Results 1 to 25 of 25
Like Tree34Likes
  • 11 Post By g1
  • 5 Post By g1
  • 1 Post By Leo_Gnardo
  • 2 Post By olddawg
  • 1 Post By drewl
  • 3 Post By TomCarlos
  • 4 Post By R.G.
  • 2 Post By Jazz P Bass
  • 1 Post By Mick Bailey
  • 2 Post By PeanutNore
  • 2 Post By DRH1958

Thread: Safety: testing Electrical outlets

  1. #1
    g1
    g1 is online now
    don't forget the joker g1's Avatar
    Join Date
    Feb 2010
    Location
    Canada, somewhere north of Fargo
    Posts
    8,954

    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.
    Certified Dotard

  2. #2
    Old Timer Leo_Gnardo's Avatar
    Join Date
    Sep 2012
    Location
    Dogpatch-on-Hudson
    Posts
    4,351
    Quote 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.

  3. #3
    Lifetime Member
    Join Date
    May 2006
    Posts
    4,163
    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.

  4. #4
    g1
    g1 is online now
    don't forget the joker g1's Avatar
    Join Date
    Feb 2010
    Location
    Canada, somewhere north of Fargo
    Posts
    8,954
    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.

    smps.jpg
    Last edited by g1; 01-05-2015 at 04:38 AM.
    Chuck H, nevetslab, bsco and 2 others like this.
    Certified Dotard

  5. #5
    Old Timer Leo_Gnardo's Avatar
    Join Date
    Sep 2012
    Location
    Dogpatch-on-Hudson
    Posts
    4,351
    Quote 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 Thumbnails Attached Thumbnails electric_hazard_bolt_yellow.jpg  
    g1 likes this.

  6. #6
    Old Timer olddawg's Avatar
    Join Date
    Dec 2007
    Location
    Carlsbad, CA and Kona, HI
    Posts
    2,379
    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.
    g1 and bsco like this.

  7. #7
    Old Timer
    Join Date
    Jun 2006
    Location
    Norristown state hospital
    Posts
    1,775
    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.
    g1 likes this.

  8. #8
    Supporting Member TomCarlos's Avatar
    Join Date
    Oct 2009
    Location
    Roseville, Ca.
    Posts
    534
    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 Thumbnails Attached Thumbnails wiggy-voltage-tester.jpg  

  9. #9
    g1
    g1 is online now
    don't forget the joker g1's Avatar
    Join Date
    Feb 2010
    Location
    Canada, somewhere north of Fargo
    Posts
    8,954
    Quote 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".
    Certified Dotard

  10. #10
    ToneOholic! big_teee's Avatar
    Join Date
    Jun 2010
    Location
    Mid-South USA
    Posts
    9,780
    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 at 08:53 PM.
    Technicians Run the World, but Bankers, Lawyers, and Accountants, Take All The Credit!
    Keep Rockin! B_T
    Terry

  11. #11
    Lifetime Member
    Join Date
    May 2006
    Posts
    4,163
    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.

  12. #12
    Supporting Member Jazz P Bass's Avatar
    Join Date
    Dec 2008
    Location
    Wernersville, PA
    Posts
    11,860
    Quote 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.
    Justin Thomas and Drewline like this.

  13. #13
    Lifetime Member
    Join Date
    May 2006
    Posts
    4,163
    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.

  14. #14
    Old Timer
    Join Date
    Jun 2007
    Posts
    4,925
    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.

  15. #15
    Supporting Member Jazz P Bass's Avatar
    Join Date
    Dec 2008
    Location
    Wernersville, PA
    Posts
    11,860

  16. #16
    ToneOholic! big_teee's Avatar
    Join Date
    Jun 2010
    Location
    Mid-South USA
    Posts
    9,780
    That is one of the selling features of EMG Active pickups.
    You take the bridge ground off!
    Technicians Run the World, but Bankers, Lawyers, and Accountants, Take All The Credit!
    Keep Rockin! B_T
    Terry

  17. #17
    Supporting Member loudthud's Avatar
    Join Date
    May 2006
    Location
    Near Dallas Texas
    Posts
    3,309
    Quote Originally Posted by R.G. View Post
    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.
    Current production Fender guitars have the CE mark. Are they just limiting thier liability?
    WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personel.

  18. #18
    Lifetime Member
    Join Date
    May 2006
    Posts
    4,163
    Interesting question.

    The CE mark is necessary for sale of electrical-ish stuff in the EU. I have some minimal understanding of CE marking requirements, so this is going to be fuzzy. As I understand it, the mark does not mean that an independent testing lab has passed it, only that the maker has certified it to pass if tested. There may have been independent testing, maybe not. If an item is suspected of not passing, one of the independent testing labs can decide to test a piece of equipment on their own and see if they think it passes or not, and cause various degrees of regulatory trouble for the maker if they find it does not, including possibly recovering fees from the maker.

    In the case of Fender guitars, it makes it simpler to sell in the EU if there is no question about them representing it as passing standards. Since makers may self-certify the mark, they may have looked at their guitars, noted that there are no hazardous voltages in it anywhere, of any kind, and no potentials for shock or thermal danger, and decided "Well, sure it passes!"

    Or someone may have sniped them about having a product with wires in it and not having a CE mark.

    Hard to say. I am doing pure speculation, obviously.

    Edit: I forgot to mention. Having a CE mark does not limit your liability. CE marking is a change from government labs certifying and thereby conferring immunity on damage claims to the US model, where it doesn't matter who said it was safe, the maker is still liable in court if someone gets hurt. As I (dimly) understand it.
    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.

  19. #19
    Supporting Member
    Join Date
    May 2006
    Location
    Staffordshire UK
    Posts
    3,165
    With regard to the 'reverse bootleg' condition mentioned in the EC&M link in post #1, my 'Socket&See SOK32' socket tester identifies a 'swapped live / earth' error (I checked!) SOK32 - SOCKET & SEE - SOCKET TESTER + F/FINDER | Farnell element14

  20. #20
    Supporting Member
    Join Date
    Dec 2009
    Location
    UK
    Posts
    2,912
    Testers also came up here;

    Grave electrical accident happened yesterday, May 25 2014

    CE marking means that the item complies with all of the EU rules that apply to it, so in the case of a guitar it could apply to the paint finish and material construction, as well as any electrical requirements. It reminds me of the British Standards - some items were tested and certified to the standards, but others were simply labelled 'Meets or exceeds British Standards', which could mean nothing. CE is just like that - meaningless unless the equipment has been independently tested.

    The cap/resistor ground connection for guitars works very well. It's also a good fix for noisy electro-acoustics with humming transducers; use a brass shim plate stuck under the bridge to contact the strings and ground it using the cap/resistor combo.
    g1 likes this.

  21. #21
    Member
    Join Date
    Jun 2011
    Location
    Pittsburgh PA
    Posts
    86
    A GFCI extension cord or outlet adapter like this might be a good idea if you aren't sure if you can trust the outlet you are using. If current starts flowing where it isn't supposed to it cuts off the circuit within 1/30th of a second.
    g1 and bsco like this.

  22. #22
    Supporting Member
    Join Date
    Jan 2012
    Location
    Eastern Canada
    Posts
    1,282
    Quote Originally Posted by olddawg View Post
    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.
    I always use a wireless system with my guitar....have done so for years.....I would never part with it.......convenience and safety.....I had purchased a set of lamps from Wal-Mart a few years back.....two end table touch lamps, a small night table lamp and a taller pole lamp as a set.....When I plugged them in, every time I went to turn on the tall pole type lamp the breaker would pop....when connected by itself it worked fine....after checking everything out, this lamp was wired wrong right from the factory...I had to take it apart and reverse the wiring connected to the lamp socket.....goes to show..you can't trust anything...

  23. #23
    Senior Member guitician's Avatar
    Join Date
    Aug 2008
    Location
    Phoenix
    Posts
    1,003
    Just sell the guitars/amps with a non-contact voltage tester (NCVT). What passes for an electrician these days is bringing us back 50 years it seems.

  24. #24
    Member Rob's Radio-Active's Avatar
    Join Date
    Jan 2016
    Location
    Des Moines, Iowa, USA
    Posts
    58
    Quote Originally Posted by TomCarlos View Post
    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.
    Plus, for those who are not experienced with operating/reading a meter with a multi-function dial, these are close to fool proof. I was a licensed master electrician for years working in industrial environments, and I still carried a Wiggy. They (most of the Wiggy types) also draw enough current to trip a functioning GFCI when connected between line (hot) and ground. This is not to imply it tests the GFCI's trip threshold properly, but it at least shows it is not completely stuck on.
    Rob

  25. #25
    Senior Member
    Join Date
    Apr 2015
    Location
    Minneapolis, MN
    Posts
    330
    As a commercial electrician for 31 years, I had numerous service calls to fix improper repairs done by unqualified personnel at various places. They had someone who said they could fix it. Well they couldn't and they ended up calling a qualified electrician to do it right. So don't forget that venue owners are in the business to make money so try to fix things themselves. It costs money to call someone who can do things right. So don't rush to judgement just because an outlet is wired wrong. Do you think the venue owner will admit it was HIM who miswired the receptacle that killed someone? Some parts of the country are not regulated as well as others and I know of NOBODY in my Minneapolis local who would do this.
    Richard and g1 like this.
    Turn it up so that everything is louder than everything else.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Special wall outlets
    By Enzo in forum Music Electronics
    Replies: 27
    Last Post: 05-24-2015, 07:07 PM
  2. Electrical engineers: is this possible?
    By Bad Daddy DeVille in forum Guitar Amps
    Replies: 63
    Last Post: 05-16-2014, 08:08 AM
  3. Electrical conundrum
    By Regis in forum Music Electronics
    Replies: 6
    Last Post: 12-31-2012, 04:42 PM
  4. Fender convenience outlets miswired
    By Axtman in forum Maintenance, Troubleshooting & Repair
    Replies: 6
    Last Post: 08-28-2009, 09:57 AM
  5. Safety and Stabilty
    By Amp Kat in forum 5 E 3
    Replies: 2
    Last Post: 10-17-2006, 01:07 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •