Duct Smoke Detectors

[jrohe]

I have a couple quick questions for the contractors out there.

1. The company I work for has always specified duct smoke detectors to be furnished by the electrical contractor for installation by the mechanical contractor. Our stance is that, when a fire alarm system is involved, the electrical contractor will typically have a better understanding of what compatible duct smoke detectors are required (subject to our review during the submittal process). We are receiving feedback that mechanical contractors typically furnish and install the duct smoke detectors and the only responsibility the electrical contractor has is getting the fire alarm wiring to the duct smoke detectors.

2. When a fire alarm system is not present, we will typically design a 120 volt circuit to power the duct smoke detectors. We are receiving feedback that the mechanical contractors will typically pull duct smoke detector power off the control power transformer within the HVAC equipment and that 120 volt wiring is not necessary. I do not like the idea of potentially overloading the CPT.

What is your experience with these?

Thank you so much in advance for your thoughts!

Jason Rohe, P.E. (NE)

 

[goldstar]

I'm going back over 20 years to when I worked in NYC and did a lot of FA work so I apologize in advance as my info may be a bit dated. Typically, if an EC is installing a FA SYSTEM, that EC provides the duct smoke detector based on the FA company's system requirements. Generally speaking, the tin-knockers do not want anyone poking holes in their duct work so, they are given the duct smoke detectors by the EC and they install them in accordance with the mfr.'s instructions.. The EC then brings the FA wiring to the duct smoke detector and wires them.

Where no FA system exists and the duct smoke detector is used solely to shut down the AC unit, the tin-knockers provide those units and install them based on whatever specs are provided. As far as wiring the units, a lot depends on what a state's requirements are with respect to electrical wiring or if there are any jurisdictional limitations based on union rules.

 

[gadfly56]

I'm going back over 20 years to when I worked in NYC and did a lot of FA work so I apologize in advance as my info may be a bit dated. Typically, if an EC is installing a FA SYSTEM, that EC provides the duct smoke detector based on the FA company's system requirements. Generally speaking, the tin-knockers do not want anyone poking holes in their duct work so, they are given the duct smoke detectors by the EC and they install them in accordance with the mfr.'s instructions.. The EC then brings the FA wiring to the duct smoke detector and wires them.

Where no FA system exists and the duct smoke detector is used solely to shut down the AC unit, the tin-knockers provide those units and install them based on whatever specs are provided. As far as wiring the units, a lot depends on what a state's requirements are with respect to electrical wiring or if there are any jurisdictional limitations based on union rules.

Pretty much as goldstar says.

We do a lot of "parts & smarts" jobs, where we do only the final connections at the panels and the programming. We let the EC and MC fight it out otherwise, but it's typically fire alarm contractor supplies the parts, the mechanical contractor installs them, the electrical contractor wires them, and the fire alarm contractor does any panel connections and final programming.

I've seen the MC pull power off the control transformer as well for stand-alone units. You are not going to overload the CPT unless you are wiring up a humongous number off a single CPT. System Sensor's Innovair D4120 wired as 24VAC pulls 65 ma in standby and 135 ma in alarm. Johnson Controls Y65A13-0 has a 40 VA output (about the smallest I found), so that would be ~1.66 amps, or 10 duct detectors.

1. The "furnish and install" may be integrated duct detectors that come OEM in the unit. We get whipsawed on this from time to time where the EC says "supply the duct detector" and then surprise! the air handling unit comes with one. I wouldn't let the MC handle this except for the installation; how do they know what the fire alarm system needs? It's tough enough finding EC's who can figure it out.

2. For this, see above.