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Thread: shocking bath tub fixtures - literally

  1. #31
    Electrician Chris75's Avatar
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    Quote Originally Posted by hj View Post
    the earth plays no role in an electrical system, other than we try to protect our system from higher voltages and lighting strikes. thats the only reason why we drive ground rods,

    Interesting. Back in the dark ages the neutral WAS called the ground. But if the ground is only for higher voltages and lightning, I guess MILLIONS of dollars are being wasted putting ground terminals on appliances and wiring ground circuits inside houses when they are protected from lightning and higher voltages. In fact if it were just a lightning thing, the ground circuit inside the house would deliver the lightning strike to, and through, the house. In those days, the plumbing systems were all metallic, and it was part of the grounding system. Then as plastic became more prevalent, those houses had a lable in the power panel, "NON METALLIC WATER SUPPLY", and a ground rod, or two, was installed. Finally, rather than guess at what kind of material was being used, and since DIY repairs with plastic could interrupt the path, all houses were attached to a ground rod.
    Look, if you dont understand it, then ask, but dont rant on something you just dont understand, I will answer any question you you ask. not trying to be an ass, just trying to educate. as hard as it is...

  2. #32

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    Here is the quote from my NEC Handbook.

    "It is imperative that Code users be familiar with the definitions in Article 100, especially those terms associated with this article (250). Specific words to to be aware of are the "grounded conductor", "equipment grounding conductor," and "grounding electrode conductor."

    Grounding can be divided into two areas: system grounding and equipment grounding. They are kept separate from each other except at the point where they receive their source of power, such as at the service equipment or a separately derived system.

    Grounding is the intentional connection of a current carrying conductor to ground or something that serves the place of ground. In most instances, this connection is made at the supply source, such as a transformer, and at the main service disconnecting means of the premises utilizing the energy.

    There are three basic reasons for grounding:

    1. To limit the voltages caused by lightning or by accidental contact of the supply conductors with conductors of higher voltage.

    2. To stabilize the voltage under normal operating conditions. This maintains the voltage at one level relative to ground, so that any equipment connected to the system will be subject only to that potential difference.

    3. To facilitate the operation of overcurrent devices, such as fuses, circuit breakers, or relays, under ground fault conditions."
    Last edited by Ladiesman271; 09-05-2008 at 07:00 PM.

  3. #33
    Electrician Chris75's Avatar
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    Quote Originally Posted by Ladiesman271 View Post
    Here is the quote from my NEC Handbook.

    "It is imperative that Code users be familiar with the definitions in Article 100, especially those terms associated with this article (250). Specific words to to be aware of are the "grounded conductor", "equipment grounding conductor," and "grounding electrode conductor."

    Grounding can be divided into two areas: system grounding and equipment grounding. They are kept separate from each other except at the point where they receive their source of power, such as at the service equipment or a separately derived system.

    Grounding is the intentional connection of a current carrying conductor to ground or something that serves the place of ground. In most instances, this connection is made at the supply source, such as a transformer, and at the main service disconnecting means of the premises utilizing the energy.

    There are three basic reasons for grounding:

    1. To limit the voltages caused by lightning or by accidental contact of the supply conductors with conductors of higher voltage.

    2. To stabilize the voltage under normal operating conditions. This maintains the voltage at one level relative to ground, so that any equipment connected to the system will be subject only to that potential difference.

    3. To facilitate the operation of overcurrent devices, such as fuses, circuit breakers, or relays, under ground fault conditions."


    First off, I dislike the handbook, 2ndly, #3 in your post falls under equipment grounding, and not system grounding.

  4. #34
    Like an engineer alternety's Avatar
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    I believe that the grounds major practical purpose (not necessarily by code definition) is to prevent voltage from appearing on the enclosure of the power using equipment if there is an internal fault to the enclosure. The ground wire is connected to the neutral at one, and only one, point; the service entrance (and I think remote subpanels). I think it may be such a fault somewhere that was causing the hot bathtub. Thinking about the bathtub, if you are getting current between the water supply and the drain, I would think that there may be an issue of either a neutral touching a pipe or there being more than one earth ground tie in the system. One on the pipe and one on the drain (well we know that is true). The drain is a natural ground. The electrical system is bonded to the pipe. It would be interesting to know what the voltage in the tub is. If there is sufficient resistance between the purposeful ground and the intrinsic ground of the drain pipe there could be sufficient voltage developed for a nice wet body to feel a current flow in the tub. The resistance of your ground can vary from pretty much an insulator to almost a piece of wire. That is one reason that the ground is not really used to carry current in the distribution system. If you all wore a dry suit while showering the problem would be minimized.http://www.terrylove.com/forums/imag...es/biggrin.gif

    An example of differential ground currents - Many years ago, in a data center far far away, I took over a computer installation. When I would have equipment moved or install new equipment, sometimes the machines would run backwards. After that happened a couple of times I borrowed a scope from the computer service guy and looked at the power. The electricians, who threatened the IBM people with physical harm if they did any more power lines to the panels during initial construction, had no idea what three phase power was. Phase order was random on the connectors. The other thing they were told was not to have more than one earth ground point. They did not get that either. So they provided two. Now we are talking more power than the normal house consumes here, but the principle remains. In the course of fixing the mess (I shut the data center down for a day for rewiring) I picked up the power connector for one of the smaller computers. It was so hot I dropped it. There was a small voltage across the connector plug and socket connector shells. They are grounded. The plug was on one ground and the socket was on the other ground. Hundreds of amps were constantly flowing through the ground components of that circuit driven by the small voltage differential of the grounds.

    In terms of lightening protection, the bolt is referenced to earth ground so the ground rod could make a difference. It is most useful when connected to surge suppressors where power, phone, and cable enter the house. At the voltage and amperage levels of a lightening strike the effects can get pretty strange. Think of your house as the other side of an air core transformer with a one turn primary coil passing thousands/millions of amps. A direct strike is not necessary to cause serious damage. I suspect that the plasma in a lightening bolt is in the range of plasma temperatures the physicists are trying to sustain in potential fusion generators.

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