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Author Topic: Spontaneous Reversal of Wires????  (Read 1397 times)

Tom Bourke

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Re: Spontaneous Reversal of Wires????
« Reply #20 on: May 09, 2014, 04:32:07 pm »

Very interesting. A quick search found an 8-channel Arduino output interface with 10-amp relays rated for 250 VAC. Cost is $19.59 with free shipping to the USA. I can't buy just the relays for that kinda money. http://www.dx.com/p/arduino-8-channel-12v-relay-module-expansion-board-142797#.U2ywpijVvpc

Gosh, I think this controller needs 9 relays for the outlet goof matrix, so perhaps I should do a Karnaugh Map and try the simplify the circuit a bit. I used to do Karnaugh Maps all the time in the 70's while designing relay logic for packaging machines. It's been a long time, but I'm betting it still works...
I would think you could simplify it, considering the tester can't tell a ground, neutral reversal.  You really only need hot and Ground/neutral switched to 3 contacts.  This works out to a 2x3 relay matrix.  I would also consider just using LEDs to show the conditions and no real power.  3 RGB leds in an outlet overlay + 3 leds showing the tester output.  Maybe a 3rd rgb LED showing, OK, wrong, Deadly.  An ardiuino can also drive an LCD display with some up down buttons.  You could show expected meter readings?  Maybe turn it into a game?
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Lyle Williams

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Re: Spontaneous Reversal of Wires????
« Reply #21 on: May 09, 2014, 04:42:49 pm »

If a game you could create a random miswiring and require correct fault identification.  It might be wise to use a lower voltage, or a specially built current-limited milliamp mains-voltage supply.
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Tom Bourke

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Re: Spontaneous Reversal of Wires????
« Reply #22 on: May 09, 2014, 05:12:59 pm »

If a game you could create a random miswiring and require correct fault identification.  It might be wise to use a lower voltage, or a specially built current-limited milliamp mains-voltage supply.
I was thinking sll low voltage with simulated meter readings on the LCD.
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Stephen Swaffer

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Re: Spontaneous Reversal of Wires????
« Reply #23 on: May 09, 2014, 05:52:55 pm »

Simulations are good-but with some people it doesn't seem to click until they see the same tester they have been using give misleading readings-there is  perception that it is a complex magic little box as opposed to 3 simple lights with a key to interpret them.

Three terminals-black, white, green each with three possible connections-hot, neutral/ground, or no connection at all gives 9 possible combinations.  But it could be done as simply and cheaply as 3 SPDT on-off-on toggle switches to a receptacle.  Feed it with a GFCI for a measure of safety if you want to leave the wiring visible (shrink tube connections so nothing bare for first line of defense).
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Mike Sokol

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Re: Spontaneous Reversal of Wires????
« Reply #24 on: May 09, 2014, 08:52:02 pm »

I would think you could simplify it, considering the tester can't tell a ground, neutral reversal. 

But I HAVE thought about adding a variation to this demonstration on how to tell when the ground and neutral wires are swapped. Can't tell that with a 3-light tester, but you can figure it out using a voltmeter and a load, and perhaps with a SureTest or INSP-3 Ground Impedance Tester. A swapped G-N creates some really strange ground-loop hum issues in sound systems.

Mike Sokol

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Re: Spontaneous Reversal of Wires????
« Reply #25 on: May 09, 2014, 08:54:36 pm »

Simulations are good-but with some people it doesn't seem to click until they see the same tester they have been using give misleading readings-there is  perception that it is a complex magic little box as opposed to 3 simple lights with a key to interpret them.

True that... I want to be able to plug in any brand/model of tester and show the kind of mis-wiring issues that confuses them. It also needs to be able to create the really dangerous RPBG (Reverse Polarity Bootleg Ground) condition. 

Stephen Swaffer

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Re: Spontaneous Reversal of Wires????
« Reply #26 on: May 09, 2014, 10:56:23 pm »

One other condition that you occasionally run into is a bad connection that tests OK under no load, but appears to "switch polarity" as soon as a load is applied.  Those can make you think you are losing your mind.

I had gotten away from using the handy little testers-its almost as easy to and more informative to use a voltmeter-but with the new tamper resistant receptacles it is all but impossible to use a voltmeter without getting into the box.
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Mike Sokol

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Re: Spontaneous Reversal of Wires????
« Reply #27 on: May 09, 2014, 11:25:33 pm »

I had gotten away from using the handy little testers-its almost as easy to and more informative to use a voltmeter-but with the new tamper resistant receptacles it is all but impossible to use a voltmeter without getting into the box.

I now use an INSP-3 or SureTest Analyzer all the time for just those reasons.

Mike Sokol

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Re: Spontaneous Reversal of Wires????
« Reply #28 on: May 11, 2014, 08:36:07 am »

One other condition that you occasionally run into is a bad connection that tests OK under no load, but appears to "switch polarity" as soon as a load is applied.  Those can make you think you are losing your mind.

I can simulate a bad connection with my outlet goof tester by adding something like a 10K resistor in series with each line as desired. That means I need a 5-position/1-pole rotary switches for each line, so I could label them H-N-G-R-O for Hot, Neutral, Ground, Resistor, Open. As long as the rotary switch is break-before-make, then this should be safe for any combination of switches. Of course, this can easily energize the chassis of any plugged-in gear to 120-volts, so that has to be considered. If I get husky rotary switches rated for 10-amps, I can actually put something like a heater load on this demo receptacle to show how to find swapped G-N lines with a meter.

I think this design is Safe, Simple and Sexy... I'll start looking for parts. 
« Last Edit: May 11, 2014, 08:44:11 am by Mike Sokol »
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Mike Sokol

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Re: Spontaneous Reversal of Wires????
« Reply #29 on: May 11, 2014, 09:55:54 am »

I think this design is Safe, Simple and Sexy... I'll start looking for parts.

I can get a 6-position rotary switch with 20 amp contacts on eBay for $2 each.

http://www.ebay.com/itm/GE-ASR7173-510-1165248-6-POSITION-ROTARY-SWITCH-120-240-VOLT-88145-/360703536601?pt=LH_DefaultDomain_0&hash=item53fb9b2dd9

I just need some cool looking pointer knobs and an aluminum box to mount everything in. Oh yes, got to isolate the receptacle ground itself so I don't energize my own test chassis. Plus I'll put a GFCI breaker in the power feed so if something goes wrong it shouldn't kill me. Anyone know of a panel mounted GFCI?
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