plug earth/ground checker by John Roberts

[kambo]

i cant find the design. it was for checking earth/ground fake/real wiring at AC sockets!

 

[JohnRoberts]

i cant find the design. it was for checking earth/ground fake/real wiring at AC sockets!

http://www.johnhroberts.com/OD1.htm  here is a link to the full story.

I abandoned the project some time ago after I failed to get a commercial partner. I was unwilling to spend tens of thousands of my own money to get UL approval and develop a product that would only sell for a few $ and scare typical consumers to even use. They are literally connected to mains voltage with >>100M insulation resistance but they could be easily scared off by misunderstanding how it operates.

It was an interesting learning experience to develop the product (not trivial, and operation is not obvious about how it works) .  I suspect the technology has other applications for human safety, but I am too old and tired to pursue it on my own dime.

JR

PS: You can do some outlet troubleshooting with a NCVT (non contact voltage tester) and an old school neon lamp probe

You can hold one lead of the typical neon lamp probe in one hand and probe with the other lead... the typical neon lamp probe has an internal resistor that will limit current to low mA.  Before you use it you can confirm it has the current limit by plugging it into 120VAC. If it doesn't catch fire, it has the internal current limiting.

 

[kambo]

thank you sir!

 

[john12ax7]

Do all the current commercial ones not work correctly? Was that the motivation for the project?

I read through the link explaining the issues, but I do remember using a commercial one to identify some reverse voltage situations.

 

[emrr]

John gives all details, commercially available units do not detect certain faults, and declare them safe. 

 

[JohnRoberts]

Do all the current commercial ones not work correctly? Was that the motivation for the project?

I read through the link explaining the issues, but I do remember using a commercial one to identify some reverse voltage situations.

Here is a picture of mine, and the standard commercial unit both plugged into the same intentionally miswired outlet, with  120VAC on the safety ground. 

The standard unit on the right says all OK,  : my tester says "danger" with red and yellow LEDs indicating  that both ground and neutral are energized. This condition is called RPBG (reverse polarity bootleg ground) and it does happen...  A musician's family sued Peavey once because his Peavey guitar amp was plugged into a miswired RPBG outlet and it killed him... UL sat at our table in court and explained that the Peavey amp was completely safe but the outlet/house wiring was wrong.... (they condemned the house until the wiring was fixed).

http://www.johnhroberts.com/OD1.htm  this link explains more than you want to know about RPBG.

FWIW the UL standard covering those outlet testers makes them add a small print warning that their approved outlet tester can not detect multiple faults.  They consider RPBG one of those multiple faults excused conditions.... I promise you nobody knows that the commercial units don't protect you against RPBG. If you see one in a store, look at the small print on the back of the hang tag, it will state the UL required multiple fault caveat...

I lost a certain amount of respect for UL while this does not kill as many people as texting while driving.  :

I was looking forward to arguing with UL that I would not add that warning to mine, because mine does detect multiple faults, but i wasn't going to spend a couple $10k just to get that one mic drop moment. I'd probably have to pay extra to get an exemption.

JR

 

[Tubetec]

Thats really interesting and not something realised could happen while using the usual 3 led testers .
Tragic situation where the family of the deceased were lead up the garden path on a wild goose chase after peavey, when it was the venue owners at fault .
Ive certainly found bad earth wiring in venues on a few ocassions and pulled the plug until a properly wired outlet could be found. Often the owners have a very cavalier attitude about it .
I remember one time a band came into the studio for a session ,there own amp was in for repair ,and the service guy had lent them a vintage Marshall 100 ,it wasnt sounding right at all ,so I took a look , one EL34 was fractured ,and the heater had burnt out ,not only that but the bulgin three pin mains connector on the amp had no ground pin at all , I explained to the lads that this was a potentially lethal situation and that when they bring the amp back they should point it out to the tech .
In the mean time I sent the lads off for a pint ,fitted a new ground pin to the socket ,and put proper tubes in the amp.
Even though it was only pre production demo's they were doing  ,they were so impressed with the guitar sound I got them the takes we did actually made it onto the album in the end .

 

[JohnRoberts]

Thats really interesting and not something realised could happen while using the usual 3 led testers .
Tragic situation where the family of the deceased were lead up the garden path on a wild goose chase after peavey, when it was the venue owners at fault .

It was a house, probably rented, and just two musicians jamming. The electrocution occurred when they tried to trade guitars. One amp was plugged into the hot RPBG outlet, and the other a properly grounded outlet (on the stove), so there was 120VAC between the two guitar's strings. Holding one in each hand created a current path through his core that stopped his heart.

It is the nature of lawyers to go after deep pockets. Like I mentioned Hartley keeps a full time lawyer busy with nuisance work.

Ive certainly found bad earth wiring in venues on a few ocassions and pulled the plug until a properly wired outlet could be found. Often the owners have a very cavalier attitude about it .
I remember one time a band came into the studio for a session ,there own amp was in for repair ,and the service guy had lent them a vintage Marshall 100 ,it wasnt sounding right at all ,so I took a look , one EL34 was fractured ,and the heater had burnt out ,not only that but the bulgin three pin mains connector on the amp had no ground pin at all , I explained to the lads that this was a potentially lethal situation and that when they bring the amp back they should point it out to the tech .
In the mean time I sent the lads off for a pint ,fitted a new ground pin to the socket ,and put proper tubes in the amp.
Even though it was only pre production demo's they were doing  ,they were so impressed with the guitar sound I got them the takes we did actually made it onto the album in the end .

Older guitar amps were designed with two wire line cords but this was before two-wire consumer products were double insulated. Even worse some old guitar amps have a "stinger" cap, shunting the chassis to neutral (0V mains return).  Since old wiring was not very consistent about polarity, and 2 wire plugs were not indexed, these old amps had a switch to alternate which lead the stinger cap was connected to (for lowest audible hum).  The wrong position can give you a tingle standing barefoot on a conductive floor, or a lot worse if the cap breaks down and conducts full mains energy. 

JR

 

[Tubetec]

Yeah Ive seen the stinger cap arrangment on a few vintage Fenders alright . Usually here if its connected to the neutral ,the amp works ,flick it onto live and the elcb cuts the power instantly . I usually disconnect it, as I cant see any valid reason for having it with a three wire mains set up.

 

[john12ax7]

Not being able to test multiple faults seems like a rather serious design flaw in the commercial units. The whole point of the device is to identify faults. If you are going to have a UL they really need to do a better job.

 

[PRR]

> a rather serious design flaw

You can detect over half of faults for $7 retail.

The other faults are NOT easy to test. The cost is uncertain since JR hasn't (won't) get to that point due to high cost of testing unusual electrics (using the user as a ground reference). While the BoM may be $7, getting it out to market in bubble-pack and enough vigorish to push it at customers (who don't know why they need it) could be $50 and profit fizzle.

I have in my hand a dandy set of bent chopsticks for poking pushing pulling and twisting wires in a junction box. I think they would be fair value for $5. link Sadly, the price is $25. Home Depot has them, but not in stores, and I suspect in a few months H-D will give up and ship 987 un-sold units back un-paid.

 

[kambo]

yes u can tune ur drums for cheap too....
using John's tuner is different league... i can tune my drums for absolute pitch to rich in harmonics!
i guess John prefers to make unusually accurate designs (in a good way  )

 

[kambo]

You can detect over half of faults for $7 retail.

can you detect life threatening faults with it ?

 

[Andy Peters]

Yeah Ive seen the stinger cap arrangment on a few vintage Fenders alright . Usually here if its connected to the neutral ,the amp works ,flick it onto live and the elcb cuts the power instantly . I usually disconnect it, as I cant see any valid reason for having it with a three wire mains set up.

I own a few vintage Fender Electric Instrument amps. With one exception, I've modified them to eliminate the stinger cap and ground switch and added a proper three-wire mains cord. There is no reason to have unsafe equipment around. 

 

[JohnRoberts]

can you detect life threatening faults with it ?

I would be more enthusiastic about making these myself, if it was a serious problem killing thousands of people but no... It is fairly rare, and involves both a mistake, and a wrong-headed (not legal) wiring practice. Somebody somewhere  thought bootleg outlet grounds was a good idea, it isn't. Combine the not code bootleg with reversed line and neutral and you have some real trouble. 

If playing in venues that have flaky wiring, carry a NCVT (non contact voltage tester) to easily identify any products with energized chassis. An extra degree of personal safety can come from carrying your own personal GFCI power drop (that would disconnect power if leakage current detected).

PRR is right, if I made these myself I would have to charge more like $100 to have any hope of breaking even in my lifetime and sales would be pretty puny, which is why I tried to get a commercial partner who had distribution and other resources to get these out at more like $15-20. (The plugs I mount mine inside cost almost that much)

I put the design out there so it is free for anybody to use, but I am not holding my breath,

JR

PS: Yes drummers don't seem to value my technology very highly either ( I am not a natural salesman, I expect the results to speak for themselves). Thank you Kambo for the kind words about RESOTUNE. It should be apparent that I am willing to think outside the box about problem solving.

 

[Matador]

That is brilliant! Thanks for sharing!

 

[Newmarket]

If playing in venues that have flaky wiring, carry a NCVT (non contact voltage tester) to easily identify any products with energized chassis. An extra degree of personal safety can come from carrying your own personal GFCI power drop (that would disconnect power if leakage current detected).

What is GFCI ?

Ground Fault Current Indicator ???

 

[JohnRoberts]

What is GFCI ?

Ground Fault Current Indicator ???

Sorry about the jargon, "ground fault circuit interrupter". These are the outlets that sense whenever current leaving their hot lead does not completely return to their neutral lead. If as much as 5mA of mains current leaks elsewhere and does not return they trip and disconnect power. These can protect humans from deadly shocks even without a safety ground connection.

In other parts of the world these are known as RCD  (residual current device) and in some areas used in the mains distribution panel to protect an entire branch circuit.

JR

 

[JohnRoberts]

My outlet tester project http://www.johnhroberts.com/OD1.htmis still collecting cobwebs because I am unwilling to pay the toll to go down UL approval road, but PRR recently brought this competing product to my attention (thanks PRR). 

https://www.lessemf.com/ground.html#452 

While the website looks like their target market is the tinfoil hat crowd they appear to have come up with a different alternate solution to detect energized safety grounds. The outlet tester looks like the typical 3 lamp tester (probably with the same blindness to reverse polarity bootleg ground), but they added an additional test step.  A touch probe that triggers a LCD display if the ground is energized. 

If the safety ground is energized to 120V it is pretty easy to imagine being able to switch on a LCD display with the voltage potential difference between that and a human body touching a screw head touch contact. I like the idea (of course), but I am unclear about the safety....  I was able to deliver >500M of insulation between my touch contact and conductors at 500V which was my interpretation of UL's safety expectation (>100Mohm).

They have boldly branded their tester with a big CE on the faceplate, from a US company selling a product that only plugs into US outlets.  : :  The correct safety agency mark would be UL or CUL.

I sent them an email with no response, and haven't bought one to take apart (yet).  I probably should.

I might recommend this if it appears safe while I have already returned the Fluke  insulation tester I borrowed.. I do worry about testing a LCD display with 500V. 

Interesting...  In hindsight they could do the same thing a bunch cheaper with a neon lamp, but not with more than 100M insulation resistance.  8)

JR 

PS: FWIW  a couple mA to light a neon lamp is not a human safety concern (IMO), but unlikely to get UL's blessing.

[edit] I have found a small screwdriver probe with neon lamp inside that works under the same principle(using human body for other contact) and claims to be UL listed.... and it's <$5
http://www.morrisproducts.com/pc_product_detail.asp?key=1962950B5A4A4EB28E1DABB310CA4228

  [/edit]

PPS: I wonder if a neon lamp with 100M of series resistance was coupled to the gate of a sensitive optical triac or mosfet??  BUT I already solved this design problem once.  8)

 

[boji]

Can't ignore the irony of UL making it cost prohibitive to approve devices that fix known safety issues.