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JohnRoberts

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I am putting the finishing touches on my most recent DIY project.

Features;
#1 standard GFCI protection
#2 additional ground current trip
#3 senses and does not work with reversed mains polarity.

This could save lives when musicians encounter hot electrically microphones.

Not a practical commercial product. The box in the middle labelled GFCI is a standard GFCI outlet. The opto-isolators are the wrong schematic symbol, they are actually opto-triacs.

Chew on this I'll answer questions later.

JR
 

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Why not commercially viable?  UL listing not gonna happen?  Too small a market?

Since the musician's entire rig has to run through this outlet, how much current can be drawn through it?  Enough for an SVT head and a pedalboard?  :)
 
Maybe I got it wrong but I think the orientation of the zener is not correct, on account BSS110 being a P-channel.

Now I don't understand at all what the circuitry around OK1 does, except heating R6 in case of ground potential difference  ;).
I want to be enlightened.

In terms of operation, I think you should add a "polarity" inverter ahead, because as it is, in case of line/neutral inversion, the muso's life is saved, but he can't earn it because the goddamn thing wouldn't turn on!  :)
 
mjrippe said:
Why not commercially viable?  UL listing not gonna happen?  Too small a market?
I am not going to drop the $10k (?) to open a UL file and pursue this, for a niche market where the costomers rather spend their disposable income on sound gear.  Also there is probably a likelihood of being sued should the muso figure out how to defeat the safety features.
Since the musician's entire rig has to run through this outlet, how much current can be drawn through it?  Enough for an SVT head and a pedalboard?  :)
Yup, 16A relays and 16A start up triacs. So adequate power for any guitar rig.

JR

PS a more practical and cost effective solution is to use a standard GFCI power drop and put a capacitor in series with the ground lead. I determined that 0.15uF will sink enough current to trip the GFCI (6 mA), while not supply enough current at 60Hz for a muso to get stuck to it. So it could still sting you, but not kill you.



 
abbey road d enfer said:
Maybe I got it wrong but I think the orientation of the zener is not correct, on account BSS110 being a P-channel.
opps... yes I grabbed the wrong schematic symbol... the mosfet I used is actually a BSS87 a N-channel 200V part.  [edit] I went back and used a correct schematic symbol but still wrong PN [/edit]

The circuit would probably work with a P channel MOSFET but C1 might need to be larger to support the relay coil current draw. As drawn when the N channel MOSFET turns on, the current can be directly supplied from the mains. A minor point but not an accident.

The zener clamp is probably not even needed if my resistor divider can keep the gate voltage within the +/-20V  range.
Now I don't understand at all what the circuitry around OK1 does, except heating R6 in case of ground potential difference  ;).
I want to be enlightened.
OK1 is actually an opto-triac (not opto-transistor). PN MOC3023.

The diode part of OK1 is in series with roughly 1/2 the ground path current so more than a few mA of ground current will cause the OK1 output triac to conduct and shunt current from the line output of the GFCI to it's neutral input. This will cause a current imbalance and trip the GFCI, which will de-energize the relay and lift the ground.  This ground current sense works independently of the GFCI so will protect the muso from a console with faulty power that energized the mic.

The interesting thing about this (for me) was the need to add C3 to prevent the triac in OK1 from false triggering from the rise time at turn on. The data sheet specs 1000V/uSec for max risetime. Without the cap the triac inside OK1 fires at turn on and trips the GFCI. The C to output side neutral keeps that cap current inside the valid GFCI loop, until the triac in OK1 is properly turned on and trips the GFCI.  The triac has enough body capacitance that I could get the circuit to work with no cap for a larger value of R6 but I didn't want to be soft when tripping the GFCI in case there were competing currents in the regular GFCI loop. With the cap it will be more repeatable.

Note: my cheap and dirty (KISS) solution to just put a 0.15uF*** in series with the GFCI ground lead would work too. While it doesn't open the ground it keeps the fault current from an external shock hazard below lethal levels (for 120VAC).
In terms of operation, I think you should add a "polarity" inverter ahead, because as it is, in case of line/neutral inversion, the muso's life is saved, but he can't earn it because the goddamn thing wouldn't turn on!  :)
I thought about this and don't like any solution that perpetuates using bad power. I'd prefer to have it zap any miswired outlets with a lightning bolt so they have to repair it.

I could add an automatic polarity swap with a second relay but that makes this even more expensive so even less commercial .

Again the KISS GFCI with stinger cap in place of the ground path, can still work and be used with miswired outlets. 

JR

*** note 0.15uF is a stinger cap value for 120VAC 60Hz... for 240VAC 50Hz that value is too large and should be adjusted for that market.. In fact this design is for 120V only
 
JohnRoberts said:
In terms of operation, I think you should add a "polarity" inverter ahead, because as it is, in case of line/neutral inversion, the muso's life is saved, but he can't earn it because the goddamn thing wouldn't turn on!  :)
I thought about this and don't like any solution that perpetuates using bad power. I'd prefer to have it zap any miswired outlets with a lightning bolt so they have to repair it.
As a scientist I totally agree with you.
As a musician, I would curse you to the fifth generation if I missed the gig because your device tries to save my life...you can't save people against their will  :)
The thing is actually here (Europe), polarity correctness is not a concern. There are rules that apply to wall sockets, but power strips do not respect polarity. In fact, many power strips are built with sockets alternating left and right, as you can see here.
http://www.castorama.fr/store/Biplite-16-amperes-facade-blanc-1er-prix-prod4630136.html;jsessionid=F1A44ABE07453B785F8A7F4C53EC5BC3.fo4atg4?navCount=0&sortByValue=relevance&navAction=push
Knowing  it was almost impossible to make sure that installations are properly done, the powers-that-be, in their magnificent wisdom, have transferred the responsibility to the equipment manufacturers, which makes sense IMO. Each pole is treated equally in terms of insulation and of course stinger caps have never been allowed.
 
abbey road d enfer said:
JohnRoberts said:
In terms of operation, I think you should add a "polarity" inverter ahead, because as it is, in case of line/neutral inversion, the muso's life is saved, but he can't earn it because the goddamn thing wouldn't turn on!  :)
I thought about this and don't like any solution that perpetuates using bad power. I'd prefer to have it zap any miswired outlets with a lightning bolt so they have to repair it.
As a scientist I totally agree with you.
As a musician, I would curse you to the fifth generation if I missed the gig because your device tries to save my life...you can't save people against their will  :)
You could just not use the GFCI and plug directly into the bad outlet, but depending on why it was tripping, you might be putting yourself in serious danger.
The thing is actually here (Europe), polarity correctness is not a concern. There are rules that apply to wall sockets, but power strips do not respect polarity. In fact, many power strips are built with sockets alternating left and right, as you can see here.
http://www.castorama.fr/store/Biplite-16-amperes-facade-blanc-1er-prix-prod4630136.html;jsessionid=F1A44ABE07453B785F8A7F4C53EC5BC3.fo4atg4?navCount=0&sortByValue=relevance&navAction=push
Knowing  it was almost impossible to make sure that installations are properly done, the powers-that-be, in their magnificent wisdom, have transferred the responsibility to the equipment manufacturers, which makes sense IMO. Each pole is treated equally in terms of insulation and of course stinger caps have never been allowed.
Polarity itself is not really a concern here BUT when dangerous wiring practices combine a "bootleg" ground  (ground is sometimes connected to neutral when real ground not available) with a reverse polarity situation , you get a safety ground outlet pin carrying full mains voltage. This is called a RPBG (reverse polarity bootleg ground) and can kill.. Years ago while i was working at Peavey we were dragged into court as the deep pockets to sue when a muso got killed by getting between two UL approved peavey amps, when one was plugged into a RPBG... After that lawsuit the judge condemned the house until the faulty wiring was fixed. 

I'm sure RPBG are illegal here too but stuff happens.

JR
 
Yes. even without reverse polarity a bootleg ground can be dangerous if the neutral line going back to the service panel has a broken wire or connection. Then the neutral-ground becomes energized and makes the chassis hot.

A bad thing.

JR
 
JohnRoberts said:
Yes. even without reverse polarity a bootleg ground can be dangerous if the neutral line going back to the service panel has a broken wire or connection. Then the neutral-ground becomes energized and makes the chassis hot.

A bad thing.

JR

I think it also makes GFCI protection useless since any current will return by the neutral and GFCI wouldn't notice that there is meat instead of a lightbulb in the middle.

JS
 
joaquins said:
JohnRoberts said:
Yes. even without reverse polarity a bootleg ground can be dangerous if the neutral line going back to the service panel has a broken wire or connection. Then the neutral-ground becomes energized and makes the chassis hot.

A bad thing.

JR

I think it also makes GFCI protection useless since any current will return by the neutral and GFCI wouldn't notice that there is meat instead of a lightbulb in the middle.

JS
A bootleg ground on the output side of the GFCI would return ground current to neutral and thwart the GFCI, but bootleg ground on the input side of the GFCI would still work.  So outlet level GFCI "could" work with bootleg ground, but this is bad practice. Bootleg grounds at outlets with a branch or panel RCD/GFCI is counter productive.

JR

PS: In a case of do what I say, not what I do, I had to wire up an outlet adapter with bootleg ground to test this. My house outlets are not grounded.  :eek:
 
I thought I would post this here, instead of starting a new thread (or talking more politics).

I have attached an outlet tester that actually works as compared to popular commercial outlet testers. An ugly secret about those generic outlet testers you can buy for $5 at the local hardware store is that they are fooled by RPBG (reverse polarity bootleg ground) connections, where hot and neutral are reversed, then a floating ground is bootlegged to what should be the 0V neutral but because of the reverse polarity is 120V, making the safety ground pin hot too.  :eek: :eek: :eek:

The difficulty in identifying this mis-wiring condition in situ is the need for an absolute ground reference. I use the human body as a local ground reference and buffer that through a high impedance mosfet.

Of course if anybody tries to play along at home be careful when messing around with mains voltage.

here is a link to post with pictures where an electrical safety forum moderator tested my prototype and confirmed that it works.  http://forums.prosoundweb.com/index.php/topic,152668.msg1423617.html#msg1423617

Be safe... even wimpy 120VAC can kill your.

JR 

PS: This simple outlet tester was a real brain teaser, lacking an external voltage reference it is hard to parse out what is going on. 
 

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> outlet testers ...$5 ...are fooled by RPBG (reverse polarity bootleg ground) connections

Gosh! Am I glad I do my own wiring! (I know who to sue....)

The local Building Inspector had one of those. I have two, and after she poked two outlets I assured her that I'd already done the barely-useful checks.

The real way is to know what is in the fusebox, run your own wires, and be very consistent about connecting them.

> I had to wire up an outlet adapter with bootleg ground to test this. My house outlets are not grounded.

I did a similar thing once. Wanted to test dirt-rod resistance. Low-voltage ohm meters are totally overwhelmed by stray soil current here. I figured to dump 110V right into the rod and measure the current. (Through light-bulb in case the rod actually grounded.) Snap, the GFI tripped! And I'd cleverly wired the garage so you could NOT reach a non-GFI outlet easily. Time to do the bad thing.

With two rods at the pole and one at the garage with 150W lamp between, I got dim glow, 60V, 0.5 Amp. 120 Ohms total. Ass-uming all three rods are equal they must be 80 Ohms each. A dead-short to dirt in a rod-sized object will flow 1.5 Amps, and will NOT trip a 20 Amp breaker.
 
PRR said:
> outlet testers ...$5 ...are fooled by RPBG (reverse polarity bootleg ground) connections

Gosh! Am I glad I do my own wiring! (I know who to sue....)

The local Building Inspector had one of those. I have two, and after she poked two outlets I assured her that I'd already done the barely-useful checks.
Those outlet testers make me crazy... People have been killed by RPBG, and those testers just indicate all good.

A building inspector depending on those cheap testers is even worse. You can figure what is what with a cheap VOM (hold the black lead in one hand and probe the outlet with the red lead)..

CAUTION be sure to use VAC scale, not current.  With my outlets I read about 50VAC on the 120V line.
The real way is to know what is in the fusebox, run your own wires, and be very consistent about connecting them.

> I had to wire up an outlet adapter with bootleg ground to test this. My house outlets are not grounded.

I did a similar thing once. Wanted to test dirt-rod resistance. Low-voltage ohm meters are totally overwhelmed by stray soil current here. I figured to dump 110V right into the rod and measure the current. (Through light-bulb in case the rod actually grounded.) Snap, the GFI tripped! And I'd cleverly wired the garage so you could NOT reach a non-GFI outlet easily. Time to do the bad thing.

With two rods at the pole and one at the garage with 150W lamp between, I got dim glow, 60V, 0.5 Amp. 120 Ohms total. Ass-uming all three rods are equal they must be 80 Ohms each. A dead-short to dirt in a rod-sized object will flow 1.5 Amps, and will NOT trip a 20 Amp breaker.
Pick up the earthworms that crawl out of the soil and use them for bait...

JR
 
I had never heard of a RPBG until a couple years ago or so. It's amazing how many people don't understand this, or that it even exists.

There should be a permanent sticky at the very top of the forums with someone knowledgeable like John explaining what is it, why it's problem, how to check for them (and other related issues), and why the little $5 three-light tester does NOT detect them.
 
hymentoptera said:
I had never heard of a RPBG until a couple years ago or so. It's amazing how many people don't understand this, or that it even exists.

There should be a permanent sticky at the very top of the forums with someone knowledgeable like John explaining what is it, why it's problem, how to check for them (and other related issues), and why the little $5 three-light tester does NOT detect them.
here is a dedicated AC power sub-forum with a knoweledgable moderator. http://forums.prosoundweb.com/index.php/board,82.0.html

JR
 
While this project is not moving very fast,,, I got my proto boards back from china this week.

This picture shows my tester reading an intentionally RPBG miswired outlet.

The red ground hot danger LED is lit, and the yellow neutral is hot warning. The green ground present is lit, but it can't differentiate between bootleg and real ground. Hopefully the red and yellow LEDs will warn the human.

Most of the outlets in my house are single green... correct polarity no ground. The outlet on my bench is single yellow, so neutral hot, but not dangerous (yet)...

JR

PS I'm way too old to hand pop tiny SMD boards . 8)
 

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FWIW: recent US GFIC outlets can detect a G-N short near the box. I believe they use an RF tone to sense too-little impedance between G and N. This became a nuisance for some hack I was doing, tho I forget details. 
 
PRR said:
FWIW: recent US GFIC outlets can detect a G-N short near the box. I believe they use an RF tone to sense too-little impedance between G and N. This became a nuisance for some hack I was doing, tho I forget details.

All the GFCI outlets I have bought and messed with lack such a sophisticated ground sense. In fact they usually ignore the ground and just pass it through. The GFCI works independently of the ground.

RF is logical since DCR is difficult to measure in the presence of other LF currents flowing in the same conductors. RF could better parse a short bootleg connection from a real ground run.

JR
 
I built up my second generation outlet tester shown on the bottom beneath the cheap commercial tester available at every hardware store in america.

The outlet they are both plugged into is intentionally miswired  (RPBG) So line and neutral are reversed, and ground is bootlegged to line, energizing the safety ground to 120V AC.

The commercial outlet tester (UL approved)  indicates all good (while being very dangerous). My tester reveals the hazardous voltages present on the safety ground.

JR
 

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