I have a small digital timer designed to replace a wall switch. As such, it runs on the 120VAC mains and has only a hot and a ground in (plus a switched hot out). Because it works without its own neutral wire, I assume it powers itself via passing a small amount of current through the load even when off.
Here is the manual: http://waterheatertimer.org/pdf/GE-15313-Manual.pdf
As you can see, it's rated for:
- Incandescent (Tungsten): 5A/600W
- Resistive: 15A/600W
The packaging specifically admonishes against using a CFL or LED load, and an inductive or motor rating is notably absent.
I was hoping to use this to control a small, "bathroom vent"-style fan until I noticed the rating. I'm going to get a different timer, but I still wonder what folks here think is the concern.
- Would back-EMF damage the electronic guts when the fan turned off?
- Would the (intentional) leakage current damage the fan?
- Are they using a semiconductor switch that requires a zero-crossing to turn off and the inductive phase-lag messes with that?
What is special about tungsten loads that warrants a much lower current rating than general resistive loads? Does it have something to do with filaments changing resistance as they heat?