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earth fault

Discussion in 'General Electronics Discussion' started by dve256, Oct 14, 2011.

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  1. dve256

    dve256

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    Jun 25, 2011
    I am building a heating pot. It works fine when not earthed to case but when I put the earth to the pot it causes the breaker to go. So I guess there must be a problem with the wiring.
    Any ideas?
     
  2. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Heated pot

    Hi dve256.
    You need to find the earth fault, although not obvious it might be a moisture problem if the pot is metallic in its composition.

    I am guessing its a heated plant pot ? or the load is to high, but i cant imagine that, as what ever is in the pot would be cooked due to excessive heat.

    Use a meter to find the fault. No pictures make it vague or hard to work out the problem.
    Dave. :)
     
  3. Resqueline

    Resqueline

    2,848
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    Jul 31, 2009
    Even ceramic bricks can conduct sufficiently to trip an earth fault breaker, but we've been through that before. What's your setup like this time?
     
    Last edited: Oct 15, 2011
  4. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Heated pot

    Even more so if damp or wet, plants need watering, if this is the case an isolator / insulator between the pot and element might work, but not a material that acts as a thermal barrier, but rather electrically isolation from the pot. Material choice is tricky, most electrical insulation is often thermal to some extent as well, hmmm.
    Dave. :)
     
  5. nepow

    nepow

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    Jul 18, 2011
    Hi dve256, Most likely an earth leakage fault caused by the heating element breaking down if everything else has been checked. Can you get some one to PAT test it for you as a reading generally below 2meg between earth and LIVE connection will cause enough current through the trip circuit and throw the breaker.
     
  6. dve256

    dve256

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    Jun 25, 2011
    Sorry for the delay in getting back.

    [​IMG]
    [​IMG]

    Its for injecting wax into a mould.
    The pot is a double skin constructed pot. The inner pot is made of aluminium and the outer pot steel. It has a pump inside the inner pot for injecting the hot wax.
    Its heated by wrapping resistance wire around the inner pot (there is a thin layer of ceramic fibre insulation between the inner pot and the heating wire) Its wired to a thermostat from a household iron to adjust the heat required.

    I appreciate all the points already made I still am not sure which is my problem though.
    Perhaps its the insulation between the pot and the element as suggested. It is a 3mm layer of ceramic fibre paper off ebay. I have had the pot on a couple of times so would the moisture in it not have been dried up by now though?

    So long as none of my live wires touch the metal pots it doesn't made any difference if I earth the pot though right? I guess they would not pat test it but its only a hobby currently.
     
  7. jackorocko

    jackorocko

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    Apr 4, 2010
    I haven't read the whole thread, but this is why they earth casings containing 'HOT' electrical wires. Simply because you can not fully 110% guarantee that the hot wire will never touch the casing. If it does and some human touches the casing and gets zapped it may well be their last time touching anything.

    Seeing as how your pot is made of metal... it has the ability to become energized.
     
  8. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Its hard to make out the unit, but the first picture looks dangerous or done quick, so no plants or watering there.

    Is the first picture an element circuit of some kind, i can make out a bi metallic switch contacts, and what looks like a neutral wire connected to a ground wire, looks like the blue neutral did not reach its termination, or something like that.

    Ive got to be honest the wiring in the first picture looks like a death trap, not something i would be happy with.

    The unit you describe for wax melting, i know what they are, but what that is looks dodgy, go buy a new unit, or build a new one using low voltage and maybe nicrhome wire, but a hefty psu will be needed, or build a mains unit thermally controlled for optimum wax melting.
    The later needs experience and a complete understanding of mains working and safety.
    Dave. :)
     
  9. Resqueline

    Resqueline

    2,848
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    Jul 31, 2009
    The workmanship in the connector/thermostat box doesn't look reassuring. Live and ground parts look perilously close (& unstable) to each other.
    Is the ceramic fibre woven or "random"? It might not be meant withstand simultaneous mechanical pressure and electrical potential.
    Do you have one layer only? Can you provide a link to a similar product? Have you tried to simply Ohm the setup with an ordinary DMM?
     
  10. dve256

    dve256

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    Jun 25, 2011
    The wiring inside the box is not pretty but I used what connectors and such I had. It is secure and no 2 wires will touch from rocking of the pot ect.
    The ceramic fibre is random fibres quite dense 3mm thick sheet they call paper.
    The wattage is around 300. I tested to see if it would burn through at all and no, the current barely sqeezes the ceramic fibre with this current. I tested the ohms with a mm to be 120.

    http://www.ebay.co.uk/itm/Accessori...fts_Glass_Art_Supplies_CV&hash=item45fd98a05a
     
    Last edited: Oct 16, 2011
  11. Resqueline

    Resqueline

    2,848
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    Jul 31, 2009
    Still sceptical about the box, things are very close in there. The fibre sheet looks quite dense indeed, so it could be ok (in theory).
    Ok, so the heater is 120 ohms, making 140W on 115V. But what about any measurements to ground, as was the issue/problem?
     
  12. dve256

    dve256

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    Jun 25, 2011
    the ground wire from the 3 core cable I attached to the outer pot.

    Please check my diagram of the wiring, perhaps this arrangement is incorrect?
     

    Attached Files:

    Last edited: Oct 16, 2011
  13. duke37

    duke37

    5,364
    771
    Jan 9, 2011
    He is in the UK so 230V and 440W.

    You need to measure the resistance between the heating element and the pot, the big pin on the plug to one of the smaller pins. The resistance should be several megohms so use your meter on the highest range.
     
  14. Resqueline

    Resqueline

    2,848
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    Jul 31, 2009
    That's right duke, so 240V maybe, and 480W. Quite a bit of power in that pot there.
    The wiring's right, but where does the ground wire from the thermostat frame go?
    (There's no need to use a 3915 x 1762 canvas for an 860 x 420 image btw..)
     

    Attached Files:

  15. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Surely thats the same termination for the thermostat earth wire, especially if its metal casing, or is it another conductor flagged as its known in the UK another colour, so not earth. ?
    Dave. :)
     
  16. Resqueline

    Resqueline

    2,848
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    Jul 31, 2009
    Green/yellow are defined (& used) as ground wires "over here", and should ultimately be connected together, but I was wondering exactly where the o/p had connected it.
     
  17. dve256

    dve256

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    Jun 25, 2011
    i just lodged it between the wooden base and the outer metal pot. I did also try putting the earth between 2 other metal objects and that still provided the fault.
     
  18. dve256

    dve256

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    Jun 25, 2011
    I managed to break my meter yesterday after taking the resistance reading I tried to switch off the dial and the thing was jammed with grit that seems to have somehow got in?! I forced it and the thing kinda fell apart :( spoze you get what you pay for.
     
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