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Voltage drop on one circuit when lights turned on, Air purifier motor slows down

Voltage drop on one circuit when lights turned on, Air purifier motor slows down

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  #1  
Old 10-13-08, 06:22 PM
R
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Voltage drop on one circuit when lights turned on, Air purifier motor slows down

Hi,
Have an older house with a 100 amp service in basement. A few years back started having flickering on one circuit periodically then it would stop. Lights would flicker, etc. Had an electrician come in and since the house is three stories and this problem was on the floor sandwiched between top and bottom access was limited when seeking junction boxes. Told him if he could find them cut plaster or ceiling to get into. He worked part of the day and said he hooked into the neutral of another circuit and all was well. Was not sure what that meant and should have gotten clarification.

Now I have a new problem on same circuit. When running our Oreck air purifier if someone turns on a light or wife turns on iron, etc. the motor tone changes and slows noticeably. Comes right back up when draw goes off. Today I put my meter into the recepticle the air unit is on with lights off had 119 to 120 volts. Turned the dimmer on all the way to max and it dropped to 113. Turned another light on in kitchen with switch and it drop to 109.

Would a good first step in troubleshooting be to pull all recepticles and drop overhead lights and look for loose connections? Or should I pull the main and check the neutral connections on the CB box? Or perhaps both? Trying to avoid another electrician if I can but don't want to have a situation that is dangerous. All other circuits show no sign of a drop so I think perhaps that rules out the electric company neutral? Luckily I have only lights and recepticles with no motors or electronics on this circuit.

I have some practice with replacing switches and recepticles as I tried to replace them all when we first moved in for good measure.

Thanks in advance,

Rob

PS- air purifier is just a little table top design with ionizer.
 
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  #2  
Old 10-13-08, 07:17 PM
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It sounds like that circuit is overloaded. It sounds like the electrician "borrowed" the neutral from another circuit and this is what could be overloaded. (Two circuits using the same neutral*.)

Do you know WHICH other circuit the electrician connected the problem circuit neutral with?

Have you added any new electrical appliances to that other circuit recently? Or to the problem circuit?

Might try turning things off on that other circuit and see if the problem goes away on the problem circuit.

*There is a way that two circuits can share the same neutral and everything will "balance out" - this is an electrician thing though.

In any case, it sounds like you need an electrician for this.
 
  #3  
Old 10-13-08, 07:51 PM
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Hi,
Nothing new has been added to the circuit that has not been there for at least a year or two with no trouble. I believe the electrician did in fact borrow the neutral from another circuit to avoid having to find junction boxes in the ceiling, etc once he determined there was a bad connection somewhere on a hidden neutral. Would I be able to look at the breaker box with the front cover off and see a neutral wire connected to another breaker and determine that is the one he shared?

I can put my meter in the electrical outlet below the dimmer switch and with the light off I have 123.1 Put it on full and it goes to 119.3 Does properly sharing a neutral mean that you need to cut the amps drawn on each circuit by half or can the neutral handle the current? Assuming it is done properly.

Thanks for the reply,

Rob

PS- I am not a big fan of messing with electricity so if it sounds like checking connections on switches and outlets will be a waste of time I will go ahead and call an electrician. Most of the wiring if not all is run in conduit also. Was told by the previous guy a few years back that was a good safety measure. It took a few trips out for him to conclude it was a bad neutral somewhere. Just about impossible to locate all the junctions, etc. He tried but could not find all the boxes.
 
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Old 10-13-08, 08:22 PM
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It sounds to me like he connected to a neutral half way (or whatever) to the panel. If this was at the panel, there would be no need to be sharing a neutral with another circuit. So no, you would not see anything in the panel.

So far as sharing a neutral, this gets complicated. If both hots are on the same "leg" of your electric service, then yes you would have half the capacity on both circuits and this would be dangerous. But if they are on opposing "legs", then everything would "balance out" and no problem.

If you have not added anything new and this problem just started happening, then yes it is probably a loose connection somewhere. And you did have a previous loose connection as well, so good possibility!

Only thing is that it is probably in that junction box the electrician could not find! (Murphy's Law)
 
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