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How can I test a monopole timer switch? Question
I have a Lutron Maestro MA-T530G.
I installed this to control an old bathroom fan which was malfunctioning. I'm planning to replace the fan anyway later, but I wanted to have a timer in the meanwhile. After some time of working as expected, the fan stopped working entirely.
I know for sure the fan is broken, because I replaced the timer with a regular switch and it still won't work. It's probably because the low-voltage timer draw didn't play nice with the fan, but that's beside the point. I'm worried now that the timer is dead also, so I'd like to check if it is.
Best way I can think of is to wire it to a light and try it. But I don't want to needlessly mess with house wiring. Regular switches are easy to test with a multimeter, but I guess the time requires a current supply to switch on at all. I tried holding it down and using a multimeter, but got no contact - so either the timer is broken or that method doesn't work.
Is there a better way to check if it works?
2 answers
Key information is in the installation manual. Unfortunately, as is often the case, Lutron doesn't have easy-to-find installation manuals on their own web site. Fortunately, Home Depot does.
This is a "leak current through switched hot to power itself" timer. The first clue is that it only works with fans (up to 3A) or incandescent and halogen lights (up to 5A). It won't work well, if at all, with fluorescent or LED lights because it leaks a bit of current through the switched hot wire to power itself.
Because of this design, you can only properly test functionality when connected to a functioning fan or an incandescent or halogen light fixture. Checking with a multimeter won't get you anywhere.
I would recommend replacing with a different type of switch. Options:
- A mechanical timer. That is actually quite common. The only catch is that they often make some sort of humming or ticking sound. But they work with any type of wiring because they don't use 120V electricity to power themselves.
- A neutral-required electronic timer. That is identified by (a) requiring neutral in the instructions (usually quite clearly, because they want to avoid returns) and (b) LED compatibility. If you put in a combination fan/light then you'll want the LED compatibility. But even if you put in a simple fan, this is a more reliable setup. But it requires the correct neutral in the switch box. I say "correct neutral" because if the same switch box has a neutral in it but for a different circuit then you can't use it to power a switch - mixing up neutrals between circuits can cause all sorts of serious problems and doesn't work with GFCI.
- A humidity sensor. This has the same issues - neutral required is best, which means only if you have a neutral. Advantage: automatically turns on (many have manual operation as well) so if you have people who don't remember to turn on the fan after a shower, this solves the problem.
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You can't test such a timer with just a voltmeter. It is possible that the timer requires the load to try to draw some minimum current, which a voltmeter probably wouldn't. Or, the timer might have a little leakage current, which would cause the voltmeter to read the full voltage even when the timer is off. A lightbulb would be a good load for testing the timer.
However, that's a terrible timer. It claims to work with "efficient bathroom fans", but gives no specs on power or current that it can switch. Since they won't tell you what it actually does, you don't know what you're buying and under what conditions it is supposed to work. Run away.
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