On the question of safety, there is no difference. Both proportional and ON/OFF can fail.

Rule of thumb for controller choice:
If you are using an ON/OFF controller on a setup, and the controller relay is clicking on and off more than once every 30 seconds, then a proportional controller is a better choice for your setup in terms of relay wear. Note that proportionals cannot be used for fans or heaters with moving parts, like space heaters.

When proportionals fail, they often fail ON. The most common cause - voltage spike or inherently defective output power device (triac, SCR). A surge protector is not a bad idea.

For safety, an ON/OFF in series with a proportional's output is the real way to have a safe system, as described by the other poster in this thread.
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Mark

[ Hide Replies ]

• Is a proportional thermostat safer? - rudykirk, Sat Oct 4 16:06:00 2008
• Absolutely!!!! - rainbowsrus, Sun Oct 5 00:30:06 2008
• RE: Absolutely!!!! - Bighurt, Sun Oct 5 12:43:25 2008
• RE: Absolutely!!!! - caz223, Mon Oct 6 01:31:08 2008
• RE: Absolutely!!!! - BobS, Mon Oct 6 11:15:29 2008
• Solid state components fail too! - caz223, Mon Oct 6 11:40:56 2008
• RE: Solid state components fail too! - BobS, Mon Oct 6 12:06:07 2008
• RE: Absolutely!!!! - caz223, Mon Oct 6 12:57:50 2008
• UPS ?......... - BobS, Mon Oct 6 13:28:40 2008
• Uninterrupted Power Supply - Bighurt, Mon Oct 6 17:28:42 2008
• Thanks np - BobS, Mon Oct 6 20:56:45 2008
• ARS racks - caz223, Mon Oct 6 22:02:53 2008
• RE: Nice responses - markg, Mon Oct 6 13:45:46 2008
• More.... - rainbowsrus, Mon Oct 6 17:34:29 2008
• RE: More.... - caz223, Mon Oct 6 22:28:52 2008
• RE: Rule of thumb - markg, Mon Oct 6 13:58:01 2008
• RE: Rule of thumb - caz223, Mon Oct 6 22:36:26 2008
• RE: Rule of thumb - caz223, Mon Oct 6 22:58:32 2008
• kill-a-watt - caz223, Mon Oct 6 23:04:46 2008
• They call them dimmer switches.... - caz223, Mon Oct 6 23:20:44 2008
• RE: They call them dimmer switches.... - markg, Tue Oct 7 12:39:07 2008