I have wired a motion detector floodlight with a single pole switching the
feed, and a 3-way spdt switching the hot that feeds the sensor lead and the
other goes straight to the lights bypassing the sensor. however the sensor
switchleg is still connected to the light leads so I am wondering if this
causes a "backfed" condition to the sensor when the switch is bypassing the
sensor. If the sensor can be activated in reverse, then the relay would
close and send power back down the other traveler leg of the 3-way? The
light is wired this way because the "toggle" function of the light was not
working reliably to switch modes from manual to auto.

The other main question I have is if this might be damaging the sensor to
have it wired this way. The only other way I could think of to cut power to
the sensor switchleg when the 3-way is set to "manual" is to install a
normally closed relay at the box, but I'm not sure if that is even permitted
by NEC.

Thanks for any help. I'm not good with text diagrams but here's an attempt:

====feed====\spst====\spdt====sensor====light
. . . . . . . . . . . . . . . . . .|=====bypass====|


[This message has been edited by part timer (edited 05-14-2004).]

I have done the same thing with a 3-way (SPDT) switch set up for automatic or manual control. This setup works fine with some sensors, but will destroy others. Heath/Zenith units in particular will be damaged by connecting a hot feed to the output terminal. It seems to destroy the output stage (TRIAC), in such a way that the motion sensor will never turn off.

If you are going to use this kind of arrangement (which is quite useful in some applications), I would suggest using a motion detector which uses an electromechanical relay for the output switching. These can be identified by an audible "click" when the light switches on or off.

Is there a source you are aware of to just replace the detector unit with a type of the kind you described? I can hear a click on this type of unit but I have heard a click on the Heath-Zeniths as well.

Some of the H/Z units seem to have relay outputs, and some are solid state. I have had good luck using the units sold by Red Dot/Mason, available at the big organge box stores.