Dimming of lights when appliances are run


Old 12-10-99, 06:24 PM
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I recently purchased a 1941 bungalow with a mixture of original and modern wiring and a modern circuit breaker panel. Since moving in the house I've noticed something puzzling:

When I run the washing machine or the coffeemaker, or when the refrigerator starts, lights dim throughout the house, even though these various lights are on two completely different circuits from the appliances in question. The part I really don't understand, however, is that the lights pulsate somewhat while the washing machine is running--in time with the agitation of the wash or rinse cycle. The pulsing is most noticable in the laundry/mudroom overhead light, which is in the same room that the washing machine is located but on a different circuit.

Also, both the coffeemaker and the washing machine are on dedicated circuits, and the refrigerator is on a circuit with nothing else that draws current.

In trying to troubleshoot the problem, I have tried attaching the additional ground wire attached to the washer to the cold water pipe. this had no effect on the light pulsing.

The house panel is a Square D 100 amp panel, and I have a gas water heater and a gas furnace/air conditioner system. The house is approximately 1,000 square feet and has yet to have a dishwasher, microwave or disposal installed at this time. I do have an electric range on a dedicated 240v circuit.

Does anyone have any ideas about what might be causing this?

[This message has been edited by MichaelS (edited December 10, 1999).]
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Old 12-11-99, 01:42 AM
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hi MichaelS,
this is a commen problem.chanses are that what is hapening is that the load in your panel is unbalanced , whin u start a moter there is a high amount of curent draw at start up, and if your load isnt balanced this will hapen. there are several other thangs that can cause this problem.
your servace could be undersized, lose nutural wire in panel.these are the most commen. id start by checking all the wires in the panel 4 loose connections be sure to turn off the main befor working in a panel (word of caution the wires that feed the main breaker will still be hot)as far as balancing your load or increasing your service size call your local electrician
Old 12-13-99, 10:34 AM
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Thanks for the reply. Your assessment sounds like it's on the mark. This weekend, I pulled the cover off the main panel and checked out the wiring for the circuits in question. (Both tested at the outlet as having an open ground.) I discovered that someone had run one 12/3 wire from the two separate 120 breakers to the two outlets, which back up to each other behind the kitchen and utility room wall. The ground wire was connected with the neutral in the main panel but not to the individual outlets.

I decided to run a new set of wires (12/2) from each outlet to each breaker, and after doing this both outlets tested as correct. In addition, I also noticed two other items of concern. The circuits that were exhibiting the most noticable dips in power were actually four circuits double-wired to two 120 breakers. What fun!

Even though I'm not an electrician, this doesn't seem a good idea. I separated one off to an unused 20 amp breaker and plan to purchase a 20-amp tandem breaker to separate the other two wires that are still attached to the one breaker. Am I right in assuming this is a safer way to wire these circuits? And, do you think this will help ensure the circuits are balanced?

Thanks for your help and advice.
Old 12-13-99, 03:15 PM
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hi MichaelS,
its a fairly commen pratcise 2 pull a 12-3 whin there are 2 circuits in close proxcimity, so im not suprised, as to your open ground my gess is there was a wirenut lose on the 12-3, and whin u replaiced the 12-3 with 12-2 u eliminated the wirenut removeing the problem. as 2 your ? on the 2 wires under 1 breaker, this is also done sometimes, and as long as the circuit isnt overloaded it shuld be fine, it doesnt hurt to split them up eather and in my opnion its better to do this. now on to the load balancing. whin we refer to load balanceing what we r saying is the there is an equal amount of current pulled off each leg of the service. it can get confuseing 4 the novice so if u would like more info on load balanceing e-mail me.

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