Wiring – use a standard on-off switch for lights on a magnetic low voltage transformer

I found a solution.

The first photo below shows the light fixture removed from the monorail, but fully assembled. The second photo shows the shade and bulb removed. Also, the fixture has been unscrewed from the mounting bracket.

I used an ohm meter to check continuity on the fixture, and decided there was an intermittent connection between the lighting fixture and the mounting bracket (the two pieces that are unscrewed). Screwing the two pieces together is supposed to make a solid connection such that the circular top of the fixture (the area right above the black band) touches a conductive area inside the mounting bracket. The connection between these two spots has become loose over the years (I don’t know why).

I took some thin sheet metal (actually the bottom of a can of mixed nuts) and cut out three circles the diameter of the top of the fixture. I carefully stacked the three pieces of metal on top of the area (above the black band) and screwed the two pieces together. The electrical connection is now tight, and the light has been working perfectly for the past three weeks.

[UPDATE 3/12/15: As requested, here are more images and notes. If you use the metal from a can, you should probably sand it to remove any clear coat on the metal. I used heavy duty scissors to cut the metal. The metal discs are cut slightly smaller than the diameter of the post they sit on top of. I think you have to prevent the discs from touching the sides of the light when you screw on the top piece (to prevent a short). Also, the light stopped working again after about 8 months. So I made a second fix where there was a loose connection on the side of the light. I cut out a crescent-shaped piece of of metal (shown by itself in the next-to-last photo) and shoved the shim into the loose joint (final photo). I might trim up the crescent shim when I have time. The light has been running fine since this second fix.]

The basic problem is that the occupancy switch that you chose to purchase is one designed to be able to work in series with the load attached to it. If the attached load is too small (too low of wattage) the switch assembly does not get enough power to operate correctly. For the particular model you have this is on the order of 40 to 50 watts of minimum load. From a technical standpoint it kind of sucks that they work this way BUT they are designed to work in place of a simple light switch that is in in series with its load.

Your Radio Shack relay does not come close to representing a 40-50W load on the switch so the only other way is to add some additional load in series with the switch (i.e. equivalently in parallel with the relay coil). As you have come to see this is not a very satisfactory solution and some other scheme needs to be found.

The best situation in this case is to acquire the alternate type of occupancy switch as mentioned in that thread that you linked. That type of switch has a live AC lead and neutral AC lead connected to it to power the switch unit irrespective of the size of the load. A separate output connection goes off to the load you are trying to switch. This type of switch may take a little re-wiring in your garage but that should be easier than trying to wire in the kludged extra load that the current switch requires. If you choose to deploy this improved version of the switch you will be able to remove the Radio Shack relay from the installation.

To make yourself feel better about the fact that you now have an extra occupancy switch you could pick a room in your house that has a tendency to get its light left on accidentally and install the extra unit in place of its light switch. Maybe this is a bathroom the kids use or a far closet that does not get used often.

BTW

It looks like Leviton now has a whole slew of different model occupancy switches that are also designed for single pole switch replacement but have removed the minimum load requirements. These do not require a neutral wire connection but do require a GND wire connection.