Reverse Polarity Bootleg Ground Testing

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Internal shock

Internal shock

I haven't had time to rebuild that ground loop graphic, but should have a chance tomorrow. In the meantime, here's a weird story about two of my attendees getting shocked internally during one of my seminars. I do a demonstration in my live sound class where I discuss the need of dynamic processing (compression) on the pastor's microphone. So I let me own voice get very soft in volume while I raise the volume fader on that channel, just like we all tend to do when somebody is talking too softly. Then I SHOUT one word which easily hits 110 dB SPL to make the point that a sound engineer can't possibly react fast enough to turn down the volume in time. Everybody typically jumps a little (I don't give them any warning) and we all laugh a bit about how this happens to all of us, and how to solve the problem electronically.

At one of my seminars last year when I did this trick, two of my attendees in the front of the speakers sort of turned pale, gasped for breath, and ran out of the room. Now, I've NEVER had this reaction before since it's just one word shouted LOUD, and it's not really ear shattering, so I took a break as soon as I could to investigate what happened. I found these two students, one a small woman and the other a really big guy in their 50's, sitting out in the hallway. The woman looked terrified and the big guy was laughing a bit. I asked them what was wrong and found that both of them had the latest pacemakers recently installed to fix heart problems. And these new pacemakers also have a built-in defibrillation function if they detect an irregular beat. When I shouted and startled them, their hearts did a little skip, and the pacemakers started shocking them internally every few seconds trying to establish a solid beat, just like on a TV show when the doctor says "clear" and shocks the heart. The said it felt like somebody was slamming them in the chest every few seconds and it was very uncomfortable. They admitted that their pacemaker software needed to be tweaked a bit to make it less sensitive, and after 15 minutes of so they calmed down enough to rejoin the class. But boy was I "shocked" at this response, which I never dreamed could happen.

Now I ask if anybody has a pacemaker before I do this part of the demonstration. But who-da thunk??? :ashamed:
 
Wonder if they detect the sound rythem of the heart to determin it beating? beter never put them in front of a set of EV MT-4's even loaded with DL-MT-18's, EVX-18's would be a killer for sure.

I use a soft knee over for most of my compression to keep from coloring the music too much, but with bands I know that like to throw the mic around and or drop it I harden the knee up a little.

With dynamic compression I don't try to color the singer as I let them set their voice as they want it to sound, but for just talking I do like you and set maintain a good level without it going into feedback or clipping.
 
Proper Circuit Checking

Proper Circuit Checking

Using only a three light outlet tester should never be considered sufficient to check for correct wiring.
These devices have long been know to have some issues with properly checking all possible incorrect wiring conditions.
There was a company called ECOS that made a high quality tester for single phase and three phase wiring in the 90's.
Not sure if they are still in business, but I have a couple of their instruments.
Their three lamp tester was about $100.00
However, that being said, you should always use do visual inspection and use other instruments to verify wiring.
You should use a good quality digital or analog multi-meter.
I also use a couple of other techniques to verify wiring such as an EMF meter and checking for net current on each branch circuit in the panel when loaded.
 
rocky99 said:
There was a company called ECOS that made a high quality tester for single phase and three phase wiring in the 90's.
Not sure if they are still in business, but I have a couple of their instruments. Their three lamp tester was about $100.00
Click to expand...

You can find anything on eBay if you look around: http://www.ebay.com/itm/NIB-USA-ECO...349?pt=LH_DefaultDomain_0&hash=item4cf97af8bd

However, while is does appear to do a lot more tests than a standard 3-light "ice-cube" tester, it doesn't perform as many functions as a modern Ground Loop Impedance Tester (GLIT) such as a Amprobe INSP-3 or Ideal SureTest. Also, unless I'm missing something entirely, it won't indicate if a Bootleg Ground Outlet is wired with "correct" or "reverse polarity". And none of these GLIT's (old or new) will tell you if somebody daisy-chained a new outlet onto a RPBG outlet with at least 15 feet of 12 gauge wire. All GLIT's will report no errors in that case, even though the ground and neutral could be sitting at 120 volts above earth potential.

In modern buildings that should never be an issue, but in renovations where extra outlets need to be added to meet code, this is a real possibility. That's why you need to establish a known-good earth reference to test all renovated outlets for hot grounds. Unless you've wired and inspected it all yourself, you just don't KNOW what some DIY "electrician" did 30 or more years ago. ;)
 
jmsokol said:
You can find anything on eBay if you look around: http://www.ebay.com/itm/NIB-USA-ECO...349?pt=LH_DefaultDomain_0&hash=item4cf97af8bd

However, while is does appear to do a lot more tests than a standard 3-light "ice-cube" tester, it doesn't perform as many functions as a modern Ground Loop Impedance Tester (GLIT) such as a Amprobe INSP-3 or Ideal SureTest. Also, unless I'm missing something entirely, it won't indicate if a Bootleg Ground Outlet is wired with "correct" or "reverse polarity". And none of these GLIT's (old or new) will tell you if somebody daisy-chained a new outlet onto a RPBG outlet with at least 15 feet of 12 gauge wire. All GLIT's will report no errors in that case, even though the ground and neutral could be sitting at 120 volts above earth potential.

In modern buildings that should never be an issue, but in renovations where extra outlets need to be added to meet code, this is a real possibility. That's why you need to establish a known-good earth reference to test all renovated outlets for hot grounds. Unless you've wired and inspected it all yourself, you just don't KNOW what some DIY "electrician" did 30 or more years ago. ;)
Click to expand...

You know Mike it feels good to have another person who come from another side of the electrical world who like me can look at things out of the box sort of speak, I have read many of your online Bio's and seen where you have extensive experience in electronic engineering and even have worked on missile guidance systems and many other areas of robotics and other types of complicated electronic control systems, and this has let you come into the electrical field with an open mind like me allowing you to see things in a much different light then many who have just went right into the electrical field, this allows us to be able to spot things out that many who have been electricians for years would never see, it is this open mind approach that I try to teach others to always keep as the electrical field is always ever evolving and will never end the need to learn more, I'm glad you found this forum and shared your findings that will allow others to learn more about our field that many times get missed through the cracks.

I too came from another side of the electrical world, but I was more into the industrial side and communication electronics, and did some research on lightning for 3 years at the University of Florida which included allot on Earth grounding and the connection to it, while I did work as an electrician while still in high school and some after, I got more into industrial electronics till things led me back to working as an electrician, working the other fields allowed me to keep an open mind as to how things were being done and why.

Thanks for all that you have shared, and keep up the great work.
 
hurk27 said:
using a neon two lead tester has been used for years to detect which wire is hot, even that PDF about GFCI's I posted made this statment and told how to do it, by holding one of the neon's test lead and touching the other to the wire or contact of the device, if it glows its hot, if not its neutral or ground.
Click to expand...

Yeah, I used to do that myself a long time ago, but in retrospect it seemed like a bad idea. I've even seen the posting of using a neon tester for this purpose "removed" from this forum at least once (if memory serves). I guess if the neon tester has a 100K limiting resistor, the max current that could go through you with 120 volts would be around 1 mA or so, way beneath any shock danger level.

What's the "official" NEC or OSHA spin on using a neon tester like this? Dangerous? Not dangerous? Just a bad idea? What? ;)
 
jmsokol said:
Yeah, I used to do that myself a long time ago, but in retrospect it seemed like a bad idea. I've even seen the posting of using a neon tester for this purpose "removed" from this forum at least once (if memory serves). I guess if the neon tester has a 100K limiting resistor, the max current that could go through you with 120 volts would be around 1 mA or so, way beneath any shock danger level.

What's the "official" NEC or OSHA spin on using a neon tester like this? Dangerous? Not dangerous? Just a bad idea? What? ;)
Click to expand...

Not sure, there is a another way by connecting about 10' of wire to the neon lead instead of your hand, if you are further away from earth you might need a little longer wire but you get the same effect as instead of your body acting as a capacitor to earth the wire will.

Never saw the removed post for this H'mmm, never thought about it as it was used like this for a long time, and some of these testers even gave this in their instructions?:?
 
Jim Brown suggests using:

OUTLET TESTERS
Outlet testers are an extremely valuable tool. People who wire electrical systems make
mistakes, and it is common for there to be wiring errors in power systems. Some errors
merely add hum, buzz, and noise to the audio system, while others can damage
equipment or even kill people. A skilled technician could drag an array of test equipment
around a facility and test each outlet under load to find those mistakes, but testing
each outlet would consume considerable field labor. Low cost outlet testers (selling for
about $30) check only for basic wiring errors. More expensive units (typically about
$300) also test for excessive IR drop under load on all three conductors and for proper
operation of a GFCI, and do it all in a few seconds.

Ideal makes both types of products for American wiring. Charvin-Arnoux, Fluke, and
Metrix make quality products for European wiring. One of the better American units is
the Inspector II, manufactured by Tasco, Inc. of Englewood, CO. Older products made
by Tasco, and by Ecos, (long out of business, but available on the used market) are also
very good. It is well worth searching out one of the Tasco or Ecos units.
One of the most problematic wiring errors, and also the most difficult to detect, is the
exchange of Neutral and Equipment Ground (PE). This error causes the full load current
to flow on the Equipment Ground rather than the Neutral. This establishes a current
loop with a very large loop area, which can result in very strong magnetic coupling of
hum and buzz into signal circuits. A magnetic field probe may be the most effective
way to expose this sort of error.


Power and Grounding For Audio and Audio/Video Systems -- A White Paper for the Real World
http://www.audiosystemsgroup.com/SurgeXPowerGround.pdf
 
Speedskater said:
Jim Brown suggests using:
One of the most problematic wiring errors, and also the most difficult to detect, is the
exchange of Neutral and Equipment Ground (PE). This error causes the full load current
to flow on the Equipment Ground rather than the Neutral. This establishes a current
loop with a very large loop area, which can result in very strong magnetic coupling of
hum and buzz into signal circuits. A magnetic field probe may be the most effective
way to expose this sort of error.
Click to expand...

I would agree that swapped G-N and double bonded G-N wires (typically in sub-panels by well meaning or unknowing electricians) causes all sorts of hums and buzzes in sound systems. And that's what causes many musicians and sound technicians to "lift" grounds on audio gear by breaking off the ground pin on the power plug or use a $1 ground lift from Home Depot. That makes for a very dangerous situation considering that most of these amplifiers and instruments are NOT double-insulated and can easily have their chassis float up to 120 volts. Of course, a musician will have wet hands and can then touch both a "hot chassis" amp and an earthed piece of gear at the same time, with the result being a shock or even electrocution.

You are correct that these G-N reversals and cross-connects are very hard to find with normal test gear, but I have a few quick and cheap testing methods that work pretty well to find them without even opening up panels. Of course, a good visual inspection goes a long way towards correct troubleshooting.
 
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