161123-2422 EST
tkbEZ:
You have provided inadequate information. What is your definition of "ground", and where was measurement made to ground? Why is ground important to a sensor other than to put metalic parts at approximately earth potential under normal conditions? Earth here means putting a screwdriver in the dirt outside the home in any one of many places, also probably meaning any copper or iron water pipes.
By ground do you mean the EGC at the sensor or LED lights, or at the ground bus in the main panel, or at the earthing rod or other element? Why are you using the EGC at the sensor for sensor power? Hot and neutral at the sensor should be used for sensor power. The EGC at the sensor should only be used for safety purposes. There are probably manufacturers of sensors that use the EGC for one of their power wires for the sensors. But they should not.
If the EGC at the sensor and the LEDs is the ground you are talking about, then you need to check its voltage relative to the main panel ground or EGC bus and the neutral bus in the main panel. If you see more than a fraction of a volt. I expect less than about 0.1 V, then go find the problem. There can be some loads with filters, such as switched power strips, that may have capacitors to EGC and thus cause EGC current and voltage drop. Also there could be stray magneyic fields, improperly wired neutrals, that cause an induced voltage in the loop of your test lead to the main panel and your EGC being measured. But this will not be multivolts in a home.
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