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Author Topic: brain storm an optimal human safety system for back line  (Read 97838 times)

John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #340 on: August 29, 2015, 12:21:16 pm »

Maybe a crazy thought-but could you put say a 50V MOV across the ground/neutral to prevent the voltage from going a full 120 volts if the ground was in fact open?  I haven't played with them much so not sure of all the implications.
That would pretty much be the same as a bootleg ground so dangerous if neutral fails open back to the panel. While it might put less voltage on the chassis in such an open neutral condition still undesirable. IMO

JR

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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #341 on: August 29, 2015, 01:24:40 pm »

I am making progress on getting a more reliable ground present indication without increasing current enough to trip the GFCI.. So far it works on my kitchen outlet that previously gave a false.  Still getting a false in the bathroom, that isn't logical so I may have to look more closely at that outlet.

Using my VOM with floating ground I coincidentally measure the exact same voltage on both the neutral and ground pin... Since i don't believe in coincidences when it comes to electricity I suspect very strongly that there is an accidental bootleg ground in that outlet. As i recall the GFCI outlet was a very tight fit in the junction box, so neutral touching the metal box could perform the bootleg.   :o  My other leaky outlet shows 4V between neutral and ground using the same floating measurements.

So I suspect I have nailed the "false" ground present indication,  ;D and have something else to fix about my home wiring.  :'(

JR

PS: I have decided to stop publishing design refinements until I find someone to license this too,,  If i keep giving away the milk, I'll never sell the cow.  This ground fix is a few more cheap components but nothing major.  8)
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Mike Sokol

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Re: brain storm an optimal human safety system for back line
« Reply #342 on: August 29, 2015, 03:54:03 pm »

Maybe a crazy thought-but could you put say a 50V MOV across the ground/neutral to prevent the voltage from going a full 120 volts if the ground was in fact open?  I haven't played with them much so not sure of all the implications.

The problem would become huge if you plugged into a receptacle with swapped hot and neutral wires. Now your 50-volt MOV would be connected between the hot and EGC. If the rectacleep had a proper ground it would short and trip the main circuit breaker. If it had an open ground, now the chassis of the gear would be tied to the incoming hot wire. In either case it would be very bad indeed.
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #343 on: August 30, 2015, 06:17:03 pm »

Kind of bizarre but I today dug into my bathroom outlet and found the accidental bootleg to neutral... I probably need to buy a new larger junction box. There was not enough clearance to wedge even a 1/16th inch thick piece of fiberglass PC stock into both sides. One fit but not two. I did put some tape over both the line and neutral screws, while they are recessed and should not have shorted to the junction box.

Now even my original outlet tester correctly registers that outlet ground as open circuit. So it looks like my testers correctly identified a ground path where they shouldn't have been one.  :o :o

JR

PS: I only have 8 fuses in my service panel, and this outlet was on the 7th fuse I tried.  8)
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Stephen Swaffer

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Re: brain storm an optimal human safety system for back line
« Reply #344 on: August 30, 2015, 10:18:37 pm »

Kind of bizarre but I today dug into my bathroom outlet and found the accidental bootleg to neutral... I probably need to buy a new larger junction box. There was not enough clearance to wedge even a 1/16th inch thick piece of fiberglass PC stock into both sides. One fit but not two. I did put some tape over both the line and neutral screws, while they are recessed and should not have shorted to the junction box.

Now even my original outlet tester correctly registers that outlet ground as open circuit. So it looks like my testers correctly identified a ground path where they shouldn't have been one.  :o :o

JR

PS: I only have 8 fuses in my service panel, and this outlet was on the 7th fuse I tried.  8)

Off topic, but I have always been OK with fuses-generally more reliable than breakers.  However, I have started running into fuse holders in older resi fuse boxes where the fiber insulator has or is disintegrating-effectively shorting out and bypassing the fuse.  I am starting to to view even properly sized edison fuses with suspicion.

Back on topic-congratulations on finding a difficult issue that would usually go completely undetected.
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Steve Swaffer

Jonathan Johnson

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Re: brain storm an optimal human safety system for back line
« Reply #345 on: August 31, 2015, 12:11:27 am »

Off topic, but I have always been OK with fuses-generally more reliable than breakers.  However, I have started running into fuse holders in older resi fuse boxes where the fiber insulator has or is disintegrating-effectively shorting out and bypassing the fuse.  I am starting to to view even properly sized edison fuses with suspicion.

Some of the really old fuse holders had mica insulators. I think that mica probably outlasts the fiber by a long shot, as long as it's protected from physical abuse.
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Jonathan Johnson

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Re: brain storm an optimal human safety system for back line
« Reply #346 on: August 31, 2015, 12:13:00 am »

I am making progress on getting a more reliable ground present indication without increasing current enough to trip the GFCI.. So far it works on my kitchen outlet that previously gave a false.  Still getting a false in the bathroom, that isn't logical so I may have to look more closely at that outlet.

Using my VOM with floating ground I coincidentally measure the exact same voltage on both the neutral and ground pin... Since i don't believe in coincidences when it comes to electricity I suspect very strongly that there is an accidental bootleg ground in that outlet. As i recall the GFCI outlet was a very tight fit in the junction box, so neutral touching the metal box could perform the bootleg.   :o  My other leaky outlet shows 4V between neutral and ground using the same floating measurements.

So I suspect I have nailed the "false" ground present indication,  ;D and have something else to fix about my home wiring.  :'(

Do I read correctly that you *thought* you were getting a false positive, when in fact your device was indicating a problem? Just goes to show the value of making assumptions!
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #347 on: August 31, 2015, 09:35:32 am »

Do I read correctly that you *thought* you were getting a false positive, when in fact your device was indicating a problem? Just goes to show the value of making assumptions!

It shows the value of testing outlets. The actual false on my kitchen outlet with the prior test circuit made me less trusting, but finding the bootleg path in my bathroom confirmed that my tester was right, and the outlet wrong.

Now all are in harmony and my outlet tester can successfully ignore the stray leakage at least around my house..

 JR



 
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #348 on: September 06, 2015, 06:07:59 pm »

Getting ready to pull the trigger on rev B (still some clean up to do. I noticed my small diode footprint wasn't correct either. ).

I fixed the too-sensitive ground present LED and some ghosting (leakage) into LEDs.

I completely rearranged the PCB so now the display LEDs are all on the bottom of the PCB and should be visible through the line cord hole in typical plugs.

I added several parts but kept the PCB the same size so it's a tight house.

I added one more LED (yellow) for power present. So when you plug in you always get at least the yellow LED. If it detects a good ground the green lights too.

Like before there are three more LEDs that light selectively when the probe is touched.

Green for line is hot.
Yellow for neutral is hot
or Red for ground is hot.

RPBG lights up the yellow and red hot LEDs.

Debating whether to take the 3 week slow boat (air mail)  shipping deal.

Progress

JR

[edit- new boards on order-- 9-9-2015 this time I paid and extra $9 for shipping from singapore instead of free from Hong Kong... we'll see if the premium is worth it... I'm too cheap to pay $33 dhl shipping for $14 worth of PCB. HK took about 3 weeks.   /edit]
« Last Edit: September 09, 2015, 05:39:07 pm by John Roberts {JR} »
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #349 on: September 09, 2015, 05:44:17 pm »

crude proof image

boards on order


JR

[edit] arrived today, so exactly 3 weeks.[/edit]
« Last Edit: September 30, 2015, 11:01:43 am by John Roberts {JR} »
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