Mc in plenum ceiling...

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tonyou812 said:
you cant use AC cable in a plenum ceiling. See 300.22 (B) NEC2005
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I am thinking that 300.22b does not apply to plenum ceilings,just the air handling

units and the spiral ducts. Majority of times you have to mount different sensors

that are in the AHU and even motors that are in there. I believe that 300.22c is

what applies to plenum ceilings. Look at the FPN under 300.22c
 
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alaskan JW said:
I am thinking that 300.22b does not apply to plenum ceilings,just the air handling

units and the spiral ducts. Majority of times you have to mount different sensors

that are in the AHU and even motors that are in there. I believe that 300.22c is

what applies to plenum ceilings. Look at the FPN under 300.22c
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im not sure i follow 300.22 (B) says Ducts Or Plenums Used for envoirmental Air and thats what the origional question was about
 
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In the OP it was asked can MC cable be installed in a plenum ceiling ,I took this to mean regular metal jacketed MC cable there was no mention of PVC coated or any other type of MC cable.
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It's obvious that an MC cable with an overall NM covering is not allowed. My point: Not all MC cable can be installed in plenums unless listed or labeled as such. It is my belief, that your every day use MC cable is not permitted in Plenums.
 
tonyou812 said:
im not sure i follow 300.22 (B) says Ducts Or Plenums Used for envoirmental Air and thats what the origional question was about
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The op was about a ceiling used for environmental
air. I believe 300.22b is about total enclosed system that does not use the ceiling at all.
 
300.22(C) has a FPN stating : 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.
 
300.22(B) seems to specifically allow standard MC cable in "Ducts or Plenums Used for Environmental Air." 300.22 specifically applies to ducts, plenums and other air-handling spaces. Based on these sections as well as the FPN following 300.22(C) I believe standard MC cable is permitted in drop ceilings used for plenums. 2005 NEC.
 
There is no doubt in my mind whatsoever that MC cable is fine for use above suspended ceilings that are used for air handling spaces.
 
iwire said:
There is no doubt in my mind whatsoever that MC cable is fine for use above suspended ceilings that are used for air handling spaces.
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On reading 300.22(C) including the FPN, I'm at a loss as to why anyone feels otherwise. The second post should have been "Yes" then move on :D
 
augie47 said:
On reading 300.22(C) including the FPN, I'm at a loss as to why anyone feels otherwise. The second post should have been "Yes" then move on :D
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I had this same discussion with an electrical inspector supervisor, and his answer was: MC cable that is not plenum rated, should not be ran in plenums. He seems to agree with me. I then called another inspector, and he said just the opposite.

Happy to see it's so simple for you! :D
 
I have as much troulble reading the Code as anybody, a lot more trouble than some in here, but..that said:

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,


seems pretty selfexplanatory.
 
My emphasis was more on NEC 110.3--presenting that not all MC Cable can be used in plenums. Yet, based on one [just one :) ]manufactures (Southwire) specifications, I?m wrong. Southwire claims all their MC (accept the NM covered) cable meets 300.22. Yet, it took southwire some time in figuring this. :rolleyes:



 
augie47 said:
On reading 300.22(C) including the FPN, I'm at a loss as to why anyone feels otherwise. The second post should have been "Yes" then move on :D
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I agree too. The problem is that some of the terminology used in this thread does not directly correlate to the OP's question. The area above a hung ceiling is defined as an "Other Space Used for Environmental Air". Once that is established we're directed to wiring methods that fall under 300.22(C)(1). This would permit both standard MC cable and AC cable.
 
Someone asked the difference between a plenum and other space for enviromental air. Here is a picture of a motor in a plenum. Since it is zoomed in on the motor you can't see the big fan to the left. This is inside a large air handler. (I know there is a better way for the photos, but I can't figure it out) EDIT add: I guess I did it right, it just did not show up in the preview message view.

http://forums.mikeholt.com/attachment.php?attachmentid=1609&stc=1&d=1209478524
 
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