1. Please take 30 seconds to register your free account to remove most ads, post topics, make friends, earn reward points at our store, and more!  

Help diagnose line voltage present on microphone

Discussion in 'Amps and Cabs [BG]' started by Chris 'Wighat' Jordan, Dec 29, 2016.


  1. At bar we've played many times. I had my meter in the truck so I checked more or less expecting to find a hot and neutral reversed and a floating ground. Had a floating ground, but hot and neutral were not reversed and there was no voltage present between neutral and ground (I used the floor for the ground which was giving me about 60 volts on the hot). My B25B was the source, ran to the house and got another amp. I've got my B25B opened up now and everything's normal at my house. I even lifted the ground and there is about 4 volts between the chassis and ground. The death cap has been removed and a 3-prong cord installed. Any idea what is/was going on?
     
    Last edited: Dec 29, 2016
  2. I assume you meant to say that the hot and neutral were NOT reversed?
    Hot and neutral reversed is bad.
    What do you mean by "floating ground"? There was a ground connection or their wasn't.
    No voltage between ground and neutral means one of two things.
    Ground and neutral are both at the same potential (good) or ground is not really ground (bad).
    So you measured 60 volts between the hot and the floor?
    You just touched one of the meter leads to the floor?
    What is the floor made of and how is it connected to ground or neutral?
    Did you get 60 volts between ground and hot?
    What you describes sounds like what you'd get from a center-tapped transformer with the center tap connected to the ground side rather than the ground side being grounded.
    It would have 120 volts between hot and neutral and 60 volts between the center tap and either side.
    Maybe you need one of those outlet testers with lights on it to tell what's happening?
     
    rufus.K likes this.
  3. Correct, not reversed, edited OP. Floating ground means there is a ground connection but it doesn't go to anything, so no ground. The floor is made of wood and it is connected to the ground/neutral in the sense that it is on pilons that are in the earth.
     
  4. Rick Auricchio

    Rick Auricchio Registered Bass Offender

    The floor, being wood, is essentially useless as a ground reference.

    If there is no third-wire safety ground in the outlet, a short-circuit in your amp (e.g. hot to chassis) can kill you. With a proper grounded outlet, this situation would immediately trip the circuit breaker feeding the outlet.

    How old is the venue? If it has three-prong outlets, then they should have a ground connected. Check a couple other outlets with an outlet tester, not your meter. These are under $10 at any good hardware store. I always carry one to check new venues before we plug in.
     
  5. To be more illustrative of the sitch, there was 120 volts between the ground and the neutral; the ground was totally hot.
     
  6. The floor is obviously not a perfect ground reference but it told me what I needed to know.

    The venue is quite old and pre-dates equipment ground. Someone replaced the two-prong receptacles with three-prong receptacles and did not retrofit a ground wire.

    Regarding tripping the breaker, yes, it would have at the bar, but I cannot find anything wrong with my amp, so that's not the (whole) story.

    I have one of those testers but I didn't have it with me at the gig. My meter does everything it does and more.
     
  7. Just because it's on the ground or even in the ground, doesn't make it Ground. Even things commonly thought to be Ground are often not. So Ground should be the third hole in the wall outlet. That sort of half round one. And even though Ground and Neutral are tied together back at the breaker box, and should be at the same potential (virtually no voltage between them) the neutral wire should not also be used as the Ground. In other words, tying the ground lug to the neutral lug at the wall outlet ain't suppose to be happenin.

    The tester we are speaking off is the one that looks like a 3 prong plug but it has three lights on the back and an explanation of what the lights mean.
     
    agedhorse likes this.
  8. That venue is dangerous and putting in a three hole outlet and only connecting two holes is dangerous and a serious code violation. One of many to be sure.

    Not to be disrespectful, but based on the floor is ground, and other comments, I would have to question if you know how to properly interpret everything the meter might be telling you?

    In general electrical Ground is derived by driving a 10 ft ground rod into the earth far enough away from a building that the rod is not just hitting backfill. Then a minimum 10 ga bare copper wire is run from the rod to the breaker box.
    You cannot, and are are not supposed to trust building plumbing as being a good ground. With the use of plastic pipe for plumbing, code allowed or not, it could break the ground circuit that plumbing can provide under the right circumstances. Wonder how many plumbing code violations are in that venue.

    Not trying the be an early to mid Twentieth Century hard right wing political party member about this, but you are at risk in that place.
     
    petey293 likes this.
  9. Ross W. Lovell

    Ross W. Lovell

    Oct 31, 2015

    The "floor" is not a perfect ground? It told you ABSOLUTELY NOTHING.

    Get the plug, your ability to properly use a meter is in question here and could KILL someone, possibly yourself.

    Tools, like meters can do many things, but that doesn't mean your are using it properly, you are not!
     
  10. agedhorse

    agedhorse SUSPENDED Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Some interesting comments here...

    First of all, the floor is not and can not be considered a "ground" (meaning at the same potential to and bonded to the building's groundING system), and since you said that the building does not have a grounding system, there will be no bond and therefore no other connection to the floor (other than capacitive, which will create or couple phantom voltage with no current potential)

    The reason for a grounding system is for all faults to present to the user "touch-safe" voltages in the event of any fault (phaste to phase, phase to neutral or phase to ground) the fault current will be routed back to the source's return without causing a rise of potential on any touchable surface. This is the reason that water pipes, gas pipes and building steel are bonded to the return conductor (called the neutral for 120/208V and 120/240V systems), and the grounding system serves as an equi-potential reference, even in a fault. The earth is also bonded to the grounding system, but since the earth has a fairly high resistance, the only purpose is to bleed any charge build-up and keeping any voltages present due to a fault common to the grounding system. This is more important under wet conditions.

    In order to get a shock from the microphone in an ungrounded power distribution system, one of two conditions must exist.

    The first case is that the microphone case is connected to either the hot or the neutral and whatever you are measuring to must be connected to the opposite conductor. This may be either a direct (ie. bonded) connection, or a high leakage path... such as a "death cap" on a guitar amp with the power plug inserted such that the death cap's leakage is from the opoosite conductor.

    The second case is that the guitar amp is connected to either the hot or neutral conductor and the microphone case is connected to the opposite conductor. Much of the same description of the first case applies.

    So, in the case presented by the OP, if there is no ground at the power receptacle, there has to be some complete circuit between the two devices, from hot to neutral, on accessible surfaces. If you investigate carefully enough, you just might find it.

    For grounded power systems, there are other possibilities, but reversing hot and neutral alone is not the cause... there has to be an additional fault.
     
  11. Thank you for your concern, but you are mistaken on all counts.

    OK, gang, it is not the case that I believe the floor of the bar is the same as electrical ground. I understand that there is considerable resistance between the wooden floor and the bond/ground rod.

    There was electrical potential between my lips and the microphone, so I was using the same path (floor to chassis) to identify the problem. Any helpful insight is appreciated and further presumption of my lack of understanding is not necessary.
     
  12. agedhorse

    agedhorse SUSPENDED Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Simple answer is that you can not use what is a floating and undefined "reference" to get any useful information.

    I am not mistaken, industrial power systems and controls was my engineering specialty.
     
  13. gumtown

    gumtown

    May 7, 2007
    New Zealand
    The bar has faulty wiring, so I would inform the bar owner of the safety issues, in writing preferably, as a formal notification, also stating that the band were experiencing electrocution.
    Then insist that it be repaired A.S.A.P, if the bar owner ignores your complaint in writing, they could be liable for criminal negligence if someone from the next band gets killed..
     
    Coolhandjjl likes this.
  14. john m

    john m Supporting Member

    Jan 15, 2006
    Floor to chassis is not the same path. Using a cold water pipe near the fault may work as a reference, but that is not even a given.
     
  15. john m

    john m Supporting Member

    Jan 15, 2006
    "totally hot" does not mean there was any sustantial current available to do any damage ( injury)- though there might be. Keep in mind that a volt meter is a high z device and presents no load to the circuit being measured- this is by design.
    Also, replacing a 2 prong receptacle with a three prong is ok if you tag the third prong back to the device box AND verify that the ground functions. With no ground present, a GFCI receptical must be installed to prevent injury ( think bathroom or kitchen or outdoor typical situations).
     
    BadExample likes this.
  16. john m

    john m Supporting Member

    Jan 15, 2006
    May I add: these days-
    NEC wants 2 ground rods driven 6 feet apart.
     
  17. Ross W. Lovell

    Ross W. Lovell

    Oct 31, 2015

    We are all born ignorant, some just work harder to stay that way.
     
    dbase and Old Garage-Bander like this.
  18. MNAirHead

    MNAirHead Supporting Member

    It's prudent to put a foam sock on all microphones.. have had it happen a few times..

    bring a fire extinguisher...
     
    dbase likes this.
  19. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    With no safety ground in the building, the added third prong on your amp obviously isn't going to be doing anything. You are down to a two prong, hot and neutral, system.

    There are several possibilities:

    Although you said that the death cap was removed from your amp, perhaps it wasn't removed from the PA amp. If this were the case, the cap in the PA could be leaking.

    In the old days with two prong amps, you had a 50:50 chance of plugging in both amps so that they were wired the same way. If you got a shock, you turned the plug around. Some amps had a ground reverse switch that accomplished about the same thing. This allowed you to have both chassis' at more or less the same potential. If you can't reverse your plug, there are 3-to-2 plug adapters available at a hardware store.

    But there can still be problems. With bad wiring, The neutral voltages can differ at two different outlets, even with outlets that are fairly close to each other. The difference in potential can result in a ground loop and hum, possibly a shock. Some test equipment have grounded banana plugs on the chassis that are used to daisy chain them together. This can be used to avoid ground loops.
     
  20. Coolhandjjl

    Coolhandjjl Supporting Member

    Oct 13, 2010
    Appleton
    Electrical inspectors are just one example of good government regulation. (If you value your life, that is)
    Also, if there is an accident, and he is cited for improper grounding, illegal wiring, or whatever, his insurance company may not pay out, leaving the victim not only injured or killed, but nothing to pay damages, medical or funeral bills. He needs to be reported to the building inspectors NOW!

    It's almost 2017 for cripes sake. Not 1917. Jeesh.....:rollno:
     
    Last edited: Dec 30, 2016
    MrLenny1 likes this.

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.