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Thread: OT: Gas dryer tripping GFCI

  1. #31
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    Quote Originally Posted by Jon Heron View Post
    Yup, and at 240 too!
    FWIW: What most people may not realize is that most injuries caused by shocks in the home are not from the current but rather what happens to them when they react to the shock. Like falling off a ladder, instant backhand to the face, cracking skull on shelves etc, these have all happened to me by the way and a GFCI would not have prevented any of these injuries.
    I have been in the trade for over 25 years now and have been involved in many accident investigations and have seen terrible things, none of which would have been prevented by a GFCI receptacle.
    Have fun!
    Jon
    Yup, reminds of an early demo someone was showing us. IIRC it was a CRT TV set or monitor with the backing removed. The person doing a demonstration had a fake arm/hand made out some type of rubber. He passed it around and it kinda felt like a real arm/hand.. Was heavy, etc... Anyway, we all knew caps and the CRT tube holds a strong residual charge but he showed us the bigger risk was to our limbs. He slid the arm between some of the steel frame/supports in the back of the monitor and pretended the arm/hand got a shock and jerked it backwards violently. Chunks of rubber went flying everywhere and it was filled with some red dye and made a huge mess. We all burst into laughter but it was definitely a realization that you just don';t want to get shocked especially if your hands are in a place where they will get cut up badly if you jerk them out quickly. I'll never forget that lesson.
    When in doubt, doubt your doubt.
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  2. #32
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    Quote Originally Posted by MattiJ View Post
    EN60065 leakage currents: thankfully smaller than GFCI trip level, I don't want my GFCI's to trip all the time

    And you need to be in middle of open-heart surgery to die at "much less than 5mA"
    Ah, but what about those high GFCI currents that you mentioned? If the GFCIs are set higher, why is there an issue at "only" 5 mA? I have only had to meet the leakage, I do not design GFCIs for the european market. (Called "RCDs" over there, I believe.)

    As for the current, the heart can be disrupted in operation by a few hundred microamps passing through it, or less, to my understanding. I searched for specific heart current limits, and did not find good data, however. One source suggested that current through the heart itself is 1000 times worse than current generally through the body, but.... it is not clear WHAT it is 1000 times worse than.

    So, the actual current needed to be fatal is dependent on what amount goes through the heart. A shock, even with high current, which passes only through your leg from knee to foot, probably will not have any significant current through the heart itself, although it may not do your leg any good.

    Arm-to-arm is obviously worse, and probably chest to back worse than that. It depends on the general conductivity of the path, and how current distributes. Numbers are all over as to what "is fatal", generally over 50 mA, but that probably assumes a certain size person and current distribution, an is dependent on path.

    So it depends on the person. A large burly guy has a big conductor cross-section, and a given current has less current density in his body. A small skinny woman has far less cross-section, and what is not close to fatal for the guy may be easily fatal for the small woman, or a skinny kid. Then there are other considerations, older, more frail people, vs 20 year old "Bubbas".... There will be differences there.

    One number cannot apply to all, even though the "average" is tossed around as if it were a certainty.

    Then on top of that, is the effect of voltage. Higher voltage apparently can start to break down the skin resistance, which leads to a better contact, and either higher current, or a different current distribution within the body. "High" may not be so high, possibly 250V or so may be adequate to see that effect. Again, the numbers are sparse and many sources quote the same studies of young people.
    Last edited by J Tiers; 10-11-2017 at 03:27 PM.
    1601

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  3. #33
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    Originally Posted by Jon Heron

    What a mess.

    ...

    Lots of discussion and testing over nothing in my opinion.
    Good luck!
    Jon

    Quote Originally Posted by 3 Phase Lightbulb View Post
    Agree. I hope this is not a side-affect of retirement? Stop farting around and do something worth while like install new GFCI outlets. Replace the water hoses with braided steel ones. Build a real shelf over the washing machine(s). Put some paper towels in the paper towel holder. Clean up those appliances and disgusting walls and paint them ANY COLOR except the current color.
    It is inappropriate, immature, and impolite to resort to disparaging remarks in an attempt to shame someone into adopting a lifestyle or maintain a home in a way that you demand. There are reasons for things being as they are, and I certainly am aware that they do not meet certain "standards" that others may hold sacred, but I am not going to attempt an explanation, and it is not your place to criticize that which is none of your concern.

    That being said (and hopefully concluded without further discourse), I used a decade box to determine the sensitivity of the GFCI that tripped on the dryer:



    I added a 10k 2W resistor in series for safety, and dialed down the resistance until the GFCI tripped, at which point the decade box read 15 kOhms:



    I measured 72 VAC on 15k, and 48 VAC on the 10k resistor, which is 4.8 mA. According to the following document, the test resistor is 15k, which corresponds to 8 mA, but the specification calls for no trip at 4 mA and must trip at 6 mA. So this GFCI is within spec. However, there are other considerations, such as time delay, which may cause nuisance tripping if it it trips too quickly because of sudden application of a load with considerable capacitance to GND. I have yet to test the other GFCI that does not trip on the dryer.

    https://www.nema.org/Products/Docume...esentation.pdf

  4. #34
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    With older residences in USA, it is possible that the ground conductor is only the metallic conduit surrounding the
    current carrying conductors. The resistance of the conduit may be high due to corrosion or looseness of the joints
    which also were typically of dis-similar metals.
    In my shop in a detached garage, I measured the loop impedance active-through-neutral to be 0.6 Ohm.
    But active-through-ground conduit is 2.8 Ohm.
    ( I don't know what a "good" value would be for a 50 foot run of mixed solid and flex with lots of joints)
    So the fault level via ground is only 42 amp. At this level the ordinary 20 Amp panel T/M breakers might not open before the
    active conductor overheats, particularly at terminals.
    So I think that GFCI s are prudent in this case, whether required by code or not.

    On industrial side, moulded case circuit breakers started to become available with internal ground fault modules around 1990.
    These were not for life protection as typically adjustable in range to a few amps
    I always though it prudent to have such a module in the top breaker of a distribution panel,
    as faults often have a ground component.
    One time I was involved with a case of green/vellow earth cables melting the insulation off cable inside
    cable ducts. The cables had been correctly sized according to the code calculations.
    The faults was traced to a failure mode in welding transformers that allowed them to continue working,
    with a low level earth fault midway in a winding.
    In that case ground fault detectors would have avoided the damage.

  5. #35
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    GFCIs are generally good, and I do not understand the advice to NOT put one in.

    The location of your pics appears to be a basement or similar sort of utility room or garage type area. Receptacles in such areas, basements and garages, are REQUIRED to use GFCIs under the NEC. The full list you will have to refer to the NEC to verify. The floors are typically concrete, and are damp, etc, providing excellent chances for a shock.

    So, it would seem that having a GFCI for each receptacle, either directly, or "upstream" if a string of outlets are supplied, is not only good as an idea, but likely required, sink or no sink. And in areas supplied by ungrounded runs, a GFCI is permitted to be used. Again, if a run is supplied through a particular receptacle, then that receptacle can be a GFCI and protect the rest as well. You do need to mark each outlet as being GFCI protected. It is not as good as having separate GFCIs, since if the outlet stops working, you have to go find the controlling GFCI and see if it tripped.

    You appear to be doing exactly what you should do per using GFCIs.

    Agreed, that when a GFCI becomes unreliable, it ought to be replaced, and that extension cords are undesirable. But I fully understand being curious as to why the particular GFCI is tripping off, when others do not.
    1601

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  6. #36
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    I tested the GFCI for the stove, and it shows a trip current of 4.1 mA. I plugged the dryer back into the original GFCI, and now it does not trip under the same conditions as before. So whatever had caused the trip seems to have resolved itself.

    I also found that the ground pin on the HiPot tester had an intermittent connection to the ground wire. When I replaced the plug, both GFCIs tripped when I plugged it in and turned it on. So there must be significant leakage to chassis, but it works OK when plugged into a non-GFCI outlet.

    The laundry is located in the first floor kitchen area of the house, which was built around 1877. I bought it in 1989, and all the plumbing was added and almost all wiring was redone or added along with extensive renovations at that time. The renovations were not completed at that time, as I was living elsewhere and I had just started my business and money was tight. In 1999 I moved in and did some more renovations including replacing rotten joists and studs. In 2010 I hired a contractor who replaced all the windows and doors and put up drywall, but not finished because the electric was not fully up to code and the wiring had to be accessible. That and other expenses took a toll on my finances. My business was doing OK, but I was not making very much. My orthopedic problems (bad back, arthritic hip, worn-out knee) limited how much work I could do myself. I also had to take care of my 2.5 acres of land, and my other house (on an adjoining property), which also took a lot of effort and money.

    Some videos showing some of the work on my house:

    https://www.youtube.com/watch?v=oxKL2p8O3EM

    https://www.youtube.com/watch?v=YlQgyPw4Seo

    https://www.youtube.com/watch?v=7G1KrogqShQ

    If you want to see a mess, here are some pictures of the homes of some other people I know:





    And pictures of the house in Towson where I grew up, and where my brother was living after I moved out and eventually I bought and evicted him:


  7. #37
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    My basement is a mess right now too...

    When in doubt, doubt your doubt.
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  8. #38
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    Quote Originally Posted by PStechPaul View Post
    I tested the GFCI for the stove, and it shows a trip current of 4.1 mA. I plugged the dryer back into the original GFCI, and now it does not trip under the same conditions as before. So whatever had caused the trip seems to have resolved itself.

    I also found that the ground pin on the HiPot tester had an intermittent connection to the ground wire. When I replaced the plug, both GFCIs tripped when I plugged it in and turned it on. So there must be significant leakage to chassis, but it works OK when plugged into a non-GFCI outlet.
    ....
    Does the stove have an ignitor or a pilot?

    With high voltage AC, it (as you know) takes a lot less capacitance to pass quite a bit of current. So it is not altogether unusual for the tester to trip a GFCI. Lead dress, and other such may help correct it, but one thing might be to float the transformer steel off the chassis.

    Is the secondary grounded or floating?
    1601

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  9. #39
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    I plugged the dryer back into the original GFCI, and now it does not trip under the same conditions as before. So whatever had caused the trip seems to have resolved itself.
    I bet the HP tester burned off whatever was causing the appliance to trip the GFI.
    As stated most HP testers will not operate on a GFI due to how they operate.
    Cheers,
    Jon

  10. #40
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    The stove has ignitors on the burners, and also a clock/timer. The stove has never caused the GFCI to trip.

    The HiPot tester tripped the GFCI as soon as I turned it on, before I adjusted the output to any voltage. I have not verified it, but I think the output leads are floating. I have used the same model HiPot to test transformers and test equipment, and tests are performed from windings to ground with no regard for polarity, so it must be floating.

    I did not use the HiPot on the dryer or anything else, so it could not have burned off anything. It is quite possible that there was a bug or dampness in the dryer that eventually dried up and became less conductive.

    Here is a good article on HiPot testing, from the same company that made mine: "Slaughter". LOL! What an appropriate name! The company I worked for from 1973 to 1989, and that manufactured and sold high current and high voltage test equipment, was located in Sparks, MD. I also worked for Phenix Technologies, a similar manufacturer, and they are located in Accident, MD. There is also an ambulance dealer there.

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