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Symptom: Lights dim when appliances or laserjet printer kick in while HVAC and clothes dryer running.

I currently have a 400 Amp service split into 2 panels each with a 200A main breaker. I'm all electric, no gas. House built in '96, one floor. Main feed comes in garage.

On one panel, I have 350A combined breakers (15A is not used, attic fan removed) and the other side 245A combined breakers (60A not used, was added for a jacuzzi that previous owners never put in).

I already had an electrician come to the house to loosen and tighten all the connections on the panel.

My thought is, I don't have proper distribution of power across the panels. However, I'm not an electrician, so I don't know for sure. But by looking at both panels, it seems the one side may be demanding a lot and not very well balanced.

I then noticed the office which has the laserjet printer is tied to the lighting in the living room and hallway. So I can see how the printer could be dimming those lights. However, the kitchen appliances are on a separate breaker which also cause the lights to dim.

I plan on running a dedicated line for the printer and office computer on the panel that consumes less power hoping this would fix it. However, I want to hear some other thoughts and possible solutions to this.

  • The side of the panel the breakers are on doesn't matter. Which "leg" the breakers are connected to does. What you didn't mention, is what size conductors are feeding the panels. You also didn't mention whether you see the problem more with the circuits from one panel or the other, or both panels equally. Photos of each panel, with the breakers labeled, would also be helpful. – Tester101 Nov 11 '15 at 16:03
  • I'm not sure what ga wire feeds the panels. They are pretty thick, maybe a nickle or bigger in diameter. Both sides show problems, although the side with more breakers seems to be the more bothersome of the two. – user2087262 Nov 11 '15 at 16:34
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    @user957902 If you have 400 amp service, that's 400 amps. Not 200 per leg. – Tester101 Nov 11 '15 at 18:09
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    Are you sure it's 400 amp service? – Tester101 Nov 11 '15 at 18:10
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    No one has yet mentioned the KVA rating of the utility transformer outside. With a small transformer most any large load can dim the lights. For example, I have an all electric house with a 200 amp main panel but the utility transformer on the pole is only 10KVA (maximum of 63 amps at 150% over rating). When I left a message with the local utility inquiring about it, they did not bother to call me back so I guess they will only worry about it if it fails. I have to remember not to turn on too many baseboard heaters. – user39367 Nov 12 '15 at 22:18
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You did the right thing first tightening the connections, next would be to use an AMP clamp meter to verify the loads connected to L1, L2 and make sure they are ballanced, if unballanced as stated above some breakers need to be moved untill they are ballanced. if they are ballanced it may be your main breaker has a weak hammer on 1 leg causing some internal arcing and the voltage drop. I had to replace a square D panel several years ago as I could not get a new main breaker from square D

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Motorized appliances (air conditioning, well pump, refrigerator) and laser printers both draw large amounts of startup current. They are essentially a dead short across the line for the first few milliseconds. In my city house these loads cause the lights to flicker since we are on the same transformer with ~10 other houses. I have checked all connections also to no avail. Also recently replaced the main breaker with no joy.

At my country house when I start up my 10 inch radial arm saw or compressor the lights are rock solid. But my country house is on a transformer all by itself.

I would say if you can't live with it and it is absolutely driving you nuts then you will have to move or get the utility to add more capacity in your neighborhood.

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I agree with everything that's been offered already. But, there are a few other things to consider. 1st, is the most up-front expensive & would require new service panels. Price & consider upgrading to a 3-phase service as this will not only provide a 3rd "Leg" in each panel to split the loads, but also may be offered at a significantly discounted rate by your utility company.

2nd & 3rd is your contribution to the remedy by greatly assisting your Electrician to the extent that you can. 2nd is to get 20 or 30 of the cheapest Night Lights you can ($1 or $2 each) to use for mapping your electrical system. Night Lights like, this, this & this would be plugged into your outlets & you turn on all ceiling & wall lights to then turn off a Circuit Breaker & detail what outlets or room lights are turned off. Also, check lighted appliances like refrigerator, dishwasher panel, microwave , washer, dryer, kitchen exhaust vent lights & oven.

Once the mapping is done & fully detailed on your computer or a couple pieces of paper. You'll want to print them out for each service panel & tape them to the inside of the service panels' doors. 3rd is to get a Kill-A-Watt meter to record & document (computer or paper again) large energy appliances start-up & running wattages.

4th is to either yourself (preferably for sake of cost) or have your Electrician verify that your outlets are properly rated to the circuit & circuit breaker & that all connections are fully seated & securely tightened. A cheap builder's-grade 15-amp outlet can cause dimming & flickering when it's capacity is approached due to its low quality. All of the above will let the Electrician competently distribute the load for no or very rare dimming or flickering events in the future.

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