Plenum Definition

Status
Not open for further replies.

safetee

New member
I need help applying the NEC definition of plenum. My company is planning to install electronic equipment in a single room with a raised floor. The space below the floor will be used for cabling and for air movement to cool electronic equipment in racks. The air movement components simple include an outside blower with a duct directing air into the space beneath the raised floor. The space under the floor is sealed, such that there is no path for smoke or flames to propagate to any other room should a fire start in this space. Is this a plenum? Must we use plenum rated cabling?
 

websparky

Senior Member
Location
Cleveland, Ohio
Re: Plenum Definition

I would read Article 645 Information Technology Equipment first to see if this room qualifies as such. If it does, there are a host of requirements! If not, then you would need to consider Article 300.22 (B) and (C).
 

ron

Senior Member
Re: Plenum Definition

Don't mess around with Article 645 unless you need the leniencies permitted by Article 645. The requirements to activate that article are brutal to your reliability.
See article 300.22(C)(1) for acceptable wiring methods.

[ July 18, 2003, 11:21 PM: Message edited by: ron ]
 

iwire

Moderator
Staff member
Location
Massachusetts
Re: Plenum Definition

As has been said in order to use the leniencies of 645 the room must meet all the following.

(1)Disconnecting means complying with 645.10

(2)A separate heating/ventilating/air-conditioning (HVAC) system

(3)Listed information technology equipment is installed.

(4)The room is occupied only by those personnel needed.

(5)The room is separated from other occupancies by fire-resistant-rated walls, floors, and ceilings with protected openings.

Then in order to treat the under floor area as not a plenium you have to meet this too.

645.5(D) Under Raised Floors.
Power cables, communications cables, connecting cables, interconnecting cables, and receptacles associated with the information technology equipment shall be permitted under a raised floor, provided the following conditions are met.

(1) The raised floor is of suitable construction, and the area under the floor is accessible.

(2) The branch-circuit supply conductors to receptacles or field-wired equipment are in rigid metal conduit, rigid nonmetallic conduit, intermediate metal conduit, electrical metallic tubing, electrical nonmetallic tubing, metal wireway, nonmetallic wireway, surface metal raceway with metal cover, nonmetallic surface raceway, flexible metal conduit, liquidtight flexible metal conduit, or liquidtight flexible nonmetallic conduit, Type MI cable, Type MC cable, or Type AC cable. These supply conductors shall be installed in accordance with the requirements of 300.11.

(3) Ventilation in the underfloor area is used for the information equipment room only. The ventilation system shall be so arranged, with approved smoke detection devices, that upon the detection of fire or products of combustion in the underfloor space the circulation of air will cease.

(4) Openings in raised floors for cables protect cables against abrasions and minimize the entrance of debris beneath the floor.

(5) Cables, other than those covered in (2) and those complying with (a), (b), and (c), shall be listed as Type DP cable having adequate fire-resistant characteristics suitable for use under raised floors of an information technology equipment room.

(a) Interconnecting cables enclosed in a raceway.

(b) Interconnecting cables listed with equipment manufactured prior to July 1, 1994, being installed with that equipment.

(c) Cable type designations Type TC (Article 336); Types CL2, CL3, and PLTC (Article 725); Type ITC (Article 727); Types NPLF and FPL (Article 760); Types OFC and OFN (Article 770); Types CM and MP (Article 800); and Type CATV (Article 820). These designations shall be permitted to have an additional letter P or R or G. Green, with one or more yellow stripes, insulated single conductor cables, 4 AWG and larger, marked ?for use in cable trays? or ?for CT use? shall be permitted for equipment grounding.

(6) Abandoned cables shall not be permitted to remain unless contained in metal raceways.
If you meet all this you can use standard cables in the under floor space.

If not 300.22(B) will apply to line voltage wiring and article 800 will govern the data cabling

[ July 19, 2003, 04:50 AM: Message edited by: iwire ]
 

hforney500

Member
Location
New Jersey
Re: Plenum Definition

Safetee, Here is another concern you might want to consider.

Would smoke detectors be required under the raised floor. If the area under the floor is not used for air movement are detectors required. Is there a difference?
 
Status
Not open for further replies.
Top