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[John Roberts {JR}]

I am scanning through an ARRL Handbook to refresh my memory.  I came across the following statement:, "A commercially available plug-in tester is the best way to test regular three-wire receptacles."  There is no warning about RPBG or caution that this is not a comprehensive bullet proof test.  Given the target audience-aspiring HAM's-and the fact that the Handbook is several hundred pages of fairly technical reading that would seem to be a prime location for a little more in depth explanation, I find this a little surprising.  Perhaps it is indicative of a widespread lack of appreciation for the shortcomings of the 3 light teater which has prevented a demand for a new improved version.

IIRC, a neon lamp creates a roughly 90 volt constant voltage drop across it, much like an LED creates a 1.2 v drop.  This should allow you to size a ballast resistor to limit current through a body to a safe value based on 30-40 volts rather than 120-130 volts.  A smaller resistor should allow a little more current which should allow a little brighter light.

I would size the current limit resistor to prevent injury even if the neon lamp was a dead short (I do not know how neon lamps fail) .. that said you could come down even lower than 20k and still be less than 7 mA with a shorted bulb which in my judgement is sub-lethal. While it could make somebody jump.

I would expect Hams to be pretty alert about grounds. Radio antennas are often earth grounded and if a power ground was dicey they would figure it out pretty quick.
 
JR

[John Roberts {JR}]

This issue is that, believe it or not I'm the guy who defined what an RPBG is and named it - Reverse Polarity Bootleg Ground. And that was just a few years ago while I was laying out the schematic for a 3-light tester using 100-watt bulbs to load the wiring a bit. After coming up with the explanation and demonstration that a 3-light outlet tester wouldn't discover an RPBG, I showed it to my contacts at Fluke, Amprobe, Triplett and Progressive Industries, plus a bunch more. None of them believed that a cube tester wouldn't find an RPBG or why it was dangerous until they built the demonstration for themselves and tried it. I did send this info to the ARRL forum perhaps two years ago, and they seemed surprised that this condition wouldn't be found with a 3-light tester. The idea that these $5 testers will find all miswiring conditions seems to be part of our DNA. While the manufacturers of these testers will include a little legal note stating that they won't find all miswiring, I don't think they're aware of just how dangerous not finding an RPBG can be. It's about as deadly as you can get.

Yes, you're correct, and some of these neon bulbs will come on as low as 60 volts, I think. I started with a 100K resistor for this first test, and will probably drop it to 33K or less and test for brightness and fault current. Remember, we need to limit fault/shock current to less than a few mA even if the electrician is standing in a puddle or water, so we have to assume worse case conditions. But with a little tweaking this would be a pretty great upgrade to the 3-light testers. Again, they already have versions of this 4-light tester in the UK for 230 volts, so it seems crazy that they wouldn't have them in the USA. I'm going to contact my guys at Amprobe and Fluke this week and try to get the inside scoop and just why that is.

I appreciate your effort to spread awareness of this. Perhaps you should trademark RPBG(tm)...

I can't speculate on what people knew or when, but as I have posted before I recall Peavey being sued back while I was still working there, so 15 years ago, because a musician was killed while using Peavey gear when he got between a mis-wired outlet and a correctly wired outlet.

I can't say that I have ever experienced one in the wild, far more open grounds than even bootleg, let alone reverse bootleg.

There should be a special room in hell for anybody doing those.

JR

[Stephen Swaffer]

Remember, we need to limit fault/shock current to less than a few mA even if the electrician is standing in a puddle or water, so we have to assume worse case conditions.
 

Sorry, but even if you design/test this, it is very unlikely this electrician will touch any kind of a contact pad while standing in water-just really makes me uncomfortable.

Seriously,this does illustrate one of the most difficult aspects of automation and testing as JR alluded to-anticipating all possible failure/defective possibilities.  Testing for a RPBG seems ludicrous-who would actually do that?-it takes at least one intentional and one unintentional miswire to get there.

I agree about HAMs being savy about grounds-as long as the newbie lives long enough to learn.  Sometimes a less than reliable test is worse than no test at all.  It would be better to go to the effort to verify with a meter than to use a simple quick test that is not "bullet proof" before putting oneself bewteen two supposed grounds.  Same as musicians on stage.

[John Roberts {JR}]

  Testing for a RPBG seems ludicrous-who would actually do that?-it takes at least one intentional and one unintentional miswire to get there.

Yes but it does happen... if not RPBG perhaps a hot guitar ground from a rogue guitar amp is what killed that musician in Argentina a couple months ago when he grabbed a mic.

JR

[Mike Sokol]

Sorry, but even if you design/test this, it is very unlikely this electrician will touch any kind of a contact pad while standing in water-just really makes me uncomfortable.

What I really want is a Non Contact Voltage Tester grafted into a 3-light outlet tester. That would do basic 3-light hot-neutral tests at the same time it was checking for a hot ground condition. And because it's capacitively coupled, there's no chance of anyone getting shocked even if you're standing in water.

Hey, I just added a 0.047 stinger cap in series with my 100K ballast resistor for the NE2 bulb, and it still lights up with hot ground just fine. Would that make you feel safer?

Note that I spare no expense in mocking this up. A rubber band is a perfectly acceptable attachment device. 

[Mike Sokol]

Yes but it does happen... if not RPBG perhaps a hot guitar ground from a rogue guitar amp is what killed that musician in Argentina a couple months ago when he grabbed a mic.

JR

All my experiments show that a standard sensitivity (90 to 1,000 volt) Non Contact Voltage Tester will reliably find a guitar or mic with a hot-chassis condition of 40 volts AC or more. I still think that's the best quick test you should do on any stage before allowing the musicians to pick up their instruments. This hot chassis test literally takes only a minute to perform, and has the potential to save lives.

[John Roberts {JR}]

What I really want is a Non Contact Voltage Tester grafted into a 3-light outlet tester. That would do basic 3-light hot-neutral tests at the same time it was checking for a hot ground condition. And because it's capacitively coupled, there's no chance of anyone getting shocked even if you're standing in water.

Hey, I just added a 0.047 stinger cap in series with my 100K ballast resistor for the NE2 bulb, and it still lights up with hot ground just fine. Would that make you feel safer?

Note that I spare no expense in mocking this up. A rubber band is a perfectly acceptable attachment device. 

You could use the 0.047uF instead of the 100k... I increased to 0.15uF for my GFCI stinger cap so the current would be enough to reliably trip the GFCI's  5+/-1mA , while still below the current that humans get stuck to. Of course you could feel it.. The .047uF worst case is only a couple mA.

JR

[Mike Sokol]

You could use the 0.047uF instead of the 100k... I increased to 0.15uF for my GFCI stinger cap so the current would be enough to reliably trip the GFCI's  5+/-1mA , while still below the current that humans get stuck to. Of course you could feel it.. The .047uF worst case is only a couple mA.

Steve S.

Would this .047 stinger cap in the line make you feel safe? It would limit the fault current to a few mA even if the neon bulb shorted out. Of course, I don't recommend that anyone stand in water while testing an outlet, but we have to prepare for stupidity as best we can.   

[Stephen Swaffer]

I would be ok with the cap and neon light in series-there is reasonable redundancy there as far as current limiting IMO.

I spent too much time fixing things that should not have malfunctioned the way they did to really feel "safe" when standing in water, but you have to draw a line somewhere.  And, reality is, someone will be asked to test receptacles during the spring when you really can't work on a dry surface outdoors for weeks.

[Stephen Swaffer]

One ergonomic consideration with regards to safety of a production tester would be to design and locate the touch pad in a location (maybe on the end?) that would make it unlikely/impossible for a shock to cause you to not be able to release the tester. That way in the highly unlikely event of a double failure, your natural reaction should protect you.

[ProSoundWeb Community]