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That little A/C receptacle tester....

Discussion in 'Amps and Cabs [BG]' started by Chuck M, Dec 6, 2017.


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  1. Chuck M

    Chuck M Supporting Member

    May 2, 2000
    San Antonio, Texas
    Played a live radio show last night. The event is a volunteer event where gifts for underprivileged folks are wrapped. I have played it for many years and this year we were in a new venue....and that is where the trouble starts.

    I arrived and the sound man for the radio station asked what I needed to get hooked up. I told him I just needed power and that he could plug in to the D.I. on my Aguilar AG 700. So he brings me power from an extension cord and I power up my amp and it is working fine until he plugs into the D.I.! Sparks...smoke..and a blown AG 700 and a blown Mackie Mixer (the radio station's mixer). Great.

    I went to my car and retrieved my back up head..Genz Benz Shuttle 9.2. Plug it in but then thought about that little receptacle tester in my bag...plugged in the tester and it showed the power was wired wrong!

    Got extension cords and ran power from a correctly wired receptacle and thought all was right. My amp powered up fine and sounded good. Then the sound guy went to plug in to the D.I. and again I see sparks fly! The Shuttle was still working but I had fears about the D.I. being damaged. Played the gig and came home and checked the Shuttle and, sure enough, the D.I. is damaged.

    The radio station is going to pay for the repairs but, man, I sure wish I had used that little receptacle tester before I turned on my Aguilar.

    This is a link to the tester.

    https://www.amazon.com/Electrical-Receptacle-Outlet-Ground-Tester/dp/B0012DHVQ0

    Get one and use it EVERY time you go to a new venue.
     
    Last edited: Dec 6, 2017
  2. jnewmark

    jnewmark Just wanna play the groove. Supporting Member

    Aug 31, 2006
    Stax 1966
    Play guitar.
    I guess I don't get it. You tested the second outlet with the tester, it indicated all was well, but sparks still hapenned ?
     
  3. Chuck M

    Chuck M Supporting Member

    May 2, 2000
    San Antonio, Texas
    Yes. The radio station replaced their blown mixer and all equipment was plugged into the same correctly wired receptacle and still something was wrong. Perhaps the mic cable they were using was damaged by the first incident with the Aguilar amp.
     
  4. jnewmark

    jnewmark Just wanna play the groove. Supporting Member

    Aug 31, 2006
    Stax 1966
    Play guitar.
    Ok, but, man, the first thing they should have done is try a different XLR cable.
     
  5. Chuck M

    Chuck M Supporting Member

    May 2, 2000
    San Antonio, Texas
    Well, perhaps they should have used a different cable but I should have insisted they use a mic! Hindsight is 50/50 and I am embarrassed by having a second amp damaged in the same fashion. I should have been more careful after the Aguilar was damaged. We were, however, being rushed to prepare for going live on the air so there was little or no time for being thoughtful about this.

    I only mention this event in the hopes that it may help some of you avoid this sort of failure. If I had just checked the A/C before plugging in no equipment would have been damaged. I will certainly be more careful in the future.
     
  6. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    This specific fault does sometimes happen, with exactly the symptoms you describe.

    The most common cause is the hot and ground reversed, causing the chassis and the pin 1 connection to be hot relative to other chassis and XLR pin 1s.

    If the mixer was plugged into such a circuit and was connected to a bass amp plugged into a correctly wired circuit, the pin 1 grounds are 120 volts apart and very high currents will flow until something burns open (or the branch circuit breaker opens, which is usually too late).
     
  7. Chuck M

    Chuck M Supporting Member

    May 2, 2000
    San Antonio, Texas
    The mixer was plugged into a correctly wired circuit but the line supplied for the bass amp was wired wrong. I believe it was ground and hot reversed.
     
    packhowitzer likes this.
  8. Spidey2112

    Spidey2112

    Aug 3, 2016
    I have a similar tester... whether I remember to use it, or not, is a whole 'nother matter...

    (putting it in the bag, as we speak... I may need it soon... Thanks!)
     
  9. Spidey2112

    Spidey2112

    Aug 3, 2016
    Maybe the DI had already taken a hit, and IT was now an extension of the original problem... ?
     
    Jazzygreg likes this.
  10. Very good advice. I hope everything gets sorted out for you.

    I guess one should not only check the outlets you plug into, but also the outlets that anything else plugs into that is connecting to your gear. But who woulda thunk?

    I am surprised that a radio station would have faulty wiring like that, and then, being I work in radio, I am also not surprised.
    It's amazing that they haven't run into this before.

    Guess that's one of those, "we don't need no engineer" radio stations.
    "The GM's nephew can fix whatever problems we have after soccer practice."
     
    Last edited: Dec 6, 2017
    Lvjoebass and Garret Graves like this.
  11. Chuck M

    Chuck M Supporting Member

    May 2, 2000
    San Antonio, Texas
    The faulty wiring was at a big hall in a theme park. The radio broadcast was a remote broadcast.
     
  12. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Absolutely! Given the cost, an outlet tester should be in every gig bad. Use it every time before you plug in. You never know what may have been changed since the last time.
     
    Chuck M likes this.
  13. Drgonzonm

    Drgonzonm

    Sep 4, 2017
    American SW
    I was manager at a plant where we had a mobile health unit come in. About $100,000 of equipment fried because one of their power cables was wired wrong. The health company wanted us to pay for their damage. They were the ones who supplied the bad cable. All we did was supply a properly wired three phase recpt. We documented the inspection with lots of pictures, just in case.
     
    Killed_by_Death likes this.
  14. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    It doesn't matter which receptacle was miswired, the cause of the fault is the voltage difference between chassis that are supposed to have zero volts difference.
     
  15. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    ! wonder who the “Electrician” was who wired up the supplies for the show!
     
    Bob Lee (QSC) and agedhorse like this.
  16. I also use a voltmeter. It is interesting how the voltage at an outlet on one side of the stage can vary from one on the other side.

    DM55-1.
     
    lowplaces and beans-on-toast like this.
  17. JGbassman

    JGbassman

    May 31, 2011
    Iowa
    I carry a tester in my gig kit and test new places I haven’t played. I know I should test every time before I plug in but I don’t. On that note, I’m usually the last to plug in so any issues would be found before I plug in
     
    Lvjoebass and packhowitzer like this.
  18. The receptacle testers are very useful. I have a bunch of them so I can usually find one when I need it. I buy the ones with the ground fault circuit interrupter device test button on them.

    There is one limitation to these testers which is the inability to detect what some people refer to as reversed hot and neutral, with a "bootleg ground". This is a condition I have encountered more than once in homes where the homeowner, or clueless handyman has reversed the hot and neutral wires, and also connected the receptacle equipment grounding terminal to the incorrectly connected neutral wire.

    Here is a website with a diagram that illustrates it better than my written description: Failures in Outlet Testing Exposed which also shows a more reliable way to test for this fault using a quality medium sensitivity non-contact voltage detector on the grounding terminal of a receptacle. Very well written article.

    One way to test for wiring errors in receptacles on different circuits that are some distance apart is to connect a three wire extension cord into one receptacle, and use an AC voltmeter at the other receptacle to see if any substantial voltage, (more than maybe 6 VAC) exists when putting the meter leads between the two grounding lugs. Likewise the neutrals should not have much difference. And a meter reading between neutral and ground should not show much voltage between them. You might see a difference of a few, or as much as 240 VAC measured between the two hots, depending on which phase of the power it is connected to in the panel.

    If you see something like thirty or forty volts between grounds or neutrals even if you don't burn something up or get a shock, you might have problems with 60 Hz noise. If you do this test with a load like a lamp plugged into one or both circuits and you see a big difference, don't connect any of your equipment to either circuit until the fault is rectified.

    I am not a licensed electrician, but I have independently studied the coursework that my local community college uses to train electricians. And I have been an electronics technician, and field service engineer in very high-tech and industrial environments for over forty years. Anyone who knows me, calls me whenever they need electrical work. And I have installed numerous service entrances and done residential, and commercial electrical work with permits and inspections, and have never failed an inspection.

    I started taking photos of very dangerous electrical installations that I have found, and some of them are shocking! Pun intended. I have found wiring blunders that were like a trap waiting to kill someone. I quit photographing them because there were so many of them. I have found poor workmanship resulting in installations that were actually smoldering, and likely within hours of starting a fire in someone's home on two occasions. One the result of improper repair work on aluminum wiring, and another involving a loose connection resulting in heat buildup due to unintentional resistance at the connection point to the wiring device.

    It is amazing how much unsafe wiring is out there.
     
    Last edited: Dec 6, 2017
    Jazzygreg, Ewo, Skerrvydog and 6 others like this.
  19. two fingers

    two fingers Opinionated blowhard. But not mad about it. Gold Supporting Member

    Feb 7, 2005
    Eastern NC USA
    I will never understand why somebody doesn't sell a cheap Woodhead and a Wiggy in one little device.

    (If you know both of those terms yer my people. :roflmao:)
     
    Gluvhand, Lvjoebass, crentest and 3 others like this.
  20. cavemanbass

    cavemanbass

    Nov 5, 2010
    Many thanks to OP for sharing, have to admit I have a tester like that and never use it. Plan to change that!

    Question about the original incident... if OP had used a simple passive DI instead of the DI in his amp, would he still have fried his amp? Just the DI box? Both / Neither? I had never thought about this, I have a passive DI on my pedal board just for convenience... but if something was going to blow I'd prefer it was a $200 box rather then an $800 box...
     
    Rev. Cornelius likes this.