Electrical A/C Power Surge

Old 08-03-04, 08:27 AM
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Question Electrical A/C Power Surge

Recently had a new air conditioning system installed with a 13 seer. When the outside unit turns on the lights in the house flicker. Installers have been unable to idetify the problem, suggest upgrading electrical in home. Home was built in 1977 and I think the current is 120.
Old 08-03-04, 01:34 PM
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If the flicker is slight, it may not be a problem.

The problem may be a loose connection in your panel, or a loose connection or undersized equipment on the power company side. This leaves you at least these three options, depending on your wallet depth, level of uneasiness, risk tolerance, and fire insurance policy amount:

(1) If you feel the flicker is slight (subjective), then ignore it.
(2) Call the power company and ask them to check their equipment, wires and connections. They will usually do this for free, and it often fixes the problem.
(3) Call an electrician to check the tightness of all the connections in your main panel.
Old 08-03-04, 02:33 PM
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Electrical A/C Power Surge

Thank you for responding so quickly. I called the power Company. Will let you know the outcome.
Old 08-11-04, 04:40 AM
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A/C Power Surge

I'm back to square one. I had the power Company come out and they said everything was okay. I had the A/C installer come out and install an easy start on the A/C and check the circut breaker, that didn't correct the problem. Was told the breakers were corroded and the panel box needed to be replaced. Had an electrician inspect the breaker box and the and the wiring, said he could find nothing wrong. Could not guarantee replacing the breaker box and the wiring would fix the problem. Said it could be the power Company cutting the power in the Summer. Now I have arranged to have another electrician come in to check out loose wiring somewhere. Will keep you posted.
Old 08-11-04, 07:06 AM
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Some (very quick) background:

Electric power is delivered as a current (flow) of electrons at elevated potential (voltage). The total power delivered is the product of the voltage and the current. In US homes, the system is arranged to keep the voltage approximately constant at 120/240V, and the current adjusts to suit the load. The greater the load, the greater the current flow. In the ideal case, the voltage would remain exactly constant, and just the current would change. But in the real world, this is not what happens.

The greater the current flowing through the supply transformer, the lower its output voltage. In addition, the greater the current flow through a wire, the greater the voltage 'lost' in that wire. The net result is that when the current flow increases into your home, the lower the voltage getting to your home.

On top of this, when you start most loads, they draw additional 'inrush' or 'locked rotor' or 'startup' current. This is only for a very short period of time, but the current consumed by these devices during startup can exceed the normal running current by a large margin. All of the voltage reduction that you get from increased current flow is similarly increased during these 'startup transients'.

When the voltage to your house goes down, the lights will flicker. Nothing that you can do about that.

You've already had both an electrician and the power company come and 'take a look' at things. Now it is time to do some calculations. I would suggest hiring an electrician with the specific instructions to calculate out the expected voltage drop when your air conditioner starts, and to then _measure_ the voltage drop when the air conditioner starts. If the voltage drop matches the expected value, then everything is working correctly. Making the lights not flicker, or flicker less would involve expensive upgrades to your electrical system or upgrades to your lights. On the other hand, if the voltage drop is greater than expected, that points to a problem that needs to be discovered and fixed.

Excessive voltage drop could be caused by a bad supply transformer, an air conditioner drawing too much current, or a loose connection somewhere in between. It could also be caused by an undersized supply system operating normally.

Another possibility: if the air-conditioner were installed on a 120V supply leg, rather than your full 240V supply, then it will draw twice as much current and cause twice as much flicker, making some lights dimmer and others brighter. This can be reduced substantially by changing the air-conditioner over to 240V.

Best regards,
Old 08-11-04, 08:56 AM
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This suggestion requires an HVAC tech., and an accurate volt-meter.

With the breaker for the A.C. system in the "Off" postion,Open the Starting-circuit of the compressor motor, which probably could be accomplished by removing a lead to the Starting capacitor. Then prevents the motor from starting.

Connect an accurate volt-meter to the Line terminals of the Main-breaker and record the voltage-reading. Complete the control-circuit that controls the compressor motor, and switch the A.C. breaker "On".

The current thru the Main-breaker is now the "continual" starting- current which would be near the rating of the A.C. breaker.You will have a period of only a few seconds which is sufficient time to observe the effect of the current which is conducted thru the system when the compressor starts. Observe the "flickering" lamps, and record the voltage-reading which is present during the "starting" cycle.The voltage should remain fairly constant during this test.

Allow only a 3-4 second period for this test to avoid over-heating the motor-winding in the compressor.

Good Luck & Enjoy the Experience!!!!

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