Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Electrical Question from Girl Without a Clue

  1. Jul 27, 2014 #1
    I am going to attempt to explain a recent situation at our home and will most likely use the wrong terminology, so forgive my ignorance in advance. Also, when you answer, can you dumb it down for me so I actually get it? :wink:

    Last week part of the power to our home went out. I was attempting to make dinner and the oven wouldn't come on. I thought that it was perhaps a problem with the oven because we have had power issues with it in the past. My husband switched the breaker a couple times and it wouldn't heat up. I then tried microwaving something, which is on another breaker, and it was running, but very, very slowly and the light was very dim. I then walked out to look at the air conditioners and they weren't running. I looked at the electrical meter into the house and it was dead. While all of this is happening, the lights are on, fans are on and the TV is on. I called the electric company and the lady at the office tried to "ping" the meter. She got nothing so she sent a tech out.

    The tech spent hours with another tech looking for the underground box that holds the lines coming into our home. Once he found them, the attachedis what he found. The wire/line/etc. that is cut almost through is the line that feeds our house. He said that it was probably knicked when our home was built in 2001 and it has been rotting out since. When he measured, he said we were only getting 98v to the house.


    Okay, here is my question... what kind of electrical problems can that cause to our home? We have had tons of issues with electricity since we moved in 6 years ago. Like I mentioned above, the issues with oven breakers being one of them. We have issues every winter (in Texas) with Christmas lights, we have had issues with GFIs popping and it even looks like we had a breaker catch fire in the breaker box at some point over the last two years.

    Could any of that been due to the power issues coming into the house??? What issues could that have caused?

    Thank you in advance for your help/answer!
     

    Attached Files:

  2. jcsd
  3. Jul 27, 2014 #2

    russ_watters

    User Avatar

    Staff: Mentor

    Welcome to PF!
    Pretty much al of that could have been caused by the undervoltage. It can be particularly bad for inductive loads like motors because depending on the type of motor, you might get an over-amperage, which is what causes them to overheat.
     
  4. Jul 27, 2014 #3

    jim hardy

    User Avatar
    Science Advisor
    Gold Member
    2016 Award

    Hey don't apologize, we're all ignorant just on different subjects.


    You can think of your house as having two separate 120 volt feeds
    Each feed supplies half of the 120 volt outlets and lights in your house.
    So, Losing just one of the 120 volt feeds because of, say, a broken wire, will kill half your lights and outlets but not the other half.
    That explains why some lights and the tv were okay.

    The 240 volt appliances in your house require both of the 120 volt feeds in order to run.
    They get current from one 120 volt feed and return it through the other one.
    So, losing one of the 120 volt feeds will kill, in addition to half your outlets and lights, the airconditioners, oven, and water heater because they lose their return path .

    Now - that causes a very confusing symptom:
    Ever heard the term "Sneak Circuit" ?
    It's a path that electricity can take which was not intended to be its path at all.
    Not a short circuit, just the electricity sneaks to where it needs to get by going through something other than its normal, intended wire.

    Okay, now let's think more about those two 120 volt feeds.
    We'll go in little steps, per your request.
    Let us name them Left120 and Right120. Or pick colors, whatever you like.

    Now back to your oven.
    Normally it is connected between Left120 and Right120 for a total of 240. So it works fine.
    But if you lose Right120 by a broken wire, Mr Oven has no return path for his current so he quits heating. His current can't get through Right120's broken wire.

    Hmmmm.. Could it sneak around that broken wire ?

    Well , in addition to Mr Oven - also connected to Right120 there are some lights and stuff.
    Current can come into Mr Oven from Left120, through Mr Oven, then go back out into Right120,
    where it'll light those other lights and stuff.
    That's a "sneak circuit" through Right120's normal 120 volt loads.

    Mr Oven won't let a whole lot of current through to Right120, perhaps enough to illuminate some light bulbs or run small appliances like fans, but apparently not enough to run your microwave.
    If there's hardly anything on Right120 side that's turned on, say only few Christmas lights or a radio, Mr Oven can and will pass enough current to burn it out. Light bulbs go pyrotechnic in that situation.
    And your symptoms will change - turning on the oven might let lights glow dim, or glow too bright and blow out, depending on what is switched on at the time..
    The hot water heater gets in the act too, and at any moment you have no idea if it's heating. So it can be very confusing .

    Sounds to me like your rotted wire may have burnt open and re-welded itself a few times, that can happen
    and i trust the electricians checked your breaker panel connections for tightness.

    Was this any help? Do not feel "talked down to" - not my intent.

    I hope you become interested in electricity,
    get an inexpensive meter ($10 to $30 at Walmart),
    and learn to use it.
     
    Last edited: Jul 27, 2014
  5. Jul 28, 2014 #4

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    JIm. You just gave a summary of why I really don't like the US domestic electricity setup.
     
  6. Jul 28, 2014 #5

    nsaspook

    User Avatar
    Science Advisor

    Our current electrical code is a nightmare of twisty little mazes, all different and it's mainly because of neutral to ground requirements (article 250 of the National Electric Code (NEC)) that produce all sorts of ground loop and lightning protection problems when people drive non-bonded ground rods for everything. The US has a complete phobia to floating power circuits today.
     
  7. Jul 29, 2014 #6

    jim hardy

    User Avatar
    Science Advisor
    Gold Member
    2016 Award

    It's the only one i've ever known....
    is yours 240 single phase , earthed on one side or center ??
    I'd have to live with yours for a while to form an opinion of it. Maybe somebody over there will need a hand with ancient Westinghouse analog control systems and i can come over... (i feel like a veterinarian who's specialty is dinosaurs... W 7100 NSSS instrumentation)

    I'd love to see those Kempton Steam Engines... weren't they the set for a "Poirot" episode ?

    IMG_1733-300x200.jpg
    http://www.kemptonsteam.org/


    We allow high impedance grounded systems for industrial settings where it's expected the denizens will be trained in their operation and maintenance, and consequences of a breaker trip can be severe.

    old jim
     
  8. Aug 9, 2014 #7
    We built a house once... the general contractor's electrician mis-wired some stuff. You would flip a light switch and the light would dim a little but stay on. With a meter and some long leads, I figured out he had some circuits wired in series. Must have been the apprentice or something. This reminded me of that.
    The town's building inspector signed off on it, which shows you how trustworthy those inspections are...
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Electrical Question from Girl Without a Clue
  1. An electrical question (Replies: 1)

  2. Shy girl electrical eng (Replies: 21)

Loading...