48 volts DC under computer room raised floor

[mike anchondo]

I have a proposed project to run 48 volts DC (140 amps)from a rack mounted power supply in a computer room, under raised floor of the computer and back up into another rack with 48 volt electronic load with in the same room. My interpetation of NEC artcle 720 is that an article 300 wiring method is not required for this application. I have heard this is a commom practice in telephone central office applications. Any comments?

 

[dereckbc]

Re: 48 volts DC under computer room raised floor

What is the raised floor being used for? If you use it for air you got problems.

 

[mike anchondo]

Re: 48 volts DC under computer room raised floor

The raised floor is used for ventilation of the information technology eqyuipment.
I think I may have just woke up. Assumimg this raised floor meets all the criteria in Artcle 645 (Information technology equipment) which I believ it does, I may not be able to find a power cable that meets the fire ratings required by 645.5D5. Is this what Dereck is alluding too?

[ March 02, 2004, 06:06 PM: Message edited by: dereckbc ]

 

[dereckbc]

Re: 48 volts DC under computer room raised floor

If the raised floor is used for any kind of ventilation, you will have to use a raceway.

 

[ron]

Re: 48 volts DC under computer room raised floor

If the room meets the criteria established by 645.2, you may use all methods permitted by 645.5(D), which isn't much help.
If you do not meet the 645 criteria, you may use the methods permitted by 300.22(C).
To find a power cable "specifically listed for the use" might be difficult. Most just install in raceway.

 

[dereckbc]

Re: 48 volts DC under computer room raised floor

I do not suggest you try to take exceptions of 645. For example if your 48 VDC has batteries involved you would be required to have a disconnects on the batteries in addition to the rectifiers. Telco's avoid 645 like the plague.

I have used raised floor area's for DC power cable distribution along with signal cables without any raceways. But the raised floor had no ventilation involved.

Modern Telco practice is to use raised floor for ventilation, SRG, and AC power distribution. Everything else goes overhead on cable racks.

The only option I know of to install DC cables under a raised floor used for environmental air is to install in raceway outlined in 300.22 or custom order Teflon cable with appropriate ratings.

How did you come up with 140-amps. The minimum cable size will be based on the OCDP, so I assume 150-amp. That would be a 1/0 minimum. If the distance is over 35 or 40 feet, you will probable want to use something larger than 1/0 plus a frame ground. Your best bet is going to be RMC, EMT, FMC, liquid tight, or FMT if it has to be under the raised floor.

Good Luck