Motion sensor causes spool of wire to hum

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  #1  
Old 06-30-12, 01:33 PM
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Motion sensor causes spool of wire to hum

Why does my wire hum and how do I fix this?

Here are the facts:

-- Tried two motion sensors -- both Heath/Zenith.

-- Thought I should try this before I buried the wire, so this test mode is with the 500' of 10/3 UF still on the spool. See attached drawing.

-- If I replace the motion sensor with a simple wall switch -- no hum.

-- If I unscrew the light in the house -- no hum.

-- It only hums with the motion sensor and the house light on. Whether the two driveway lights are on or off makes no difference.

-- The driveway GFCI has been included and excluded and it has no effect on the hum. Tried a different GFCI and it also made no difference.

-- Hum is coming from the spool of wire, not any of the other components.

-- Hum sounds like an RF hum out of a speaker, and not a crackle like a damaged connection.

-- I get 125v at the end of the 500' run, but only 108v out of the motion detectors. They are different models, but the reading is the same.

-- My handy-dandy wiring plug lights up at the GFCI and says everything is wired correctly.

-- Tried different house fixtures and light bulbs -- still makes the wire spool hum.

I hate to bury this wire if it isn't right. Any ideas?

Thank you so much.

Tom
 
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  #2  
Old 06-30-12, 02:09 PM
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Why are you running 10/3? What is the purpose of the additional wire in the group? How is it energized? And where? Running 12/2 from your panel in essence gives you the voltage drop capability of 12 gauge wire, not 10, so there is a fault at that juncture. It needs to be 10 gauge all the way. I feel there is something else amiss, but I'll wait on answers.
 
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Old 06-30-12, 03:04 PM
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The electrical store recommended I get 10 gauge because of the 500' distance and related voltage drop. In my test mode, with the wire still on the spool, still shows it at 125v. Given that it is being tested with 12 to the panel and I have no voltage drop at 500', I guess I should have gotten 12 gauge wire. I can wire the 10 gauge to the panel if that will stop the hum, but I didn't think that was the problem. Seems like it is a voltage issue only and that isn't a problem with the 125v down at the driveway lights.

The additional wire (red) was to turn on a light in the house when the driveway lights come on with motion activation. Sort of a security thing -- might make a bad guy think someone might be home.

The red wire is energized by the feed from the motion detector. It takes the B and W in and the red coming out feeds the light bulbs. Of course, the light bulbs also have a white wire to complete the circuit.

Yes, there is somethng else amiss -- I just can't figure out what it might be.
 
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Old 06-30-12, 03:40 PM
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With only a light bulb on the end, you may not have problems with your 12/10 combination. I doubt you will experience enough voltage drop to matter much. BUT it could be a problem if you decided (or a future owner) to put a pagoda out there with lighting, receptacles, electrical drawing components.....see where it goes. You have a bottle neck at the 12/10 connection. If you are using 20 amp OCP, then you're ok as far as overload goes.
Your connections on your drawing don't make any sense as far as the black in relationship to the red. The bulb at the driveway after the sensor should be connected to the black and white wire if that is where the power is coming in. What is connected to the black wire after the sensor?
 
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Old 06-30-12, 04:00 PM
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Ummmm..whether the wire gauge is right or not or any of the other questions are relevant I don't think really matters.


Wire on a spool is basically a transformer...transformers can hum. Unspool the wire and your hum issue will probably go away.
 
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Old 06-30-12, 04:02 PM
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The wiring of the sensor and two light bulbs is the factory wiring by Heath/Zenith. It is a two-light motion detector. If this was to be the only fixture in a 12/2 circuit, it says to conect the W to the W, the B to the B, and the ground to the Green. The factory wiring has the W lead from each bulb connectioned to the incoming W. The factory wiring also has the B from each bulb connected to the R coming out of the motion detector. To add the additional house light to this system, I connected this R coming out of the motion detector to the R in the 10/3 bundle. Back at the house outlet box, I connected this R feed to the B wire of the light and connected the light's W wire to the W.

Heath/Zenith didn't use the B wire for anything, so neither did I. Seems like if I use it to feed back to the house, I will have bypassed the motion detector.

What do you think?
 
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Old 06-30-12, 04:36 PM
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OK, so the switching is done in the sensor. Take the kinks out of the coil and see what happens. Do the lights operate as planned???
 
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Old 06-30-12, 05:38 PM
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The electrical store recommended I get 10 gauge because of the 500' distance and related voltage drop.
Not necessarily a reliable source of information. Lets start over tell us the details of what you want to do and we will help you.
 
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Old 06-30-12, 06:56 PM
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Agreed. Probably sold me what they had in stock.

Pretty much like the drawing. At 500' away, I'll have two 100w bulbs and a motion sensor which draws a very neglible amount of current. Not on the drawing is a 500milliwatt battery charger for a battery powered gate.

I've also got that 100w light in the house on that same motion circuit. Not sure how to look at that one. It is in the house and connected to the white wire, but it is also connected to the red wire, which is bringing power up the driveway and all the way back to the house. Is that down and back for 1,000' or just the 20' inside the house?

I don't plan to run a security camera down there or a big electric motor for a big sliding gate, but someday someone might. I don't want to put in big wire for something I don't plan to do.

As to that hum, Gunguy45 got it right. Unspooling it either stopped the hum or spread it out over 500' so I couldn't hear it anymore. Thanks.

Any advice you have on how to wire it or what size of wire to use, would be greatly appreciated.

Tom
 
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Old 06-30-12, 08:28 PM
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So if I understand correctly
1>One light is near the house.
2>One light is at the far end of the driveway.
3>The sensor will be at the far end of the drive way.
4>The sensor will control both lights.
5>The third conductor (red) carries power back to the light near the house.

Your plan sounds good. So long as you keep total loads to 10 amps or less.
 
  #11  
Old 06-30-12, 09:36 PM
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The hum is caused by the triac in the motion sensor.
 
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Old 07-01-12, 09:19 AM
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The hum is caused by the triac in the motion sensor.
The hum issue was solved by unspooling the wire/cable. The spool was acting as a coil.
 
  #13  
Old 07-01-12, 09:46 AM
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Thank you all for your kind assistance. I believe we have this problem solved!

Tom
 
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Old 07-01-12, 09:59 AM
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Sometimes even a blind dog finds a bone...

Haven't really worked with electronics for 20 yrs....but I remember a few things.
 
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