Let's clarify some things. (This is about sirens)

[MOStormChaser]

That's why. If a Whelen runs longer than 5 minutes, it will shut off. It does that to protect the components of the siren and the controller.

[gman 1]

Thank you guys so much!!!

[uncommonsense]

That's why. If a Whelen runs longer than 5 minutes, it will shut off. It does that to protect the components of the siren and the controller.

No. It's on a timer. Period the end. There's nothing stopping someone from immediately restarting the unit.

[MOStormChaser]

That's why. If a Whelen runs longer than 5 minutes, it will shut off. It does that to protect the components of the siren and the controller.

No. It's on a timer. Period the end. There's nothing stopping someone from immediately restarting the unit.

That's what I meant to say. Sorry and thanks for clearing that up.

[rdfox]

Yeah, in general, sirens are set to automatically shut off after 3-5 minutes through their controllers, to prevent overheating damage to drivers (for electronic sirens) or motors (for electromechanical sirens). Back in the Civil Defense era, most government buildings (including libraries) had posters up on public billboards that explained the signals for the sirens, at least in my area, including that there would be no all-clear signal given for a tornado, and "if you hear more sirens, it means more storms are coming".

While I've said that certain beasts (like Moore, Oklahoma, in 2013, and the Rochelle EF4 from last week) were "run 'em 'til they die!" situations, that really meant more that they should have hit the start button again *immediately* upon the sirens timing out... and such situations where I figure it's worth accepting the possibility of damaging the sirens are extremely rare, because if you DO burn out a siren by having it sound constantly for a monster like one of them, what happens if you get another one five days later?

[flatlandsparky]

Whelens default to a 3 minute cycle time (adjustable to a max of 5 mins) Same thing with ANY siren on a timer. Very few places run them continuously during a storm.

Logan countys ema here in Colorado installed radios in every town in the county with sirens. Last summer, (first year with county wide simultaneous activation) Sterling's dispatch would send out Alert tones, and Fleming's two sirens ran at least 20-30 minutes each activation not including the Friday 30 second weekly test. I've heard the SD-10'S motor is starting to go out according to local firemen. Sorry if this seemed to derail the topic.

[Daniel]

AR and AF timers had a timing motor that made one revolution every three minutes before cancelling itself.

[Ziginox]

AR and AF timers had a timing motor that made one revolution every three minutes before cancelling itself.

And there was also a variant of each that ran for five minutes, I think it was AR-5 and AF-5 but I'm not sure.

Anyway, back to the sirens shutting off thing. As mentioned earlier, sirens don't run constantly because otherwise their longevity would significantly drop. All electric motors have a duty cycle, and I believe (Ian can correct me if I'm wrong here) that most of the ones used in sirens have a duty cycle of around thirty minutes. If they run too long the motors will overheat and all sorts of nasty stuff happens (field winding insulation melting, causing the wires to short, etc.) Electronic sirens have a driver that moves, which creates heat. Run that too long and it melts.

There's a video of a T-128 on fire after getting stuck on somewhere, but I can't seem to find it right now.

[murrfarms]

All electric motors have a duty cycle, and I believe (Ian can correct me if I'm wrong here) that most of the ones used in sirens have a duty cycle of around thirty minutes. If they run too long the motors will overheat and all sorts of nasty stuff happens (field winding insulation melting, causing the wires to short, etc.) Electronic sirens have a driver that moves, which creates heat. Run that too long and it melts.

Correct. The only exception that I'm aware of is any of Sentry's AC-powered sirens, which have fan-cooled motors rated for continuous-duty operation. A lot of ACA's omnidirectional sirens could have easily been continuous-duty (or fairly close to it) as well if they had only provided enough clearance in the siren's bracket/shroud design on the Screamer and Banshee, for the motor's cooling fan and its cover to remain in place. Both of those sirens' motors have a little stub shaft poking out the opposite end bell, which in normal applications is where the fan would be mounted (under a cover) to provide airflow over the motor for aiding in cooling, and on rotational ACA sirens is where the gearbox would be driven from. What their reasoning was for removing those components and not incorporating that into their siren designs is beyond me.

[shodowhater]

And there was also a variant of each that ran for five minutes, I think it was AR-5 and AF-5 but I'm not sure.

Yup, that's it.

There was also video of a T-128 on fire after getting stuck on somewhere, but I can't seem to find it right now.

http://youtu.be/UDU5mkIi1-E