Lights flicker every time AC turns on


Old 09-08-07, 06:33 AM
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Lights flicker every time AC turns on

House is 7 years old now, new construction. wired 110. I have a suspicious feeling they used 12/2 wire to hook up the AC. Does this sound right? Anyway, didn't seem usual for the lights to flicker every time the AC kicks on, am I wrong?

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Old 09-08-07, 06:39 AM
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is this an central ac or window type???????
central ac used 40 amps cutoff switch
for window a seperated circuit 2/12 on an 20 amps should be fine
if lights flicker could be ac startup compacitor might be defective.
or you have other think connected on that circuit
Old 09-08-07, 08:24 AM
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Sorry ... Central AC on it's own 40AMP circuit.

Lights have always flickered, it's not something new.
Old 09-08-07, 09:00 AM
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Is this a 200 amp main service?? They defintly shouldn't have used12/2 for the compressor. more like 8/2, although typically they use 10/2 with a 30 amp breaker. Are you sure the 12/2 isn't going to your airhandler? because thats usually fine.
Old 09-08-07, 11:23 AM
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There is one thing you have to understand with some of HVAC and motor load related with wiring size. this part will get very tricky what most diy's will not catch on this part

the NEC code [ CEC is very simuair to this as well ] do have pretty good part related to the oddball way to run the wires for HVAC load also motors load as well it will be in art 440 area but right now i just cant paste it in for some reason it not working with me with this computer [ cussed in french ,, sorry ]

Most HVAC units we will sized the wires and breaker per manufacter nameplate stated typically most resdential area central AC typically used 10-2 wire for outside compressor unless it say diffrent

for inside airhandler/ furance typically 12-2 useally do it majorty of the time unless you have standby electric heat then all bet is off then we have to follow the nameplate for that as well.

Merci , Marc
Old 09-08-07, 12:40 PM
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I just went in the basement and verified the wire going OUTSIDE to the AC sub box is a thick black cable and is 8/2. This makes more sense, the 12/2 may have been going to the furnace blower.
Old 09-08-07, 02:10 PM
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Maybe the lights you see flicker are on same 'leg' as the condensor fan and furnace or handler blower (with the compressor sharing both legs). And you have to consider amp draw is higher at capacitor start up, than when it is settles into the run mode.
Old 09-08-07, 02:24 PM
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Most of the time the lights will dim, its the result of voltage drop from the compressor starting up, as far as the size wire required to the outdoor unit, look at the nameplate and see what is required, if you don't like the lights dimming you can invest in a hardstart kit, but most people just deal with it...
Old 09-08-07, 02:58 PM
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Like said Id have a AC tech put a hard start kit on the AC. Might also have the tech Amp the compressor out, see if its ok.
Old 09-09-07, 10:59 AM
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I think this is normal, to a certain extent. Our lights flicker when the 18k btu window unit kicks in.

They even flicker slightly when the neighbor's central unit kicks in (we're on the same transformer).
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