I have never installed a switch and never seen one. You state its a code rule, can you please cite the code reference?
As an aside, where I work now we have many smoke purge systems and the dampers to the outside are held closed with a spring and when theres a fire it powers the damper open so the smoke can escape.
As a second aside, how long do damper motors last that are energized all the time? We had some complaints of no AC and/or no heat that was discovered to be motors that no longer worked (burned out maybe?) and had sprung shut during normal operation. These were about 20 years old. This also caused mold problems in one building due to lack of airflow.
Drillman, Ok, your questions got me digging through my codebook, (which is a good thing).
I guess that I was looking at the damper as a motor that would require a disconnect under 430-IX. However, after thinking about it that might be an incorrect classification of a smoke damper. It might be better described as an appliance in which case the OCPD will suffice as a disconnect, (422.31(A)). There is no restriction for line of sight or distance in 422???
I'm willing to learn here and could very well be wrong so your opinions are welcome.
The only dampers that I have dealt with are powered open, spring closed. As far as motor life with the power applied, I really don't know. That is the way they are designed to work, and I've never had to change one out. That would probably fall to the HVAC guys in any case.
"An interesting subject, I have never thought to, or have seen disconnects for smoke dampers and my first reaction is "bad idea""
I've been putting them in on dampers that are power opened, spring closed. The only hazard I see is that if the switch is opened there can be no airflow through that ductwork. It does make service work easier and safer.
But if it's not code required then I have been costing the company money installing switches that are not needed and may not even be a good idea????? If that is the case then I'll stop doing it.
I am not saying the code does or does not require a disco but have never seen one or even seen it in the plans.
Intresting thing about the smoke evac fan discos. We have some of those and you are correct that if someone turns them off or an overload opens or a belt breaks the fire alarm panel has no way of knowing this.
Just another reason to remember that smoke evac systems need to be maintained and fully tested on a regular basis.
As for the fail open or close thing, here the wires that energize the evac fan motor starter also energize the damper motors. So they all spring to normal mode and energize to fire mode. It does not make sense to me either. I guess one could say that if theres theres no power, the fan will not run and the dampers are not needed.
We have some gravity dampers, those tend to stick open after a test and let in cold/hot air depending on the season.
Last but not least, if a damper motor burns out and spring closes the damper and closes off the air flow and nobody notices for awhile (possible in a big building) there may end up being a mold problem. That did in fact happen in one of our buildings.
After reading this and recently having the same discussion between our mech. insp, elec., insp and fire it came down to this- fire dampers are part of the mech. equipment and requires a safety switch for service, appliances per mech. code include materials,fittings, devices,and apparatus used as partof or in connection with installations regulated by this code.
A couple of thoughts…I am not up on NFPA 72 or its regional variants.
It may be appropriate to install switches that can be locked in the closed position.
Also, supervisory contacts to generate a trouble alarm on switch opening may be desirable for the subject disconnect switches. ‘Stock’ auxiliary contacts are routinely available for heavy-duty XOP disconnect switches, but that might not be the case with light-duty versions. An acceptable substitute may be to use an otherwise unwired switch pole for supervision.