ECN Forum Forums Code Related Discussion NEC & other Code issues Receptacles under raised floors

George- I don't buy your table analogy here but I have been shown here that a "standard" receptacle is legal under the computer room floor as long as it is wired using the methods discribed in 645.5(D). While Greg feels it's not a good idea, he won't use them, I'm sure they are being used legally by others.

I saw plenty of regular receptacles under the floor.
The problem is coming up with a way that they can be used legally. The under floor receptacles are supposed to serve computer equipment and that will come with the IEC309 or Russell Stoll plug cap. In traditional computer rooms they won't even bring a neutral to the computer supply panels. Everything is on a L/L circuit.
I suppose things may be different in the PC crazed world we live in now but that also eliminated the need for most 645 regulated raised floors. What used to be a room full of boxes now resides in a few 19" racks, bolted together. The HVAC chiller might be bigger than the "computer".

We have recepticles under a raised floor here at work. We use NEMA locking connectors and SOOW cord to feed the 19" equipment racks above.

I doubt SOOW cord meets the flame test

If it is an IT room, you don't need the DP rating. See 645.5(D)(2).

HUH? 645.5(D)(2) refers to the branch circuit that serves the receptacle, not the line cord. SO is not one of the wiring methods anyway.
We had to rip out all of the SO cord under the floor in the mid 70s. That is where I got my welder extension cord.

645.5(D)(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.


645.5(D)(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.

I doubt you will see much pre 1994 equipment these days. It was pretty much all gone when I retired in 96. There was a significant technology change in that timeframe. Disks went from the large format media to racks full of 3.5" drives similar to what is in a PC. Processors, controllers etc went from transistor logic to CMOS logic which allowed smaller boards and very much lower operating currents. That was the end of the "glass house" computer room as we knew it. That room full of walk in freezer sized boxes became a rack.
I lost interest in computers when they stopped having hydraulic pumps in them

gfretwell-"I doubt SOOW cord meets the flame test"
Yeah tell me about it. I somtimes wish a that I could bring a camera to work and post the miriad of code violations that I see on a regular basis. Unfortuneatly we build a lot of classified systems for the military and cameras are strictly prohibited behind the perimiter fence. Thankfully the violations that I have seen aren't major safety hazards, just ignorant EE's that have no idea what is and isn't code compliant.

IanR,
You work at an interesting shop, where the EE's install circuits.
Usually the guy installing the circuit can give an opinion too.

This issue causes me no end of grief. The whole idea of a raised floor has been wrecked by the NEC, and NEC 645 doesn't provide enough relief. How many of you have seen power cable or interface cables with a DP listing? I've never seen one. I suppose I could buy the cable and make up some, but I shouldn't have to. The interface cables are many times impossible to make up ourselves (proprietary connectors). What we've done in most of our 645 areas is to put 5" holes in some floor tiles and then mount a receptacle box on unistrut so it is directly under the hole. This way, only the cord cap is "under the floor" and only for about an inch.

The other thing that burns me up is that liquidtight flex is not allowed under our floors unless it is secured every 4 (?) feet. This again defeats the purpose of why you want a raised floor computing lab area. Fortunately, we have a contractor that is allowed to make UL Listed IT cable assemblies, so they do basically what we would do with the flex, but they can put a UL label on it.

Are any of you required to secure your phone or network cabling under the floor? I can't seem to find a code section that covers it. I used rip ties to every other floor post, and the inspector didn't seem to like that.

These inspectors don't seem to care that the layout of our computing rooms is constantly changing.

All IBM interface cables after 1993 were DP listed/labelled. (usually tan colord)
The blue ones were also compliant but not labelled. The grey ones were not. Generally speaking, anything "riser" or "plenum" rated is OK for "DP" (CLxR or CLxP).
All IBM ESCON fiber was "DP" AFAIK.
The stuff on the branch circuit side has to comply with 645.5(D)(2)