Mains Voltage Safety Tips/Tricks

Discussion in 'General Electronics Chat' started by Still Learning, Nov 5, 2010.

  1. Still Learning

    Thread Starter New Member

    Jul 19, 2010
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    Wondering what your tips or tricks are for working with and safely isolating Mains Voltages in projects? Anything is better than nothing, but no short cuts that could get anyone hurt, please!!

    I use:
    - Double Heatshrink around connections
    - Silicone Gel when required
    - Earth WIRES and not solder, cos I don't want it to melt out before the fuse blows!

    Found a good post by Gootee I think the name was, here:
    http://forum.allaboutcircuits.com/showthread.php?t=41876&highlight=Mains+voltage+safety
     
  2. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Kermit2,

    "All transformers provide isolation."....except auto-transformers!

    Ken
     
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Yes that distinction was made in the article. UNFORTUNATELY, it was in a paragraph previous to the ones I copied.

    Thank you for pointing out the omission. It IS and important one.

    Other safety considerations would be "Not touching any live circuits", but most everyone has discovered what happens when you touch a hot circuit.

    One device that is handy to have for work on AC mains circuits, is a wiring checker that shows reversed hot and neutral and open ground, and reversed neutral and ground. They most often come as a small plug with three lights that you plug in to the socket. If the lights come on they tell you what is wrong with the circuit, or that it is wired correctly.
     
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Good info, but you should include a link to the article where it came from. Some lawyers have found a hey-day in suing websites over "Fair-Use" copying.

    Mostly applies to news stories being posted on forums, forum content generally isn't copyrighted unless stated as copyrighted. Some sites get grumpy about losing ad revenue when info is copied from them and pasted to a forum without a link to the original.
     
  5. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Kermit2,

    A problem with the 3-light testers is they "don't" recognize a reversed ground-neutral.
    Unless I'm mistaken, only:
    open hot
    open neutral
    open ground
    reversed hot-neutral
    reversed hot-ground

    Ken
     
  6. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    I had to go get the do'hickey out of my tool box and look at it. You are right, it doesn't show reveresed ground and neutral.

    Don't trust my memory. I sure don't. :)
     
  7. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    I only remember because years ago I had to convince Facilities Maintenance people at the hospital of that limitation, with an actual bench demo.

    Ken
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    Until some proper attribution can be made to that long passage Kermit2 copied, I have caused it to fade from sight.

    To the OP, a question. What is
    I am familiar with silica gel, a drying agent, and silicone adhesive. I would guess you mean the adhesive.

    Are you aware that the usual stuff cures with the loss of acetic acid, which causes corrosion of copper wiring and terminals? There are some varieties from GE that are rated for electrical usage, but I wonder what all the gooping of adhesive is about. Proper practises are meant to contain mains wiring in non-hazardous fixtures.
     
  9. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Sometimes I use a "Dries Flexible" adhesive for strain relief on a repair or prototype. I use stuff like Shoe Goo (Called something else now). It tends to look Ugly though, so proper strain relief past the grommet is desired.

    Thinking a design through results in not requiring "bulk adhesives". It may cost a bit more for a better enclosure with double O-Ring seal, or Panel mount switches/LEDs with weatherproofing in the mount, and similar items, but designs last longer.
     
  10. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Permatex automotive gasket sealer, I believe the high-temp red dries up just like silicone seal yet has no acid in it.

    Isolated or not, I'm just extremely careful around anything I know that can shock me.
    (And this from a guy that works on live 480V 3-phase on a frequent basis.)
     
  11. DonQ

    Active Member

    May 6, 2009
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    Safety tips:

    #1) When working on voltages that can hurt you, put one hand deeeeep in your pocket and leave it there! (Eliminates the possibility of the current path that would go in one arm, straight across the heart, and out the other arm.)

    #2) Don't lean on things. Insulated shoes on a non-conductive floor will save you from lots of dumb things, but not if you're leaning on a firmly grounded chassis.

    And this one I heard on TV. "Use caution when doing dangerous activities."
     
  12. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Also heard on TV: "Do not attempt this at home"

    The one hand rule and insulated footwear are extremely important, the worst case is if the current passes through the chest area.

    Another rule is NO jewelry. Remove your watch, any rings, bracelets or necklace type stuff you may normally wear.

    I can also speak from experience that no matter how well insulated you think you are, unless you're wearing high voltage gloves at the same time rubber soled shoes are not always enough. Granted, one leg of a 480V circuit is only 277V, but with thick rubber shoes and on a scissor lift that has rubber tires just making slight contact with it can hit you pretty hard. I don't know if it's due to the humidity being high or just the capacitance of my body to the platform I'm standing on but one finger brushing against a live 277V wire will bite.

    Although far more harmless, it's nice to know that most techs will never have to face CRT voltages in a television set anymore. A true tube Sony is the absolute worst, their CRTs had far more capacitance than any others and could hold an amount of charge that could literally send you flying backwards.
     
  13. Still Learning

    Thread Starter New Member

    Jul 19, 2010
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    As for the Silicone Gel technique, I use a 'form' of this stuff known in Australia as Selley's Roof and Gutter Sealant. Non acidic, non corrosive, and only $9 Aus for a full 400gram tube of the stuff! I considered normal silicone originally until just the other day when in another post, another Aussie used this stuff too.. Works a treat!! Also has a 150degree C tolerance..

    One of the most confusing parts I found with Mains wiring was the use of so many different terms for Ground/Earth. I just use Earth mainly, but some get confused by what I mean!!

    So how do you Earth your PCBs? To chassis then earth, or direct to earth? I've seen some interesting stuff under the covers of some old outboard music equipment!!!
     
  14. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Pilot's version: "Use caution when approaching the boundaries of air."

    The Trinitron tubes were not only about the heaviest around, but the best looking and the flattest prior to LCDs. They sure packed a punch when you forgot to drain them before yanking the flyback off.
     
  15. marshallf3

    Well-Known Member

    Jul 26, 2010
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    You'd know why they were so heavy if you ever broke one apart. The glass is not only super thick but the shadow mask assembly was an iron frame holding a precision laser-cut paper thin mask.

    After you drained one you had better put a cliplead from the anode to the dag somehow or they'll actually build another almost as potent charge back up from the glass dielectric being polarized for so long.
     
  16. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    I've never seen the actual "stripe mask" from a Trinitron. I have a shadowmask from a small color TV, thought it'd be neat to get the vertical wire one to match, but now that LCD and LED displays are around, it doesn't seem that "neat".
     
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