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    New Year's resolutions of mysteries




    LETTERS

    New Year's resolutions of mysteries


    By Kathleen Atkins

    Life in our digital world is much like life in the organic world: you can count on sudden failures, persistent difficulties, and disconcerting discoveries.

    Windows Secrets readers are never shy about telling us what they think we missed in a story or what problems they encountered when using our advice.

    The full text of this column is posted at windowssecrets.com/letters/new-years-resolutions-of-mysteries/ (paid content, opens in a new window/tab).

    Columnists typically cannot reply to comments here, but do incorporate the best tips into future columns.

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    Regarding Ken's HomePlug system and the power company controlling power down to individual circuits in the home -- Ken must have an interesting way of connecting his home to the grid. Without multiple connections, there would be no feasible way of controlling individual circuits -- it could not be done! If his office is connected separately from the house -- that can make sense, but that would mean two meters and two bills...

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    I don't know where Ken Goldstein came up with his fantasy, but it does not happen, and is impossible. It will remain so until the manufacturers start putting microcomputers and unique identification codes in circuit breakers. Even then, it would be possible to thwart any such spying by simply buying new circuit breakers and installing them. How would the power company know which breakers to address?

    His wife is obviously not an electrical engineer and the "equipment necessary" would be a simple voltmeter you can buy at any hardware store for under $20.

    If he is seeing such voltage differences in his house, then he has a serious electrical problem somewhere that could lead to a fire - potentially burning the whole house down. When it occurs, it is almost always due to a bad neutral conductor connection somewhere - I have never seen any other cause.

    The difference is not between individual breakers, but between the two sides of the split single phase feed to the house. You check it by measuring the voltage between the two hot conductors and the neutral. Depending on the loads on the system, one voltage will be higher than normal and the other will be lower. The differences will change as loads vary.

    The visual symptoms are lights that brighten or dim momentarily. If the problem is severe, then the lights might brighten or dim and stay that way until the load changes.

    He needs to get a qualified electrician in to find the problem immediately.

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    It's a wiring problem

    I concur with the other posters that Mr. Goldstein's problem is unlikely to be related to experiments at the power company. What he is probably seeing are the symptoms of a poor connection in the neutral line of his house wiring. When there is not a good neutral connection all the way back to the transformer, varying the load on one side of the line will rasie or lower the voltage on the other side of the line. A good electrician should be able to track this down. Depending on where the fault is (in the house or at the transformer), correction may require work by the power company.

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    I had a friend that had been having light dimming/brightening problems for months and slowly getting worse, when he happened to mention it to me.

    Since the symptoms are classic, I told him to contact the power company immediately. They had a lineman at his house within an hour. The lineman found that the neutral was almost completely broken at the middle of the span from the power pole to the entrance mast. The lineman spliced in a new section of wire and the problem went away.

    My friend told me that a tree limb had fallen on the wires a few years ago in a wind storm, then fell the rest of the way to the ground. Apparently that damaged the neutral and, over time, strands started breaking as the wire swayed in the wind.

    On my house, about 20 years ago, the bad connection was where the neutral wire connected to the power transformer (pole pig).

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    I see that most people agree with my assessment of Mr. Goldstein's situation. In my house, I have one pair of wires (plus a neutral/ground) coming into my service panel. I believe that is typical of most installations. There is simply no way that my kitchen has a very different voltage than the living room -- unless there is a high resistance somewhere in the wiring. The power company cannot change the voltage in my kitchen and not in my living room.

    Furthermore, I seriously doubt that they can change the voltage coming from the nearest transformer, without having a technician move a tap on the transformer. While it might be possible to do that in the future, there would have to be many transformers replaced with some that are controllable externally.

    I also believe he has a high-resistance connection in the neutral coming into his house.

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    Those bad neutral wiring issues definately need quick attention. While the vast majority of residential service is two phase which leads to the potential (pun intended) of two different voltages at a given instant in your home, some residences and most industrial locations have three phase service which leads to the possibility of three different voltages , one each on the set of circuits wired to each phase.

    If you have lights that dim when an appliance starts there is a problem needing attention from a qualified electrician! Hire the best, it is cheap insurance.

    This is a personal opinion. J.M., Institute of Electrical and Electronic Engineers (IEEE) Life Senior Member
    Last edited by J.M; 2013-02-07 at 12:12.

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    Actually, that is a common misconception. Residential power is split single phase. It is very rare for individual residences to have three phase service, as the transformer is much more expensive and it is totally unnecessary.

    With split single phase, there is no difference in the instantaneous voltage at any time . You can prove this easily with a dual channel oscilloscope. There can be a current phase shift if loads that are not purely resistive are connected.

    With three phase services, the instantaneous voltages can be different, but the absolute voltages will be the same. The three hot wires will be 120 degrees out of phase with each other.

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    Mr. Goldstein needs to have someone check out the wiring (grounding and neutral) of his solar system if he is consistently seeing wide differences in voltage between the 2 phases. If one leg goes down and the other goes up, he most likely has an open neutral somewhere. There will usually be some small difference due to load, but the voltage should be the same everywhere in the house on that same leg. Always have an electrician check the voltage on each leg at the meter panel and then on the feed to the house main panel to insure that the service cable neutrals are intact.
    Last edited by TwoDogsLoving; 2013-02-07 at 12:49.

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    It is single phase, not two phase. There were very few two phase systems ever installed, for a number of reasons.

    The neutral does not have to be open, just of relatively high resistance.

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    It is split single phase and there is indeed a difference in instantaneous voltage between them - 180 degrees out of phase. If you doubt this, just put a jumper wire from one of your breakers to the next one below it.
    If a neutral is open in a branch circuit, you will have no current in that particular circuit, so obviously it would be a high resistance condition. But if the service neutral is crimped or has high resistance due to corrosion or broken strands you will definitely have a series-load problem resulting in low voltage on one leg and high on the other.

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    Of course breakers will trip. You are shorting across the transformer winding. That has nothing to do with phase, just voltage differential between the top and the bottom of the winding.

    If the load in both legs is balanced, then there is no current flow in the neutral - agreed? If that is the case, you can remove the neutral without affecting anything. So how can the legs be out of phase? Removing the neutral cannot affect the phase, only the magnitude of the currents.

    Draw out the instantaneous current flows - magnitudes and directions. I think you will see why I am correct.

    As a hint, assume 2 amps is flowing in one leg and one amp in the other. You will find that one amp is flowing in the neutral - back towards the center tap on the transformer. The other amp is flowing through the leg carrying 1 amp. Now look at the current flow directions. If you draw a diagram with the transformer on the left and the current flowing upward in the transformer winding - then the current is flowing clockwise through the connected wires - all of them.

    I know it is counter intuitive. It took me a while to understand it when I studied power distribution systems - way back in the 70's.

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    Of course breakers will trip. You are shorting across the transformer winding. That has nothing to do with phase, just voltage differential between the top and the bottom of the winding.

    If the load in both legs is balanced, then there is no current flow in the neutral - agreed? In that the case, you can remove the neutral without affecting anything. So how can the legs be out of phase? Removing the neutral cannot affect the phase, only the magnitude of the currents - even for unbalanced loads.

    Draw out the instantaneous current flows - magnitudes and directions. I think you will see why I am correct.

    As a hint, assume 2 amps is flowing in the top leg and one amp in the other. You will find that one amp is flowing in the neutral - back towards the center tap on the transformer. The other amp is flowing through the bottom leg back to the bottom of the transformer.

    I know it is counter intuitive. It took me a while to understand it when I studied power distribution systems - way back in the 70's.

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    They are 180 degrees out of phase. If they were in phase you would measure 0 volts across them, instead of 240. Why would they bother to run an extra wire to every house if they were in phase? 3 phase is 120 degrees out, that's how they get 480 across each leg and 277 to the neutral. The center tap in a residential transformer is the neutral wire, the unbalanced current flows back through it. I was in power distribution for years also, have an EE and spent 30 years as an electrician, 4 as an electronic tech. You are assuming that since they call it single split-phase that there is no difference, but that's not true, the voltage difference of 240 exists because of the phase created by the neutral, which is grounded. At the instant that one leg is 0 volts, the other is 120. There should never be any current flowing between legs, that's why they center-tap the xformer and run a separate neutral to it. The only time that happens is in a 220 ckt, when you use both legs without the neutral. My last post, if you don't believe it, check the theory books.

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    Quote Originally Posted by dlaskowski View Post
    Regarding Ken's HomePlug system and the power company controlling power down to individual circuits in the home -- Ken must have an interesting way of connecting his home to the grid. Without multiple connections, there would be no feasible way of controlling individual circuits -- it could not be done! If his office is connected separately from the house -- that can make sense, but that would mean two meters and two bills...
    Newer electrical circuits are zoned through the breaker box. Each zone controls electric circuits which service specific areas of the structure. Each breaker could conceivably have its own feed, but only two phases are normally fed in from outside. The power grid could only control the zones if a computer or controller modules were built into the interface. This is not generally the case in the United States last I knew. However, such appliances as air conditioners and programmable thermostats can be controlled through the Smart Grid, and this relies on the ability to program the appliance, not the circuit itself.
    -- Bob Primak --

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