zen

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.

__________________
I can break an unbreakable plate,,,yes i can,,,

Nephi

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

RIVETER

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

Nephi

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

Nephi

sound good

Bob Badger

Is the price really that different?

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

Nephi

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

RIVETER

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?

user4818

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.

Nephi

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

Nephi

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

goose134

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

zen

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

__________________
I can break an unbreakable plate,,,yes i can,,,

Bob Badger

Same here, 50 amps for steam generators.

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

zen

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...

__________________
I can break an unbreakable plate,,,yes i can,,,

mattsilkwood

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.

manchestersparky

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

cdnelectrician

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.

Bob Badger

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)

Nephi

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.