strange electrical problem

Hello all,
This is a long explanation, but basically I am looking for what could cause a light bulb to light up only dimly. Could it be a short to GND or some other leakage?
Here's the situation. I have a three floor apt. building with a common panel feeding a lighted fire escape. They are not switched, always on for safety. On this same circuit, before reaching the stairwell is a single light in the basement. No problems with this light. There are 2 other leads I have not yet verified where they go (either disconnected or feeding something I am unaware of). On the outside of the stairwell is a spot light with a motion sensor to go on at night when you go around back. The problems started with the spotlights remaining on all the time. Not knowing the age of the sensor I replaced it, wired as directed on the package. Since it was summer, I don't know if it ever worked properly. I was unable to test it fully. Later, I noticed the spots were very dimly lit. The stairwell lights were full power and lit properly. I removed one spot and the other would light fully. I left it that way, but still unsure if the motion sensor is working properly. Again weeks later, now the lights are out in the stairway. I've been using fluorescent bulbs. The bulbs light up in other sockets on another circuit. I replaced one with a regular incandescent and it is barely lit.
I test the motion sensor by turning off the breaker, then turn it on. The single spot lights up brightly, but the stairwell lights are out (except for the dim incandescent). Then after 2 mins. the spot goes out and so does the dim bulb!
The stairwell lights are NOT switched by the sensor. I have removed the sensor completely, and these bulbs are still not lighting up.
How can the sensor affect the stairwell lights? Why would they not get enough power to turn on completely?
Obviously, I am not an electrician, but I do have a clue how this stuff works. I'm about ready to re-wire the darn stairwell.
Any advice?
Greg
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There is clearly a voltage drop at the fixtures you are having problems with. I am not sure I understand exactly what happens when, but I would start by taking the motion floodlight out of the loop so you can eliminate (or isolate) it as the problem.
I suspect a fixture in the middle of the run was miswired... e.g. you wired it in series rather than in parallel (not something you normally think about with 120V AC wiring!!). That is, if you have a fixture in the middle of the run wired like: hot->fixture black -> fixture white -> hot out, then tied the in & out two neutrals together, you might find that things in the series before that fixture worked, but things afterward barely work. I have never tried this sort of thing (as it is clearly wrong) so can't say for sure that's what might happen, but it seems logical that this could result in a things before it working normally, and things after it getting very low voltage

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gccch wrote:

The dim lights are caused by one of two things. You may have a floating ground or you have a poor (high resistance) connection somewhere between where you have good power and where you have the problem. BTW a floating ground is also a type of bad or missing connection.
I really can't get a good idea of what is going on with your description.
Try this. Find the circuit breaker or fuse the controls the light. Turn it off or remove it. Now check to see if either of the lights still work. If they are now both off, I would suspect a poor connection or two. Someone need to open up each box along the way including the ones the lights are attached to and check each connection.
If one is now off and the other is on, that sure sounds like a floating neutral.
How comfortable are you at going into the service box. If not totally comfortable, then it is time to call in the pro who will likely fix the problem in just a couple of minutes.
--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math
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Greg, This is difficult to diagnose over the internet with the small amount of information given, but here are my thoughts:
I think that you may actually have two separate problems. First is that you wrongly wired the motion sensor. I'm not sure if you are aware of it or not, but there are certain motion sensors that are made to light up the bulbs at half brightness when it gets dark and when someone crosses the path the bulbs will light fully.
You provided a clue in your statement: "I test the motion sensor by turning off the breaker, then turn it on. The single spot lights up brightly, but the stairwell lights are out (except for the dim incandescent). Then after 2 mins. the spot goes out and so does the dim bulb!" Sometimes a motion sensor will react that way when power is turned off and then back on.
Look for some other problem with the fluorescent lights in the stairway. Maybe you have a bad ballast or a loose connection. The fact that the fluorescent problem surfaced weeks later indicates that it may not be connected to the motion sensor. Open up the fluorescent lights and see if you have 120 volts. Try connecting a pigtail socket and bulb to the feed and see if it lights normally.
John Grabowski http://www.mrelectrician.tv

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John Grabowski wrote:

Why did I not see that. I even have one of those. I think that is likely it and that helps make the rest make sense.

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John and all,
Thanks for the advice. I probably could have provided more detail, for instance, the circuit breaker box is completely new one year ago, by a very competent electrician (not me). The wiring to the old stairway lights is BX conduit with old copper. I have had problems in other fixtures with the older wiring in this place, so I should have comsidered the potential (no pun intended) of a floating neutral or loose connection. I'll go through each of these next to check them out.
I'm pretty sure this sensor is not the two stage you suggest. The reason it goes on after being powered off and on is this is how it is tested. It remains lit for 2 mins. then goes out. Afterward, it is dependent on darkness and movement. At any rate, I will remove it again when I check the old wiring in the stairwell.
The stairwell sockets are normal sockets which I can place ordinary bulbs. I have the compact fluorescents in them except for the one incandescent I tried to check the socket. That's how I discovered the "half lit" bulb.
Thanks again,
Greg

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