Lights dim when AC/furnace kicks on

We've only been in our house (30 year old home) for a few months. We can tell whenever the AC or furnace kicks on because there's an almost imperceptible dimming of the lights. Can someone explain the possible reason(s) for this? We have a home warranty and if this is something serious then we'd like to have it addressed quickly.
Thanks!
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I think you have a case of the new home owner jitters.
As long as the dimming remains "almost impercetable", and remains confined to when large appliances are started, I wouldn't worry about it.
Large appliances draw a lot of current, especially when starting, resulting in the dimming you see.
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snipped-for-privacy@yahoo.com wrote:

That's probably normal. It's when the lights get *brighter* (or dim drasticly) when something kicks on that you need to investigate it.
Bob
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Is the furnace on its own circuit, is panel 60 A? A furnace should pull load at startup but not enough to dim other lights unless 60A is your service. AC on the other hand pulls alot more. More info needed.
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On Fri, 21 Jan 2005 14:24:05 -0600, snipped-for-privacy@webtv.net (m Ransley) wrote:

Obviously you've never seen an old belt drive blower motor with a bad start winding. What exactly do you do because it sure isnt this. Bubba
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On 21 Jan 2005 10:57:35 -0800, snipped-for-privacy@yahoo.com wrote:

So is it the Furnace or the A/C or both? Bad motor, capacitor, loose wire connection or wire, old furnace, failing compressor, inadequeate electric service to the home, etc. etc Bubvba
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snipped-for-privacy@yahoo.com wrote:

Welcome to the world of 1960-70 homes. It sounds about normal. A large dimming or any brightening is a sign to all the electrician. This is not.
--
Joseph Meehan

26 + 6 = 1 It's Irish Math
  Click to see the full signature.
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This is Turtle.
First you did not give enough data to even start to see or get a guess at it. Here is what you need to give.
1) Is the dimming happening during cooling mode ? Heating mode ? during both modes ?
2) Is the furnace a gas , Propane, All Electric , Gas furnace and Heat Pump Combo, or heat pump only type heat with back up electric heat ?
3) Do you live in a very far out of town area ? Or in a city ? Or in a Big City ?
4) How Bad do the lights blink as 1/10 of a second or more that a full second ?
5) What is the name of the Home warranty you have ?
TURTLE
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Well bubbaass I sure dont do hvac, but I sure enough know more than you on boilers even though you say your a pro, Im just a H. O. I think you are a rude trailer hack, wood stove crack, but no HVAC pro. Just a looser to go
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On Sat, 22 Jan 2005 05:36:13 -0600, snipped-for-privacy@webtv.net (m Ransley) wrote:

Actually its what you THINK you know and what you THINK you know I could put onto the head of a pin. Thats why you are a webtv pinhead living in a trailer. You arent even a wannabe hack. You're just pathetic. Now go wipe that drool off your chin, get off that dog and quit french kissing your sister, boy. Bubba
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This is Turtle.
When did I change my name to Bubba ? I'm Turtle.
TURTLE
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On Sun, 23 Jan 2005 01:19:15 -0600, "TURTLE"

Dont mind the webtv boy. He's just not been right since the lobotomy. He seems to think that a Weil-Mclain installation manual is gospel, cant seem to interpret between the lines and thinks he is a hotwater and steam boiler genius. Hes just a wannabe. Always has been, always will be. Bubba
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This is Turtle.
Hey why don't you two take a evening off and think up some good insults to use and start over tomorrow morning with a fresh mine and you can fire the freshly thought up insults at each other and really do a much better job at it. A freshly Planned out attack is always better that a off the cuff attack.
TURTLE
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A few suggestions here.
1 Now being able to see the amount of dimming there is no way of telling if you have a problem over the net 2. There are three things that can cause this that I know about, maybe four 3 You have to think of the wire in your home as water pipes to help understand what I'm going to tell you
A If there is something wrong with the AC this could cause this problem, to much power required to start a tight compressor B If there is a loose wire this could cause this problem, causing high amp draw, think of a valve downstream of the main. C A bad electrical panel D Corroded wires at the pole or mast.
I have seen two jobs that were serious in nature and a dozen that weren't. Older homes had smaller electrical entrances and that is like smaller water pipes, your only going to get so much water through a small pipe. The same is with wire, only so much power and if you have a lot going on and the AC starts your lights will dim for a second. This is normal but not desired, but not necessarily dangerous by any means.
I have seen a homes lights dim when a belt drive 1/4 hp motor started on the furnace, ALL the lights dimmed. I knew then that the wire (think of a pipe) somewhere at the box supply entrance to the utility pole outside had to have problems. Told them I would not put a furnace or AC in until its repaired. They called an electrician out and he said I was crazy. Called another and they didn't think there was any problem. I still refused and the homeowner called the utility guy out. Here the wires connect at the mast, (wires outside the house connected to utility wires) were completely corroded and ready to fail! The utility company replaced the wires from the street to the home and solved the problem. This could have caused the home to burn down
The other major problem was corrosion INSIDE the main electrical panel itself. Once again and electrician didn't think there was any problems. I used my inferred thermometer and found one circuit dangerously hot!! The buss inside the panel was corroded on one breaker. Changed the breaker box out and problem was solved.
So, you may not have a problem and yet again this may be an indication of major problems in the future.
Hope this helps Rich
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What's that, an "inferred thermometer"?

Thanks,
David
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The guy can not spell any beter than I can.
infrared thermometer
http://www.omega.com/prodinfo/infraredthermometer.html
If you really want to know.
They pick up heat without touching anything.
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