have all this figured out, how do you plan to support whatever you use along the 75 foot path?


 im only the code look up guy, but i think your about to open my eyes,,,i cant use the ceiling wires that are there for the ceiling support so i have to make holes in their finished ceiling for mine and if thats the case im running emt and your right.


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## Nephi (Mar 20, 2010)

300.22(c). this section shall not apply to the joist or stud spaces of dwelling units where the wiring passes through such spaces perpendicular to the long dimension of such spaces


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## RIVETER (Sep 26, 2009)

Nephi said:


> 300.22(c). this section shall not apply to the joist or stud spaces of dwelling units where the wiring passes through such spaces perpendicular to the long dimension of such spaces


Would you be able to paraphrase your statement and explain in what context you are using this code section?


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## Nephi (Mar 20, 2010)

in other words when a hvac contractor uses a stud bay or a floor joist bay as a cold air return because its not considered a duct or used for heating it is permitted to run through it perpendicular to the long section


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## Nephi (Mar 20, 2010)

sound good


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## Bob Badger (Apr 19, 2009)

zen said:


> is the price difference gonna cause anyone to have a nervous break down,,,im asking because i m thinking flex and thhn is a lot less than 8/3 mc


Is the price really that different?

100' of 8/3 MC = 100' of FMC, 300' 8 AWG and 100' of 10 AWG.


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## Nephi (Mar 20, 2010)

in no case can romex be ran through an actual duct or in a ceiling being used as a cold air return


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## RIVETER (Sep 26, 2009)

Nephi said:


> in other words when a hvac contractor uses a stud bay or a floor joist bay as a cold air return because its not considered a duct or used for heating it is permitted to run through it perpendicular to the long section


Okay, I think I see what you mean. How does this apply to the running of flexible metallic cable through 75 feet of ceiling return air space?


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## user4818 (Jan 15, 2009)

Bob Badger said:


> Is the price really that different?
> 
> 100' of 8/3 MC = 100' of FMC, 300' 8 AWG and 100' of 10 AWG.



Plus the labor to assemble it all. I will guess off the top of my head that the price of the MC does not even compare to the FMC.


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## Nephi (Mar 20, 2010)

i didnt know to what extent his run would come in contact with his return air and thought i would just add that tid bit


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## Nephi (Mar 20, 2010)

i have never seen a steam generator need a number 8. all the ones i have installed pulled 20 some amps


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## goose134 (Nov 12, 2007)

Nephi said:


> i didnt know to what extent his run would come in contact with his return air and thought i would just add that tid bit


I thought he said it was a plenum ceiling. Sounds like 100% of the run is in return air.


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## zen (Jun 15, 2009)

Nephi said:


> i have never seen a steam generator need a number 8. all the ones i have installed pulled 20 some amps


 this is typical for wire size on the steam units we wire for,,and the whole ceiling is considered a return air.


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## Bob Badger (Apr 19, 2009)

zen said:


> this is typical for wire size on the steam units we wire for,


Same here, 50 amps for steam generators.



> and the whole ceiling is considered a return air.


That is weird, I cannot picture a sheet rock ceiling being a return. Around here that is usually only in grid ceilings.


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## zen (Jun 15, 2009)

i thought so too,, its a high rise building 20th floor ,,,all the a/c duct look like any others you might see and the returns are only spots that are vented right into the ceiling,,,the ceiling has main and cross t's held by ceilig wire and the sheet rock is secured to the grid w-sheet rock screws then the sheet rock is done in venetian plaster that im told is slow to work and expensive to repair,,,something like 12.00 a ft,,,but im not a painter so dont hold me too that.i will get some pictures next week if i can...


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## mattsilkwood (Sep 21, 2008)

Bob Badger said:


> That is weird, I cannot picture a sheet rock ceiling being a return. Around here that is usually only in grid ceilings.


 I have seen quite a few like that. I worked an old building renovation a few years back and it was all hard ceilings all plenum.


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## manchestersparky (Mar 25, 2007)

If he is fishing in his FMC in a finished ceiling ........

348.30 Securing and Supporting. 

FMC shall be securely fastened in place and supported in accordance with 348.30 (A)and (B). 

*(A)* *Securely Fastened.* FMC shall be securely fastened in place by an approved means within 300 mm (12 in.) of each box, cabinet, conduit body, or other conduit termination and shall be supported and secured at intervals not to exceed 1.4 m (4 ft). 

*Exception No. 1: Where FMC is fished between access points through concealed spaces in finished buildings or structures and supporting is impractical.* 

Exception No. 2: Where flexibility is necessary after installation, lengths shall not exceed the following: 

(1) 900 mm (3 ft) for metric designators 16 through 35 (trade sizes through 1) 

(2) 1200 mm (4 ft) for metric designators 41 through 53 (trade sizes 1 through 2) 

(3) 1500 mm (5 ft) for metric designators 63 (trade size 2) and larger 

Exception No. 3: _Lengths not exceeding 1.8 m (6 ft) from a luminaire terminal connection for tap connections to luminaires as permitted in_ 410.117(C)_._ 

Exception No. 4: Lengths not exceeding 1.8 m (6 ft) from the last point where the raceway is securely fastened for connections within an accessible ceiling to luminaire(s) or other equipment. 
*B)* *Supports.* Horizontal runs of FMC supported by openings through framing members at intervals


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## cdnelectrician (Mar 14, 2008)

zen said:


> is the price difference gonna cause anyone to have a nervous break down,,,im asking because i m thinking flex and thhn is a lot less than 8/3 mc.we have a shop guy who will get the flex / thhn ready so the cost for that labor would mostly be on the install..


If you run MC cable instead of flex, I do not think you would have to support it like you would conduit which FMC falls under. Since you are technically fishing the cable you would save on the labour not having to support the FMC in the ceiling space. In which case you might as well install EMT.
For the minimal cost savings and frustration involved with using FMC, I would just use BX (MC) cable.


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## Bob Badger (Apr 19, 2009)

mattsilkwood said:


> I have seen quite a few like that. I worked an old building renovation a few years back and it was all hard ceilings all plenum.


Just a side note, if it is a 'plenum' you cannot run any wiring in it that is not directly needed for the plenum. 300.22(B)

The space we are talking about is 'other space used for environmental air' 300.22(C)


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## Nephi (Mar 20, 2010)

that is rediculous. you mean to tell me the only wires allowed in a plenum ceiling are those that feed hvac sytems. no. why would they go through the trouble of making cat 5, coax etc. plenum rated if they are not permitted to be in such spaces. in many cases the whole area above a drop ceiling is being used for a return air and every wire regardless the type is in violation thats rediculous. your not allowed to penitrate an existing enclosed duct and use it for a chase.


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## Bob Badger (Apr 19, 2009)

Nephi said:


> that is rediculous. you mean to tell me the only wires allowed in a plenum ceiling are those that feed hvac sytems. no. why would they go through the trouble of making cat 5, coax etc. plenum rated if they are not permitted to be in such spaces. in many cases the whole area above a drop ceiling is being used for a return air and every wire regardless the type is in violation thats rediculous. your not allowed to penitrate an existing enclosed duct and use it for a chase.


You should really pick up the code book and read the sections I quoted. :thumbsup:


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## B4T (Feb 10, 2009)

Bob Badger said:


> You should really pick up the code book and read the sections I quoted. :thumbsup:


300.22(C)*
(C) Other Space Used for Environmental Air. ​*​​​​This section
applies to space used for environmental air-handling
purposes other than ducts and plenums as specified in
300.22(A) and (B). It does not include habitable rooms or
areas of buildings, the prime purpose of which is not air
handling.​
FPN: The space over a hung ceiling used for environmental
air-handling purposes is an example of the type of other
space to which this section applies.​_Exception: This section shall not apply to the joist or stud
spaces of dwelling units where the wiring passes through
such spaces perpendicular to the long dimension of such
spaces.​_*(1) Wiring Methods. ​*​​The wiring methods for such other
space shall be limited to totally enclosed, nonventilated,
insulated busway having no provisions for plug-in connections,
Type MI cable, Type MC cable without an overall
nonmetallic covering, Type AC cable, or other factoryassembled
multiconductor control or power cable that is
specifically listed for the use, or listed prefabricated cable
assemblies of metallic manufactured wiring systems without
nonmetallic sheath. Other types of cables, conductors,
and raceways shall be permitted to be installed in electrical
metallic tubing, flexible metallic tubing, intermediate metal
conduit, rigid metal conduit without an overall nonmetallic
covering, flexible metal conduit, or, where accessible, surface​
metal raceway or metal wireway with metal covers


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## Nephi (Mar 20, 2010)

thanks b4t


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## Nephi (Mar 20, 2010)

maybe you should take a better look at the section you quoted


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## Bob Badger (Apr 19, 2009)

Nephi said:


> maybe you should take a better look at the section you quoted


Maybe you can explain what you think is wrong with what I posted.



Bob Badger said:


> Just a side note, if it is a 'plenum' you cannot run any wiring in it that is not directly needed for the plenum. 300.22(B)
> 
> The space we are talking about is 'other space used for environmental air' 300.22(C)


You cannot run wiring in plenums except as specified in 300.22(B).


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## RIVETER (Sep 26, 2009)

If I am understanding the above code section, it appears to exclude the use of any PVC coated cable or conduit. Is that correct? If so, why do you think that is?


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## Bob Badger (Apr 19, 2009)

...............................


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## Bob Badger (Apr 19, 2009)

RIVETER said:


> If I am understanding the above code section, it appears to exclude the use of any PVC coated cable or conduit. Is that correct? If so, why do you think that is?


It is talking about a space for environmental air why do you think that is?


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## RIVETER (Sep 26, 2009)

Bob Badger said:


> It is talking about a space for environmental air why do you think that is?


Yeah, that had crossed my mind. I guess I was wondering if they expected some warmer temps. that would cause more of the PVC, in PPM to be expected. Thanks.


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## JohnJ0906 (Jan 22, 2007)

Bob Badger said:


> It is talking about a space for environmental air why do you think that is?


Smoke in the case of fire.


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## Bob Badger (Apr 19, 2009)

JohnJ0906 said:


> Smoke in the case of fire.


I believe that to be correct but I always like to answer Riveters questions with a question. :jester:


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