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voltage drop on lighting cicruit

Asked Aug 2, 2012, 11:05 AM — 30 Answers
A/C unit comes on and lights dim for brief moment. i have tighten the conection related to a/c unit including breakers and disconnect and neutrals.

Can other applinces have an effect on the a/c unit if they are turned off. can loose connection for other applicances effect lights when a/c comes on?

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30 Answers
tkrussell's Avatar
tkrussell Posts: 9,673, Reputation: 3698
Senior Electrical & Lighting Expert
  
#2

Aug 2, 2012, 12:19 PM


The AC may be causing the dimming lights due to a loose connection anywhere beginning at the utility system, your meter, and panel.

You may be able to check conections in the panel, however, if the problem is in the meter and/or the utility system, you may need an electrician and/or the utility to check those connections.
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ma0641's Avatar
ma0641 Posts: 6,237, Reputation: 2489
Plumbing Expert
  
#3

Aug 2, 2012, 01:58 PM
AC units draw a lot of power on startup. Depending on your panel rating, it is possibly just too much momentarily. I have a 150 AMP panel and the AC causes a very brief dimming, less than 1 sec.
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mike 165278's Avatar
mike 165278 Posts: 168, Reputation: 31
Junior Member
  
#4

Aug 2, 2012, 07:01 PM
The A/C unit drawa quite a bit of power for the first few cycles when the motor kicks on. It's that inrush of current that makes the lights dim. Are the lights and the A/C on the same circuit? Putting the A/C on a dedicated circuit should solve the problem. If not, don't worry about it too much. As long as you don't have electronics on the circuit nothing really to worry about.
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tkrussell's Avatar
tkrussell Posts: 9,673, Reputation: 3698
Senior Electrical & Lighting Expert
  
#5

Aug 3, 2012, 02:43 AM


A well designed system in good condition should never result in lights dimming from an air conditioner starting.
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butch 17's Avatar
butch 17 Posts: 10, Reputation: 1
New Member
  
#6

Aug 3, 2012, 10:16 AM
Quote:
Originally Posted by tkrussell View Post
A well designed system in good condition should never result in lights dimming from an air conditioner starting.
could a loose neutral on other circuits cause the light to dim? the a/c is installed properely and the electrical to it is in excellent shape!
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tkrussell's Avatar
tkrussell Posts: 9,673, Reputation: 3698
Senior Electrical & Lighting Expert
  
#7

Aug 3, 2012, 10:35 AM


A neutral of other circuits should not be affected by the AC, but a loose neutral in the panel, meter or utility could.
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butch 17's Avatar
butch 17 Posts: 10, Reputation: 1
New Member
  
#8

Aug 3, 2012, 11:45 AM
All connections from power company meter to panel to disconnect to a/c unit are secure! Change the breaker and the disconnect. lights are still dimming. only briefly but enough to notice! all connections in panel are tight so i don't understand . didnt know if neutrals in other parts of the house would cause the lights to dim if they were loose. Thanks for your help
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tkrussell's Avatar
tkrussell Posts: 9,673, Reputation: 3698
Senior Electrical & Lighting Expert
  
#9

Aug 3, 2012, 12:44 PM
What type of AC do you have? What type and size circuit?

If possibilities all I mentioned are fine, there could be bad contacts on the Main Breaker.

Could be the utility line is too small, and/or too long.

I have found both of the problems i just mentioned causing dimming also. Any chance you could post some photos of the meter, panel, AC disconnect, and perhaps the utility feed, if at all possible.

Also, the distance of the utility feed to a utility transformer.

To check the breakers, a simple test is to measure the millivolt drop across the breaker contacts. however, you need special test instrument to measure millivolts.

Is the main breaker a plug in ata meter/disconnect, or bolted to bus bar in the panel?

There are so many points of possible failures. We will keep going until we find something.
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mike 165278's Avatar
mike 165278 Posts: 168, Reputation: 31
Junior Member
  
#10

Aug 3, 2012, 12:45 PM
What size service do you have? Do you know what the A/C draws?
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