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Author Topic: 3-light tester RPBG upgrade  (Read 31298 times)

Mike Sokol

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Re: 3-light tester RPBG upgrade
« Reply #10 on: February 22, 2015, 09:25:53 AM »

I started out with an electronics interest and "added" the electricians license because it was/is a more viable career in a rural area-but it is hard to sell the "added value" of  understanding electricity (of course, I understand more than they do, how much I still need to learn-which is why I am here!)

I originally went to school for Mechanical Engineering, added Electrical Engineering, then got my Master Electrician license back in 1978. When I built nuclear missile guidance systems back in the 80's I learned all about calibration and designing test procedures. So I'm super curious about how this stuff actually works and love test gear. I guess that's why I like this forum, it really gets my neurons pumping... ;D

John Roberts {JR}

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Re: 3-light tester RPBG upgrade
« Reply #11 on: February 22, 2015, 10:17:08 AM »

One thing to be aware of is that the SureTest and Amprobe analyzers won't indicate a bootleg ground on a branch circuit located more than 15 feet from the G-N jumped outlet. That's because 15 ft of wire has sufficient resistance to get over the "bootleg" G-N threshold.
Understood.... If I were to design a bootleg and/or reversed neutral-ground tester (and I am not) I would design a two part tester. First a transmitter plugs into a distant outlet. The transmitter switches or toggles a load on/off between line and neutral, while switching another load between line and ground. These loads could be switched at different identifiable rates to differentiate which is which.

This test ASSumes that this first outlet is wired correctly. The second part a receiver, plugs into outlets between it and the panel to identify if the ground has the ground signal, neutral has the neutral signal, and both have different signals. If none of the downstream outlets have different signals perhaps the first outlet is bootleg. Of course once you identify that things are not correct you need to start taking wiring apart to identify what is what.

Opening up ground at the panel should quickly identify a neutral/ground swap when that outlet stops working.   
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The thing that I've found when troubleshooting hums with a qualified master electrician at my side is that very few of them really understand how ground bonding and series resistance works. I'm not saying that they don't know their job, because they are mostly qualified for wiring installation and probably know code inside and out. But troubleshooting botched up systems requires another level of understanding how electricity really works. I'm not sure that most home inspectors have any real knowledge of electricity, while many (hopefully) will understand obvious code requirements.
Rules and wiring standards are used to deliver safety without requiring understanding about how the electrons and holes behave.

I still think an audio output for the receiver end of my two part outlet tester might be more sensitive than a go/no-go tester. Perhaps in addition to.

JR
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Mike Sokol

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Re: 3-light tester RPBG upgrade
« Reply #12 on: February 22, 2015, 12:27:04 PM »

I still think an audio output for the receiver end of my two part outlet tester might be more sensitive than a go/no-go tester. Perhaps in addition to.

JR, as I'm sure you're aware, you've set a pretty high bar with wanting a sender receiver that might be simple enough to act as a go/no-go tester. Of course this would be pretty straightforward with a properly wired system that might have a single failure. But USA wiring is full of combination fails, where something goes wrong and is then patched up incorrectly multiple times, sometimes over decades. Perhaps your instrumentation needs an external SOP test document with a flow chart. That is, a specific series of tests with branches you take depending upon results of each test. So if you start at the top and follow the flow chart, then you'll likely come up with an answer. I then like to do a completely different test and compare results to be sure I'm not fooling yourself. I do think your bootleg tester could be a very important part of this test. I'm just not sure we can replace logical training of the person doing the test. For instance, there's an awful lot of "gut" when I'm doing audio troubleshooting. That is, I keep playing with the circuit in question until something seems to jump out at me. Of course, hindsight is 20-20 but if you see enough failure mechanisms enough times, then that should be the first thing you test for. I think that's the sort of intel that should be included in any Test SOP (Standard Operating Procedure).     
« Last Edit: February 22, 2015, 12:29:25 PM by Mike Sokol »
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John Roberts {JR}

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Re: 3-light tester RPBG upgrade
« Reply #13 on: February 22, 2015, 01:32:46 PM »

You can design a lot of decision making capability (thousands of lines of code) into a cheap micro, but to do this you must anticipate all those decisions and quantify limits or bounds for good/bad. This is why I like the concept of an audio sniffer so you can literally listen to the quality of the grounds.

Back a hundred years ago when I was designing audio, I would not only measure how much distortion a circuit made, but listen to that distortion product output to determine how nasty or benign it sounded.

No tool can replace experience, but a good tool can open a window into troubleshooting problems. Back in the day old school electricians could get 99% of it done with a simple neon lamp probe, maybe a lamp load. Modern tools should provide more info and as you have recognized some simple tool are too simple to be safe.

JR
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Mike Sokol

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Re: 3-light tester RPBG upgrade
« Reply #14 on: February 22, 2015, 01:52:44 PM »

No tool can replace experience, but a good tool can open a window into troubleshooting problems. Back in the day old school electricians could get 99% of it done with a simple neon lamp probe, maybe a lamp load. Modern tools should provide more info and as you have recognized some simple tool are too simple to be safe.

I've seen a few demonstrations of AED's (Automatic External Defibrillators) in action, and I've got to admit that they come pretty close to being fool proof since they "talk" you through the procedure. They're so good that emergency rescue teams generally hook them up first thing to feed the patient's vital signs to the hospital. Now, those are expensive devices and have lots of development time since lives are at stake and government mandates in place. But maybe something like that could talk an electrician or inspector through an outlet test procedure. Heck, you can get a Valentine's card that will play back an on-board audio file through a speaker for $5, and a GPS with a voice synthesizer for $100. I know those are high volume products, but maybe there's a little filter down technology that could be incorporated into your tester. For instance, I have trouble getting clients to tell me if they're hearing hum or buzz or power supply hash. Those are all caused by different things, yet are often lumped together in the diagnosis. 

John Roberts {JR}

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Re: 3-light tester RPBG upgrade
« Reply #15 on: February 22, 2015, 02:07:49 PM »

If there is an audio output to listen to the ground, and a micro, it is relatively simple to add speech output. There is probably enough onboard memory inside a modern micro to hold a bunch of words.

 Not sure I would embrace this completely.....   "Is the unit plugged in (dumb ass)?" .

JR
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Re: 3-light tester RPBG upgrade
« Reply #16 on: February 22, 2015, 02:20:42 PM »

Tim McCulloch

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Re: 3-light tester RPBG upgrade
« Reply #17 on: February 22, 2015, 03:27:42 PM »

If there is an audio output to listen to the ground, and a micro, it is relatively simple to add speech output. There is probably enough onboard memory inside a modern micro to hold a bunch of words.

 Not sure I would embrace this completely.....   "Is the unit plugged in (dumb ass)?" .

JR

"I'm sorry Dave, I'm afraid I can't test for that.  You're making dumb ass mistakes."  HAL 8999 (pre Miss Manners personality infusion)
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Stephen Swaffer

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Re: 3-light tester RPBG upgrade
« Reply #18 on: February 22, 2015, 04:13:15 PM »

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.
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Mike Sokol

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Re: 3-light tester RPBG upgrade
« Reply #19 on: February 22, 2015, 04:35:32 PM »

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 tester which has prevented a demand for a new improved version.

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.

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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.

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. 

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Re: 3-light tester RPBG upgrade
« Reply #19 on: February 22, 2015, 04:35:32 PM »


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