HVAC Duct Over Switchgear 4

[nightfox1925]

Is there any rule not to route an HVAC duct over a switchgear or a switchboard. I assume that there are instances where condensed air liquify to water and drift on the MCC/Switchgear/switchboard. In this case I may establish to avoid routing HVAC ducts over these electrical equipment. Any comments?

GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata

 

[rbulsara]

Yes, this requirement has been there in NEC (for where it is applicable) for years. It used to be in the Article for "Switchboards and Panelbpards". Now, I beleive it has been moved to Article 110.

 

[dpc]

If this is a "foreign" duct, it is not supposed to be there. However, if it there to serve the electrical room, or equipment, it is probably allowable.

 

[peebee]

I agree with rbulsara. Sorry dpc, but a duct is NOT allowed to be installed above the equipment just because it serves the room. It is certainly not unusual to request the AHJ for an exception to this requirement, particularly in cramped existing installations. But get it in writing....

Per NEC 110.26(F)(1)(a), "the space...extending from the floor to a height of 1.8m (6 ft) above the equipment or to the structural ceiling, whichever is lower, shall be dedicated to the electrical installation. No ... ducts... or other equipment foreign to the electrical installation shall be located in this zone."

The NEC Handbook goes on to explain that you can't put any ducts in that dedicated space, but you can put ducts in ABOVE that dedicated space so long as you drip pan them.

 

[dpc]

Yes, I should have been a little more specific.

I know what the NEC says, but you will have to get ductwork into the room, and in many rooms it will be difficult to do this without infringing on the space somehow.

 

[BJC]

I have had AHJs allow duct over switchgear if it had a "gutter" under it. It was not a good thing to do but in the particular installation it was all we could do.
The installation assumed that somehow the HVAC duct leaked water. The "gutter", a pan about 3' wide assured the water never got near the gear.

 

[EEJaime]

The required free area above switchgear was increased from 3 ft x the footprint of the gear to 6 ft in the latest code version as quoted by peebee. This area is to allow conduit to enter the gear and provide necessary working space. We tell our HVAC/Plumbing guys that nothing is allowed in our rooms at all unless it is serving the room. Often it is not physically possible to accomplish, but we try. This is quite common when we have motor control centers and distribution switchboards in areas such as in central plants or mechanical rooms. In some cases it is not possible to avoid the gear's footprint, in which case we often resort to drip pans, etc.... Most AHJ's are realistic enough to work with us if we make every effort to provide an electrician with as safe an environment as we possibly can, and protect the gear as best we can.

 

[jraef]

02101972,
Looking at some of your other postings in this forum, I guess that you are in the UK somewhere, in which case all these references to the NEC (US National Electrical Code) are pointless for you. Maybe some of our other UK members can lend their experience, but for future reference (and for the benefit of other readers who are thinking of posting), when asking about "rules" etc. it is a good idea to state where you are located. Rules vary from country to country.

JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
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[nightfox1925]

Jraef, I am presently in Kuwait and in this part of this world, BS or IEC is being used although I was very much inclined with ANSI/IEEE/NEC when I was still working in KSA.

Going back to the subject matter, the concern is that based from the HVAC details, the diffuser take out is facing downwards to the top of the equipment and this were the concern is. I am thinking of coordinating with the HVAC designer to re-route his HVAC ducts avoiding the top of the switchgears or placing the take-out diffusers on the sides of the duct (if this is possible). Any suggestions?

Another HVAC duct is routed above the MCCs but it this duct is for the In-take diffusers. This is not a concern since the air goes inside and there is no possibility of water drifting out...(any comments?)

Hoping for your suggestions since I am still arranging things up with our design contractor. Thanks



GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata

 

[waross]

The reason for the drip pans and the general concern for water impingment is also for condensation on the outside of the duct.
There are two possible problems;
1> The air in the duct is warmer than the ambient temperature of the space through which the duct passes.
If the ambient temperature falls below the dew point of the air in the duct, there is a possibility of condensation on the inside surfaces of the duct.
2> The air in the duct is cooler than the ambient temperature of the space through which the duct passes.
If the temperature of the air in the duct falls below the dew point of the ambient air in the space through which the duct passes, there is a possibility of condensation on the outside surfaces of the duct.
respectfully