Should we disconnect the cable from its source in case of fire ? 1

[miblec2009]

Hi Guys,
I have been looking days and days for something in the code to help me in my inquiry but it seems it will take long time, so i decided to take it short to here for any help , I have in my project 122 Air Handling Units suspended to the ceiling of an IKEA Mall here in Cairo, Egypt & at the original design the consultant is putting a DOL Stsrter (BESIDE EACH AHU) in a seperate enclosurem and it is needed to shut down the AHU in case of fire by the BMS @ area or zone having fire, so you will shut down all AHU's in areas having fire, but i have already the cable feeding these AHU's a Non-Fire Resistant Cable, moreover when the BMS disconnect the starter in case of fire at that zone, you will still having power at the feeder cable feeding the starter itself? is it logic? we discussed with the consultant to transform the power panel in the electrical room suppling these units to be an MCC and cancel all these starters, i.e. centeralize the feeding and control from one panel located in the electrical room, the consultant is convinced but he needs any support from any code NEC or NFPA saying any recommendations regarding. 1) centeralizing the feeding and control of the units. 2) The feeder cables have to be changed to Fire Resistant Cables? 3) The most wanted code article is the one recommend that in case of fire we should disconnect the power cable from its source, and its not recommended to leave any cable (not fire resistat) having power in the same area having fire.

Thanks & Best Regards.

 

[DRWeig]

Are the circuits to the air handling units not in metal conduit?

I'm in the US. I have never seen a code requiring any of this, nor have I seen it done. All the other circuits in the building are still energized too. In my experience, power must be left available to the air handlers and tied to a firefighter's panel that is in a ground-floor area separated from the building. Are your air handlers not sources of outdoor air and possibly part of the smoke control system?

To my knowledge, the only requirement for fire protection of a circuit is the one feeding a fire pump.

Wait for others to respond, though. Your local codes may be different.

Best to you,

Goober Dave

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[miblec2009]

Thanks for your quick reply, but what i need to confirm that its recommended for sure to not allow any cable energized in case of fire except for the critical loads you have which is supposed to be fire rated cables, but all my feeders to the AHU's are normal PVC cables and by that way if i will keep the design, i'll have the power to the starter beside the AHU is still energized and the disconnection only is from the starter to the AHU, and all this cable About 150 meters long to the AHU starter, will be under fire and also energized which causes the increased risk of fire and cable smoke and add more danger, so i need to disconnect from the power panel itself which is the source of this cable, and unforunatly it is a normal power panel, contains only Miniture circuit breakers, so our suggestion is to transfer the starter (which is beside each AHU) to be inside the power panel, which means transferring the power panel to be MCC, by this we avoid keeping(non-fire rated cable) to be energized during fire.



Eng. Mohamed El Sayed
Technical Office Manager

 

[waross]

ou are adding a level of complication and risk by moving the starters away from the area of the air handlng units. Under some codes, you will still have to install a local disconnect switch. When the starters are remote from the AHUs trouble shooting becomes more difficult. Techs tend to take short cuts which may add hazards to workers.
Air handling is shut down in fire situations to prevent smoke and toxic fumes from being spread to areas not affected by the fire. Shutting down air handling also avoids the possibility that fresh air may be fed to a fire.
The fire rating or lack of fire rating on a cable has nothing to do energization. It has to do with the amount and the composition of the fumes given off by the insulation when subject to flame or high temperature. It may also be related to the ability of the insulation to support combustion.
Any plastic insulated cable subjected to fire will fail. Then the branch circuit protection is expected to disconnect the failed cable.
A non-flame rated cable subject to fire will give off quantities of noxious fumes even when it is de-energized.
No need to relocate the starters.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[miblec2009]

Waros,
The cables already in a cable tray, and its protected by normal miniture circuit breakers and not MCCB's and it will take time to disconnect due to overlaoding by the heat, in many malls all AHU's is supplied by centeralized MCC's and also fed by a fire rated cable, and by the way there is already a disconnect switch (GE) NEMA 3R for each AHU. We need urgently to manufacture the Centeralized MCC's instead of the seperate starters (It is a decesion have been made by the main contractor - A money wise issue) and the consultant will approve this solution if we get any code saying even in general that it's preferred to disconnect the cable from its source, do we have something like that or even close to that meaning IN ANY CODE ?? & sorry for disturbing and wasting your time man.

Eng. Mohamed El Sayed
Technical Office Manager

 

[waross]

The use of fire rated cables has to do with the building and fire codes. In some areas of a building fire rated cables must be used to limit the exposure of persons to smoke and fumes and to limit the spread of the smoke.
If the cable is in a space used as a return air plenum then fire rated cable must be used.
There are advantages to local starters and there are advantages to central MCCs. The control scheme may favour one system over another. If the mall has or may have in the future a computerized system to control the heating and cooling and ventilation, then a central electrical room with MCCs may be the best choice.
If you have a lot of individual tenants, each responsible for their own electric and ventilation systems then local starters may be a good choice.
If you wish to justify an MCC installation, then suggest the greater ease of interfacing with a central control computer and the cost advantage.
Sorry I can't help with codes.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jghrist]

I agree with Bill. The fire rating of the cable has nothing to do with your requirement for shutting down the AHUs in case of fire. You need to install some control to shut off the AHUs when fire is detected. It shouldn't depend on the fire burning up the cable to trip the MCCB to shut off power to the AHU.