ProSoundWeb Community

Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: Ron Kimball on December 15, 2013, 11:49:15 am

Title: AC Circuit Load Tester?
Post by: Ron Kimball on December 15, 2013, 11:49:15 am
Would this be useful?
http://tools.woot.com/offers/extech-ac-circuit-load-tester-1
Title: Re: AC Circuit Load Tester?
Post by: TJ (Tom) Cornish on December 15, 2013, 01:44:11 pm
Would this be useful?
http://tools.woot.com/offers/extech-ac-circuit-load-tester-1
I picked one up from the last time it was offered on Woot. It gives a lot more information than a simple voltage test, and does seem to be useful. The big advertised feature is the load test. I'm not positive if this matters yet, but it doesn't directly do a load test by putting 20A on the line; it does some kind of indirect measurement or calculation.

I'm going to put mine through the paces and then do a review at some point. So far thoughts are mostly positive.
Title: Re: AC Circuit Load Tester?
Post by: Mike Sokol on December 15, 2013, 01:49:40 pm
Would this be useful?
http://tools.woot.com/offers/extech-ac-circuit-load-tester-1
I actually have that same Extech tester, plus three other brands including the Ideal SureTest, Amprobe INSP-3, and a near antique British Woodhead GLIT tester I bought in the 70's (see below). All function similarly by pulsing a single line-cycle of current between the hot wire and the safety ground wire, then measuring the voltage drop and calculating the impedance of the ground fault circuit. They also predict how much voltage drop you'll get with a 15 or 20 amp load, plus perform GFCI testing by injecting a 5 mA fault to see if it trips the GFCI. The Extech is the least sophisticated of the three modern models, and doesn't have an internal battery to keep the screen on when the outlet circuit is tripped from a GFCI test.

I really like the Ideal SureTest for its very bright screen and quick tests. But the Amprobe INSP-3 has better measurement screens for my taste. Here's a video of me testing a SureTest: http://www.youtube.com/watch?v=_04HmpFBxdQ and here's one using the INSP-3: http://www.youtube.com/watch?v=XfAPkJVYUpY

Note that the video camera made the SureTest screen flicker, as it looks stable to the naked eye. I don't have a video of the Extech tester already, but if I get time this week I'll try to post a quick video of it in action. For the money, the Extech is hard to beat since the other's cost around $300 each.

I do think that a GLIT (Ground Loop Impedance Test) is a great way to verify both the load wiring integrity as well as the ground fault capability of the circuit. But also note that it CAN'T find an RPBG (Reverse Polarity Bootleg Ground) outlet.   
Title: Re: AC Circuit Load Tester?
Post by: Johnny Diaz on December 16, 2013, 08:32:55 pm
Mike,

I was wondering if these tester's discussed are really needed if one has a Fluke DMM? 

Johnny
Title: Re: AC Circuit Load Tester?
Post by: TJ (Tom) Cornish on December 16, 2013, 09:47:14 pm
Mike,

I was wondering if these tester's discussed are really needed if one has a Fluke DMM? 

Johnny
A DMM alone isn't enough - you need to do a load test, and potentially a non-contact tester to test for reverse polarity bootleg grounds.
Title: Re: AC Circuit Load Tester?
Post by: Lyle Williams on December 16, 2013, 09:59:27 pm
Mike,

I was wondering if these tester's discussed are really needed if one has a Fluke DMM? 

Johnny

In a perfect world, none of this is necessary.  All power work is done correctly and no faults occur over time.

That said, this sort of tester is getting well away from consumer territory into electrician territory.
Title: Re: AC Circuit Load Tester?
Post by: TJ (Tom) Cornish on December 16, 2013, 10:16:39 pm
In a perfect world, none of this is necessary.  All power work is done correctly and no faults occur over time.

That said, this sort of tester is getting well away from consumer territory into electrician territory.
Unfortunately, those of us in this industry need to start thinking like electricians, rather than ignorant consumers.  Knowing how to verify correct receptacle function is absolutely critical, particularly since we often use multiple circuits, which can amplify the dangers of wiring failures or errors.
Title: Re: AC Circuit Load Tester?
Post by: Ron Kimball on December 16, 2013, 10:25:24 pm
This one look similar but quite a bit less expensive:
http://www.ebay.com/itm/190978962970
Title: Re: AC Circuit Load Tester?
Post by: Johnny Diaz on December 17, 2013, 09:11:35 am
A DMM alone isn't enough - you need to do a load test, and potentially a non-contact tester to test for reverse polarity bootleg grounds.

Tom,

True the DMM won't do a load test but I always thought that as the amperage goes up the voltage will go down unless using a voltage regulator.  Is my understanding correct?  Is the ac circuit load tester able to determine if the ground and neutral are tied together?  If so, I can see how this is beneficial.   

Johnny
Title: Re: AC Circuit Load Tester?
Post by: TJ (Tom) Cornish on December 17, 2013, 09:21:39 am
Tom,

True the DMM won't do a load test but I always thought that as the amperage goes up the voltage will go down unless using a voltage regulator.  Is my understanding correct?  Is the ac circuit load tester able to determine if the ground and neutral are tied together?  If so, I can see how this is beneficial.   

Johnny
http://soundforums.net/hub/1856-basic-receptacle-testing.html
Title: Re: AC Circuit Load Tester?
Post by: Mike Sokol on December 17, 2013, 10:28:08 am
A DMM alone isn't enough - you need to do a load test, and potentially a non-contact tester to test for reverse polarity bootleg grounds.
I would agree. A load test using any of the four Ground Loop Impedance Testers I mentioned will test the wiring for not only its ability to supply load current, but perhaps more importantly for the safety ground's ability to provide a low-impedance path for ground fault currents. That's because it will likely be obvious if your circuit has a corroded connection for the line path or you're drawing too much amperage, since a brown-out situation is pretty easy to detect (lights dimming, amps clipping too easily or going into alarm mode, circuit breakers tripping, etc...). But if the safety ground path fails you can have a situation where your entire backline or PA system has all the gear chassis elevated to 120-volts above earth potential. Then touching a mic or guitar strings and anything else will allow the fault current to flow through the meat puppet.

If you think this doesn't happen in the modern world, just look below for what happened to Chad Gilbert from New Found Glory a few months ago. I don't know exactly what caused it, but this was a close call that could have killed him. Of course if all wiring was up to code and properly maintained, then testing wouldn't be necessary. But considering that we put many 10's to 100's of thousands of dollars of sound gear on the line when we plug into an unknown venue, not to mention that humans will be grabbing metal objects connected to these sound systems, spending 5 minutes to verify the wiring voltage, polarity, and grounding is pretty cheap insurance. 

Update: Chad Gilbert is now out of hospital and has tweeted of his recent experience.

Last nights incident!

While recording the NFG live album at the chain reaction last night I was shocked by the microphone. In between songs I grabbed the mic to speak and when I did it felt like I couldnít let go. I was being shocked and it froze me in place and when I was able to release my hands off of the mic I collapsed. When I came to I had friends standing over me and it felt like I was asleep in one of those Sci Fi movies when they wake up after traveling for 3 years to fight an alien. My friends escorted me off the stage. I told the band to finish the set for the sake of the audio recording. At that point I still was in a daze. The ambulance came and picked me up and drove me to the nearest Emergency Room. After getting numerous tests off and on for about 12 hours from the friendly people at UC Irvine I was released. They checked my heart for most of that time to make sure the electrical current didnít make my heart beat irregularly. Everything came back positive. I am gonna play the show tonight but this time with a wireless to settle my paranoia of this happening again because man it hurt and sucked. Thanks to all my friends and fans around the globe for the sweet messages!

Chad
Title: Re: AC Circuit Load Tester?
Post by: Mike Sokol on December 17, 2013, 10:30:19 am
This one look similar but quite a bit less expensive:
http://www.ebay.com/itm/190978962970
Looks like it could work and does the right things, but I've never tested one. I'll see if they'll send me a sample for review.
Title: Re: AC Circuit Load Tester?
Post by: Lyle Williams on December 17, 2013, 02:31:01 pm
Unfortunately, those of us in this industry need to start thinking like electricians, rather than ignorant consumers.  Knowing how to verify correct receptacle function is absolutely critical, particularly since we often use multiple circuits, which can amplify the dangers of wiring failures or errors.

There are two paths that I think are followed:

1. Knowledge about circuit behaviour and fault conditions leads to a desire to measure for the presence of these fault conditions.  With specific tests in mind, and an understanding of the limitations of those tests, a tester is purchased and operated.  Each test can detect the specific common faults we have though of but will not detect a smaller subset of more exotic dangerous conditions we haven't though of.  This is the thinking like an electrician path and it probably leads to greater safety.

2. A test appliance is purchased and operated with the hope that the test appliance can somehow make a safe/unsafe decision.  I think this path probably leads to greater danger.
Title: Re: AC Circuit Load Tester?
Post by: Mike Sokol on December 17, 2013, 06:10:01 pm
There are two paths that I think are followed:

1. Knowledge about circuit behaviour and fault conditions leads to a desire to measure for the presence of these fault conditions.  With specific tests in mind, and an understanding of the limitations of those tests, a tester is purchased and operated.  Each test can detect the specific common faults we have though of but will not detect a smaller subset of more exotic dangerous conditions we haven't though of.  This is the thinking like an electrician path and it probably leads to greater safety.

2. A test appliance is purchased and operated with the hope that the test appliance can somehow make a safe/unsafe decision.  I think this path probably leads to greater danger.

I try my best to do the #1 path and also set up failure scenarios on my test bench to measure and analyze what is actually happening under strange wiring situations. If you assume that everything is wired correctly and 100% to code, then you could be making a deadly mistake.  For instance, RPBG (Reverse Polarity Bootleg Ground) outlets should NEVER happen. But in old buildings wiring shortcuts are often taken either to save money, or simply because a DIY guy didn't know any better. That's what makes older church wiring so dangerous. Many times receptacles have been rewired by church volunteers who have no knowledge of electricity and certainly are not licensed to be doing electrical work.

A lot of my RV readers do the #2 path and simply want to plug in something like a SurgeGuard voltage protector to give them a confirmation that everything is wired correctly at a campground outlet. Unfortunately, there are no RV voltage protectors that will detect or disconnect an RV from the hot ground in an RPBG outlet. Still, these same readers will insist that they don't need to measure any campground outlets since they have a $300 black box on their shore power plug that protects them under all conditions. I also did a gig with a guitar player who claimed that his $100 surge strip would protect him from getting shocked, even though he had the ground pin broken off of its power plug. Nope, not a GFCI, just a fancy surge strip with RF noise filters. That's just crazy, but he believed it. Yikes!!!

I did a survey 2 years ago on PSW which revealed that 70% of the 3,000 musicians and technicians who answered had been shocked on stage or by sound gear at some time in their career. We tend to accept getting shocked as just part of the business. But every shock is an indication that something is seriously wrong with the wiring somewhere and it's time to get out the meter for a closer look. Of course it would be far better to be proactive and find wiring problems BEFORE they shock and possibly kill someone.

Keep fighting the good fight for electrical safety and understanding. And NEVER accept getting shocked as normal.
Title: Re: AC Circuit Load Tester?
Post by: Lyle Williams on December 17, 2013, 11:14:09 pm
Amen brother.
Title: Re: AC Circuit Load Tester?
Post by: frank kayser on December 21, 2013, 04:44:11 pm
I also jumped on the Extech CT70.  Of course I want a "plug in magic black box" to give me an irrefutable go-nogo power status.  I have been reading here and am learning that particular holy grail does not exist. 

My question - probably due to my misreading something and assuming I had it correct, I was under the notion that the the trouble with detecting a RPBG connection was the inability of most meters (all contact meters) to figure whether hot and neutral are exchanged. 

Never mind.  I re-read EC&M article on RPBG.  The key I missed was testers can't detect fault when both neutral AND ground are hot - they can detect -OR- just fine.

Even with my new toy (euphemism) I will continue to test with the non-contact tester as described in addition to the Extech. 

Trust no one, test, and think like an electrician.
Title: Re: AC Circuit Load Tester?
Post by: Mike Sokol on December 21, 2013, 07:15:21 pm
Never mind.  I re-read EC&M article on RPBG.  The key I missed was testers can't detect fault when both neutral AND ground are hot - they can detect -OR- just fine.

Yup, that was exactly my discovery. And after figuring this out I contacted all the Tester manufacturers (Amprobe, Extech, SureTest, Triplette, etc...) and every one of them argued with me that their testers would easily find an RPBG. But after I sent them a simple diagram and asked them to repeat my experiment, they all called me back and confirmed they had missed that mis-wiring possibility.

So how do RPBGs happen? Well in a perfectly wired world they shouldn't exist at all. However, if you're plugging into a building originally wired before around 1968, then there's a real possibility of one existing in a grounded receptacle. It's way too easy for an electrician or DIY guy to simply jumper from the neutral screw to the ground screw, instead of running a new wire with a ground back to the service panel. See diagram below. If someone in the past also swapped the hot and neutral wires in the wall, then it's an RPBG which can't be detected by any normal test methods, including 3-light testers, Ground Loop Impedance Testers, or even measuring H-N, H-G and N-G with a voltmeter. While you could run a separate wire to a ground stake outside and measure between it and safety ground wire  on the receptacle, a far simpler way is to simply point a NCVT near the ground slot on the receptacle. It it beeps at you, then the ground is at an elevated voltage above earth potential. Plus you can use the same NCVT to do a quick stage check for hot-chassis guitar amps or microphones. Believe me, the first time you point one at a mic or guitar and it lights and beeps, that will get your attention fast. 

Quote
Trust no one, test, and think like an electrician.

So true....
Title: Re: AC Circuit Load Tester?
Post by: Philip Roberts on December 21, 2013, 09:51:03 pm
Is there a reason that a NCVT couldn't be built into an outlet tester? Have it be "non contact" to wiring inside the tester once it's plugged into the outlet but before engaging other test circuitry.

Philip
Title: Re: AC Circuit Load Tester?
Post by: Mike Sokol on December 22, 2013, 08:03:59 am
Is there a reason that a NCVT couldn't be built into an outlet tester? Have it be "non contact" to wiring inside the tester once it's plugged into the outlet but before engaging other test circuitry.

I've made this very suggestion to the key players in the outlet testing industry. It would be pretty simple to kludge together a 3-light cube or Ground Loop Impedance Tester with a NCVT. In fact, you can buy a current model DMM with a built-in NCVT on the top of the case. However, these DMM models will only test a wide area to see if the outlet is powered up, not a small enough spot to differentiate between the hot and neutral sides. But it could be used to check for a hot-chassis on a mic, guitar or mixing console.

So for now, at least, I still think it's the best policy to use a NCVT to double-check outlets and stage gear for hot-ground conditions in addition to a voltage and polarity test.
Title: Re: AC Circuit Load Tester?
Post by: John Roberts {JR} on December 22, 2013, 11:56:04 am
I haven't thought about this for a while, but it seems like it shouldn't be too heavy lifting to design a smart outlet strip with NCVT that automatically detects hot on ground and opens that connection path. In combination with GFCI the meat puppets could be protected and show could go on. Even if RPBG outlet is all the power that is available. It could flash an irritating red light (maybe even built into the plug) when ground is corrupted to annoy everyone and inform them that something is horribly wrong with that outlet. 

Anyone these days who is not using GFCI on back line is taunting the grim reaper. It seems GFCI should trip and prevent the shock from continuing, but will stop the show... a smart NCVT outlet strip could keep the show going, while it is debatable if that is worthwhile, or merchantable. One can easily argue the RPBG outlets should not be tolerated under any situation, and the market for these would probably be tiny (market that would buy them, not market that could use them).   

JR

PS: The smart outlet strip might even remap the hot and neutral but that adds more cost for perhaps only modest benefit (in combination with GFCI), The hot ground seems like the dominant danger so that could be opened with one power switching device. 
Title: Re: AC Circuit Load Tester?
Post by: Lyle Williams on December 22, 2013, 01:06:51 pm
I find my NCVT to be one of the least objective test tools I own.  Lots of false positives and false negatives.  The results are very subjective; earth and neutral normally light the thing up, just a bit less than the real live.  Normally it takes quite a bit of waving and prodding and switching for me to be confident of a result.
Title: Re: AC Circuit Load Tester?
Post by: Mike Sokol on December 22, 2013, 02:45:48 pm
I find my NCVT to be one of the least objective test tools I own.  Lots of false positives and false negatives.  The results are very subjective; earth and neutral normally light the thing up, just a bit less than the real live.  Normally it takes quite a bit of waving and prodding and switching for me to be confident of a result.

I have at least six different brands/models of NCVT's on my bench, and find they're close to 100% accurate in indicating a hot-microphone, guitar, or mixing console with at least 40 volt AC. And all will beep/flash an inch or two away from a RPBG outlet due to the increased metal area biased to 120-volts. However, I do find that the original thing they were designed for (testing outlets or wires for power) is probably the worse thing they do, occasionally needing lots of waving and prodding. What brand/model do you have? I do know that the earlier models (more than 5 years old) were much worse at consistent testing. 

The argument that a NCVT shouldn't be used to confirm a panel is dead before reaching your hands inside is probably also a good one. I always use a meter to confirm a panel is off before grabbing anything potentially hot. But realize that even a DMM can fool you. I once used a voltmeter to confirm a power supply was dead, but as I was reaching my hand into the circuit I noticed that one of my meter leads had popped out and was laying on the test bench. I stopped in my tracks, plugged in the meter leads, then found the supply was indeed "hot". It's always good to double check before trusting ANY technology with your life. And I always scrape a knuckle on the wires that I've just confirmed were "dead". That way if it is live, your hand will jump away from the wire, not grab onto it and not being able to let go. Been there, done that...
Title: Re: AC Circuit Load Tester?
Post by: Tim McCulloch on December 22, 2013, 03:29:53 pm


On second thought...

(big edit)

Every tester is a little different.  Knowing when you're looking at an invalid test takes time & experience.  Not knowing you're looking at an invalid test is why I say "test, test again, and have someone else verify".
Title: Re: AC Circuit Load Tester?
Post by: Mike Sokol on December 22, 2013, 04:58:10 pm
Every tester is a little different.  Knowing when you're looking at an invalid test takes time & experience.  Not knowing you're looking at an invalid test is why I say "test, test again, and have someone else verify".

There are OLD electricians, and there are BOLD electricians, but few OLD & BOLD electricians. Something on the order of 1,100 people per year are electrocuted in the USA alone, most of them in the trades. One of the highest electrocution rates belongs to outside painters, who often get their aluminum ladders tangled with overhead power lines. Plant electricians take another big hit. Always remember you're working with deadly power whenever you're hooking up any sound or lighting gear.

Let's be careful out there...
Title: Re: AC Circuit Load Tester?
Post by: Lyle Williams on December 22, 2013, 09:12:44 pm
Fluke 2AC.

Australian power outlets don't have extra metal for ground - it's just another hole for a pin.

With this outlet geometry, I'm pretty sure I couldn't pick a RPBG with the tester.  Fortunately our electrical history has travelled a path that make this condition very rare here.
Title: Re: AC Circuit Load Tester?
Post by: Mike Sokol on December 22, 2013, 10:01:57 pm
Fluke 2AC.

Australian power outlets don't have extra metal for ground - it's just another hole for a pin.

With this outlet geometry, I'm pretty sure I couldn't pick a RPBG with the tester.  Fortunately our electrical history has traveled a path that make this condition very rare here.

Most interesting. So you're saying that there's no extra metal strap on your outlets? In the States there's generally a metal strap that extends across the entire NEMA 5-15 receptacle which provides mounting tabs on the ends. If that strap is electrified by a hot ground then any NCVT in the area will light up.

I've attached what I assume to be a picture our your outlets "down under" as well as the USA version. I believe that you're correct that it may be difficult to find a hot-ground in your outlet design since it doesn't have all the extra surface area of electrified metal. However, I think that most any NEMA 5-15 outlet in the states with a hot ground would make your Fluke 2AC beep and flash from an inch or more away.
Title: Re: AC Circuit Load Tester?
Post by: Lyle Williams on December 23, 2013, 03:02:18 am
Interestingly enough the Australian plug is actually a US plug that got borrowed in (I think) the 1920's but then faded into obscurity in the US.

The NCVT certainly lights up when it comes near a live Australian outlet.  Sometimes the ground pin side of the outlet produces a lesser response, but can sometimes produce a significant response especially when the wire in the wall leads downwards towards the floor.
Title: Re: AC Circuit Load Tester?
Post by: Steve M Smith on December 23, 2013, 06:45:28 am
The UK socket also has no grounded metal parts exposed - except for the fixing screws.

(http://www.sparksdirect.co.uk/image/cache/data/zencart/sections/922B-298x298.jpg)

However, we do also have metal versions nut they are not so common.

(http://www.rbstarelectrical.co.uk/images/magictoolbox_cache/361677da275a7e717d76196daca26e0e/1/2/12305/original/506fc1bac2f68e5048b02a75a18260bc.jpg)

For stage use, this is the sort of thing which would be put out for musicians to plug into.

(http://uk.farnell.com/productimages/farnell/standard/42262538.jpg)


Steve.
Title: Re: AC Circuit Load Tester?
Post by: Jason Lavoie on December 23, 2013, 11:37:13 pm
I haven't thought about this for a while, but it seems like it shouldn't be too heavy lifting to design a smart outlet strip with NCVT that automatically detects hot on ground and opens that connection path. In combination with GFCI the meat puppets could be protected and show could go on. Even if RPBG outlet is all the power that is available. It could flash an irritating red light (maybe even built into the plug) when ground is corrupted to annoy everyone and inform them that something is horribly wrong with that outlet. 


JR

PS: The smart outlet strip might even remap the hot and neutral but that adds more cost for perhaps only modest benefit (in combination with GFCI), The hot ground seems like the dominant danger so that could be opened with one power switching device.

I suspect that the NCVT works by using the user as a reference, which under normal circumstances should act like a ground of sorts.
I think if you were isolated and touching a hot chassis with one hand and used an NCVT with the other it wouldn't light up.

If I'm correct, then putting an NCVT into any device would require a known good ground for it to be useful, otherwise it isn't any better than a neon bulb.

I could be wrong..

Jason
Title: Re: AC Circuit Load Tester?
Post by: Mike Sokol on December 24, 2013, 02:37:58 am
I suspect that the NCVT works by using the user as a reference, which under normal circumstances should act like a ground of sorts.
I think if you were isolated and touching a hot chassis with one hand and used an NCVT with the other it wouldn't light up.

If I'm correct, then putting an NCVT into any device would require a known good ground for it to be useful, otherwise it isn't any better than a neon bulb.

I could be wrong..

Jason

Jason, you are correct on all counts. A NCVT capacitively couples through your body to the earth, listening for the 60 Hz (or 50 Hz) hum. If you're standing inside a vehicle with its chassis elevated to 120-volts above earth potential (what the RV crowd calls a "hot-skin"), then a NCVT will not beep if you get near any of the metal within your Faraday cage. However, you can reach outside and point it at the ground and it will beep.

The NCVT manufacturers also warn that if you're standing on a tall fiberglass ladder you might not couple to the earth sufficiently and get a false negative. Some goes for testing inside a 3-phase power panel since it's possible (but I think  unlikely) to find a null spot in the middle of the 3-phases that will give a false negative.

But building a NCVT into a tester is pretty simple as long as you intend it to test while someone has his hand on the side of the tester to provide the earth ground capacitive reference. I also have a short video of me with a Amprobe NCVT taped on the side of my Sprinter van with a little light-pull chain handing down to a few inches above the earth. Whenever the chassis/skin of the van is electrified with AC voltage, the NCVT will start alarming without anyone touching it. That's because the body of the tester is coupled to the side of the van, while the sensing tip to coupled to the earth via a paper clip and a little chain.

More to experiment along these lines later, but it sure is interesting.
Title: Re: AC Circuit Load Tester?
Post by: John Roberts {JR} on December 24, 2013, 10:35:50 am
I suspect that the NCVT works by using the user as a reference, which under normal circumstances should act like a ground of sorts.
I think if you were isolated and touching a hot chassis with one hand and used an NCVT with the other it wouldn't light up.

If I'm correct, then putting an NCVT into any device would require a known good ground for it to be useful, otherwise it isn't any better than a neon bulb.

I could be wrong..

Jason
While I haven't designed one yet, and probably won't, I did think it through.

Indeed all voltage is relative. My hypothetical "smart" outlet strip would presumably have some products plugged into it. With none of those products energized, their mains cords should all be pretty quiet. Using a high impedance voltage detector to measure for voltage between outlet ground and all the mains plugs (H+N+G) we should be able to identify a hot outlet ground lead. About the only scenario that would create a false OK is if one or more of the unpowered mains cords had a hot voltage present too.

This scenario is extremely unlikely, but possible, I guess.  For extra insurance I could poll between the multiple product mains cords plugged in separately. It seems even less likely that "all" mains leads would also have hot grounds too. So if significant voltage is detected between outlet ground and "any" one mains cord ground that outlet ground is disconnected, and the red LED starts flashing. If the outlet ground is hot and the product ground is ALREADY hot I didn't make the situation worse by connecting them, and the GFCI should still disconnect power if it detects leakage.

So I believe it could be done, but like many of my ideas, the world is not likely to beat a path to my door to buy one, well many just one to Jason to prove it works.  8)

JR
Title: Re: AC Circuit Load Tester?
Post by: Jonathan Johnson on December 25, 2013, 11:02:25 pm
Interestingly enough the Australian plug is actually a US plug that got borrowed in (I think) the 1920's but then faded into obscurity in the US.

The NCVT certainly lights up when it comes near a live Australian outlet.  Sometimes the ground pin side of the outlet produces a lesser response, but can sometimes produce a significant response especially when the wire in the wall leads downwards towards the floor.
(http://forums.prosoundweb.com/index.php?action=dlattach;topic=147401.0;attach=9748;image)

Yes, Lyle, I believe you are correct. For many years, 240V heaters on a 15A (or was it 20A?) circuit in the United States used this plug configuration.

The version now accepted for this application is a NEMA 6-20 (compatible with NEMA 6-15) and is shown below.
Title: Re: AC Circuit Load Tester?
Post by: Jonathan Johnson on December 25, 2013, 11:12:46 pm
...The key I missed was testers can't detect fault when both neutral AND ground are hot - they can detect -OR- just fine.

Even with my new toy (euphemism) I will continue to test with the non-contact tester as described in addition to the Extech. 

Trust no one, test, and think like an electrician.

The only way to truly test for a hot or floating ground (RPBG) is to meter between the grounding contact and the ground. That is, meter to a trusted reference ground, which could be the framing of a metal building, metal water pipes (that have a conductive path to the earth), or a ground rod driven into the earth.

Always test the tester. Before metering a circuit and declaring it dead, did you test the meter on a known live circuit? If not, you don't know that it's dead. (Sometimes I test the tester both before and after.)

When I'm identifying which circuit breaker controls a particular light, receptacle, or other point of use, I have a helper watch a test light. When I flip off a breaker and the helper says the light's out, that's not enough... I flip the breaker back on, verify that the light comes on, then off again. Don't want to fall into a trap of simultaneous failure.