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Strange power problem: when 110 + 110 ≠ 220

  1. Jan 15, 2012 #1
    My understanding of the way that power distribution worked in the US was that the pole pig or distribution transformer dropped down from the higher voltage to a 240 volt secondary winding, but that this winding had a center tap which was connected to and used as 'ground'. So if you ignore the center tap and just connect to each end you should always get 240 VAC (or 220 depending on local conditions). There are 3 wires entering my house that go to my breaker box. An uncovered aluminum ground wire that connects to the ground bus and two black insulated wires that connect to my 100 amp main breaker which then connects to the two hot buses.

    If I connect my multimeter across the two hot wires connected to the main breaker I get a reading of 0 volts. There doesn't seem to be any voltage across them at all. But the reason I am able to type on this computer right now is that there is a voltage (109 volts) between each of those insulated 'hot' wires and the aluminum ground wire.

    main breaker wire 1 to ground wire = 109 volts
    main breaker wire 2 to ground wire = 109 volts
    main breaker wire 1 to main breaker wire 2 = 0 volts.

    I don't understand how this is possible if my understanding of power distribution is correct. How could you have a transformer secondary winding where you had voltage between the center tap and each end but not from end to end?

    I have had this problem since the summer. So it can't be a problem with the distribution transformer itself or the electric company would have fixed it by now because other people would have complained when their stoves and electric dryers stopped working. Actually I only noticed the problem when my instantaneous hot water heater stopped working. Oh, and the electric meter doesn't seem to work. I'm wondering if the broken meter is somehow causing this. Although I don't see how. Any ideas?
  2. jcsd
  3. Jan 15, 2012 #2
    Call the power company immediately. Your pole pig is a roasted ham. If it decides to loose insulation between primary and secondary it will burn your house down.
  4. Jan 15, 2012 #3


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    It could be a number of things. Somewhere between your main service disconnect and the transformer one of the legs is open. Your instantaneous water heater or other 220 volt loads that you apparently don't miss are most likely able to feed back from one leg to the other. If you disconnect all 220 volt loads (flip the breaker) you will likely find one leg goes dead.
  5. Jan 15, 2012 #4

    jim hardy

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    yep open feed in one line, and it is being fed backward through a big load.

    dont be surprised if it's your meter that's failed open.
  6. Jan 15, 2012 #5


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    Incidentally, if the meter is still good then your trouble is between the meter and transformer. If the meter is receiving 220 volts and all the current is being drawn through one leg at the meter, your meter should still register what you are using. However, if the meter does NOT receive 220 volts then no matter how much current you draw through it in any manner, it will never measure it.
  7. Jan 15, 2012 #6

    jim hardy

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    i took this to mean at METER side of breaker (be VERY careful! ), probably top.
    if you read at house side could be open main breaker pole. cycle it.

    yep, as s'nova said, meter multiplies volts X amps X cosine of angle between...

    i'm going to GUESS you'll find a burnt up connection in the meter box where the meter blade slides into the spring loaded gripper.
    Bad news, usually that's considered the homeowner's responsibility. from weatherhead in is yours, only meter itself is theirs. hopefully it's internal to meter, or in their wiring.

    is transformer humming unusually loud? that'd indicate what Antiphon said....

    ""Actually I only noticed the problem when my instantaneous hot water heater stopped working. "" those things draw a LOT of current and will flush out any weak links. when you get it going again feel around the whole installation for hot spots.

    Good Luck!!
    Last edited: Jan 15, 2012
  8. Jan 15, 2012 #7


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    It varies from one company to the next as to whos responsibility it is. Even different parts of the same company have different policies from one state to the next. I would say just hope it is on the pole. Definitely not your problem then. :)
  9. Jan 16, 2012 #8
    Well the power company has been charging me estimated rates based on the previous year of the same month. Strangely this system is surprisingly accurate, based on my sense of how much electricity I'm using. I think I was slightly undercharged in the summer and now slightly overcharged in the winter. Actually they are charging me for somewhat more kWh per billing cycle now than in the previous year, which does dampen my enthusiasm for this flat rate thing. I haven't told them about the problem because I was curious about this flat rate electricity thing and frankly I was expecting them to fix it after a certain number of non-reads. The meter is one of those newer fancy RF ones that transmits to a drive by meter reader and displays the kWh on an LCD display. I don't know why they haven't come by to investigate why my meter isn't transmitting.

    I live in a neighborhood with many houses. Although I don't know for sure I would imagine that the same pole pig connects to more than one house. So why haven't any of the other houses complained? I would entertain the idea that the flat rate electricity also appealed to them, but they are wealthy and I don't think the lure of being able to use slightly more electricity than they are paying for has quite the same appeal that it has for me. Besides if the power company were getting a whole bunch of non reads surely they would come to investigate after 6 months. So, unless it only connects to my house, I think a bad pole pig is unlikely.

    But assuming it is a bad pole pig, what could cause only half of the secondary winding to go bad? It's just a single winding with a tap at its center. If just one half shorts or burns out I could see how you could still get voltage between the tap and the good side, but I don't see why that would happen in the first place. IIRC this situation did somewhat coincide with a hurricane we had here in the northeast US last summer. So if something were going to happen to a pole pig that would be a good time for it. Also the failure seemed to happen gradually and intermittently. My hot water heater didn't seem to fail all at once. It would work for a while and then stop for a while and then work for a while. So of course at first I thought it was a problem with the heater. Until I measured the main breaker voltage and got zero.

    The 240 volt heater was immediately replaced with a spare 110 volt one, and I don't have any other 240 volt appliances (no stove or dryer etc). Also, when the problem first occurred one of the very first things I did was pull every single breaker from the box except the main and check the voltage again. IIRC, I got the same result. No voltage across the two hot wires and 110 volts from each hot to ground. I may try this again just to be sure.

    Well the LCD display on the meter is blank and every meter read since the summer has been an estimate. So it does seem likely that the meter is bad. I just went outside to see if I could check the pre-meter voltage, but unfortunately all the wire is insulated from the meter box right up to the pole itself. I'd have to climb a pole to get to bare wire to check the voltage between the pole and the meter (which I'm obviously not going to do even though I'm curious). In fact the wires are in a conduit right up until they leave the roof, so even a clamp DMM wouldn't help me unless I want to get up on a ladder.

    Your assumption was correct. These measurements were taken at the meter side of the main breaker. I should have been more clear on that.

    To be more specific, it measures volts x amps (and phase angle) between the two hot wires and not between either hot wire and ground? Otherwise the meter should be working. What if the meter itself is the 240 volt appliance that is feeding current back through the bad leg? But then that implies that the pole pig is bad, which is strange if it supplies more than one house.

    Oh wait... No it doesn't. There could be a broken connection somewhere between my meter and the pole pig (very dangerous!). The meter only sees one leg and gives no reading, but feeds back the current through the bad leg to me. Since this problem seemed to start after a hurricane this makes it even more plausible. My supply wires wind right through the branches of many trees before reaching the street. That puts a lot of stress on them, especially during a hurricane. Maybe one of the leads pulled right off the pole pig. I'm going to go out and look for any obvious breaks in those wires going to the street.

    A burnt or broken connection in the meter box, probably on the input side, is possible of course and it may then feed back the current to both legs on the output side. The wire is strain relieved at the roof, but a wire may have pulled out anyway. I suppose lightning could have caused just one lead to burn out. My measly 100 amp main breaker should have prevented any of my loads from burning out a lead through normal use. Those are some thick wires.

    I thought transformer hum was supply frequency related. Presumably in this case it should be a 60 Hz hum. And I would guess the amplitude should be proportional to the current. So why would a bad transformer hum more loudly? Maybe because it needs more current to supply the same power with a lower voltage? In that case the transformer would be about twice as loud as normal.

    This sort of thing makes me want to know for sure what the problem is before I go complaining to them about it. I don't have the money to hire an electrician, and I can see them deciding to turn off my non-reading meter until it is fixed if they consider the repair to be my responsibility. Or maybe they would just fix it themselves, bill me for it, and then shut off my electricity when I cannot afford to pay their huge bill. There's a saying about sleeping dogs that comes to mind. My 220 volt heater is much better than my 110 volt one, but I could be stirring up trouble if I'm not sure who is responsible for the repair. 110 volts is better than none at all.
    Last edited: Jan 16, 2012
  10. Jan 16, 2012 #9

    jim hardy

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    ""I thought transformer hum was supply frequency related. Presumably in this case it should be a 60 Hz hum. And I would guess the amplitude should be proportional to the current. So why would a bad transformer hum more loudly? Maybe because it needs more current to supply the same power with a lower voltage? In that case the transformer would be about twice as loud as normal.

    indeed the transformer will hum at 60 hz (well, probably 120)
    the hum is from the magnetic flux moving things ever so slightly
    so it's in proportion to magnetic flux
    which is in turn in proportion to applied voltage.
    so it should hum a teeny bit louder on high voltage days than on low voltage days.

    if it has a shorted turn inside, that turn will be getting very hot and in the location of the shorted turn there will be very large magnetic forces opposing one another. so some magnetic flux will go where it shouldn't, making more hum,. and voltage will be low like you measured.
    i think that's what Antiphon was warning about.

    a shorted turn should have destroyed the transformer by now, i would think. i once saw one literally blow its top.

    lastly - where i lived, if you called power company and notified them you were going to work on your panel and needed to remove the meter, they'd make a note of it so meter reader didn't initiate a federal case over broken seal on his next visit. So you could maybe pull your meter and look at the innards of box.
    again be VERY careful, for that pole pig can deliver enought current to make an electrical explosion equivalent to a magnum shotgun blast.

    you soundlike pretty handy sort - you'll solve this one.

    by the way - i am curious about those instant heaters. to me it's incomprehensible to get that many BTU's per second out of a wall plug.
    How many amps does it draw? What's nameplate rating?
    Will it give you a nice hot shower?
    do they suffer from lime buildup?

    old jim
  11. Jan 16, 2012 #10
    As far as the heaters, they don't connect to a wall plug. They connect directly to a circuit breaker in the panel. The nice one is rated at 12 kW. Meaning it pulls nearly 50 amps at 240 volts. On the inside it's pretty interesting actually. The design uses electrified copper tubing instead of nichrome wire coils. The water is immersed in the coil instead of the coil being immersed in the water. It was originally made by an American company (in Vermont I think) which was bought out by a German one some years ago. Bosch I think. It works quite well for a point of use shower heater.

    The other heater I bought off the street in Cuba many years ago for $30 I think. It's made in Brasil. It is also an interesting design due to its simplicity. It's basically a closed plastic watering can containing a nichrome immersion coil. The heated water just falls on top of your head. About as simple a system as you can get. Unfortunately when I first started using it many years ago the coil and every other part of the system would be constantly breaking. So I just modded it to be even simpler. A coil of wire that connects to a breaker with nothing else in between. It turns on and off by flipping a breaker on the panel. That heater runs on 110 and draws about 40 amps for a total of about 4.4 kW. It was strictly intended as an emergency back up if the good heater failed, but I've been using it since the summer.

    As far as the strange problem, I'm not sure that I even want to solve it right now. I'd just like to figure out what it might be. The mystery of getting 110 on each leg but not getting 220 was bothering me. Now I'm thinking that one of the wires from the pole pig must be open circuit before the meter somehow and the meter itself is working as the 240 volt feedback loop. I was trying to think of some way of running my 240 volt heater on 110 by using a step-up transformer, but I soon realized I would need at least a 12kVA transformer. Haha. Expensive to buy and difficult and expensive to make. Also my main breaker is only 100 amps and at 110 volts the heater would actually draw about that much.
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