Substantial voltage drop when A/C kicks on.

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  #1  
Old 07-13-06, 11:49 AM
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Substantial voltage drop when A/C kicks on.

I am in the middle of a remodel, and I currently have 2 panels: the old, original panel, and the new 200 amp panel to which the service feeds. When the 5 ton A/C kicks on, I have substantial drop in voltage. I took 3 measurements using a kill-a-watt device, and here are the results.

Office: 110/114 - 9 amp load
Kitchen: 113/114 - no load
Den: 113/116 - no load

The first number is when the A/C is on, second is when A/C is off. The Den is on a circuit still connected to the old panel. The numbers are rounded off, as the voltage fluctuates a couple tenths.

The run from the new panel to the office is at MOST 50 ft, using 12/2 romex. The office contains many computers, all on battery backups. My first indication of a possible problem was that these batteries are compensating for the drop in voltage (a light comes on the batteries when there is a low voltage)

So what do you experts think? What could be the problem, or is there a problem?
 
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Old 07-13-06, 12:13 PM
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Originally Posted by hondaciv
Office: 110/114 - 9 amp load
Kitchen: 113/114 - no load
Den: 113/116 - no load
So what do you experts think? What could be the problem, or is there a problem?
To start with you have substantial VD with out the AC. Your voltage should be 123 volts or in that area. You utility is short changing you. Give them a call. You probably are too far from the transformer. I would have added a feeder and a panel in your office for your computers. 50 ft is a long way.
 
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Old 07-13-06, 05:07 PM
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You are experiencing voltage drop due to the large inductive load of your AC unit. Your voltage is a little low but within the average of 110-125v, If you do not have any highly sensitive electronic devices in you house I would not worry. If it does bother you maybe switching to a more efficent AC unit or just have a qualified AC & heating company come check it out. For cleaning options check out Personal website removed. Please read the forum rules before posting.
 
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Old 07-13-06, 05:16 PM
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Originally Posted by M8 Electric
You are experiencing voltage drop due to the large inductive load of your AC unit. Your voltage is a little low but within the average of 110-125v, If you do not have any highly sensitive electronic devices in you house I would not worry. If it does bother you maybe switching to a more efficent AC unit or just have a qualified AC & heating company come check it out. For cleaning options check out Personal website removed. Please read the forum rules before posting.

Its a 14 seer Trane, only a year old.
 
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Old 07-13-06, 05:23 PM
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I think you are border line low to begin with at 114 w/no load. I've seen instances where putting the a/c breaker in the highest slot or nearest to the incoming service where it wouldn't cause drops as bad. But your a little on the low side to begin with. Have you called the poco and had them out to look at your incoming electrical service voltage ?
 
  #6  
Old 07-14-06, 06:35 AM
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is the ac fed from the new or the old panel. Have you measured the voltage drop on your incoming lines when the ac kicks on? If the mains drop, then you might have a poco feeder/transformer issue, if they don't drop, then you have an interenal issue
 
  #7  
Old 07-15-06, 11:41 AM
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Most devices are designed to take a plus or minus 10% voltage (i.e., 108 to 132 volts on a 120 volt base).

At our POCO, we try to limit the drop in our system to 5% at the meter (114 volts). This allows for the additional 5% drop in the customers system.

However, from a practical standpoint, we try to maintain around 116 volts. Sounds like your POCO might be a little low.
 
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