[Solved] sense line of 2475s locked on by RAB Motion Sensor

[mink]

I solved a problem with the in-linelinc w/sense 2475s and my motion sensor (RAB stealth, commercial grade). The MS in the off state had a slight leakage current that was just enough to pull the yellow sense wire point up above the 2475s turn on threshold. Smarthome tech said they had seen this a few times but gave a less good solution than mine. The motion out ac from the RAB at the yellow connection in the OFF state was 70 vac. It likely uses a TRIAC to achieve a very small size with a 500W load rating, rather than a relay. Using a 22K ohm resistor wired from the yellow/motion load point to neutral pulled the voltage down to between 2-3 vac which is low enough that the 2475s switches off properly now. I calculated that this resistor load is about 0.400 Watts RMS using a 0.6 load factor for ac when the MS is outputting 120 vac. Just in case I used a 2 W I had lying around (actually the only 22K I had around ). FWIW a 62K did not pull down the voltage enough and my 2475s had an open circuit resistance of about 250K yellow to white(neutral). Hope this saves someone some time; I also told Smarthome as initially they told me the 2475s needed a true zero vac to shut off and I'd likely need an air gap relay. I was careful to protect the resistor but YMMV and use at your own risk.

 

Cheers