Intermittent voltage sag on one leg of 110/220

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  #1  
Old 01-19-13, 12:39 AM
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Intermittent voltage sag on one leg of 110/220

Hello. First time posting here; I don’t see any previous points that are quite on point.

My 70-year old California Ranch house (220/110) is experiencing significant but intermittent voltage sag on roughly half its branch circuits. The other branch circuits remain fine. Oddly, the affected circuits are in both the main panel (which is old) and in a newer, adjacent sub-panel. Both panels contain breakers for 110 branches and 220 devices.

Over the past few weeks, the suspect circuits have “sagged” on three or four occasions, for an hour or two at a time, then back to nofirst, we attributed the problem to rain/moisture, but it’s now clear that that’s not the problem. The intermittency has made it tricky to pin down.

One thing the affected circuits may have in common is in being sourced from the same leg of the service. I say “may” because while the affected circuits in the main panel are definitely all on one leg, I’m not yet certain that the affected circuits in the sub-panel are all sourced from that same leg (I hope to confirm that tomorrow).

One weird thing is that when I turn on the 220 clothes dryer, all lights and other loads on ALL of the “sagging” circuits immediately see proper voltage and light up fully! So, it appears the problem isn’t that we’re not getting full voltage from the PoCo. Rather, my hunch is that there’s some issue with a neutral somewhere – but I’m not sure about what/where to troubleshoot next.

(The trouble doesn’t seem to be with the dryer circuit itself. The dryer is right next to the panel and I’ve confirmed its whole circuit with a sniffer and a multimeter.)

This forum post sounds sort of close to our situation (except our problem is just on one leg):
http://www.doityourself.com/forum/el...tage-drop.html
One similarity is that our circuits suddenly start to behave as in series: turning on each additional light or appliance will sag the voltage lower, to the point where lights are barely illuminating... then turn on the 220 dryer, and all lights up fine!

The ground paths for most circuits are via the old-style metal flex conduit. Several newer replacement circuits have been run with 12/3 Romex, with their equipment grounds bonded at the main panel (only). There appears to be no correlation between the grounding method and whether the circuit is affected.

FWIW, I’m an audio engineer, and understand electrickery, but only to a point. I can wire a branch circuit to code, read a schematic diagram and a multimeter, and I’ve even installed a few panels. But I’m the first to admit that my grasp on theory starts to get weak....

Any brainstorms would be much appreciated.

- K Hill
 

Last edited by Seamonster; 01-19-13 at 01:17 AM.
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  #2  
Old 01-19-13, 04:03 AM
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Hi, welcome. I like your idea of a bad neutral connection. Either at the main bus, in the meter base, splices in the service drop, or at the transformer. The only one you can safely get to is in the main panel. The power company will check the transformer for free. An electrician can check the meter base.

This is a similar problem on a different forum-

VERY odd problem... HALF a power outage??
 
  #3  
Old 01-19-13, 06:16 AM
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Here the meter base is checked by the electric company. Be sure to call the emergency number not the customer service number.
 
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Old 01-19-13, 07:34 AM
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I suspect your problem is either in the meter socket or at utiloity connections at the weatherhead or pole. You say the problem is experienced only on half of your circuits.

My 70-year old California Ranch house (220/110) is experiencing significant but intermittent voltage sag on roughly half its branch circuits. The other branch circuits remain fine.
This leads me to belive the problem is not the neutral, but one of the hot leg connections. Regardless, your power company has 24/7 emergency service and normally there is no charge for this. Call them as already suggested.
 
  #5  
Old 01-19-13, 08:19 AM
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Welcome to the forums!

First, a technical point: Your house doesn't have 220V or 110V power. It has a 240V single-phase service fed on two 120V legs. IOW, a 240/120V service.

One thing the affected circuits may have in common is in being sourced from the same leg of the service. I say “may” because while the affected circuits in the main panel are definitely all on one leg, I’m not yet certain that the affected circuits in the sub-panel are all sourced from that same leg...
It sounds like you have a loose connection on the one of your ungrounded feeds. How have you determined that the affected circuits are all on the same leg? Which breaker positions are being affected?

One weird thing is that when I turn on the [240] clothes dryer, all lights and other loads on ALL of the “sagging” circuits immediately see proper voltage and light up fully! So, it appears the problem isn't that we’re not getting full voltage from the PoCo. Rather, my hunch is that there’s some issue with a neutral somewhere – but I’m not sure about what/where to troubleshoot next.

(The trouble doesn't seem to be with the dryer circuit itself. The dryer is right next to the panel and I've confirmed its whole circuit with a sniffer and a multimeter.)
While neutral and ground are critical components of a complete electrical system, it doesn't seem that what you're experiencing would likely result from a problem with either of those. A loose neutral connection, for example, often creates a higher penitential on some of the ungrounded (hot) conductors.

Because the dryer is next to the panel, it may be that the vibration from the dryer, or some other effect from its operation, may serve to re-establish a good connection of the feed. Looked at from the other direction, the dryer's operation could be one source of the problem.

My hunch is that one of the connections where the feeders from your meter are terminated to the lugs in your panel (even if those lugs are part of your main breaker) is a bit loose. Ideally, all of the termination screws in a panel should be checked for proper torque once a year. In homes, that is not usually done.

I would ask the PoCo to check their supply. It should be a free call. Do use their emergency service number to make the request, as Ray suggested.

Once that is done - or in the meantime - you can look for the torque values for the terminations in your panel on the label on the inside of its door, or on the breakers themselves. You can turn off individual branch circuit breakers and check the tightness of those screws, and you can check the torque on the neutrals and grounds, including the utility neutral and the grounding electrode conductor termination(s).

If you are totally prepared to work on a live, unfused conductor, you can also check the torque on the two screws that terminate the hot feed conductors. My advice, though, is that you hire a qualified electrician to do that.
 
  #6  
Old 01-19-13, 08:25 AM
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I had a similar issue a few years ago. It turned out that one of the hot legs at the service drop had partially broken due to a tree pushing on it. When the wind blew, it would separate that leg and we'd get half the circuits to brown or black out. When the oven was turned on, the downed circuits would come back on. Near as I can figure, the oven was providing a sufficient current across the heating elements so that it was basically back feeding the broken leg.

You may find that, while the dryer turns on, it is only getting partial power and not drying as well as it should.
 
  #7  
Old 01-19-13, 10:53 PM
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Thanks for all the replies, folks. The problem is fixed – with your collective help.

We had the PoCo out here a few weeks ago and they found nothing wrong then. As it turns out, that was after the old line from the power pole to the weatherhead had gotten wet. It had shorted on ONE LEG, but then evidently moisture kept the connection working, more or less, for a few weeks. Yesterday the weather suddenly turned very dry – and we were back to having only one leg. So today the Poco (two trucks and four guys) strung up a new wire and now all is back to normal.

Thank you to those who suggested that the problem could still be on the PoCo side. It helped me get past the assumption that it couldn't have been their problem because they had vetted their side a few weeks before.

Amazing that that one simple fault was the source of such mysterious voltage variations throughout the house.

Best,
K Hill

P.S. My original post has some sketchy/unintelligible sections, due to my browser's inability to accurately process this forum's reply box. When I'd think I was deleting something in one place in the text, this reply box was invisibly deleting text elsewhere in the post. Weird. (FWIW, I'm running Mac OS 10.4.11 – old machine – using either Safari or Camino browsers.)
 
  #8  
Old 01-20-13, 07:22 AM
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Try Firefox as your browser. Generally it works well in all OSes.
 
  #9  
Old 01-20-13, 07:22 AM
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Glad you got it fixed - and for free! - and thanks for telling us how it was resolved.
 
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