momentarily dimming lights

Discussion in 'Electrical Forum discussion & Blog' started by chuck_r, Jul 10, 2007.

  1. chuck_r

    chuck_r New Member

    We own a house that we rent out that we had lived in for 20 years or so. It was built in the 1950s. The tenants recently said that the lights have been dimming for a few seconds at least once a day, perhaps more, usually in morning and afternoon, and all lights in house seem to be affected. Sometimes it seems related to dishwasher or furnace coming on, sometimes not. They've been tenants for two years and say it has been happening more in last couple of months, and they just informed me because I'm coming out to do annual maintenance (we live in another state).
    My electrician said to call the power company first to check the pole and weatherhead; in his experience that fixed about a third of such cases--so I did.

    The tech from the power company, who I talked with by phone, said that he tested the voltage on the two legs of the supply line using what he described as being essentially like "two meters and a hair dryer". At the main panel, he put the load on leg A, and voltage dropped on leg A and rose on leg B. He put the load on leg B and the voltage dropped on leg B and rose on leg A. He said it changed about 8-10 volts, which is much more than normal. He checked at the pole and weatherhead and voltage was good. Then he pulled the meter and tested behind the meter and found the same problem, which really surprised him, so he put the meter back in and tested the weatherhead again and it was good there. He concluded that there must be a neutral problem in the conduit that runs from the weatherhead to the meter and that we should get it fixed ASAP. He advised the tenant not to turn on any expensive appliances, or too many at once, or she might burn out some appliance from a rise in voltage (on the opposite leg, I assumed). He said the only time he's seen this problem is when someone tried to tap into the supply line before the meter to get free power, and he was apparently suspicious that was the case here--he asked how long we had owned the house, etc.

    Since the problem is recent, last few months, and the tenants we have would almost certainly have not done something to the electrical system, I find it puzzling. I also think that if the problem were as he described, the tenants would see half the lights in the house brightening at the same time the others are dimming. My electrician hasn't yet visited the house to confirm this, but I wonder if the power company's service tech actually knows what he is talking about.

    On another forum (gardenweb), someone said the following:
    "I had the exact same thing. I talked to people on this forum....checked all the neutrals up to the meter...disconnected and reconnected. Still had same problem. Called in the power company and they plugged their latest gadget into the meter socket that put a load on the incoming feed and said everything was normal. They also checked the connections behind the meter.Problem persisted. I went through all the neutrals in the panel, ect. again and the problem persisted. Called the power company and this time their supervisor told them to do new connections at the pole and the weatherhead. They disconnected, cut wire and reconnected. Problem solved!"

    Does anyone have any experience with something like this?

  2. snafflekid

    snafflekid Electrical Engineer

    Anytime the voltage drops when loads are added, it means there is resistance in the wiring, which could be due to a bad or corroded connection. It seems that the tech has found the problem is somewhere between the transformer and the meter, which is the power company's domain. A loose neutral here would be bad for 120V equipment, i.e. the power company would be buying you a lot of new appliances.
  3. Alectrician

    Alectrician DIY Senior Member

    Loose, coroded or undersized neutral.

    Happens all the time.

    Fix it before it drops out completely or you will have a LOT of things to replace.
  4. BrianJohn

    BrianJohn DIY Senior Member

    This should be addressed ASAP, if in a loose neutral you will fry equipment and possible have a fire.

    The house is from the 50"s but you did not mention the age of the service lateral, or if it is overhead or underground. Conductors d go bad, connections exposure to the environment break down, moisture ect., stresses from loads, age. LOTS of things result in the breakdown of insulation and conductors, there is a limited life span and it may be time to replace or repair.
  5. chuck_r

    chuck_r New Member

    It's an overhead service connection, and I don't know the age of the service lateral, but it is at least as old as mid-1970's

    I thought the cable from the weatherhead to the meter was the homeowner's responsibility.

    I am having it checked by an electrician today and I'll post what the final resolution was.
  6. snafflekid

    snafflekid Electrical Engineer

    I missed the part about overhead power. You supply the weatherhead, conduit and meter box...probably. It was determined there's not a bad splice at the transformer?
  7. chuck_r

    chuck_r New Member

    I just heard from my electrician. He went up to the weatherhead and pulled on everything while testing it and found the neutral splice was a bit loose in the crimp. He redid it and everything tested OK, and he said he's 99% sure that fixed it. He was surprised the power company technician missed that. He suggested I call the power company and tell them my electrician suggested that they redo all their splices.
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