I found these two videos on isolation transformers from “Uncle Doug” interesting.
Isolation Transformers
Isolation Transformers: Internal Design and Safe Use with Oscilloscopes
Good discussion on what they can and can’t do with respect to safety.
Isolation Transformers
Isolation Transformers: Internal Design and Safe Use with Oscilloscopes
Good discussion on what they can and can’t do with respect to safety.
Imho, isolation transformers as proposed and used in those video's should be banned, as a way to force any diyer or service section to implement better safety practices. That form of isolation transformer use has effectively elevated it to a position of #1 means to implement safe practices - which may have been somewhat practical 60 years ago when there was scant safety rigour applied across the board. To compound that, the video has (I think) no forceful directions about any mains side changes being done by competent people only, and so heads off to provide a cursory layman's description of protective earth operation - so sad.
Isolation transformers were important in the days of hot chassis radios and tv's. Things have changed a lot in the last 60 year's.
Still different countries have different practices. The best are pretty similar but some aspects of power distribution require some country specific solutions. GFCI's or their equivalent are pretty important as a safety tool.
Still different countries have different practices. The best are pretty similar but some aspects of power distribution require some country specific solutions. GFCI's or their equivalent are pretty important as a safety tool.
That incident happened in 1982, and it was an old 1940s era machine that had seen a lot of use before I ever worked there. The pedal itself operated a lift on the machine, was mounted on a wooden platform about two feet high (.6 meters) that the machine operator stood on. It had an "up" switch, and a "down" switch, and was connected to the main machine body through a four conductor umbilical. When I got shocked, I was holding on to the lift that was in the raised position, while I jumped off of the platform and simultaneously pushed the "down" switch to lower the lift...that's when the "lights went out" and I hit the floor. I had performed that exact same maneuver dozens of times before, but that was my lucky (not!) day. An isolation transformer in this case would have prevented my most unfortunate incident.
Mike
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Can you provide substance to your objections? What about these videos do you find objectionable? I'm not suggestion you're wrong or trying to argue, I'd just like to understand the reasoning.
Failure to isolate
Please forgive this off-topic ramble, but I can’t help reliving some nightmare experiences.
Circa 1969, I had a summer job as a construction electrician at the new high school in Connersville, IN. The morning’s assignment was to trouble-shoot non-functioning lighting circuits. My work buddy let out a yelp, said he’d been shocked, and complained that he’d burned out his brand-new pen-light (battery) continuity tester. At lunch break, he keeled over with a heart attack. Coincidence? Unconscious when EMTs arrived, he was back at work a few weeks later.
Circa ’66, another summer job sent me to a commercial granary in Seymour, IN to replace a failed solenoid coil in a motor starter contactor (i.e. a giant relay). My voltage tester confirmed volts across the coil, but no energize action, so I switched off the disconnect handle, confirmed no coil volts, and started to remove the failed coil. I got a very nasty buzz that left me shaking with realization of a very close encounter. Reinvestigation revealed that I’d disabled the control circuit but not the mains--- 440VAC, 3-phase. To this day, I shudder when I recall.
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Finally, my most bizarre experience:
My dad was a farmer, but with lots of electrician experience, and he was a wizard with relay-control logic. He did quite a bit of farm automation as a sideline, and toyed with becoming a full-time contractor. One of his projects was to automate/wire a grain dryer and associated grain handler setup on a farm in Evansville, IN. I was one of his helpers, about 14 or 15 years old---which took me to the top of a grain elevator, about 60 feet up, where I sat on a service platform installing and wiring limit switches to a grain distribution turret. A thunderstorm loomed, so I climbed down till it passed.
Immediately after the rain ended, I climbed back up to resume and I remember the service ladder and work platform were still wet with rain. I was ready to connect weather-tight flexible conduit to the limit switches, and the associated wires were hanging out beyond the conduit end, awaiting connection. When I reached for the end of the free-hanging flex and touched the wires, I got shocked. I yelled down to my dad that I’d been shocked but he assured me there was no power anywhere and double-checked anyway. So I tried again and again got shocked.
Then I noticed that the flex conduit and its wires were hanging off the edge of the platform out into midair and that tiny, hard-to-see, thready sparks (perhaps a quarter or half inch long) were leaping out into thin air. It was eerily scary and I scrambled down as fast as I could and didn’t return until skies were clear blue.
=============================================
Now I’m 72, having survived these and other less dramatic events. I’ve learned I create most of my own hazards, but many are unexpected. Stay alert, stay safe. May you live long.
Please forgive this off-topic ramble, but I can’t help reliving some nightmare experiences.
Circa 1969, I had a summer job as a construction electrician at the new high school in Connersville, IN. The morning’s assignment was to trouble-shoot non-functioning lighting circuits. My work buddy let out a yelp, said he’d been shocked, and complained that he’d burned out his brand-new pen-light (battery) continuity tester. At lunch break, he keeled over with a heart attack. Coincidence? Unconscious when EMTs arrived, he was back at work a few weeks later.
Circa ’66, another summer job sent me to a commercial granary in Seymour, IN to replace a failed solenoid coil in a motor starter contactor (i.e. a giant relay). My voltage tester confirmed volts across the coil, but no energize action, so I switched off the disconnect handle, confirmed no coil volts, and started to remove the failed coil. I got a very nasty buzz that left me shaking with realization of a very close encounter. Reinvestigation revealed that I’d disabled the control circuit but not the mains--- 440VAC, 3-phase. To this day, I shudder when I recall.
=============================================
Finally, my most bizarre experience:
My dad was a farmer, but with lots of electrician experience, and he was a wizard with relay-control logic. He did quite a bit of farm automation as a sideline, and toyed with becoming a full-time contractor. One of his projects was to automate/wire a grain dryer and associated grain handler setup on a farm in Evansville, IN. I was one of his helpers, about 14 or 15 years old---which took me to the top of a grain elevator, about 60 feet up, where I sat on a service platform installing and wiring limit switches to a grain distribution turret. A thunderstorm loomed, so I climbed down till it passed.
Immediately after the rain ended, I climbed back up to resume and I remember the service ladder and work platform were still wet with rain. I was ready to connect weather-tight flexible conduit to the limit switches, and the associated wires were hanging out beyond the conduit end, awaiting connection. When I reached for the end of the free-hanging flex and touched the wires, I got shocked. I yelled down to my dad that I’d been shocked but he assured me there was no power anywhere and double-checked anyway. So I tried again and again got shocked.
Then I noticed that the flex conduit and its wires were hanging off the edge of the platform out into midair and that tiny, hard-to-see, thready sparks (perhaps a quarter or half inch long) were leaping out into thin air. It was eerily scary and I scrambled down as fast as I could and didn’t return until skies were clear blue.
=============================================
Now I’m 72, having survived these and other less dramatic events. I’ve learned I create most of my own hazards, but many are unexpected. Stay alert, stay safe. May you live long.
Nowadays, to sell electrical equipment requires it to meet a variety of standards and pass tests/inspections from specific country based regulatory bodies. Even the act of modifying electrical equipment and then plugging it in to the electric utility, or modifying electrical wiring/circuits/services in a building or domestic premises, requires certain tests/inspections to be passed/approved in many countries.
At the core of many electricity distributions is the TNS earthing distribution scheme, where a protective earth arrangement is extended and controlled such that all mains powered electrical equipment has to incorporate that protective earth in defined ways (except for the double insulated class of equipment).
Decades of advancing that protective earth safety scheme, through changing and tweaking country standards, and regulations, and education and processes for electricians, and the more recent requirement in some countries for periodic PAT testing (certainly for any business) and GFCI or imbalance fault protective devices keeps raising the bar for how electrical equipment is maintained in a safe operating condition, with the least likelihood of someone being electrocuted.
So it is sad to see someone showing an audience of incompetent viewers how to alter electrical equipment, to bypass the protective earth arrangement. I use the word 'incompetent' as the alternative to 'competent', where often regulations require that a 'competent' person has to perform certain electrical test processes (such as PAT testing). For example, an electrician is a competent person to make alterations to electrical circuits as they have achieved a level of education and experience covering the relevant standards and regulations for a particular country or region or utility.
At the core of many electricity distributions is the TNS earthing distribution scheme, where a protective earth arrangement is extended and controlled such that all mains powered electrical equipment has to incorporate that protective earth in defined ways (except for the double insulated class of equipment).
Decades of advancing that protective earth safety scheme, through changing and tweaking country standards, and regulations, and education and processes for electricians, and the more recent requirement in some countries for periodic PAT testing (certainly for any business) and GFCI or imbalance fault protective devices keeps raising the bar for how electrical equipment is maintained in a safe operating condition, with the least likelihood of someone being electrocuted.
So it is sad to see someone showing an audience of incompetent viewers how to alter electrical equipment, to bypass the protective earth arrangement. I use the word 'incompetent' as the alternative to 'competent', where often regulations require that a 'competent' person has to perform certain electrical test processes (such as PAT testing). For example, an electrician is a competent person to make alterations to electrical circuits as they have achieved a level of education and experience covering the relevant standards and regulations for a particular country or region or utility.
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The standards you are referring to are for equipment being operated in it's intended fashion. If you are in the process of constructing or repairing a device, it's not operating in its intended fashion. I.e - A device with it's cover removed and main's connections exposed.
From my understanding, the isolation transformer as described in the videos provides a layer of protection to the technician while actively working on the device.
That's how I see it.
And to suggest that the audience is entirely "incompetent viewers" is unfounded.
From my understanding, the isolation transformer as described in the videos provides a layer of protection to the technician while actively working on the device.
That's how I see it.
And to suggest that the audience is entirely "incompetent viewers" is unfounded.
Unfortunately in the US there is no legal requirement generally that your product has met safety standards. Some locales do have the requirement but that just means you order online. . . Part of our liberty seems to be the liberty to buy stuff that can kill the consumer. However the product liability legal consequences generally keeps companies honest. However smaller players and companies who practice "ask forgiveness not permission" business models do push the envelope. And safety testing can be quite expensive for some products. For UL testing of a surge protector its around $50K + 25 units to be destroyed in testing. For an audiophile grade product with a BOM in the $100's that adds up fast. Amps are less expensive but still far from free. And that is assuming you designed it to meet the standards.
Many other countries do impose safety requirements before products can be sold which is ultimately more rational.
Many other countries do impose safety requirements before products can be sold which is ultimately more rational.
Please read my post again as to the use of the word 'incompetent' - it has a defined meaning, certainly in my country, for those people who are allowed to do certain approved electrical related tasks.
1audio, yes that is the sad aspect of some Youtube and other internet related posts - they allow anyone from anywhere to assume that what is shown is 'standard', especially if they offer up no warnings about how or where the advise may not be typically allowed.
I do appreciate that there are many different country and region and even utility based regulations and standards, as well as protective earthing schemes and historical wiring and equipment practices, so have tried to make that part of my posting discussion.
I do appreciate that there are many different country and region and even utility based regulations and standards, as well as protective earthing schemes and historical wiring and equipment practices, so have tried to make that part of my posting discussion.
You're using loaded language. It's like me calling someone an "idiot" and then saying I define idiot as a person who wears yellow. And I then act surprised when someone takes offense to me calling them an "idiot".
"Not competent" is the legal terminology used here in Oz for someone who is unqualified.
It doesn't mean someone is incapable or stupid in that sense of the word 'incompetent' - just that they are not legally qualified to perform whatever it is that they are doing.
For example I cannot legally change a mains connected light switch or wall outlet because I am not a qualified electrician. I'm (in the eyes of the system here) not competent.
It doesn't mean someone is incapable or stupid in that sense of the word 'incompetent' - just that they are not legally qualified to perform whatever it is that they are doing.
For example I cannot legally change a mains connected light switch or wall outlet because I am not a qualified electrician. I'm (in the eyes of the system here) not competent.
Yes 'not competent' was what I was after. Incompetent has a more general dictionary meaning of "not having or showing the necessary skills to do something successfully".
One aspect of using an isolation transformer for amp testing is that it may not alert the tester to an unexpected active to chassis connection. Another aspect may be that the tester is less inclined to make themselves well aware of the mains wiring and exposed touchable circuits, and not make the effort to put in place means like shrouds/barriers, or to do initial conductivity or insulation resistance tests, to mitigate that risk. Perhaps what is more needed is a better listing and awareness of the risks of having to use an isolation transformer and a list of ways to mitigate those risks, and a listing of alternative ways to servicing that may not require an isolation transformer.
One aspect of using an isolation transformer for amp testing is that it may not alert the tester to an unexpected active to chassis connection. Another aspect may be that the tester is less inclined to make themselves well aware of the mains wiring and exposed touchable circuits, and not make the effort to put in place means like shrouds/barriers, or to do initial conductivity or insulation resistance tests, to mitigate that risk. Perhaps what is more needed is a better listing and awareness of the risks of having to use an isolation transformer and a list of ways to mitigate those risks, and a listing of alternative ways to servicing that may not require an isolation transformer.
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Cultural differences. It reads different here in the US. I apologize for misinterpreting.
I don't prescribe to the paternalist argument. It's like saying that motorcycle helmet or airbag laws are damaging because they increase driver carelessness because of the safety factor afforded (studies have confirmed this - or so I'm told from social psychology classes in grad school). But I'm OK if we choose to disagree on this argument.
What I hope to get out of forum discussions like this is a better appreciation myself of the ways others manage their particular situations, which can often help me modify my own practices or at least better review my own practices and change them for the better. As the decades roll on, I become more aware of risks, and it is easier time-wise and financially to put in place means to mitigate some of the risks.
Yes, in some ways DIY is similar to very public activities like driving a car, where there are a myriad different paths taken by manufacturers, countries etc relating to safety and reducing deaths or damages. Different countries have taken quite different tacks on many issues such as electrical safety, so the benefits or otherwise start getting very political and ingrained in to other issues as 1audio raises in post #29 for the US.
This sub-forum is general, so my view is often blinkered to amplifier related equipment that has very simple AC mains connected internal circuitry, rather than more open-minded to some who may want to work on mains side regulation or control circuitry where there are fewer safety choices when fault finding or developing/testing circuitry and perhaps go the easier or more cost-effective route, or their only known route of using an isolation transformer.
Yes, in some ways DIY is similar to very public activities like driving a car, where there are a myriad different paths taken by manufacturers, countries etc relating to safety and reducing deaths or damages. Different countries have taken quite different tacks on many issues such as electrical safety, so the benefits or otherwise start getting very political and ingrained in to other issues as 1audio raises in post #29 for the US.
This sub-forum is general, so my view is often blinkered to amplifier related equipment that has very simple AC mains connected internal circuitry, rather than more open-minded to some who may want to work on mains side regulation or control circuitry where there are fewer safety choices when fault finding or developing/testing circuitry and perhaps go the easier or more cost-effective route, or their only known route of using an isolation transformer.
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Right, the only thing who save lives is "turn the **** off" nothing else.
regards,
Pierre