Weird power fluctuations


Old 10-03-00, 09:14 PM
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We're adding onto our house & have done the following in this order:

1) Migrated all circuits from our main breaker panel (100A) to a 125A sub-panel temporarily still fed power from the main panel. Everything worked fine in this mode for several weeks.

2) Had an electrician install a new 200A main breaker panel with a 125A feed to our subpanel...not connected at first.

3) Had the utility company cut over power from the pole from our old 100A main panel to the new 200A main panel and simultaneously connected the 125A feed to the sub panel.

The main panel currently only has an 8' driven rod ground, since the rough plumbing isn't complete enough to bond to the cold water pipes.

Since the cut-over, I've noticed that our lights dim several times through the evening. I connected an AC line voltage monitor and can see the needle spike down significantly coincident with the lights dimming.

I did a little detective work & I'm beginning to convince myself that the brown-outs coincide with our neighbors air conditioner turning on.

What is the likely cause of my new-found coupling with my neighbor's power consumption? Is it an issue for the utility company? Could my lack of a cold water ground contribute to this? Could anything be wrong with the 200A main breaker or 125A feed breaker to the sub panel? Could there be a problem with his air conditioner?

Thanks for the help!

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Old 10-04-00, 10:05 AM
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First, I don't think ground is bonded to the plumbing any more. Though I suppose your local code might require it as a holdover from past practice. A ground rod, in the ground is definitely required. I think the current NEC says not to bond your ground to the plumbing, but I'm not 100% sure.

Your power fluctuations may be due to a poor neutral return connection in your, or your neighbor's, service drop. I would report this to you power company so they can check for bad connections on their side of things. It would not hurt to have your electrician double check his stuff too. I assume you and your neighbor are fed from the same tranformer, and that means the problem could be due to something on his property.

[This message has been edited by ranck (edited October 04, 2000).]
Old 10-04-00, 10:45 AM
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My neighbor and I are fed from the same transformer. In fact, I think we're the only two houses fed from the transformer on the pole in the corner of my property.

What exactly does the utility company do on the pole to supply me with 200A service vs. the 100A I had before? Is it just a change in the wire gauge or is there something different about the connection at the pole?
Old 10-04-00, 03:56 PM
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If you have a metal water pipe type plumbing the these metal pipes must be bonded to the grounding of the panel. If you have at least a 3/4" trade size water pipe that is at least 10' underground then you must use this water pipe connected closest to the entrance of the water pipe as your grounding service conductor's source with a made electrode or other grounding source such as rebar if available as you secondary ground source. This secondary grounding source is required in case that the water pipe is changed to plastic.

If you have metal water pipe design with no 3/4" pipe horizontal at least 10' and at least 2' deep then you are just bonding the metal water pipes making these metal water pipes one with the grounding system. This is required in order to send a signal back to the panel if the water pipes become energized by a frayed wire etc. If this bonding is not present then your whold metal water pipe can become energized waiting to shock even to death anyone coming in contact with these non grounded water pipes.

If you have short pieces of metal water pipes and you have a mostly plastic water pipe system then the water pipes do not need to be bonded to the panel.

Now as for you dimming, I suspect that you may have a neighbor that has a stuck compressor that is cycling trying to start but can't. Ask you neighbor to shut down his a/c for an hour or two and if the dimming continues then the a/c is eliminated as the culprit. If the a/c is innocent then contact your energy company suspecting a bad squeeze on connection at the transformer if both houses are experiencing the dimming. If just your house is dimming and the a/c is innocent then check for a loose connection in the meter or you panels at the feeder connections

Good luck


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