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Old 05-31-2010, 11:19 PM   #1
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House lights dim for a few seconds


Hi Everyone,

I know that this topic has been covered in other posts, but I couldn't find one that really fit my scenario.

I have an older house (1955) that had old Federal Pacific breakers and panels when we purchased the house a year ago. At the recommendation of the property inspector, we promptly upgraded all the breakers and the input power to the house (from 40 A to 125 A, permits and inspected). When we did the upgrade, we had all the outlets grounded and separated into smaller circuits since originally the house only had 3 or 4 circuits.

Before and after the upgrade, the bathroom lights would dim slightly whenever we turned the blow-dryer on. Since the light and the outlet was on the same circuit, I didn't think much of it - believing it was due to the draw of blow-dryer causing an under-voltage situation temporarily.

We recently had Air Conditioning installed and the problem happens whenever the AC unit or the furnace fan kicks in (obviously on separate circuits).

Just yesterday I noticed other lights in the house dimming periodically unrelated to any appliance running. I checked the sub panel and all the connections seem to be tight and secure.

Does anyone have any idea what the problem might be? Any help or advise would be greatly appreciated. Thanks in advance.

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Old 06-01-2010, 12:00 AM   #2
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House lights dim for a few seconds


If the lights in the house get dim or brighter it will be good time to call the POCO to check their side and they will come out they are on call 24/7 and most case they will not charge to come out and check thier system.

Most common curpit useally loose connection if the POCO side is good then it will be on your load centre or meter socket { this part it will need electrician to deal with meter socket for safety issue }

Merci,Marc

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Old 06-01-2010, 08:23 AM   #3
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House lights dim for a few seconds


Quote:
Originally Posted by Dimmlylit View Post
the bathroom lights would dim slightly whenever we turned the blow-dryer on. Since the light and the outlet was on the same circuit, I didn't think much of it - believing it was due to the draw of blow-dryer causing an under-voltage situation temporarily.
I'd expect a 3v drop with this arrangement, depending on if you have #12 or #14 and how far it is to the panel.
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Old 06-01-2010, 09:15 AM   #4
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House lights dim for a few seconds


Momentary slight dimming of lights as a large appliance (or even a hair dryer) is turned on is usually normal.

You need to be handy with a volt meter to analyze it for sure.

If any lights brighten for a moment or for a long time when something is turned on, or dim way down, then you have a major abnormality. All electronics including microwave ovens should be disconnected until the problem is found and fixed.
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Old 06-02-2010, 12:11 AM   #5
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House lights dim for a few seconds


Hi everyone, thanks for the responses - they've been very helpful. Below is some additional information.

I checked the voltage on the circuit with the blow dryer and the lights and the voltage dropped from 120 VAC to 114 VAC for as long as the blow dryer is on.

Our house previously did not have that many circuits (I think 4) and when we did the electrical upgrade we separated all the outlets, but the original lighting circuit is intact. This lighting circuit includes all the lights for half of the house and the outlets in the bathrooms. I can't tell the wire gauge, but it's old (from 1955) so I'd imagine that it's 14 AWG. The circuit probably extends about 40 feet in a straight line and the outlet that is used for the blow dryer is near the end.

I measured the voltage of some outlets when I turned the AC on (AC is on independent circuit) and the voltage dipped from 120 VAC to a little less than 114 VAC for less than a second, but then increases back to 120 VAC even while the AC unit is on.

Voltage doesn't seem to increase at all (not that I noticed), though the measured value did fluctuate +/- 1.5 VAC

Is there any way to remedy the blow dryer issue? Anything I can do to alleviate the inrush issue with the AC unit?

Thanks again!

Last edited by Dimmlylit; 06-02-2010 at 12:13 AM.
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Old 06-02-2010, 07:57 AM   #6
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House lights dim for a few seconds


When you run the blow dryer, does the voltage dip for every receptacle in the house or just the receptacles on the same circuit as the blow dryer?

(You will need an experienced electrician for this one) Does the voltage, as measured in the big service wires (not the lugs) as they enter the main breaker, dip when the air conditioner kicks on?

It is not unusual for the voltage to dip at all the homes on the street fed by the same pole transformer, when an AC unit or a heat pump kicks on in one of the homes. Here, a momentary dip from 120 to 114 is not considered abnormal.

While you are at it, you can retorque (loosen a quarter of a turn and then retighten quite hard but not with tremendous strength) all the set screws on the neutral and ground terminal strips (or bus bars) and all the screws holding the hot wires in the breakers (turn off each breaker in turn first). Loosening the screw first helps clean off oxidation and improve the connection. Have an electrician do the main breaker big lugs for you.

You may get some improvement in voltage stability if you go from one outlet or switch to the next, undoing one at a time any back stab (push in) connections and using the screw terminals instead, and also retorquing all existing screw connections.
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Last edited by AllanJ; 06-02-2010 at 08:13 AM.
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Old 06-02-2010, 11:16 AM   #7
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House lights dim for a few seconds


Quote:
Originally Posted by Dimmlylit View Post
I checked the voltage on the circuit with the blow dryer and the lights and the voltage dropped from 120 VAC to 114 VAC for as long as the blow dryer is on.
. . .gives you a 15% drop in incand. bulb brightness.

If it's a 10A dryer [look on the nameplate for the dryer] you have [120-114]/10 = 0.6 ohms of wire resistance.
At 2.6 ohms per 1000' of #14, it should be 1000[0.6/2.6]/2 = 115' of Romex. If it's not that far to the panel I'd say you have a bad wirenut connection.


For the AC problem you could get a 'soft start' kit.

Last edited by Yoyizit; 06-02-2010 at 11:21 AM.
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Old 06-02-2010, 05:22 PM   #8
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House lights dim for a few seconds


It is also possible that your loads are not balanced at the panel. Two circuits to the bath room may be on the same leg in the panel.

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