Electrical Problems ???

[malsackj]

I came across this on Pro Sound Web and feel it is very important for anyone working on older homes. People with bands and such that a simple set of testers will help to prevent injury or damage to gear.


Re: freak accident? help!
« Reply #18 on: May 03, 2012, 05:00:44 pm »

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Guys... this is not a freak accident. It was caused by something I call a Reverse Polarity Bootleg Ground (or RPBG). This occurs when an old building has new grounded outlets added by bonding the ground screw to the neutral screw because there was no separate ground wire to begin with. That by itself is electrically safe (however, it's illegal per the NEC), but many older buildings had black power wires for both the hot and neutral, and some were simply wired backwards with the white/neutral wire being hot and the black/power line being actual neutral. See the attached diagram. In that case any piece of gear plugged into a Reverse Polarity Bootleg Grounded outlet will have its chassis energized to 120 volts. If you then connect that piece of audio gear to something else that's plugged into a correctly wired outlet, you can have 20 amps or more of current flow down the shield, which melts wires and destroys gear. The really scary thing is that a 3-light tester will tell you that this reversed outlet is wired correctly, when in fact both the neutral and ground contacts are at 120 volts and the hot side is at earth potential. Please see http://www.youtube.com/watch?v=_pwCY4_L ... redirect=1 for a video I did a few weeks ago that describes how you can use a $20 non-contact AC tester in conjunction with a cheap 3-light tester to qualify grounds in power plugs. That's the only easy way to determine if an outlet will blow up your gear.

After discussing this testing issue with a few meter manufacturers, it seems that the entire industry has missed this problem. In fact, electrical inspectors routinely use a 3-light tester to qualify outlets in renovated buildings, but that's where the hot and neutral wires in the wall are most likely to be reversed.

I'm covering a lot of this on http://www.noshockzone.org and trying to get Lowes and Home Depot to offer training to consumers and electricians on how to check for this condition. Please contact me with any questions or comments.

Mike Sokol - mike@fitsandstarts.com

* Bootleg Ground Demo.JPG (83.56 kB, 776x565 - viewed 835 times.)
« Last Edit: May 19, 2012, 01:36:07 pm by Mike Sokol »
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Mike Sokol
mike@fitsandstarts.com

 

[malsackj]

Re: Electical Problems ???

Mike Sokol who wrote the above and video is visiting my area with this statement attached.


FYI: I'm going to be presenting a 90-minute No~Shock~Zone seminar for the student AES chapter at Shenandoah University in Winchester, VA on Wednesday, Sept 18 starting at 6 PM. It will include a bunch of different NCVT demonstrations on various electrified objects such as guitars and microphones, as well as my Ground Loop hum diagnostics clamp procedure, and an introduction of my latest theory on GLID (Ground Loop Inter-modulation Distortion) in sound systems and how it affects bass clarity. We'll take some pictures and post them here after the seminar. It's free and open to the pro-sound public, but you should contact me directly in advance if you want to attend so I can put your name on "the list".

I will be in eastern Texas Oct 12 thru 17 next month. I've taught seminars in the past at Austin Community College, and since I'll have downtime on Monday-Wednesday that week, I've already contacted the staff there to see if I could hookup with the student AES chapter to do a No~Shock~Zone presentation. Is anyone on this forum with the Austin student AES chapter, or any other pro-audio organizations in the area? If so, contact me directly at mike@noshockzone.org.

I plan to try an attend this in DC area next week but I am returning from a trip in Wisconsin that day. I am interested in what the effect is on the bass and or the sub.

 

[malsackj]

http://forums.prosoundweb.com/index.php/board,82.0.html

Mike now has a link and forum on ProSoundweb.com forum.

He is including on his link Generator and large 50 amp plug services.
Not many home theaters will need the 50 amp service but the generator usage might be interesting.

He also has an answer for anyone wanting to know why a guitar will hum when there is no contact witht he strings. Answer will be done in a few days.

The visit this Wednesday at Shenandoah University was 90 minutes of good information for the band and music people. Most of this will apply to ground loop and pin 1 problems. Sub Electrical pannels creating ground loops in the buildings.

I feel I have heard the sound of 60 hz ground loop affecting the bass of the sound systems after reviewing his papers and discussion. From the lectures it looks like he will be down around Texas soon so check his schedule and see if others can attend and find this helpful.

 

[malsackj]

Here is a good paper to read. Use of Sub panel, Isolated Ground.

http://www.middleatlantic.com/~/media/m ... ashx?la=en

 

[malsackj]

New home built and I asked the electrician about the ground rod and I received a reply

There are no ground rods, only the eufer ground.

This may be acceptable for the house and building code !

What do you think about for the music and Sound. Time and wear and old age.


A properly installed Ufer ground is supposed to be better than a ground rod, especially in sandy or dry soil. For those who've never heard of a "Ufer Ground" here's a pretty good explanation. http://www.psihq.com/iread/ufergrnd.htm

 

[heeman]

^ Interesting.....never heard of it!

Will you drive a ground rod also?

House is looking good!

 

[Towen7]

I recall reading an article about the "best" way to ground an electrical system for AV purposes. IIRC it required multiple ground rods surrounding the premises, all connected by heavy gauge wire (essentially a ring grounding system).

 

[Towen7]

This is exhausting to read but may be what your looking for ...

http://audiosystemsgroup.com/SurgeXPowerGround.pdf

:text-link:

 

[Botch]

Something I've never understood: how can one line be "hot", and another "neutral", if it's A/C power going through them both? Don't electrons travel up one wire and down the other, then reverse, 60 times a second (in the US)?

 

[Towen7]

Only when connected by a load.

 

[Botch]

Understood. But, at one instant the electrons are flowing up the hot and back on the neutral, then the next instant they're flowing up the neutral and back on the hot.
So, what's the difference between between a hot and a neutral line?

 

[Zing]

So, what's the difference between between a hot and a neutral line?

One hurts really bad when you touch it.

 

[Flint]

A hot line actually has a power source connected to it. A neutral line does not necessarily have a power source on it - it could be a simple ground somewhere.

In fact, your house is getting a 240V connection with a + and a - line each with a complimentary out of phase 120V source on each leg of the line. Neutral is the ground between the two phases of the 240V incoming power which is usually connected to the neutral pin of the transformer, but which could be a ground line.

The extra ground is to provide additional grounding for power differentials in case of poorly designed circuits, electronics, or a fault somewhere.

 

[heeman]

In a 120V rms configuration; the wall outlet, with a Hot (Blk) and Neutral (Wht) and a Ground (bare) there is theoretically zero volts between the Neutral and Gnd and 120V rms Between the Hot and Neutral and Hot and Ground. The Neutral is tied to ground back at the circuit breaker/distribution panel. Looking at it on a scope you would see a 60Hz sine wave with a Peak to Peak voltage of approx. 340.

The Ground (bare) is a safety ground typically. Older homes did not have the Third, Ground Prong on the outlets or plugs. Today's NEMA 5-15 plugs have the ground prong.

Years ago, take power tools for an example all had metal enclosures that was tied to the safety ground. In case of a motor fault, the voltage would connect to the ground and trip the breaker or blow the fuse. Current tools that do not have the Ground are typically double insulated that insures during a fault condition, the user is not susceptible to being shocked and/or electrocuted.

Flash back to my UL Days...............

Not sure if this clears up your question Botch?

 

[Botch]

Not sure if this clears up your question Botch?

Flint's comment:

A hot line actually has a power source connected to it. A neutral line does not necessarily have a power source on it - it could be a simple ground somewhere.

...is actually a revelation to me. I always thought a power source, be it DC battery, AC, other, had to send out and return to operate.



This may have had an entire, crippling effect on my education, and my professional life.

 

[Flint]

Not sure if this clears up your question Botch?

Flint's comment:

A hot line actually has a power source connected to it. A neutral line does not necessarily have a power source on it - it could be a simple ground somewhere.

...is actually a revelation to me. I always thought a power source, be it DC battery, AC, other, had to send out and return to operate.



This may have had an entire, crippling effect on my education, and my professional life.

An AC power source resonates. The Hot side "pushes" electrons into the ground then "pulls" them from the ground, and once the current stops flowing, everything returns to normal. That's for a single-phase AC line.

 

[malsackj]

I see the power as being unbalanced signal. So you have an Audio sine wave of 60 hz on the Tip or center conductor and the neutral as the completion of the loop.

The microphone works as balanced like a telephone system with two wires working with equal signal but 180 opposites.

The unbalanced does not have the equal but 180 opposite on the second wire.

The Ground is by design and definition supposed to be better in dryer soils. Because of the larger surface area, contact with the earth it self, the Concrete holds some moisture.

Now I need to double check my electrical because one question that did occur is the Concrete can make it easy to have a problem. With bare concrete one should be using GFCI on the outlets to help prevent injuries.

People I have been talking with are being driven to this by code for new homes and updates because they believe this to be less maintenance and ware and tear problems.

There still needs to be maintenace at the connection point. Crimp connection. 5, 10 , 15 ??? how many years and what is the maintenance.

 

[malsackj]

Ufer ground is connecting the ground for the electrical to the rebar in the foundations and concrete.

 

[heeman]

Another explanation:


http://www.nojolt.com/Understanding_240_volt_circuits.shtml

 

[malsackj]

Another explanation:


http://www.nojolt.com/Understanding_240_volt_circuits.shtml

Some of this transition to 4 wires is because the the device becomes a distribution point and the metal body is connected to the ground like a second service panel. The commons being separate from the ground. The ground and common are only bonded together at the main service panel.

My band sound system has a 240 connection with 4 wires. The Common and ground are not connected at the box with the breakers. When not plugged into. You can meter the ground and common and will get no connection.

The first link on here also talks about the second breaker panel along with isolated grounding.