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  • Safety: testing Electrical outlets

    Saw the following article on another forum and thought it would be good to post here. If someone wants to make it "sticky", that would be good.

    Failures in Outlet Testing Exposed | Contractor content from Electrical Construction & Maintenance (EC&M) Magazine

    The issue may have been covered on the forum before, but I thought this gave a very good explanation of the danger of putting too much faith in standard "3 light outlet testers".
    There is a type of miswiring that can occur which a regular outlet tester will not detect. This type of failure can result in live chassis.
    I know many who gig regularly take the precaution of testing for grounded outlets, but as the article explains, there is still the chance of a lethal fault that regular outlet testers will not find.
    "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

  • #2
    Originally posted by g-one View Post
    Saw the following article on another forum and thought it would be good to post here. If someone wants to make it "sticky", that would be good. - snip -
    There is a type of miswiring that can occur which a regular outlet tester will not detect. This type of failure can result in live chassis.
    I know many who gig regularly take the precaution of testing for grounded outlets, but as the article explains, there is still the chance of a lethal fault that regular outlet testers will not find.
    THANK YOU very much indeed g-one! That's the second-scariest thing I've read all day. (First was a series on local political-police-judicial corruption, oh boy!) I never heard of the "bootleg ground" before, and thank hevvins haven't seen outlets wired that way. BUT that doesn't mean others don't cut corners on installs, repairs & extensions. I learned a long time ago that neutral and ground are bonded only at the breaker box, but not everybody got that lesson.

    Last question was, what about modern switchmode supplies? I'm not exactly satisifed with the answer posted by one reader, "they have to conform too." No fooling. "Theoretically" everything has to comply. It's when somebody sees an opportunity to save money and/or time, the rules get broken, somebody eventually gets fried or gear or wires catch fire.
    Enjoy. Every. Sandwich.

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    • #3
      Really good to know, g-one.

      I think what I'd carry away from reading that is that although a plug-in tester reveals many faults, it can't get them all. To me, that doesn't say to not use the quick tester, because it's not 100% inclusive. Instead it says use the plug in tester for quick tests and worry about the remaining few.

      It's kind of like buying a small fire extinguisher. You're pretty sure that it won't handle all possible fires. But it sure comes in handy for a large number of small ones.
      Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

      Oh, wait! That sounds familiar, somehow.

      Comment


      • #4
        SMPS have small transformers between the line side and output side (to the best of my knowledge, see below).

        RG: agree the plug in tester is still good for quick tests. Then a NCVT at the outlet ground, or, spark test between grounds. Easy enough to do on stage, hold your instrument without touching the strings, contact the strings to mic stands, other instrument strings, etc. Or plug your cord into your amp but not your instrument, hold the cord (not the plug) near the instrument end, touch the 1/4" plug shell to any other grounds. Any sparks from any above tests mean you have serious problems.

        Click image for larger version

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        Last edited by g1; 01-05-2015, 03:38 AM.
        "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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        • #5
          Originally posted by g-one View Post
          Easy enough to do on stage, hold your instrument without touching the strings, contact the strings to mic stands,
          One of my long time friends and customers used to count in this method to keep him from getting sizzled at the blues jam he founded (still going on in some form 30 years later!) One day he did his usual spark test, and he got lots of sparks all right. Five strings burnt off the guitar, and the sixth was welded to the frets. After he recovered vision from the welding flash, swapped out the amp entirely - which later landed on my bench - also took out his spare guitar and on with the show. Lucky for him he's a bit of a maintenance luthier and was able to get his frets back into shape too. So friends, I'd be very cautious about spark-testing with a guitar this way. All it takes is one shorted "death" cap or some other AC fault to chassis and you'll be arc welding, not Neil Young style.

          I've used the rat shack 3-lamp tester for years, recommended it too, and never thought another thing about it 'til I read this article. Now I'd better get one of those capacitive testers, can't cost all that much.

          Years ago - I mean @ 30 - there was a device called a D-Zap. You plugged your guitar cable into it, other end of the guitar cable into amp (or whatever pedals etc) then touch the button at the end of the D-Zap to mics, stands, other instruments and gear. 3 LED's showed low (half a volt), medium (40V IIRC), and high (120V) charge conditions. No LED = no shock supposedly. Faster and more handy than lugging a meter around. Might still be in my road toolbox.
          Attached Files
          Enjoy. Every. Sandwich.

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          • #6
            One of the reasons I always use a transmitter (other than walking into crowded or on tables) is that I NEVER trust an AC mains at any venue and almost never have time to check it. You could have a brand new modern outlet wired backwards with no earth ground. Happens all the time. Especially in remodels.

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            • #7
              A voltmeter would reveal a bogus ground as there should a few millivolts between neutral and ground and not a dead short.

              Another reason I use a wireless.

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              • #8
                If you are using a cheap voltmeter for these kinds of ac tests, stop. Get yourself a "Wiggy." Wiggy is a brand. These meters are known as "solenoid" volt meters and there are many other brands out there. Solenoid meters require ample current in order to register a voltage. This helps cut down on inaccurate readings that low end VOMs can give.
                Attached Files

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                • #9
                  Originally posted by Leo_Gnardo View Post
                  So friends, I'd be very cautious about spark-testing with a guitar this way. All it takes is one shorted "death" cap or some other AC fault to chassis and you'll be arc welding, not Neil Young style.
                  Thanks Leo, this is a potentially dangerous method, and only preferable to non-testing. In the event of a fault, my personal belief is that equipment failure and some "welder eye" is preferable to electrocution. That fellows life may have been saved by his guitar.
                  But yes, exercise extreme caution if "spark testing".
                  "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

                  Comment


                  • #10
                    I tested outlets on a regular basis in phone offices as one of my Installation duties.
                    I used the deluxe testers, plus I always did a basic test with a multimeter.
                    Everything in a phone office is grounded, so I would check hot on small blade, neutral on large blade and ground on the 3rd wire ground terminal.
                    Never had any issues!
                    Also on tools, installers were required to use Ground Fault Extension cords.
                    These cords usually pick up all voltage potential problems.
                    T
                    Last edited by big_teee; 01-05-2015, 07:53 PM.


                    "If Wishes Were Horses, Beggars Would Ride!" Scottish Proverb 1600s
                    Terry

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                    • #11
                      It's worth noting that the bridge (and hence the strings) of most guitars are solidly connected to the signal ground with a wire. There is a mod I saw once that put a 220K resistor in parallel with a 0.01/1kV cap in series with the bridge grounding wire. The 220K keeps the strings at DC ground, but won't let lethal amounts of 50/60 Hz in, and the cap "shorts" the strings for RF frequencies and keeps RF buzz down.

                      I did this to my strat, and it seems to be quiet. I don't know how well it works in the larger world, but if it does work well, seems like it ought to be a standard feature of electric guitars.
                      Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

                      Oh, wait! That sounds familiar, somehow.

                      Comment


                      • #12
                        Originally posted by R.G. View Post
                        It's worth noting that the bridge (and hence the strings) of most guitars are solidly connected to the signal ground with a wire. There is a mod I saw once that put a 220K resistor in parallel with a 0.01/1kV cap in series with the bridge grounding wire. The 220K keeps the strings at DC ground, but won't let lethal amounts of 50/60 Hz in, and the cap "shorts" the strings for RF frequencies and keeps RF buzz down.
                        As safe as this 'mod' appears, why is it not a standard.
                        You would think the regulators would be all over this one like flies on p**p.

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                        • #13
                          I don't know, exactly, but like always I have an opinion.

                          First, it adds complexity, and I'm sure that in some cases, it would let some hum sources through. Solidly grounded beats capacitor- or resistor-grounded every time. And that's the way it has always been done, so guitar makers have no incentive to do it.

                          Second, in the mostly-standard safety standards for the world, there is a lot of commentary about all user-accessible metal, for which guitar strings qualify, being grounded solidly enough to conduct 25A at the local mains frequency, which this thing clearly will not do.

                          And probably thirdly, the issue only arises when the guitarist makes himself a bridge between two pieces of equipment, each of which independently might be judged to be compliant with standards, and which rely on a third part (that is, the building and its wiring) to make the accessible metals on both pieces of equipment be safe.

                          We had a saying back at Three Initial Corporation: if there are more than two signatures on the document, the blame will never be placed. I'm guessing that might be behind the issue too.

                          Hmmm. Fourthly (he pontificated...) the electric guitar is not an electrically powered appliance. For the purposes of electrical safety, it could be considered a wire which is connected to the amplifier's accessible metal and held in the hand. In and of itself, it has no requirements whatsoever for electrical safety review, and I bet the guitar makers would fight tooth and nail to keep it from being subject to review.
                          Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

                          Oh, wait! That sounds familiar, somehow.

                          Comment


                          • #14
                            I seem to recall that back in the late '60s Dan Armstrong was recommending the use of a 0.1uF cap to connect the strings to ground.

                            I'd guess that one of the many problems is that there are so many grounded metal parts on the typical electric guitar that you're bound to get zapped somehow.

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                            • #15
                              Electrocuted On Stage:https://www.google.com/search?hl=en&...64.gJ2QtMJEzuo

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