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Sherlock Ohms

Porch Light KOs Door Bell

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NedFreed
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Silver
Re: What were they thinking?
NedFreed   7/21/2014 8:00:15 PM
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The Married with Children episode "User Friendly" (Season 9, Episode 23) may be of interest to you.

NedFreed
User Rank
Silver
Found the same wiring years ago in my home
NedFreed   7/21/2014 7:55:23 PM
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1 saves
Except it was an outlet, not a doorbell. The outlet was inset into the top of a built in desk and the light was a 75W bullb in an adjacent closet. The outlet had been used for years to power stuff like tape recorders or rechargers for  various electronic gizmos, which all worked fine because the 100W bulb allowed more than enough current to flow through.

Things got a bit wierd, though, when my father plugged in an electic typewriter. it worked, but ran a bit rough and the bulb was also glowing and flickering as he typed. It apparently never occurred to my father - a doctor - that this wasn't how things were supposed to be.

This went on for years, until one day I happened to be getting something out of the closet when he turned on the typewriter. It was immediately obvious to me that the circuits were intertwined, but I didn't figure out exactly how until I traced out the wiring. It turned out that the AC line, switch, and outlet wires all ran to the light socket, so it was easy to move the outlet neutral to the line neutral where it belonged rather than to the switch leg it was on.

I'm not sure what I would have done if the outlet wire ran  to the switch. This wiring was new circa 1950, so needless to say there were no ground wires in sight that could be repurposed. About the only option short of tearing into the walls would have been to put a pull string on the bulb and put a blank cover where the switch used to be.

Mr. Wirtel
User Rank
Gold
Re: What were they thinking?
Mr. Wirtel   7/21/2014 6:37:32 PM
It is not necessary for a house to be 100 years old for it to have wacky wiring. We just moved into a house built in the late sixties and have found that amongst the many updates and improvements we have switches in three rooms that do nothing. At first we went around the house trying to figure out if anything was being turned on and off. Then I got an electrician in here to do some other things and he found numerous loose dead wires in the attic along with empty junction boxes. We talked to the previous owner and she told us her husband was in the process of redoing things when he got called out of state for a different job and they needed to sell the house with the changes incomplete. So the switches, wires and boxes were part of a plan never completed, but at least there were no live wires exposed anywhere.

dougs
User Rank
Iron
reflected impedance works
dougs   7/21/2014 5:17:48 PM
been a long time since i have used this trick.  put in a 24 volt doorbell transformer and a 24 volt coil ac relay in series with it.  add some fuses then run the line out to say the pumphouse put in another couple of fuses and an electronic grade transformer (similar wattage to the relay coil) with the 24 volt secondary connected to the signal line.  connect the primary to the unused terimanls on the pressure switch.  you have unused terimanls because the switch drives a contactor which runs the pump but only uses one of the two contacts of the pressure switch. when the power is off to the pump because you are on emergency power you can sense the pump condition without powering the pump. when the presure switch closes the low impedance is transferred across the transformer isolator to the low voltage sense circuit and the far end relay closes.  the low voltage circuit is isolated from the mains voltage by the transformer and protected by the fuses.  but try it on the bench with the signal wire you intend to use so the signal path inductance is not excessive too often we only look at the loop resistance and then have to backtrack. the alternative is usually a second pressure switch at the generator location but then you have to keep the two switches adjusted so the pump switch operates higher and lower than the remote switch not something to mess with durring an emergancy. or you can use the dc sense used by marine generators for start on load but now you need a relay state machine several timers and to not put line voltage on your dc circuit.

William K.
User Rank
Platinum
Good job of diagonsing the problem
William K.   7/9/2014 10:14:00 PM
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This is an xample of good diagnostic thinking, and solving a quite interesting problem. Old wiring that has been worked on by folks of different skill levels can produce very interesting results, as you discovered. Good job also in using the story to make a class demonstration more interesting.

jhmumford
User Rank
Gold
Re: What were they thinking?
jhmumford   7/9/2014 3:29:06 PM
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If I had to guess, I'd say they didn't want to be bothered by the doorbell unless the porch light was on.  Of course this is not the correct way to achieve this functionality, but I guess it worked well enough for the previous owner.

Lousy teenagers playing "Ding-Dong-Ditch"!

fm
User Rank
Gold
What were they thinking?
fm   7/9/2014 8:56:45 AM
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You just have to love old houses and wacky wiring!

patb2009
User Rank
Gold
a sketch would be nice
patb2009   7/8/2014 2:35:08 PM
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A picture would help. 

tekochip
User Rank
Platinum
Similar Problem
tekochip   7/8/2014 2:07:40 PM
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I had a similar problem once and only noticed after a fluorescent bulb was installed instead of an incandescent.


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