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[Mike Sokol]

I don't know anything about construction practices in NYC, but I would guess you're most likely to find RPBG in anything built before the safety ground conductor was required, which I think was about 1974 (based on limited research).

Probably more likely in an older church (volunteer "electricians") or a converted home (DIY) than in a building that's always been a commercial structure. Of course, electricians can make mistakes just like anybody.

This Wikipedia article on cheater plugs includes a short discussion about audio ground loops.

You're absolutely correct. Modern wiring should be nearly impossible to hook up incorrectly (note I say "nearly") since you just hook the colors together. Mostly I see swapped H-N connections in modern buildings because some electricians can't tell the diff between a brass screw and a silver screw. Swapped H-N connections are what most of us think of as "reversed polarity". But it's not really dangerous to consumers since modern appliances and gear really don't care if the Hot and Neutral are reversed. That wasn't true in the old days because AC/DC radios and a few early guitar amps (I have one) didn't have power transformers, just a bunch of tubes who's filament voltages added up to 120 volts. That meant the "neutral" wire on the ungrounded power cord was directly connected to the chassis via a "polarized" plug. Hook it up backwards, and the chassis was energized by the now "hot" neutral wire.

However, any building from the early 70's on back never had grounded wiring to begin with. And inspectors in the 80's and 90's required that outlets be updated to NEMA 5-15 outlets with a ground connection. Many millions of bootleg grounds were likely done to get buildings to pass inspection. Of course, if the Hot and Neutral lines are swapped somewhere in the walls, or knob and tube wiring was originally used (everything is black), then at least some of these bootleg outlets were wired with reverse polarity. Just how many RPBG's were created nobody knows, but RPBG outlets are so dangerous because they test as safe using any conventional testing methods such as a 3-light tester or even using $300 Ground Loop Impedance Testers like an INSP-3 or SureTest. You either have to run a test wire to a known earth source such as a copper water pipe or use a non-contact tester which finds earth reference by capacitively coupling through your hand and body. You become the earth reference ground plane.

What's really disturbing is that I contacted the engineering departments at Amprobe, Extech, and SureTest (and a few others) to ask them if they thought their fancy $300 testers could find an RPBG outlet and all them said their products would easily find it. I then showed them my initial demo video and sent them a schematic asking them to duplicate the demonstration. Every one of them acknowledged that they were wrong and that their testers will report an RPBG outlet as having "correct" polarity. Pretty scary, isn't it? 

That's why I think we have to test outlets in all older building (pre 1970's) ourselves. Churches are notorious for not having enough extra money for proper wiring upgrades, and don't get me started on old bars. I'm guessing Tootsies in Nashville could have some RPBG outlets, so perhaps I'll have to spend some time there testing beer and outlets next time I'm in Music City. 

But I am making headway with the information and now writing a feature article for EC&M magazine (Electrical Construction & Maintenance) which is a printed monthly publication going to 120,000 electricians, inspectors and engineers. That will be a great start. I'll let you know when it's available online.

A final note on the Wikipedia link you reference, there's an error when they describe a correct polarity bootleg outlet as being dangerous. It really isn't dangerous unless the neutral wire becomes loose or corroded. Then the appliance body can be energized via it's own load leakage. You'll likely know something is wrong because an open neutral will shut down the appliance. I'm more worried about REVERSE Polarity Bootleg Grounds since there's a 100% certainty that they'll energize the chassis of anything with a grounded power plug to 120 volts AC. And any "grounded" appliance plugged into an RPBG outlet will operate normally, albeit with its chassis energized to 120 volts. 

[Mike Sokol]

Thanks Mike. Might be useful insurance in some of the substandard buildings we play in. By the way, how often would one expect to encounter a RPBG in real life playing clubs in NYC or NJ? I have never heard of anyone around here getting electrocuted or seriously zapped just playing a gig, although the OP's experience is sobering.

Nobody knows just how many outlets are miswired because up to this point there has been no simple way to test outlets for all reversal conditions. And because RPBG outlets operate completely normal (except for the electrocution and burned up gear possibilities) they can exist for years and never produce any problems. My 18 year old boy just found an RPBG outlet in his bedroom that's been there at least 30 years, way before I bought my house. Since it's in his bedroom on a hardwood floor with only the air-conditioner plugged into it, this was unknown until last week when he tried a VoltAlert on it for grins. Unless he cross connects his computer on a correct outlet to a grounded printer on that RPBG outlet, it could go on for another 30 years without causing problems.

But since this is a 30 second test (at most) that takes around $20 worth of gear, I think it's a good thing to check for in any unknown old building. 

[Mike Sokol]

Per your PM'ed requests (plus a few of my readers in the EE community) I've replaced the steel screw in the center of the RPBG outlet with a nylon one. That's right, it's electrified to 120 volts AC and a serious shock hazard. You're all correct that I shouldn't take unnecessary chances with electricity. That' s just not setting a good example for the readership. And certainly I'm way too distracted when trying to capture the demonstration on video camera while talking about it. I normally focus completely on the task at hand while working on live circuitry since it only takes a second of inattention to end up dead.

Thanks for the heads up... 

[George Dougherty]

I found it at Sears for less than $14  http://www.sears.com/shc/s/p_10153_12605_SP101A11576S6083631101P?sid=IDx20070921x00003a&ci_src=14110944&ci_sku=SPM6045437007

Plus about $7 shipping. 

$15, free shipping.
http://www.ktool.net/servlet/the-6985/VP-dsh-600SB/Detail

Added one of these guys and I'm at $19
http://www.ktool.net/servlet/the-3994/AMPROBE-ST101A-Socket-Tester/Detail

Money very well spent.  Thanks for converting a young fool into a careful tester.  My Multi-meter's going into the kit as well.

[Mike Sokol]

Plus about $7 shipping. 

$15, free shipping.
http://www.ktool.net/servlet/the-6985/VP-dsh-600SB/Detail

Added one of these guys and I'm at $19
http://www.ktool.net/servlet/the-3994/AMPROBE-ST101A-Socket-Tester/Detail

Money very well spent.  Thanks for converting a young fool into a careful tester.  My Multi-meter's going into the kit as well.

Good find on the price(s). Yup, with $20 worth of testers you can slip in your pocket, you should be able to diagnose nearly every outlet mis-wiring condition I can think of. You can even discover when a 120-volt outlet has been jury-rigged for 240 volts. If your non-contact tester beeps on both the hot and neutral slots, but not on the ground slot, then there are two hot wires connected into it. That's how 240 wiring is done on the correct style outlet, but must never be done on a NEMA 5-15 or  5 -20 (Edison) outlets.

That's why I think the best test sequence is to use a non-contact tester on the outlets first, followed by the 3-light tester. Just sweep your non-contact tester from the Hot (small slot) to Neutral (tall slot) to Ground (u-shaped slot), then back to Hot. You always start with the "energized" slot first to verify that your batteries aren't dead in your non-contact tester. If you get the correct pattern of Beep-Silence-Silence-Beep, then plug in your 3-light tester and confirm you get 2 amber lights and no red light. If the outlet passes both tests, then you're good to go. Now this test wont find abnormally high (130+ volts) or low (100-) volts, but those are extremely rare circumstances on installed wiring. However, generator power is its own can of worms.

If you do a lot of festival work outside with generators, I would follow up your basic outlet test with a digital meter and check that H-N measures between 115 and 125 volts unloaded. Of course, if your amplifiers are pulling a lot of watts you might see their AC supply dropping below 110 volts on loud passages (I've seen 105 volts a few times on my own racks) which is not dangerous, but you really want your starting (unloaded) voltage to be as close to 120 volts as possible. At some point I plan to write a piece on testing generator power, including frequency and proper grounding. 

Lots to do...

[Jordan Wolf]

At some point I plan to write a piece on testing generator power, including frequency and proper grounding. 

That would be a welcome article for this industry to have, Mike.  I think the biggest problem most people have is not knowing why, in a particular situation, to do something one way and not another (i.e. how to wire the gennie when you plug straight in to it vs. using a spider box/distro that's distant from the gennie). 

I think it would be a good idea to start a new poll thread to get some ideas for specific topics that apply all-around (following the NEC, of course), but may not be necessarily be mandated in all areas of the country due to more-lax interpretations and utilizations of The Code, etc.

[Mike Sokol]

Just an update on Reverse Polarity Bootleg Ground (RPBG) information. My article in EC&M Magazine "Failures In Outlet Testing Exposed" was published in the July issue and is now available online. Here it is: http://ecmweb.com/contractor/failures-outlet-testing-exposed

Just in the last month I've answered dozens of inquiries from electricians and inspectors around the country about outlet testing, which should eventually translate into safer power for our sound systems. But don't take electrical power for granted. Be sure to test any unknown outlets BEFORE plugging in your expensive sound gear.

Mike Sokol
[email protected]
www.NoShockZone.org 

   

[Marjan Milosevic]

Must admit i didnt read all of the comments but one thing got my attention.
Swapping hot and neutral.
How can this make any problem?
I can only conclude that your system is far different fro the Euro standard where you can plug any way you like. Hot and neutral connectors are same. You can put the plug in both ways.

[John Roberts {JR}]

Must admit i didnt read all of the comments but one thing got my attention.
Swapping hot and neutral.
How can this make any problem?
I can only conclude that your system is far different fro the Euro standard where you can plug any way you like. Hot and neutral connectors are same. You can put the plug in both ways.

I bet you can find the answer earlier in this thread...

JR

[Steve M Smith]

Swapping hot and neutral.
How can this make any problem?
I can only conclude that your system is far different fro the Euro standard where you can plug any way you like. Hot and neutral connectors are same. You can put the plug in both ways.

It's not a problem for us in Europe where all outlets have a ground connection.  It also isn't a problem in the US when using three way outlets with a correctly wired ground connection.  In all of thse cases, live and neutral being swapped makes no difference.

There appear to be cases in the US where outlets have been changed from two pin to three pin grounded where rather than run a separate ground wire, it has been done on the cheap and the earth pin has been connected directly to the neutral pin at the outlet.

If the live and neutral are correct, the ground pin is connected to ground via the neutral wire.  However, if live and neutral were reversed at the outlet terminals, the ground pin would now be connected to live - not ideal or safe.


Steve.

[ProSoundWeb Community]