Smoke Detector Controlled Power Shut Off

Summary

This site describes a smoke detector controlled power shut off. If smoke is detected, power is shut off. It is currently in use with a 3D printer, but could be used with any device that has a chance of catching fire.

Parts Required

Smoke Detector - Kidde i12040 used but any similar one with a alarm output will work.

Smoke Relay Module - Kidde SM120X

Magnetic Switch - Powertec 71054 used but any similar one should work.

Panel Mount Fuse Holder - Cooper Bussmann BK/HKP-R , 6.3 X 32mm used but other similar will work

Fuse - I used Bussmann AGC-5 5 amp fuses. Use what is appropriate but not more than 10A.

Electrical Boxes - Three Leviton 42777-1GA Surface Mount Backbox, Single Gang, Grey, 1.89" used but you may chood different ones.

Standard Outlet - I used a nice white outlet and faceplate, but any standard 15A outlet may be used.

Wire Nuts - As needed

Wire - I used SVT Type power cords and cut the ends off. This is 18 AWG wire suitable for 10A. The relay module is rated at 10A

Here is the schematic diagram:

Theory of Operation

Power comes from the power plug and feeds the smoke detector and the relay module. The neutral wire also goes to the input of the magnetic switch. The red alarm wire is connected to the relay module. The hot wire goes through the relay module, in the common blue wire and out the normally closed contact to the orange wire. That goes to the hot side of the magnetic switch input. The output of the magnetic switch goes to a standard outlet.

The magnetic switch is designed for power tools. It has a big green on button that latches the switch on. If the really big red paddle is hit, or if power is removed, the switch will open up and not turn on again until the green on button is hit again. It is designed so that if power fails, and no one remembers to turn off the power tool, it will not restart when power is restored.

Normally, the smoke detector senses nothing and the relay module keeps the normally closed contact connected to the common. You can turn on the magnetic switch and powe stays on. If smoke is detected, even for an instant, the smoke detector sends a signal to the relay module. That opens up the normally closed contact. That causes the magnetic switch to shut off and it stays off, even if the smoke dissipates.

This uses all UL listed components. I believe the SVT type power cords are appropriate for this usage.

Note

If this is connected to a standard uninterruptible power supply, and power glitches, the change over to battery power will likely not be fast enough and the magnetic switch will drop. An online type UPS will likely be required.

Example Usage

Here it is installed on my 3D printer enclosure. The smoke detector is mounted on one electrical box inside. The switch and outlet are mounted outside.