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Dimming of lights #41110
08/15/04 09:22 AM
08/15/04 09:22 AM
Kennyvp  Offline OP
Joined: Oct 2003
Posts: 21
New Jersey
I have noticed a dimming in our home lights when a larger item starts up, heater , vac., hair dryier etc. THis also takes place in our two neighbors homes both which come off the same transfomer? I would have to take a chance and say it sounds like maybe there is a voltage problem at the pole/ anyone have any ideas. these homes all have a heavy electric load as we are oil heat. so everything is electric, stove,water heater,ac, etc

Work Gear for Electricians and the Trades
Re: Dimming of lights #41111
08/15/04 09:39 AM
08/15/04 09:39 AM
Ron  Offline
Joined: Mar 2002
Posts: 582
White Plains, NY
Is it a new problem or forever?

Re: Dimming of lights #41112
08/15/04 09:43 AM
08/15/04 09:43 AM
iwire  Offline
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
In my opinion you already have answered your own question. [Linked Image]

How many homes are connected to the same power company transformer?

What size is this transformer?

The power company has a very different method of sizing conductors and transformers than the NEC does.

The power company's methods work for them and you may have to just accept the dimming lights when other loads start.

It does not take much of a voltage sag to be seen in incandescent lighting.

You may also have some loose connections at the transformer that the power company might check if you ask them to.


Bob Badger
Construction & Maintenance Electrician
Re: Dimming of lights #41113
08/15/04 10:13 AM
08/15/04 10:13 AM
e57  Offline
Joined: May 2003
Posts: 2,876
Could be a wide range of things.....

Circuit seperation, common to have lights and plugs on the same circuit, but contributes to this problem.

Loose connections, anywhere, or everywhere all the way back to the transformer. Bad CB's too.(When your lights dimm from someelses house... that's a problem!)

Undersized wiring....

You mentioned all motor loads, and if these are all from different circuits, and tightening connections in your house doesn't help, like iwire mentioned try to get the PoCo to check theirs. These type of things can be really hard to track down sometimes.

Mark Heller
"Well - I oughta....." -Jackie Gleason
Re: Dimming of lights #41114
08/15/04 12:34 PM
08/15/04 12:34 PM
Bjarney  Offline
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
Aside from voltage drop, a loose connection usually causes undesirable heating and consequent damage, so a onceover of inside-the-building splices and terminations is probably in order. It will also give you a “bargaining chip” to deal with the utility.

There are usually two parts of a circuit with different “owners”… and both can contribute to lamp dimming during heavier loading. Remember that the obligation for voltage support by the utility effectively ends “at the meter.” Motor starting is often a tricky issue, and there can be seasonal conditions that may have to be tolerated.

Re: Dimming of lights #41115
08/16/04 02:20 AM
08/16/04 02:20 AM
Lostazhell  Offline
Joined: Feb 2004
Posts: 1,431
Bakersfield, CA (Originally Or...
Ahhh, this gives me flashbacks to a service upgrade I did in a really old neighborhood!

Old 1920's area here where the original services were 30A 240V a house.. I installed a 200A 240V service as the homeowner was having A/C installed & also wanted one of the fancy glass top electric cooktops... Did the service changeout, no problems.. (Municipal utility area, so the city runs the show from start to finish)
Well, it seems 2 other homes on the same transformer had recently been upgraded also, and had added some serious loads also...
I got a call back out after the H.O. I did the work for had his A/C, cooktop, a range & 2-50A Kilns in his garage... It seems on hot days, things wouldn't work right... I read voltage at the panel & it seemed a little low, but still in operating range (114V/112V) with about 120A load on the new panel. So I phoned the utility to check their system.... He calls me back the next night & says they checked & their voltage was fine. (They didn't check it when much of a load was on) I went out there again that night & had him turn everything on... The streetlights were dimming! I read 109V/111V.
This also amused his neighbor behind him who ran some kind of internet server deal.. The voltage fluxuations kept booting his computers into kaos...
After some time yaking with a utility planner I talked him into meeting me out at the H.O.'s house... Turned out a 25KVA transformer was running about 12 houses & had been on the pole since 1919. 2 75KVA transformers banked & some beefier secondaries throughout later.. Everythings fine! [Linked Image]


Re: Dimming of lights #41116
08/17/04 03:41 AM
08/17/04 03:41 AM
Scott35  Offline

Broom Pusher and
Joined: Oct 2000
Posts: 2,708
Anaheim, CA. USA

A few things need to be addressed first off, as follows:


[*] What is the intensity of the dimming problem,

[*] How long does the dimming last,

[*] Is the dimming predictable and constant during various times &/or days of the week,

[*] Does the dimming occur in one general area of the Homes, or on a certain circuit only,

[*] Does the dimming occur most noticably with Incandescent Lamps,

[*] Does the "opposite" ever occur frequently

As to "A", does the light level dim very drammatically, gradually taper down, or just come and go very transiently?

For "B", does the dimming last for several seconds, vary in time per type of load starting, or is the dimming more like a "Flash"?

Per "C", can you intentionly start some hard starting load and get consistant dimming results at all affected locations, and will this be the same every day - regardless of the time of day?

As to "D", is the dimming confined to "Certain Areas" of the House(s)?

For "E", Incandescent Lamps + Humans' perceptions of light levels are - to say the least - "greatly emphasised by minute changes", meaning small changes in Voltage cause Incandescent Lamps to react drammatically - and the Eyes also react drammatically.
Fluorescents will dip slightly, but normally are unnoticed when Transient Voltage sags come along. Flicker is more noticed.

As to "F", do any Incandescent Lamps tend to get brighter when Motors start?


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Re: Dimming of lights #41117
08/17/04 12:06 PM
08/17/04 12:06 PM
Bjarney  Offline
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
Scott, your questions are an excellent approach to begin to resolve the problem.

There is sort of a “treaty” that North American utilities, state utilities commissions and appliance producers have for voltage limits. ANSI C84.1 terms and enforceability are a bit complex, but one range is 110-126 volts, and in some cases 106-127 volts.

[This message has been edited by Bjarney (edited 08-17-2004).]


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