Question on 3/8 FMC use on an oil furnace

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SAC

Senior Member
Location
Massachusetts
Hello,

If an oil furnace, as provided with the factory wiring, uses 3/8 FMC, is it permissible under 348.20(A) to use 3/8 FMC for additional furnace controls beyond those provided with the furnace? If so, under what clause is the 3/8 FMC use exception granted?

Thanks!

-Shawn
 

Buck Parrish

Senior Member
Location
NC & IN
As long as you don't alter the UL Listing.

Also, their may be some exposed to physical damage issues.
Could you be more specific?

Welcome to the forum:smile:
 

mdshunk

Senior Member
Location
Right here.
I don't think I've ever really had the need to run 3/8" FMC on a boiler, but I have used a great deal of MC cable on boilers. What controls did you have in mind where it would be easier to use FMC as opposed to MC cable?
 

Volta

Senior Member
Location
Columbus, Ohio
. . . is it permissible under 348.20(A) to use 3/8 FMC for additional furnace controls beyond those provided with the furnace? . . .
Maybe:
(1) not a motor?
(2)a. utilization? Might work for an electromechanical relay or contactor,
b. not a listed assembly,
c. not to a luminaire,
(3) not a manufatured wiring system,
(4) not a hoistway,
(5) not for luminaires.

Looks like it can be used for equipment that will utilize energy. That won't include switches, or connection devices, but might be ok for relays, meters, and indicators.

Hope that helps.:smile:
 
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peter d

Senior Member
Location
New England
Once upon a time 3/8 flex was the choice method to wire furnaces and boilers here. I think the only reason was tradition. I upheld this tradition myself.I don't wire many a year but now the choice is MC cable. Although I prefer AC cable because it can be a pain in the rear to make up the EGC's in those small boiler control enclosures.

Hmmm..maybe a good excuse to try out some MC-Ap. :cool:
 

SAC

Senior Member
Location
Massachusetts
Sorry - I'll see if I can be more specific.

As an example, additional zone control relays may be added to the furnace control system in order to control additional heating zones. These zone controllers need to be tied into the factory furnace control system. A typical application is to mount the control boxes on the side of the furnace and wire them into the factory control system.

I have seen cases of 3/8 FMC used on both the factory and the additional controls. However, as I didn't install them, I can't say for sure why FMC was chosen vs. cable. FMC may have more general flexibility in terms of conductor choice when dealing with the varied requirements installers tend to encounter?

I believe I understand the expection allowing 3/8 FMC for the controls delivered with the furnace, but I'm trying to understand how the additional controls would fall into a 3/8 FMC exception. I don't see how they would be covered under any listing of the furnace unit or the individual control units.

Thanks,

-Shawn
 

SAC

Senior Member
Location
Massachusetts
Maybe:
(2)a. utilization? Might work for an electromechanical relay or contactor,
b. not a listed assembly,
c. not to a luminaire,

Looks like it can be used for equipment that will utilize energy. That won't include switches, or connection devices, but might be ok for relays, meters, and indicators.

I guess that must be it. I hadn't thought about such a controller as being in the category of "utilization equipment", but they almost always contain relays, indicators, or other components that do "utilize" energy.

Thanks!

-Shawn
 

yanici

Senior Member
Location
Atlantis
Occupation
Old Retired Master/Journeyman Electrician
My home boiler is wired in EMT and 3/8 flex. I think it looks purdy, too! Oh yeah, I've still got the Push-o-matic breakers, too.
 
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