Non plenum cable below raised floor allowances

[AJSmith135]

Context - I'm in a situation where an EPO for a datacenter is getting removed by a project due to the distribution board where all of the shunt trips were getting removed.

In addition to this, a bunch of data cable was to be installed during the outage. The datacenter manager incorrectly purchased non plenum rated cable that is to be run under the raised floor. Below this raised floor is considered a plenum in this case as it is pressurized to support airflow to the datacenter.

None of this data cable is to be run in a plenum rated fully metal enclosed raceway

We are trying to comply with 645.10 (B). I believe we meet all the requirements except (5):

"cables installed under a raised floor, other than branch circuit wiring, and power cords are installed in compliance with 645.5(E)(2) or (E)(3), or in compliance with Table 645.10(B)."

Table 645.10(B) refers to the general requirements for data cables (Article 800). In short the cables will need to be enclosed in metal raceways (essentially refers to article 300.22 (C)). Doesn't apply to us in this case due to the lack of enclosed raceways.

Article 645.5(E)(2) parts (4) and (5) say data cables in a below raised floor plenum can only be non-plenum rated "where the air space under a raised floor is protected by an automatic fire suppression system".

This datacenter has an automatic fire suppression sprinkler system at the ceiling of the datacenter. it does not have any sprinkler heads below the raised floor, but there are perforated tiles used for airflow.

My ultimate question being, does this count as protecting the air space below the raised floor?

My hunch says no. The code seems to imply what I believe as well. Unfortunately, I cannot find anything across several code books that explicitly defines that the protection above the raised floor can or cannot be considered for protection below the raiser floor.

The best I found was NFPA 13 article 8.15.1.2.2.1 which says (paraphrasing) that concealed spaces of noncombustible and limited-combustible construction, even with small openings such as those used as return air for a plenum, with limited access and not permitting occupancy or storage of combustibles shall not require sprinkler protection.

non-plenum rated cables would be the combustibles making this exception untrue for us. however this still doesn't explicitly state what I'm looking for as some could still interpret this space as protected from the above system.

Side note - as far as I understand, keeping the EPO in place would still not waive the requirement to have either plenum rated cables, or sufficiently protected non-plenum rated cables as defined in 645.5(E)(2) or 300.22(C) correct?

Basically the only time non-plenum rated cable can be under a raised floor plenum, is if it is in a plenum rated conduit per 300.22(C), or one of the exceptions in 645.5(E)(2)(4) w/ automatic fire suppression system protection (assuming all of 645.4 is also met).

 

[suemarkp]

I believe so. None of the server rooms I had were NEC 645 compliant (it is an optional section). That being said, the rooms with underfloor smoke detection and fire suppression (halon or CO2) were the only ones with non plenum cable. At one time we could hve a limited amount of non plenum cable if we had underfloor smoke detection. The fire marshall said we could have this much, putting his hands together a making a circle with his fingers. Not sure what document drove those decisions. I asked for the guy with the biggest hands.

 

[Fred B]

The reasoning of the plenum rating is the off-gassing of toxic fumes from heating or burning of the sheathing. In an air plenum the toxic fumes can be carried well beyond the source of heating or burning, and overwhelming any person in the area served by the plenum prior to a fire even being detected.

Don't know for a fact related to fire suppression in the plenum and how rapidly it is deployed as to whether it would mitigate the toxic fumes from entering. My limited experience with fire is that even when dousing a substantial amount of smoke is still present

 

[Fred B]

I believe so. None of the server rooms I had were NEC 645 compliant (it is an optional section). That being said, the rooms with underfloor smoke detection and fire suppression (halon or CO2) were the only ones with non plenum cable. At one time we could hve a limited amount of non plenum cable if we had underfloor smoke detection. The fire marshall said we could have this much, putting his hands together a making a circle with his fingers. Not sure what document drove those decisions. I asked for the guy with the biggest hands.

Seems this would have to be in concert with a air intake and exhaust shutdown linked to the fire detection/suppression system.

 

[ron]

You are out of luck. They need to be plenum rated.

In addition, many AHJs will arm wrestle you to the ground to remove an EPO once it is installed. They will look for liquidtight under the floor, and there is almost always someone that puts some under there, even though FMC is just as good in this application.

 

[suemarkp]

Seems this would have to be in concert with a air intake and exhaust shutdown linked to the fire detection/suppression system.

These werent fully 645 compliant and may have been grandfathered. The underfloor chiller was in the same room and EPO shut it down. Building air still came in through the ceiling.

We also had plenty of liquidtight under the floor too, even in areas without fire suppression. I think we had a low smoke zero halogen vatiant of LFMC, but finding those details was difficult. Later changes were done with regular FMC.