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Thread: Electrical Shock

  1. #21
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    Default Re: Electrical Shock

    Quote Originally Posted by South_Texas_Sun
    Devry Institute of Technology BSEE
    Ah, I stand corrected.
    Mark
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    Default Re: Electrical Shock

    One thing I never quite did understand is the logic behind bonding the rebar in a concrete deck since all of the rebar is surrounded by a fairly good insulator (concrete). I guess it is in case the rebar comes in contact with other metal that is exposed but I cannot think of any other reason.

    Also, I think I remember from one of my power courses that ground, the dirt kind, can and does have changing potential from the house to the power company although they work pretty hard not to have that problem. So it is not inconceivable that the ground near the pool is at a different potential than the ground of the house/pad and both the house and the pool are not at fault.

    The source could be from a neighbor's problem or a burried line that has become exposed. One possibility is 12v landscape lighting. It could be close enough to the pool and exposed to the soil to create some potential difference to the bonding wire. One way to confirm this is to test the voltage between ground at the pad and the soil near the pool vs ground at the pad and the grounding rod for the house. Unfortunately, you will need a lot of extra wire to make the runs.

    It will certainly take some detective work to find the source.
    Mark
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  3. #23
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    Default Re: Electrical Shock

    Quote Originally Posted by mas985
    One thing I never quite did understand is the logic behind bonding the rebar in a concrete deck since all of the rebar is surrounded by a fairly good insulator (concrete). I guess it is in case the rebar comes in contact with other metal that is exposed but I cannot think of any other reason.
    Wet concrete is a pretty good conductor. Connecting the rebar to the bonding grid or putting a bonded metal mesh in the concrete does a fairly good job of connecting the concrete to the bonding system when the concrete is wet.

  4. #24
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    Default Re: Electrical Shock

    Quote Originally Posted by JohnT
    Wet concrete is a pretty good conductor. Connecting the rebar to the bonding grid or putting a bonded metal mesh in the concrete does a fairly good job of connecting the concrete to the bonding system when the concrete is wet.
    I agree that wet concrete is a good conductor on the surface, but when concrete gets wet, I could be wrong but I would not expect the moisture to get all the way down to the rebar which is 2-3" below the surface. The concrete surface is somewhat porous but not as much to allow moisture to get down 2". What I could imagine is that when the concrete cracks it could allow some of the moisture to reach the rebar and then it would make a difference.
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

  5. #25
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    Default Re: Electrical Shock

    Quote Originally Posted by mas985
    I agree that wet concrete is a good conductor on the surface, but when concrete gets wet, I could be wrong but I would not expect the moisture to get all the way down to the rebar which is 2-3" below the surface. The concrete surface is somewhat porous but not as much to allow moisture to get down 2". What I could imagine is that when the concrete cracks it could allow some of the moisture to reach the rebar and then it would make a difference.
    Mark, in one of my past "lives" I worked in a government building where they would periodically test the concrete conductivity as an indicator for the corrosion to the rebar embedded in the concrete.

    As it turns out, much of the world's population housing and the existance of skyscrapers, bridges, and even nuclear power plants, rests on the natural "miracle" of nearly exact coefficents of thermal expansion between rebar and concrete. Move over, Fibonacci.

    But what worried me about ....(shading eyes to avoid embarassing direct eye contact of thread-hijacking complaints)......dsamples VINYL pool problem was that his vinyl liner is possibly masking some greater electrical fault that would normally trip a breaker, but doesn't because of the insulation-to-ground properties of the vinyl liner.

    I'm not an electrician, but I would imagine that the newly required NEC "grid" requirements mentioned by John are a response to some poor soul's accidental electrocution by a situation very similar to dsamples current dilemma.

    I hope it gets fixed, if only for the peace of mind.

    STS

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    haze_1956 is offline ** No working email address ** Thread Analyst haze_1956 0
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    Default Re: Electrical Shock

    From original post -

    When I disconnect the bond wire from the pump lug, the shock goes away, but there is a potential difference of 4.5vac between the pump case and the bond wire.
    If I understand this correctly,

    The pool is being enegized with a 4.5 vac current running from the pump case to the pool via the bonding wires. Then when the pavers are touched, the current grounds and gives a shock. Hence the code requirement for a bonded grid below the pavers.

    Might running a bonded wire below ground, around the entire outer perimeter of the pavers work?

  7. #27
    Poconos is offline SuperMod Emeritus Whizbang Spinner Poconos 4 stars Poconos 4 stars Poconos 4 stars Poconos 4 stars Poconos 4 stars Poconos 4 stars
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    Default Re: Electrical Shock

    Wow, what an interesting thread. Funny too in a way. In the electronics world we don't consider concrete a conductor but yes...you can get shocked bad given the right conditions. Cracks me up sometimes when I go into an electrical supply store and they start rattling off 100 amp wire etc.....I know what I want...Ohms law tells me that. Not criticizing Electricians or the professon but there are those that just follow codes and those that understand the theory. Never read the full NEC but some of the rules don't make sense.
    An interesting exercise for those in an urban or suburban location is to take a clamp-on ampmeter and measure currents on water pipe entrances, ground lines off power poles, phone grounds, and anything else you can find. You can totally disconnect your house by dumping the two hots and still find potential differences and currents. BIG difference in rural areas with large distances between sources and many fewer problems.
    Someone commented about degrees....from what I've observed in the industry, an engineer is degreed. we all know the definitions:
    BS -- Bull ****
    MS -- More ****
    PhD -- Piled Higher and Deeper.

    I'm full of Bull from the place voted the ugliest campus in the U.S. on a Princeton survey per the national news in the last couple days.

    I needed some humor today.
    Al
    Last edited by Poconos; 08-24-2006 at 12:52 PM.

  8. #28
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    Default Re: Electrical Shock

    Quote Originally Posted by South_Texas_Sun
    dsamples VINYL pool problem was that his vinyl liner is possibly masking some greater electrical fault that would normally trip a breaker, but doesn't because of the insulation-to-ground properties of the vinyl liner.
    There has been a move to add a requirement to code to put a plate in the pool for vinyl and fiberglass pools to bond the water. It has been rejected so far because there isn't an agreement on the need, and the size requirements etc. are unknown due to the variety of water conditions and pool sizes. Realistically, the ladder SHOULD function as a bonding electrode for the water, and any current from a household line should clear its ground fault via the ladder--bond wire--pump housing--panel ground path.
    Most of the time, the source of such voltage is the poor neutral wiring practices of the utility, so there is no fault to clear.

  9. #29
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    Default Re: Electrical Shock

    Quote Originally Posted by Poconos
    Wow, what an interesting thread. Funny too in a way. In the electronics world we don't consider concrete a conductor but yes...you can get shocked bad given the right conditions. Cracks me up sometimes when I go into an electrical supply store and they start rattling off 100 amp wire etc.....I know what I want...Ohms law tells me that. Not criticizing Electricians or the professon but there are those that just follow codes and those that understand the theory. Never read the full NEC but some of the rules don't make sense.
    An interesting exercise for those in an urban or suburban location is to take a clamp-on ampmeter and measure currents on water pipe entrances, ground lines off power poles, phone grounds, and anything else you can find. You can totally disconnect your house by dumping the two hots and still find potential differences and currents. BIG difference in rural areas with large distances between sources and many fewer problems.
    Someone commented about degrees....from what I've observed in the industry, an engineer is degreed. we all know the definitions:
    BS -- Bull ****
    MS -- More ****
    PhD -- Piled Higher and Deeper.

    I'm full of Bull from the place voted the ugliest campus in the U.S. on a Princeton survey per the national news in the last couple days.

    I needed some humor today.
    Al
    I graduated from "Durvee Tech" as we used to call it, in 1974....the first of 3 degrees. Back then we used slide rules instead of calculators for trig functions because the 4 banger calculators wouldn't do sin, cos, tan etc, and besides.......the instructors (correctly, I feel) thought that doing the powers of 10 in your head left less room for error. You actually had to THINK about the (im)probability of your numbers. My dad had a this huge Tektronix storage o'scope that did a paper strip chart of 30 seconds worth of 1 channel data. I used it to get myself hired as a TV tech to put myself through school.

    FF to now......I can't do math anymore because I lost my HP in the RV at the river. And I can't read the tiny printing (because of multiple language instruction manuals) of my other calculator, so I just use it as a four banger. Everything else is software.

    The Tektronix is a family "heirloom", permanently awaiting long-discontinued tubes, while my Fluke DSO (that can be held with one hand while talking on a cell phone at the same time) has a hall-effect DC current clamp accessory that will run a 24 hour strip chart and let me see an AC+DC waveform and display peak and "lo" RMS or instantaneous transient values. Like you mentioned (Al) it's suprising how durable today's gadgets are, given the vagaries of local power utilities and their aging infrastructure. Our line freqs aren't even constant out here. (Tx hill country)

    Everything has changed except the time it takes to get finished with work.The only thing I can think of that is pretty much the same, then as now, is the fun of going swimming.

    STS

  10. #30
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    Default Re: Electrical Shock

    Quote Originally Posted by JohnT
    There has been a move to add a requirement to code to put a plate in the pool for vinyl and fiberglass pools to bond the water. It has been rejected so far because there isn't an agreement on the need, and the size requirements etc. are unknown due to the variety of water conditions and pool sizes. Realistically, the ladder SHOULD function as a bonding electrode for the water, and any current from a household line should clear its ground fault via the ladder--bond wire--pump housing--panel ground path.
    Most of the time, the source of such voltage is the poor neutral wiring practices of the utility, so there is no fault to clear.
    Ladder?????

    (slapping forehead)......I knew our new pool was missing something!

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