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Author Topic: brain storm an optimal human safety system for back line  (Read 103947 times)

Mike Sokol

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Re: brain storm an optimal human safety system for back line
« Reply #130 on: January 30, 2015, 08:09:25 pm »

The big dog relay and blinky lights is a premium product offered for sale to unappreciative cheap bastaads... (pearls before swine). This stinger GFCI could be cheap and easy (practical, sellable, etc). 

I agree. This old-school fix in combination with a GFCI is likely the best and simplest way to protect performers from every failure combination I can think of.
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #131 on: February 03, 2015, 01:41:37 pm »

Here is the guts of the commercial GFCI power drop.

Not much room inside, but I'm going to shoe horn in an on-off-on toggle switch for testing with a .047 uF stinger cap.. so the switch will select between ground connected, ground lifted, and ground connected through .047uF stinger cap.

I will use a 100V cap I had laying around since this is not a final version.  I think I can fit a proper Y cap inside this without a switch but first want some feedback regarding the cap's effectiveness at quieting any guitar rig plugged into it.

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I will order a proper Y cap after I work out a few details for something else I'm scribbling in my late night design musings. My latest thinking is that I might be able to make a solid state low mA sensitivity fuse with three power mosfets that can stand off 400V when open (devices are maybe $0.35 ea so not crazy) there will be some glue circuitry to turn on the fuse, and to latch it off when tripped. The fuse when on would have something like 100 ohms in series and detect the voltage drop across that 100 Ohms. Much lower Z than a stinger cap.

I am thinking instead of using a micro processor and relay for my smart outlet strip, perhaps this $1-2 dollar electronic ground fuse, a couple dollars worth of power triacs to switch on line and neutral. After start up testing and for as long as the sense circuits are happy it will connect power to the output side.

If the sense circuitry senses that neutral is hot using a non-contact sense circuit (as simple a small active device comparing neutral to some arbitrary environmental ground) a fault state is latched and the power triacs never turn on. If the ground fuse senses more than a few mA it likewise trips the triacs off and ground open.

If this works this is getting cheaper...and an open ground is safer than than even a stinger cap. The GFCI unit is the most expensive single part, but off the shelf GFCI outlets are not that expensive, and probably cheaper in quantity.

 OK back to my day job...

JR
« Last Edit: February 03, 2015, 02:34:45 pm by John Roberts {JR} »
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frank kayser

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Re: brain storm an optimal human safety system for back line
« Reply #132 on: February 03, 2015, 02:34:47 pm »

I love to see this progress.  Thanks!  Keep up the good work!
frank
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Stephen Swaffer

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Re: brain storm an optimal human safety system for back line
« Reply #133 on: February 03, 2015, 09:57:23 pm »

Every so often, I see stand alone GFCI devices-look like a gfci recptacle, but no place to plug in anything-clearanced in the big box stores.  Pretty sure my local Menards had some clearanced for $6 or $7-these were P & S  not no name junk.

Just a thought, if you are needing some cheap experimenter devices.
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Steve Swaffer

John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #134 on: February 05, 2015, 12:17:18 pm »

In my late night design sessions I am pondering the danger of boot strapping ground? I know the danger from a bootstrapped ground to neutral should that neutral open up, since ground would then become energized,,,, but if we have ground current sensing, and reverse polarity sensing, it seems that the open neutral would be detected and protected against.

I guess my question comes down to how to act if I plug into an outlet that is correct polarity but lacking a ground connection?

#1 blink a "no ground" LED but still work since GFCI will still work?
#2  or internally bootstrap the floating ground to neutral?

I am reluctant to just not work if open ground is detected since that will just encourage most users to bypass the safety device and plug into the unprotected outlet.
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Likewise a reverse polarity with open ground should be safe to use with GFCI, so RP with floating ground should get a warning but work, RPBG would warn and not power up.
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RP with ground complicates my electronic ground fuse, but I may have a work around for that.
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? Another question for Mike... How much voltage have you seen between real grounds and neutral? I should be able to ignore up to several volts of AC between them for my ground current sense, but do I need to?  I guess if I tolerate RP I need to ignore full voltage between should be neutral and is ground.

RPBG is killer, and BG is bad practice, but just BG with current/voltage sense and protection might be OK?

Cheapest and easiest to design is just not work at all if there is no ground or reverse polarity but I doubt that would stop players from plugging into rouge outlets. The show must go on... :o

JR
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Mike Sokol

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Re: brain storm an optimal human safety system for back line
« Reply #135 on: February 05, 2015, 01:32:47 pm »

? Another question for Mike... How much voltage have you seen between real grounds and neutral? I should be able to ignore up to several volts of AC between them for my ground current sense, but do I need to?  I guess if I tolerate RP I need to ignore full voltage between should be neutral and is ground.

So here's how to visualize G to Neutral voltage. Let's assume a properly wired system where the ground isn't carrying any current. Assume you're starting with 120 volts at the service panel. Without any current draw from the outlet you'll still have 120 volts there. So there's no voltage drop because there's no current, and there should be zero volts between the Ground and Neutral.

Scenario #1 is different though. Let's assume you have a big amplifier plugged into an outlet that's drawing significant current. And if the Hot to Neutral voltage drops down to 110 volts, then that's not all on the black wire. It's actually 5 volts on the neutral wire and 5 volts on the hot wire. So an outlet that bouncing between 120 and 110 volts on H-N with current draw should read between 0 and 5 volts G-N. That's normal and expected. When you DON'T read a fluctuating voltage between G-N that's 1/2 of the total drop under load, that's a sign that there's a bootleg ground. That's one really quick test I do on an outlet to quickly catch a bootleg ground. Put a DMM between Ground and Neutral. If it measures ANY voltage up to 5 volts, then it's NOT a bootleg ground. If it measures 0 volts (Zed for Steve, I think) then there might be no load on that leg, so throw a 1,000 space heater or PAR light on the same outlet and look for a voltage rise between G and N. If it does NOT rise to 1/2 of the total drop, then it's a bootleg ground. If it DOES rise, then it's NOT a bootleg ground.

One other thing you would like to catch in your tester is swapped Neutral and Ground wires. Happens a lot more than one would expect and causes all sorts of ground loop hum that varies under load. This is the basis of my hypothesis on GLID (Ground Loop Inter-modulation Distortion).   
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #136 on: February 05, 2015, 02:07:49 pm »

So here's how to visualize G to Neutral voltage. Let's assume a properly wired system where the ground isn't carrying any current. Assume you're starting with 120 volts at the service panel. Without any current draw from the outlet you'll still have 120 volts there. So there's no voltage drop because there's no current, and there should be zero volts between the Ground and Neutral.
Got you... My plan is to handle a couple back line units so hopefully not that much current but yes I need to tolerate 10V or more.
Quote
Scenario #1 is different though. Let's assume you have a big amplifier plugged into an outlet that's drawing significant current. And if the Hot to Neutral voltage drops down to 110 volts, then that's not all on the black wire. It's actually 5 volts on the neutral wire and 5 volts on the hot wire. So an outlet that bouncing between 120 and 110 volts on H-N with current draw should read between 0 and 5 volts G-N. That's normal and expected. When you DON'T read a fluctuating voltage between G-N that's 1/2 of the total drop under load, that's a sign that there's a bootleg ground. That's one really quick test I do on an outlet to quickly catch a bootleg ground. Put a DMM between Ground and Neutral. If it measures ANY voltage up to 5 volts, then it's NOT a bootleg ground. If it measures 0 volts (Zed for Steve, I think) then there might be no load on that leg, so throw a 1,000 space heater or PAR light on the same outlet and look for a voltage rise between G and N. If it does NOT rise to 1/2 of the total drop, then it's a bootleg ground. If it DOES rise, then it's NOT a bootleg ground.
This gets me back to my microprocessor where I could switch in a test load and look at all three lines. I lean toward very briefly pulsing a load for maybe one cycle to keep heat dissipation low. But this is getting more expensive not less.
Quote
One other thing you would like to catch in your tester is swapped Neutral and Ground wires. Happens a lot more than one would expect and causes all sorts of ground loop hum that varies under load. This is the basis of my hypothesis on GLID (Ground Loop Inter-modulation Distortion).
Again this requires the smarter microprocessor approach.  I was mainly focussed on low cost safety mitigation rather than a full boat tester, but that may be a different market. 

[edit] Ok, is that a trick question? I do not know how to test for swapped ground-neutral in a single outlet. If the impedance of the ground wire is reasonable it will test and act like neutral would relative to that outlet. The problem with swapped neutral-ground is mainly the cross contamination to the ground quality elsewhere, and neutral to the local ground. 

I guess you could sniff the ground and neutral before you start testing for which one is quieter but what do you use for your 0V reference? It's hard enough to sniff for a polarity swap without a solid ground reference, trying to parse out mV of noise on ground vs, neutral before you connect will be difficult.  I'll think about this but It seems hard.   [/edit]

What do you think about the lesser hazard of bootleg connection when ground current and/or polarity sensing is used? 

JR
« Last Edit: February 05, 2015, 07:57:55 pm by John Roberts {JR} »
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Robert Lofgren

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Re: brain storm an optimal human safety system for back line
« Reply #137 on: February 05, 2015, 05:48:35 pm »

I just wanted to mention that I bought a socket safety tester today. It is branded with a swedish company logo but is possibly some OEM.

It tests voltage on earth connection, broken earth wire, broken neutral wire, broken live wire, interchanged neutral and live, interchanged earth and live, interchanged earth and live with broken earth, function test of RCCB 30mA, what pin of the socket is live.

Only thing it can't detect is interchanged neutral wire and earth wire.

http://www.malmbergs.com/frmProductDisplay_new.aspx?item=4200450
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Mike Sokol

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Re: brain storm an optimal human safety system for back line
« Reply #138 on: February 05, 2015, 05:59:51 pm »

I just wanted to mention that I bought a socket safety tester today. It is branded with a swedish company logo but is possibly some OEM.

It tests voltage on earth connection, broken earth wire, broken neutral wire, broken live wire, interchanged neutral and live, interchanged earth and live, interchanged earth and live with broken earth, function test of RCCB 30mA, what pin of the socket is live.

Only thing it can't detect is interchanged neutral wire and earth wire.

http://www.malmbergs.com/frmProductDisplay_new.aspx?item=4200450

I'll bet you a 6-pack of the beer of your choice or a dozen donuts that it won't find an RPBG (Reverse Polarity Bootleg Ground). See http://ecmweb.com/contractor/failures-outlet-testing-exposed

Without an external ground reference there's no way for it to know if the Hot is at zero volts above earth, and the Ground and Neutral are both at 120 volts (or 230 volts in Europe).
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Mike Sokol
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Robert Lofgren

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Re: brain storm an optimal human safety system for back line
« Reply #139 on: February 05, 2015, 06:12:23 pm »

I'll bet you a 6-pack of the beer of your choice or a dozen donuts that it won't find an RPBG (Reverse Polarity Bootleg Ground). See http://ecmweb.com/contractor/failures-outlet-testing-exposed

Without an external ground reference there's no way for it to know if the Hot is at zero volts above earth, and the Ground and Neutral are both at 120 volts (or 230 volts in Europe).
They have added a touch point similar to neon-based 'screwdriver' tester that will act as a reference point for RPBG testing. By touching that PE-test point it will tell you if your ground is live.

I've not seen that feature on any other socket tester until today...
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Re: brain storm an optimal human safety system for back line
« Reply #139 on: February 05, 2015, 06:12:23 pm »


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