Low voltage lighitng wiring in plenum

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hamburgerpatty

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I am currently supervising a low voltage lighting project (12 volts), and the wiring will run from the transformer to the fixtures within the plenum. Do I need to use a CL2P type cable for this installation. If so is there such a cable, i.e. #12awg two conductor type CL2P listed for lighting. I have not yet checked the supply house. However I will be checking soon.
 
Re: Low voltage lighitng wiring in plenum

Is it really a plenum or is it an enviromental air handling space such as above a suspended ceiling? The cable type has to be suitable for the intended use, per table 725.61.
Is this an article 411 application or is an article 725 application?

[ November 07, 2003, 11:16 PM: Message edited by: tom baker ]
 
Re: Low voltage lighitng wiring in plenum

It is an enviromental air handling space such as above a suspended ceiling. The exact application is in a Hospital in the return air plenum. (I was under the impression that the space above the suspended ceiling was a "plenum")
This is a Article 411 application, however the wiring will be located above the suspended ceiling. Does this make it a 725 application. If it does, then I will need to find a CL2P cable for my lighting circuit conductors.
 
Re: Low voltage lighitng wiring in plenum

Its a common misconception the area above a suspended ceiling is a plenum, but its not, if you will review the art 100 definition of plenum. But we used "plenum" wire in the area above a suspended ceiling.
Now as to if its a art 411 application or 725, I looked at art 411 and it makes no mention of cable type, however Art 411 is a listed system application, and 110.3(B) applies, IE the instructions are followed. I must be missing something on Art 411...as I don't see any reference to the wiring methods.
 
Re: Low voltage lighitng wiring in plenum

I agree, I am making the same assumption. I also am making the assumption that the circuit is a Class 2 applicaion, even though it is also a lighting circuit. It will be supplied by a Class 2 Transformer. If I refer to Sec 725.61 (A) I need to use CL2P cable, or maybe I am assuming incorrectly that lighting systems operating at 30volts or less are also classified at Class 2 wiring.

Am I also misunderstanding the cold air return (the entire space above a suspended ceiling) is not a plenum?
 
Re: Low voltage lighitng wiring in plenum

Based on your description, unless the cable is in a patient care area, you will need the plenum rated cable (CL2P) to use in this air handling space (not a plenum). Articles 411, 725 along with 300 need to be considered.

Patient care areas are basically metal wiring methods.
 
Re: Low voltage lighitng wiring in plenum

...Am I also misunderstanding the cold air return (the entire space above a suspended ceiling) is not a plenum?

Plenum A compartment or chamber to which one or more air ducts are connected and that forms part of the air distribution system.

Plenum is otherwise referred to as an environmental air handling space. They are one and the same. The tip off that the space is environmental air handling or plenum is the presence of return air registers in place of one or more ceiling tiles in most rooms. These will have no duct work and open into the ceiling space. When in doubt err on the side of caution and use plenum rated cable. The cost, except in the case of CAT5 ethernet, is not that much more.

Now, as for CL2P. CL2 is the lowest on the totem pole which means that you can always go better. You can substitute CL3P or even the regular Class 1 wiring methods such as MC which is listed for environmental air spaces.
 
Re: Low voltage lighitng wiring in plenum

hbiss,

300.22 (C)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.
Click to expand...
As of the 2002 code, there is a distinct difference between a "Plenum" and " Other Space Used for Environmental Air". The differences are explained here;
Section 300.22 limits the use of materials that would contribute smoke and products of combustion during a fire in an area that handles environmental air, and 300.22(B) provides for an effective barrier against the spread of products of combustion into the ducts or plenums.
This section applies to sheet metal ducts and other ducts and plenums specifically constructed to transport environmental air. Because equipment and devices such as luminaires and motors are not normally permitted in ducts or plenums, the wiring methods in 300.22(B) differ from those permitted in paragraph 300.22(C).

Section 300.22(C) applies to other spaces that are used to transport environmental air and are not specifically manufactured as ducts or plenums, such as the space or cavity between a structural floor or roof and a suspended (hung) ceiling. Many spaces above suspended ceilings are intended to transport return air. Some spaces are also used for supply air, but they are far less common than those used for return air.
Click to expand...
 
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