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Old 09-01-2010, 10:59 AM   #1
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lights flicker when AC turns on


I get a momentary flicker of lights when my AC compressor kicks on- it's just long enough to notice, a split second.

The compressor data plate says: 23A minimum draw, 40A max breaker. There is a 30A breaker at the unit outside and a 30A breaker at the main panel. It is wired with 10 ga from the main panel to outside breaker. There is a few feet of flex conduit running from the outside breaker to the unit so I'm not sure what's there but I'd assume more 10 ga.

Oh, one other thing... over ~15 yrs the outside breaker has tripped twice for no apparent reason- reset it and everything is "ok" .

Thanks in advance for any feedback and ideas.

DOH! this should obviously be in ELECTRICAL. Can someone move it??? sorry.

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Old 09-01-2010, 01:08 PM   #2
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lights flicker when AC turns on


I'm not 100% on this, so I'd wait for someone else to verify my thinking, but I'm pretty sure based on the "40A Max Breaker," you should be able to change your 30A breakers for 40A breakers. This would probably eliminate the random tripping, though it will do nothing for the flickering lights.

Motor loads, like A/C units, are one a few instances where you can use a larger breaker than the wire size would normally allow.

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Old 09-01-2010, 07:44 PM   #3
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lights flicker when AC turns on


Mine does this sometimes also. Though I don't know how its wired.
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Old 09-01-2010, 09:58 PM   #4
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lights flicker when AC turns on


Just like any motor load when they start up under the load the light will flicker for a second or two the most that useally normal but if the lights get really dim then you have serious issue like loose connection at the breaker box or meter socket or POCO connection one of the three.

As long they are tight and clean it probly normal due many POCO do not put a oversized transfomer at all they will sized to the common load and that it.

If you have couple other house share the same transfomer if they have mometary flicker for a second or two then it is normal but if they do get pretty dim as well then call the POCO they will deal with it useally with no charge for that { yeah they are open 24/7 }

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Old 09-02-2010, 08:29 AM   #5
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lights flicker when AC turns on


thanks. I did some more experimenting last nite. I have a large air compressor, 240 VAC, 30A running, it is on a 50A or 60A breaker, and when it fires up it will also make the lights flicker. I have never noticed this before because the garage lights are fluorescent, but if I go upstairs the incandescent lights will flicker when it kicks on also.

Note the flicker is just for a fraction of a second, there is no dimming.

So, it sounds like this is fairly normal when the current spikes at startup. Oh, and I do have 200A service.
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Old 09-02-2010, 08:33 AM   #6
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lights flicker when AC turns on


Quote:
Originally Posted by McSteve View Post
I'm not 100% on this, so I'd wait for someone else to verify my thinking, but I'm pretty sure based on the "40A Max Breaker," you should be able to change your 30A breakers for 40A breakers. This would probably eliminate the random tripping, though it will do nothing for the flickering lights.

Motor loads, like A/C units, are one a few instances where you can use a larger breaker than the wire size would normally allow.
I will probably not change the breakers, but for the pros out there, would I still be able to keep the 10ga wire with a 40A breaker?

That doesn't sound right, but I'm not obviously not an electrician

I am pretty sure my air compressor setup uses and 50A breaker and 6 ga wire.
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Old 09-02-2010, 09:19 AM   #7
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lights flicker when AC turns on


The #10 with a 40 amp breaker for the A/C might be correct. The nameplate on the A/C will have the information needed. It will have two things, minimum circuit ampacity which determines the wire size and maximum overcurrent protection which tells the breaker or fuse size.
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Old 09-02-2010, 09:29 AM   #8
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lights flicker when AC turns on


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Originally Posted by Jim Port View Post
The #10 with a 40 amp breaker for the A/C might be correct. The nameplate on the A/C will have the information needed. It will have two things, minimum circuit ampacity which determines the wire size and maximum overcurrent protection which tells the breaker or fuse size.
Thanks Jim. This is from my original post:

The compressor data plate says: 23A minimum draw, 40A max breaker. There is a 30A breaker at the unit outside and a 30A breaker at the main panel. It is wired with 10 ga from the main panel to outside breaker. There is a few feet of flex conduit running from the outside breaker to the unit so I'm not sure what's there but I'd assume more 10 ga.

Oh, one other thing... over ~15 yrs the outside breaker has tripped twice for no apparent reason- reset it and everything is "ok" .
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Old 09-02-2010, 09:31 AM   #9
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lights flicker when AC turns on


Unless the 30 amp breaker in the panel is tripping, then changing to a 40 amp breaker will do nothing for you but cost time and money!
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Old 09-02-2010, 01:14 PM   #10
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lights flicker when AC turns on


I will just leave the breaker alone for the A/C unit due you are in the middle of the specs of that unit required and with NEC code art 440 and 430 they have variations it can allow bigger breaker for Motor loads but only for hardwired units.

Merci.
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