Wiring Methods Under Raised Floors

[DJFNEC2005]

Hi Guys,
My question is a 2 part question to help me understand wiring methods under raised floors a little better. Thanks in advanced for all replies.

I'm bidding on a project that has a couple of Data room raised floors and I am trying to understand why I see most of the power wiring methods under these floors installed in liquid tight flexible conduit with devices installed in whether tight FS boxes and covers?

Going through the NEC I see that MC Cable is allowed and MC Cable is also plenum rated. The project I'm bidding does not fall under section 645 because it does not meet one of the five requirements for fire rated walls so I am referring back to section 300-22. The room does have its own HVAC system and a pushbutton to shutdown all equipment within it.

Questions:
1. If not required by the project specifications to be installed in a specific wiring method would MC Cable be acceptable to meet NEC?

2. Why do I see most power wiring under raised floors are installed in Liquid Tight conduit? Is it a NEC requirement that I'm missing or possibly just the requirements of the project specifications?

Thanks Again

 

[cosmos]

Liquidtight conduit may have been used if there were sprinklers under the raised floor.

 

[suemarkp]

I don't think it is required. Many data centers have HVAC units which use chilled water. These can leak. But just because something can leak doesn't mean this is a wet area. Some of these areas has under floor water detectors. Perhaps there was a fear that a leak would go undetected so it could be wet for a long time.

I've seen many data centers with liquid tight flex, or EMT with rain tight compression fittings and FMC whips to floor boxes. I don't know if in years past LFMC was allowed under the floor unsecured, as that is how they were typically done. We can't do that any more.

For me, I'd just run flex metal conduit and secure it at the required intervals. An ideal floor would be one that has bolts in a 4' grid so you could easily unbolt conduit clamps, relocate things, and bolt the conduit back down again. MC is probably OK too, but you lose the option of changing conductors when growth occurs (or the customer decides they want a superneutral or something).

 

[Sierrasparky]

I don't think it is required. Many data centers have HVAC units which use chilled water. These can leak. But just because something can leak doesn't mean this is a wet area. Some of these areas has under floor water detectors. Perhaps there was a fear that a leak would go undetected so it could be wet for a long time.

I've seen many data centers with liquid tight flex, or EMT with rain tight compression fittings and FMC whips to floor boxes. I don't know if in years past LFMC was allowed under the floor unsecured, as that is how they were typically done. We can't do that any more.

For me, I'd just run flex metal conduit and secure it at the required intervals. An ideal floor would be one that has bolts in a 4' grid so you could easily unbolt conduit clamps, relocate things, and bolt the conduit back down again. MC is probably OK too, but you lose the option of changing conductors when growth occurs (or the customer decides they want a superneutral or something).

In the past I've used emt HR's to 4's deeps or 5's boxes and whips of liquid tight to the racks. We used the liquid tight only because the stuff doesn't break open as easy. We found this better in the long run than data centers run with MC/ Ac cables.

 

[ItsHot]

Sj /so

Sj /so

I see a lot of sj /so cord under raised floors.