Reverse Polarity Bootleg Ground Testing

[jmsokol]

I'm a technical instructor who teaches sound system installation at churches around the country, but my background is in industrial power and robotics control, and I earned my Master Electricians license in 1978. Over the last 10 years I've heard of many instances of musicians and preachers getting shocked on stage and in baptismal pools, so I'm always teaching about wiring safety for musicians and installers.

However, while drawing up a schematic of how 3-light outlet testers work, I noticed that they miss one really dangerous condition; something I call an RPBG (Reverse Polarity Bootleg Ground), where the Ground and Neutral contacts end up at 120 volts and the Hot contact is at 0 volts. See diagram below. Not to be confused with a CPBG (Correct Polarity Bootleg Ground), RPBG outlets are a very serious shock hazard since the grounds and neutrals are now at 120 volts, while the hot contact is at zero volts. Anything with a grounded power cord plugged into an RPBG outlet will seem to operate normally, but its chassis will be electrified to 120 volts which is extremely dangerous. The RV and Pro-Audio industry calls this a "hot-skin" or "hot-chassis" condition.

In pre-70's building renovations (without safety grounds) there's a need to install grounded receptacles. Electricians upgrading to grounded outlets sometime take a short cut, bonding the Neutral and Ground screws together in the outlet box creating a False/Bootleg Ground. If the white wire is actually neutral, it's not an immediate shock hazard (but against code). However, sometimes the white "Neutral" wire in the outlet box could actually be Hot. That's because black and white wires are sometimes swapped inside the walls, or there was knob and tube wiring which is all black. Note that an RPBG outlet will not show up using any ANY 3-light tester or even an advanced tester such as a Amprobe INSP-3, Ideal SureTest, or Extech CT-70. These advanced testers will show it's a Bootleg ground, but not detect it's an RPBG with a hot ground. See http://www.youtube.com/watch?v=iLk-6pvSlWg for a video.

With that in mind, here's a simple test I've developed using a non-contact AC tester to find RPBG outlets. A standard non-contact AC tester such as a Fluke 1AC-A II VoltAlert or Amprobe VP-600SB VoltProbe is sensitive enough to differentiate between the Hot and Neutral contacts on a NEMA 5-15 or 5-20 outlet, and will beep if the ground is hot. So my recommendation is to supplement your standard 3-light tester with a non-contact tester by checking the outlet in this order. Start on the Hot contact to make sure your tester beeps and doesn't have dead batteries, then move to the Neutral contact which should not beep, then the Ground slot which should not beep, then back to the Hot slot, which should beep. If the outlet is mis-wired as a RPBG, then you'll likely get beeping inches away from it since the front strap and entire metal box (if it's metal) will be energized to 120 volts. An RPBG outlet should be marked "out of service" until it can be repaired. Yes, most likely it should be replaced with a GFCI outlet and marked as "No Ground".

I'm already teaching this technique in my seminars for sound system installers, but it goes way beyond the music stage to every older home and office building that's been renovated to include grounded outlets. Please let me know if any of you have experienced this type of mis-wiring problem and how you found it. I appreciate your input.

Mike Sokol

 

[iMuse97]

This reversed polarity problem seems to appear in some of those places where DIYers have tried their hand at electrical work. Churches could easily be one of those places, since a member may offer to fix something that he or she is not really qualified to repair.

In my previous home, the first owner of the house finished out the basement and detached garage in BX armored cable. He cut the armored sheath and the bonding wire back so that his open-air splices behind the panelling and above the ceilings would not be hindered by that armor, and thus he eliminated his EGC throughout the system. Further, he managed to cross the neutral and hot enough times that there was no way to make heads or tails of it. I demo'd all of it.

I've also run into several installations that still had the knob and tube wiring in place. As time goes along, it gets more and more difficult to distinguish the white from the black, especially in a dark attic or wall cavity. In many of these situations, added portions of the electrical system have a polarity reversal problem.

 

[jmsokol]

This reversed polarity problem seems to appear in some of those places where DIYers have tried their hand at electrical work. Churches could easily be one of those places, since a member may offer to fix something that he or she is not really qualified to repair.

Yes, and the real problem is that a 3-light tester will light up properly (two amber and no red lights) telling the user that an RPBG outlet is wired correctly, when in fact it will electrify anything plugged into it. Now, if you plug in two different pieces of gear into two outlets, one wired correctly and the other an RPBG, interconnecting the gear with a signal line such as an XLR or USB cable will result in full short circuit current flowing in the shield. This current will melt mic lines and blow up mixing boards and whatever else gets plugged in. See graphic for the fault current flow. If a musician touches these two pieces of gear at the same time, that same 120 volts will flow through their heart with severe shock and electrocution very possible.

I've been a musician all my life and can't count the number of times I've plugged really expensive sound gear into unknown and shady looking power outlets. If you're lucky, you only get ground loop hum, but if you're unlucky the gear can blow up in your hands or the cables melt down and catch on fire. We ran a survey on ProSoundWeb last year that showed 70% of all musicians report having been shocked on stage by a mic or instrument.

Now that sound systems have become so large and interconnected, especially in churches, it's vitally important that all power outlets are tested for proper ground and polarity. An inexpensive non-contact tester like a Fluke VoltAlert can identify these "hot ground" outlets before they burn up gear or kill a person on stage. They'll beep on a microphone, guitar or mixer with AC voltages as low as 40 volts, and are safe to operate by unskilled volunteers. I've been training my seminar attendees not to rely on 3-light testers as the final test.

 

[ActionDave]

I agree this is a problem, but using a non-contact voltage detector is not fail-safe; in my opinion it can be used as a diagnostic tool only.

 

[masterinbama]

Fixed this problem just the other day at a residence. The woman's refrigerator was shocking her when she touched it and the stove. She had just bought the fridge and was positive it was in the wiring, which it was.


He husband came home about the time I was finishing and settling up the bill.


His first words were I'm glad it was not the cord on the fridge again, the appliance guy charged me $175 for a new cord and a service call on the old one.


I asked if he knew what the guy had actually done and he produced the 10 year old bill that clearly stated the appliance guy had removed the three wire cord and replaced it with a two wire one.

 

[iMuse97]

the appliance guy charged me $175 for a new cord and a service call on the old one. I asked if he knew what the guy had actually done and he produced the 10 year old bill that clearly stated the appliance guy had removed the three wire cord and replaced it with a two wire one.

Yep!

 

[don_resqcapt19]

...We ran a survey on ProSoundWeb last year that showed 70% of all musicians report having been shocked on stage by a mic or instrument.
...

and how often was that caused by faulty equipment and a grounding conductor that was removed to eliminate hum?

 

[jmsokol]

and how often was that caused by faulty equipment and a grounding conductor that was removed to eliminate hum?

I would agree that many stage shocks are caused by broken off ground pins or $1 ground lifts from Home Depot. But interestingly, those hums are generally caused by ground loop currents due to double-bonded Neutral-Grounds in subpanels and who knows what else. Once Neutrals and Grounds are tied together on branch circuits, any voltage drop in the neutral will be reflected in the grounds. Now you have a voltage difference between two pieces of sound gear connected with an XLR cable. That shield in the XLR cable will try to equalize the 1 to 3 volts ground difference, which turns into 1 to 3 amps of ground loop current, which I've measured it in my lab. That's where the hum comes from. Musicians then cut off the ground pins on their power cords in an attempt to stop the hum, which of course creates yet another shock hazard.

That being said, I've been shocked on stage in dozens of clubs in my youth, and finally bought a Woodhead Ground Loop Impedance Tester to start checking outlets. I found all sorts of mis-wired outlets everywhere, and rewired a lot of stages to protect my musicians. Some stage outlets had open grounds, some had hot grounds, some had grounds connected together that were never bonded to the service panel, etc....

It's not simply the musician's fault for cutting off their ground pins. They're just reacting to improperly wired outlets.

 

[jmsokol]

Fixed this problem just the other day at a residence. The woman's refrigerator was shocking her when she touched it and the stove. She had just bought the fridge and was positive it was in the wiring, which it was.

I was teaching a NoShockZone class at the BSU T-Com center in Muncie last year, and one of my students said her family had a refrigerator in the basement with "a messed up ground" (her words). They would get shocked when touching the door handle, so they jumped in the air when opening the door. Hey, I'm not kidding!!! When I told them they were going to kill a visiting repair man or neighbor, she seemed unconcerned. Since she grew up with a refrigerator that shocked her, it seemed normal to the family.

We need to train consumers that it's NEVER OK to feel a shock from an appliance.

 

[renosteinke]

Beware of unintended consequences!

OK, the plug-in tester can be fooled .... that's no surprise to this forum. It's great for noticing when ONE thing is wrong, but add multiple faults and all bets are off.

What the OP has done is educate the irresponsible in another way to fool the testers.

 

[jmsokol]

Beware of unintended consequences!
What the OP has done is educate the irresponsible in another way to fool the testers.

I don't follow your logic. Please elaborate....

 

[jmsokol]

I agree this is a problem, but using a non-contact voltage detector is not fail-safe; in my opinion it can be used as a diagnostic tool only.

True, but it will find all sorts of electrified appliances and guitar amps. I built a test rig that will let me bias anything up to 120 volts and have found that a standard 90 to 1,000 volt non-contact AC tester (such as a Fluke 1AC-A II) will reliably beep on an energized surface with as little as 40 volts AC on it. The larger the surface, the further the trigger distance. See http://www.youtube.com/watch?v=Y8h64X33aKg&feature=plcp for a video of me testing a 40-ft RV that I've forced to have a hot-skin condition with various voltages. (Don't everyone get excited, I did this in a closed RV service shop, so nobody was going to get shocked by walking up behind the RV)

It's also useful on music and performance stages by just touching all microphones and guitar amps with a VoltAlert or VoltProbe non-contact tester. If there's at least 40 volts AC on the mic or guitar, it will beep. There should NEVER be more than 1 or 2 volts AC on any stage gear, and that's caused by ground loop currents. Maybe it's not a perfect test, but one of the guru's on the ProSoundWeb forum advocated grabbing a guitar with one hand and licking the microphone to prove to the musicians that the stage was wired safely. (I'm not making this up). A non-contact tester is a very quick and easy way to check for dangerous stage voltages, which is WAY better than licking the mic.

 

[don_resqcapt19]

I have only seen one case of a bootleg "ground" connected to an ungrounded conductor since I started in 73. Is it really that common? It would seem to me that anyone using equipment connected via a 3 wire cord would quickly find out that something is not right.

 

[K8MHZ]

I have only seen one case of a bootleg "ground" connected to an ungrounded conductor since I started in 73. Is it really that common? It would seem to me that anyone using equipment connected via a 3 wire cord would quickly find out that something is not right.

Do you do many re-mods?

That is where I find them. And, pray tell, how would a device with a 3 wire cord be able to distinguish between a proper and a bootleg ground?

 

[jmsokol]

Do you do many re-mods?

That is where I find them. And, pray tell, how would a device with a 3 wire cord be able to distinguish between a proper and a bootleg ground?

Yes, re-modes are where I find them. I'm a musician and sound engineer, so I get into a lot of churches and bars where the wiring is very old and has been "upgraded" many time to accomodate newer sound and lighting systems that require a lot of power. Sometimes these upgrades are nothing more than an extension cord poked through a hole in the wall to reach another room. And sometimes they look safe, so my guitar player may be getting a big shock when I KNOW his amp is properly grounded because I did the maintenance myself. My 18 year old boy just found that his airconditioner outlet in his bedroom has been a Reverse Polarity Bootleg Ground for at least 30 years, and I've lived in the house 25 years. It tests as OK with a 3-light tester, but beeps using a VoltAlert. The entire chassis of the air-conditioner beeps like crazy when you get anywhere near it with a non-contact tester. Of course, on hardwood floor there's littel chance of contacting anything grounded, but that doesn't make it safe. If I had a guitar amp plugged into the other properly grounded outlet in the room and reached over the adjust the air-co with my free hand, that would be a big shock, I'm sure.

I believe the reason that many of you have never seen an RPBG outlet is that there's no easy way to test for them. Gear with a grounded plug seems to operate just fine when plugged into one, until you touch the chassis while touching something else grounded. Then you KNOW something is wrong. Here's a pic of 3-light testers in a Properly Grounded Outlet, a Correct Polarity Bootleg Grounded Outlet (CPBG) and a Reverse Polarity Booleg Grounded Outlet (RPBG). The lights all say the outlets are correctly wired, when we know they're not.

It's just a shame that the big box stores (Home Depot, Lowe's, etc...) sell every type of outlet and panel to anybody who has the money, and will also sell them a 3-light tester for $5 which they assume will tell them if their re-mod is safe. And it may not be.... Adding a non-contact tester into the situation will at least find more dangerously wired outlets than before (but certainly not all of them).

 

[K8MHZ]

Yes, re-modes are where I find them. I'm a musician and sound engineer, so I get into a lot of churches and bars where the wiring is very old and has been "upgraded" many time to accomodate newer sound and lighting systems that require a lot of power. Sometimes these upgrades are nothing more than an extension cord poked through a hole in the wall to reach another room. And sometimes they look safe, so my guitar player may be getting a big shock when I KNOW his amp is properly grounded because I did the maintenance myself. My 18 year old boy just found that his airconditioner outlet in his bedroom has been a Reverse Polarity Bootleg Ground for at least 30 years, and I've lived in the house 25 years. It tests as OK with a 3-light tester, but beeps using a VoltAlert. The entire chassis of the air-conditioner beeps like crazy when you get anywhere near it with a non-contact tester. Of course, on hardwood floor there's littel chance of contacting anything grounded, but that doesn't make it safe. If I had a guitar amp plugged into the other properly grounded outlet in the room and reached over the adjust the air-co with my free hand, that would be a big shock, I'm sure.

I believe the reason that many of you have never seen an RPBG outlet is that there's no easy way to test for them. Gear with a grounded plug seems to operate just fine when plugged into one, until you touch the chassis while touching something else grounded. Then you KNOW something is wrong. Here's a pic of 3-light testers in a Properly Grounded Outlet, a Correct Polarity Bootleg Grounded Outlet (CPBG) and a Reverse Polarity Booleg Grounded Outlet (RPBG). The lights all say the outlets are correctly wired, when we know they're not.

It's just a shame that the big box stores (Home Depot, Lowe's, etc...) sell every type of outlet and panel to anybody who has the money, and will also sell them a 3-light tester for $5 which they assume will tell them if their re-mod is safe. And it may not be.... Adding a non-contact tester into the situation will at least find more dangerously wired outlets than before (but certainly not all of them).

Great pic!

May I print it out and use it in my upcoming test equipment class??

 

[jmsokol]

Great pic!

May I print it out and use it in my upcoming test equipment class??

Yes you may. I can send it to you in hi-rez if you like.... give me an email address.

Mike

 

[K8MHZ]

I believe the reason that many of you have never seen an RPBG outlet is that there's no easy way to test for them.

When I get into old places, many times I have to run a conductor directly to a known neutral to reference from. That usually entails a connection in the panel. Then, I connect a pigtail to it so I can plug a long extension cord into it and drag that around for my reference.

A solenoid tester is a must.

I have been in rentals that had every imaginable wiring error and reversal possible. It's amazing how stuff plugged into it stays working.

Finding the proper polarity bootleg grounds is a bit harder, as all the receptacle will be referenced correctly. It takes experience, but after a while suspicion is aroused any time a new 3 wire receptacle tests OK in an old, old house with mostly 2 wire conductors.

 

[K8MHZ]

Yes you may. I can send it to you in hi-rez if you like.... give me an email address.

Mike

Thanks, it might be OK as it is.

I'll let you know.

Did you build the display?

 

[K8MHZ]

Oh, and another thing....

DON'T push the button.

Imagine this scenario:

You are checking receptacles to see if they are GFCI protected. The first stop is the bathroom. You plug your tester in and hit the GFCI test button. As one would expect on a GFCI protected receptacle, the power goes out.

So your plan is to reset the GFCI and continue testing.

BUT....

There is no GFCI anywhere in the residence. And I mean none.

I have found them on posts in gardens overgrown with vegetation. In garages hidden behind permanent shelving. On outside walls underneath decks.

I think you get the picture.

Only test GFCI receptacles with the built in button. THEN test other receptacles for power.