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Author Topic: brain storm an optimal human safety system for back line  (Read 104207 times)

Stephen Swaffer

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Re: brain storm an optimal human safety system for back line
« Reply #360 on: October 08, 2015, 10:38:25 pm »

From my experience most homes that have 1-15 receptacles still have 2 wire either  K & T or  Romex.  Bootleg grounds are common, as is reverse polarity. As Mike has repeatedly warned this can be a dangerous combination.

The other thing that might be creating odd readings on JR,s beta device could be the lack of a grounding electrode and or bonding.  This could cause the neutral to appear to be at any potential with respect to ground and other metal objects/systems.  Not sure how a body's capacitance would play out as far as grounding if the only true reference is hundreds of feet away?
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #361 on: October 08, 2015, 11:26:13 pm »

From my experience most homes that have 1-15 receptacles still have 2 wire either  K & T or  Romex.  Bootleg grounds are common, as is reverse polarity. As Mike has repeatedly warned this can be a dangerous combination.

The other thing that might be creating odd readings on JR,s beta device could be the lack of a grounding electrode and or bonding.  This could cause the neutral to appear to be at any potential with respect to ground and other metal objects/systems.  Not sure how a body's capacitance would play out as far as grounding if the only true reference is hundreds of feet away?
The secret sauce for my tester is to use the human body as a local 0V reference. Of course nothing is exactly 0V but close enough.(+/-10V?) I buffer that human voltage reference with a high input impedance MOSFET. 

AFAIK the design is getting mature and works as expected everywhere I have tested it so far (perhaps a half dozen different buildings).

The results Mark reported made me concerned the prototype was faulty... (hand soldered by an old man), but when I got it back it worked exactly like it did when it left.

I'll get him a second generation prototype that has some minor improvements, less spurious leakages..more robust ground present indication etc. If he still gets spurious results I will ask him to do more testing of his power.

I fell like this tester design is getting pretty close to ready for prime time... The final resistor values I need to finish tweaking this are ordered and shipped so just a matter of days.  ;D

JR
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Rob Spence

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Re: brain storm an optimal human safety system for back line
« Reply #362 on: October 08, 2015, 11:28:53 pm »

Neat!

I want one.


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Mark Cadwallader

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Re: brain storm an optimal human safety system for back line
« Reply #363 on: October 09, 2015, 01:11:29 am »

Update:  Follow-up testing (using a Fluke 323 clamp meter w/probes and Fluke 1AC-C NCVT) show that the NEMA 5-15 receptacles do NOT appear to have a RPBG condition. Tested as per Mike's link (above).

I'll repeat the tests this weekend to check my work.  I'll also check using two other NCVTs I have, and a different DMM, and report back.

Edit:  Pending additional testing, the above results should probably be qualified as "initial" or "preliminary". I think that I know how to conduct the testing, but I don't want to assume too much, or rely on a single result with only one set of test instruments.
« Last Edit: October 09, 2015, 01:25:34 am by Mark Cadwallader »
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #364 on: October 09, 2015, 09:48:53 am »

I also like neon lamp probes, or using a VOM with the body serving as the ground reference but BE CAREFUL to make sure VOM is in AC Volts scale, since using ohms or current scale could deliver a dangerous shock hazard.

My NCVT is useless for determining outlet wiring (too sensitive). It goes off when I get anywhere near my bench with it.

JR

PS: Using my trusty old ratshack VOM, and JR_as_ground I measure 50 VAC on line, 11 VAC on neutral, and 1 VAC on an open floating ground. Not very precise but good enough to differentiate line from neutral. Just be careful when probing hot power circuits.
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Jonathan Johnson

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Re: brain storm an optimal human safety system for back line
« Reply #365 on: October 09, 2015, 10:42:17 am »

I also like neon lamp probes, or using a VOM with the body serving as the ground reference but BE CAREFUL to make sure VOM is in AC Volts scale, since using ohms or current scale could deliver a dangerous shock hazard.

My NCVT is useless for determining outlet wiring (too sensitive). It goes off when I get anywhere near my bench with it.

JR

PS: Using my trusty old ratshack VOM, and JR_as_ground I measure 50 VAC on line, 11 VAC on neutral, and 1 VAC on an open floating ground. Not very precise but good enough to differentiate line from neutral. Just be careful when probing hot power circuits.

Sounds like a test for Darwin Award nominees.
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frank kayser

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Re: brain storm an optimal human safety system for back line
« Reply #366 on: October 09, 2015, 10:58:13 am »

Neat!

I want one.


Sent from my iPad using Tapatalk HD


I'm with you!  Been a big cheerleader of this project from the start - and am thrilled that JR is in discussions with a manufacturer.
One way or the other, I REALLY want one, too!
frnk
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #367 on: October 09, 2015, 12:17:13 pm »

Got my new resistors in today, so this weekend I should be able to finalize this.

Slow and steady but moving forward...

JR
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Don't tune your drums half-ass. Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

Mike Sokol

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Re: brain storm an optimal human safety system for back line
« Reply #368 on: October 09, 2015, 12:44:08 pm »

Edit:  Pending additional testing, the above results should probably be qualified as "initial" or "preliminary". I think that I know how to conduct the testing, but I don't want to assume too much, or rely on a single result with only one set of test instruments.

The  Gold Standard test is to run a long wire to the frame-ground of the service panel, and use a low-impedance meter between it and the Line, Neutral, and EGC-Ground contacts in each receptacle. I also do some loading between the various lines with a 100-watt bulb to make sure there's no open line that's being "phantom" energized via capacitive coupling.

BTW: If you use enough of a load (I have a little 600/1,200 watt space heater for this) you can also figure out if there's a swapped neutral and ground in an outlet. While a swapped N-G won't show up with any standard (unloaded) test, it does create all sorts of ground loop hum in sound systems. I've found swapped N-G lines in several church installs during the last two years of looking, but I was only looking because of a reported ground loop hum. It may be fairly common in new installs done by non-electricians. Another fail that a 3-light tester won't find, and JR's gadget won't find it either.
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #369 on: October 09, 2015, 01:39:53 pm »

Yup I only confirm that a ground connection is present and then test for hazardous voltages. My tester even says RPBG ground is present,,, but it also warns that the safety ground happens to be hot.  >:( (danger Will Robinson)

I believe I could come up with a microprocessor based outlet tester that could parse out ground quality too, but first things first. A simple outlet tester that accurately reports hazardous voltages seems a useful start and the far more important need.

JR
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Don't tune your drums half-ass. Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

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Re: brain storm an optimal human safety system for back line
« Reply #369 on: October 09, 2015, 01:39:53 pm »


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