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What's the problem? #1795 05/31/01 10:39 PM
Joined: May 2001
Posts: 38
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bhester Offline OP
Member
I had a guy ask me what would cause all of his lights to dim whenever a motor would kick on. The house is around 2200 sq ft it has gas heat,water heater, and cooktop.He claime the electrician has changed the service disconnect and still no fix ,the checked the panel for loose connections the only solution was either the wire from the transformer was to small or the service entrance cable could have a nail or something in it.He said whenever the refrigerator kicks on the lights dim as the washer, and the A C any solutions?

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Re: What's the problem? #1796 05/31/01 10:58 PM
Joined: Nov 2000
Posts: 2,236
sparky66wv Offline
Member
It's pretty common for the inrush current of motors to dim lights; most residential Xformers are about 25KVa (Good for about 104 Amps at 240V) and split between 2 to 4 200A services. It's easy to imagine that even under diversified loads, peak times could test the Xformer's ability to provide steady voltage.

If #14 was predominantly used and used in long homeruns, then voltage drop would be aggravating a poor situation.

I think Scott35 refers to this phenomenon as Flicker factor .


[This message has been edited by sparky66wv (edited 05-31-2001).]


-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI
Re: What's the problem? #1797 06/01/01 10:19 AM
Joined: Mar 2001
Posts: 2,056
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Redsy Offline
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The voltage drop on a system that is a result of motor starting currents is probably most noticeable on incandescent lighting. This is due to the fact that the relationship between applied voltage and light output is not linear. For example, a 15% reduction in voltage could translate into a 40% reduction in light output.

It might pay to invest in a few compact fluorescent bulbs for the most annoying locations to see if they ride through the motor starts with less noticeable dimming.

[This message has been edited by Redsy (edited 06-01-2001).]

Re: What's the problem? #1798 06/01/01 01:09 PM
Joined: Nov 2000
Posts: 2,236
sparky66wv Offline
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Good Point and very well explained...

Man I love this forum!

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-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI
Re: What's the problem? #1799 06/01/01 06:51 PM
Joined: Jan 2001
Posts: 1,044
Tom Offline
Member
I think Redsy is on the right track, there is almost a 3 to 1 reduction in light output versus voltage drop.

Take a look at the pole & see how many services are connected to the transformer. If more than 3 or 4, could be too much load.

Another thing that can be tried by a qualified person with extreme caution is to measure the voltage drop at the weatherhead. if the VD is high, pretty well narrows it down to a power co. problem.

Tom


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Re: What's the problem? #1800 06/02/01 12:39 AM
Joined: May 2001
Posts: 38
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bhester Offline OP
Member
Thanks for all the info,I'm unsure of what wire size was used but I think they used #12 for homeruns and #14 to the lights. I was told there was a vacant lot next to the above ground Xformer.It wouldn't suprise me if they didn't load the circuits with 12-13 lights on a 15 amp circuit in my opinion might be some of the problem and I know the next time I see him I'll probably be going over to investigate myself (aaaaaagh) I hate troubleshooting others mistakes.

Re: What's the problem? #1801 06/02/01 09:10 AM
Joined: Oct 2000
Posts: 5,389
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sparky Offline
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ya,
especially when you have to 'wrong' the last guy.

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