We have a 200 amp service. Uderground service comes to a meter pedestal, then underground to the house. My breaker box is Cutler Hammer and I am in the US. Sometimes the power goes off in all the rooms but two. Sometimes in the rooms where the power is off something small like an LED clock will still be on, but dim. When the power eventually comes on it is weak, dim lights etc. This happens at times when something extra is turned on and at other times when we are just sitting or even asleep and nothing extra is on. The house was built in 2002. When this happens the breakers never kick off. Could this be in the breaker box. The main breaker where the service comes into the box? Could one leg just be out? If so what is the best way to test. Thanks.

 

Call the electric company. Don't let this continue or you'll suffer permanent and expensive damage.

 

I agree with John Nelson. Often the power company will come out for free and tell you what the problem is. If you need an electrician, they will certainly tell you and you're not out for the cost of the service call. Sometimes it is the power company's problem and they fix it at no charge. But various power companies have different policies, so no guarantee. But the first step should definitely be to call your utility.

In my travels I have found a "weak" main fuse on one of the two legs of the incoming power. So on one leg some juice was getting through it but not all, resulting in very dim lights in those rooms. And on the other leg it was fine and circuits conected to that leg had no problem whatsoever.

If you have a main circuit breaker, it could be a defective breaker or poor connections that have carbon all over them.

Just a couple ideas, or possibilities anyway. But I'd still call the utility first.

Juice

 

Thanks. I think that one leg is out. One question? Does it mean that on each of the hot wires coming into the main breaker that they would each have 100 amps to total 200? What would it be in volts? I did notice also that some breakers on each side are out while others work. Does this mean anything to you? Thanks. I called the power company, however due to the ice storm we are on a waiting list with several other people. Just to clarify the ice storm was several days before we started having trouble.

 

A loose service wire in either the meter base or panel mains. Last week I got a call similar to this; they had the power company out and they "fixed something" but the next morning they had the same problem, intermittent voltage serving half the house. But when "they tapped on the side of the meter base" they got power back.

Turns out they had a loose service wire on the load side. The lug was tight but the foot on the bottom of the captive bolt had bound inside the fitting short of the wire-so it never had been compressed as it should have. And the power company should have caught it....

Just my 2 cents...

 

200 amp service means that each of your two hot wires can carry up to 200 amps. But you don't get to add these together. I always use the example that if each of the four tires on your car is going 25 miles per hour, your car is still only going 25--it's not going 100.

The voltage of each hot wire to ground is always 120 (unless there is a fault, which it seems is what you have), and the voltage between the two hot wires is 240.

It is important to realize that side of the panel is different than leg of the service. In many panels, the odd numbered breakers go down the left side, and the even numbered breakers go down the right side. But one leg of the service supplies spaces 1, 2, 5, 6, 9, 10, 13, 14, 17, 18, ... and the other leg supplies 3, 4, 7, 8, 11, 12, 15, 16, 19, 20, ... So when you have problems with your service, you sometimes lose one or the other of those sets. When you do, power can be backfed through a 240-volt appliance (e.g., oven, water heater) to the open leg. This can cause some really bizarre things to happen. People report things such as the lights in their basement coming on when they turn on the oven. You can't let this continue, since your appliances are getting more or less voltage than they are designed for. This can sometimes destroy your television, stereo, oven controls, and lots of other expensive stuff in your house.

While you are waiting for the power company, if you continue to have problems, I recommend you shut off every double-pole breaker in the panel to avoid this backfeeding.

 

Thanks for shedding some light on this for me, ha,ha. You have really helped me to better understand how this system works. The power company came out in the middle of the night and told me that everything on their end was fine. He said that he thought it was the main breaker in the service panel off the meter. He said I should have it checked. This morning I began calling electricians. We are in Ohio in the middle of the ice storm. Over two different cities there are no electricians available until next week. I had a problem similar to this a year ago when there was some excavation work being done in our front yard and a bulldozer cut one wire of our alluminum 3 wire 4/0 service entry cable. The similar things happened then. The wire was spliced and a new piece was put in with a weatherproof underground splice. I started to wonder if the splice did not hold up, or if there was another nick in the wire they did not find. I put a volt meter on the service panel at the meter and it showed 123 volts on one leg and 125 volts on the other. 350 feet away at the house I checked the cable coming into the house and one was 123 and the other was .45. What do you think, is the splice my problem. I thought this may help the electrician when he is able to come. If it is this is there an instrument to locate the damaged wire? Or will I have to replace the whole length?

 

I agree that the splice (or an additional nick) is a very likely suspect. The intermittent nature of your problem could be that the fault depends on the moisture content of the soil.

 

Above where the splice was at is a sheet of ice. That area is a little lower than the rest of the yard and prior to the ice storm there was alot of rain. It collected there making this area very wet, eventually freezing. I will let you know as this goes and again I appreciate your help!