Underfloor intallations

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msine

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Can type rhh/rhw be installed without a raceway under a raised floor in a computer room. The under floor area is not a plenum but does have notification equipment for an FM 200 system. Can it also be spliced and tapped without an enclosure. This cable is being used for the DC feeds from a rectifier to a phone switch and batteries. I'll assume 24 volts.

[ September 15, 2004, 05:26 PM: Message edited by: msine ]
 
Re: Underfloor intallations

FWIW it is probable -48 VDC, and can be installed under a raised floor that is not used as plenum. The taps will need listed covers such as the ones used for "H" taps.
 
Re: Underfloor intallations

This is the basic rule:
300.3 Conductors.
(A) Single Conductors.
Single conductors specified in Table 310.13 shall only be installed where part of a recognized wiring method of Chapter 3.
Click to expand...
 
Re: Underfloor intallations

It is not installed in cable tray. Also I have been using 645.5.D.2 as support for the intallation of this type of cable under the floor but am not clear if the 48 volt DC power wiring falls under this article.
 
Re: Underfloor intallations

645.5(D)(2) refers to various acceptable raceways, not conductors laying on the floor.
In addition, are you sure you are compliant with 645.2, it is very restrictive?
 
Re: Underfloor intallations

Originally posted by msine:
As for the splice, Is the splice manf defining the use of the splice?
Click to expand...
Not sure what you are asking, but the "H" tap I used the most is T&B HTC50040-4WC. The "WC" indicates with cover. The cover is Listed (UL) for use with the 500-to-4/0 tap. Personnaly I prefer to use a "Christmas Tree" arrangement rather than taps on DC plants.

I certainly hope you are not trying to take advantage of Article 645 in a under raised floor enviroment. For one, you would not want a electronic disconnect installed on battery feeders to a switch.

-48 VDC is no different than any of power system in the NEC eyes, and the same rules apply.

In short you can run the cables under the raised floor on a cable rack provided the space is not used for any type of air handling, otherwise it would have to be enclosed, or the insulation would have to be Teflon.
 
Re: Underfloor intallations

This is a very interesting question, which is not asked very often.

No. 1. This installation is less than 50V and it provides power to equipment, it's not for remote-control or signaling (Article 725). Therefor this installation must be installed in accordance with Article 720 - Circuits and Equipment Operating at Less Than 50 Volts.

No. 2. The general requirement is that all installations must be installed in accordance with Chapters 1 through 4 [90.3]. These chapters require all conductors to be in a listed wiring method [300.3(A)] and splices must be contained in boxes [300.15].

No. 3. Chapters 5 through 7 can modify or add additional requirements to Chapters 1 through 4 [90.3].

Since Article 720 does not have any provision to allow single conductors, this installation is not permitted.

I have to get back to work and finish up my 2005 products, which I know many of you will enjoy.

God Bless,

Mike
 
Re: Underfloor intallations

Mike good to hear you chime in. Two points I would like to make.

1. A -48 VDC plant operates at 52-to-54 volts.
2. The splices I refered too are in boxes, plastic and listed.

[ September 16, 2004, 09:21 PM: Message edited by: dereckbc ]
 
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