mechanical countdown timer

[MrEd]

I am not sure exactly what to call this, but I am looking to buy a plug in timer (preferably a mechanical one), that I could use to turn something on, and then it would automatically shut-off after a preset amount of time (i.e. 2 hours, 6 hours etc). Most timers I have seen you can tell it to turn on/off and certain times of day, but in this application (roof heating/ice melt cables), I want to be able to turn them on, and know that no matter what, in X number of hours it will shut-off. They will only get turned on when needed, manually, but the timer will be the fail-safe to make sure they get shut-off.

Alternatively, I am wondering what the best way might be to deal with ice melt cables on the roof, as I go away on vacation. I can't just leave them on 24/7 for weeks on end, and for the person staying here, I can't risk that they turn them on and forget about them for days at a time - when there may not even be any snow/ice to deal with.

Suggestions?

 

[mole]

Mr Ed,
Search " Intermatic 6 hr timer". They make a 6hr and a12hr timer that should do the job.
JR

 

[ewdudley]

Here's a for-instance of the timer part of the problem, but you will also need a relay as well if the heater draw exceeds the capacity of the timed switch.

http://tinyurl.com/yeostpk

 

[pybyr]

Google "single shot time delay relay" and you may find some things that might suit what you are trying to accomplish.

 

[Gooserider]

They make a variety of different scale count down timer light switches, I've seen anything from 30 minutes or so, up to several hours, same basic form factor and will mount in the same size electrical box as a standard toggle switch. As I recall most roof deicers are fairly low power draw, so something like that might be all you'd need.

Gooserider

 

[RobC]

Spring Wound Auto-Off Timer
Never used these guys but this will give you 12hrs at 20A.
http://petesdepot.com/508873.html
Energy saving commercial timers use no electricity to operate and are designed to replace any standard wall switch, single or multigang. Automatically limits the ON time of fans, lights, motors, heaters, and other energy consuming loads. Rugged time-dial plate takes the abuse encountered in commercial environments. Time saving up front terminal connection with teeter type terminals and an easy press-on knob design ensure quick and easy installation. Brushed metal finish. 20A/120V AC 50/60Hz, 10A/277V AC 50/60Hz.

On a side note we had some friends in town that got a roof fire going with deicers. The fire dept. said that a couple of wires had crossed and started the fire, some how, not tripping the breaker. When doing the fall clean up, or chimney cleaning that might be another thing for the to do list. GREAT ! Check deicing cables, make sure their secure and not chaffing. I'm thinking that the cables work on resistance and the breaker would just keep throwing juice to them regardless of their condition.
On the up side they do a nice job at what their made for......
Rob.