I have a variac called a S encore powernite which is a variac and it’s also an isolated supply So there are some good variac that are isolated

Mist are just autotransformers.

or, isolate the scope's power cord ground and then be REALLY careful...lol (Classic Bad Move) Dual trace scope with invert option for one channel (using no probe ground at all) is another way to risk riding the lightning.

Damn... Glad you are okay... That could have been the final moments of your life...

Do a leakage check.

The isolation transformer is to protect service personnel from accidental contact with a live wire and ground. It's a safety device for when you're working on equipment and isolates the equipment from the mains.

There are electrical currents moving through the ground. Drive 2 ground rods seoerated by say 30 feet and throw a meter between them. You will read the potential difference between them. This is why you see spread out through the community cathodic anodes driven into the ground. They typically put about -48 vdc at many amps directly into this electrode driven into the ground at the base of a pole . This neutralizes ground currents that would otherwise attack underground metal pipes such as gas or water mains causing erosion. We have submarine high voltage lines in my community that feed the island and before the cathode installation it was causing failure of water mains. Anyway back to the 2 ground rods you will see only perhaps 1 volt difference but if you short them together you can pull several amps of current. This is why ground bonds need to be connected together. An isolated ground can have a difference in potential.

I'd say it's more a handy/useful selected reference level, and other voltages can be both above and below it. Often it's related to something physical like the/Earth, or a car chassis, but it also might just the most common voltage level in your circuit (ie a useful reference level) Today cars typically have the negative pole tied to the chassis/engine block/etc, and equipment are supplied nominal +12V. But for instance older British cars often had the positive terminal tied to the chassis/engine block/etc, and equipment was supplied with nominal -12V. For equipment without a grounded chassis, or an output that is grounded (the early lower output power radios with 3 wires for 2 speakers, left/right/ground) it doesn't really matter, they operate on the difference between the lower and higher voltage supply wires - those wires could be anywhere with respect to 'ground', like say +40 and +52, or -12 and -24, as long as an actual connection to ground is made or needed, the unit would happily run on the 12V difference. More high power output stereos have 2 wires for each speaker channel, so that a symmetrical (+ on one wire and - on the other, to provide twice the possible voltage swing (and 4 times the possible power, instead of having one side of the speaker tied to 0V/ground.

Mike Ochs, do you mean a negative ground in a car battery? Ground in that case is not "Earth" ground, but "Chassis" ground which is a large conductive chassis that carries the current from the negative side of the battery to the load. If the positive side of the battery is connected to the chassis, then it would be a positive ground. The word "ground" is just a misnomer and is not to be confused with earth ground.

@@zulumax1 in the telephone industry the positive terminal of the battery is ground and is earthed at the central office and it the tip side if the loop. The negative terminal is what is connects to the ring side of the loop.

@@zulumax1 No, I mean like I remembering seeing circuit schematics where ground was specified as a negative number. I always equated ground with zero volts (so no electrical activity at all) so I never understood how ground could be anything less than zero.

Because there is no "hot" on the secondary as it is isolated from earth. You will get bit I'd you touch both secondary wires.

Well that is what standards are. You can't just dictate that all plugs and sockets be changed. Could you imagine the chaos this would cause if everyone had to change all the sockets and plugs on everything. If something like that was mandated everyone affected would expect all the work to do this be fully paid by the government. So it's not going to happen. There isn't even a requirement to put in polarized outlets on old homes or upgrade them to 3 prong grounded.

I have one if their single tube projectors. It used a liquid cooled indextron tube. No aprature grill, single electron gun like a b/w tube.

​@@12voltvids Yea, very nice. I watched your old 8/9/2016 video; that index technology is classic Sony innovation and yours is much newer and more complex. I checked my ~34" 3:4 screen, the box says VPS-400 with PNs 4-316-806 and 3-701-355 lol, ~Dec 1975 As I recall, the Sony "prototype" contained a simple TV chassis (requiring an isolation transformer) in a large wood cabinet, maybe KV-1212, no cooling with a single glass lens. I don't recall if it even used a mirror. About the same time the first Beta deck (in a console w/monitor) appeared. BTW, I still use that old Sony isolation transformer PN 442-523-11 5FYI Thanks Dave, your videos bring back so many memories... and repair nightmares too. Do you remember the KV-1920 repairs requiring an external 19V and 130v power source hooked up to hunt down actual cause without blowing the SG-613 gate controlled switch (again)? A conventional tiny 130v regulator transistor would just blow like a fuse if the set did not properly start up within a millisecond. lol

@@FindLiberty SG613 oh God i am having flashbacks now. There were many days when i asked myself why i ever went down the road . Electronic repair was never my first choice. i originally planned to go into television broadcasting.

You are still only using a single phase for apliance or equipment. Isolation transformer will still isolate you. We have 3 phase here too. 208 / 120. Yours 400 / 230 . 3 phase uses 4 wires. 3 hot 1 neutral.

@@12voltvids is the problem that the main transformer neutral is connected to ground? if thats so, what's the reason trafo neutral is grounded? isn't that the only difference between iso-trafo and main trafo?

Medical grade isolation transformers bond the neutral to ground at the plug for the secondary. This is done to reduce noise on the line not to isolate the secondary from ground reference. "Isolation" in that case means "noise isolation" not ground isolation. Furthermore in order to meet electrical code the secondary MUST have a ground wire which is connected to chassis and outputs on the outlet of the transformer secondary. These are not designed as tech isolation transformers. They are not designed for that purpose so no need to hold them to a standard to which they were never designed. If you wish to use a medical grade isolation transformer for ground isolation then they need to be modified.

Neutral is bonded to earth at home and at pole. It carries the entire load back to the transformer. Of course if both sides of the line are pulling equal power there current on neutral will be zero. However say you are pulling 15 amps on one leg and 10 amps on the other leg, there will be 5 running down the neutral at 0 (or close to it) volts.

Just to clarify my comment. I am NOT implying that GFCI is a replacement for an isolation transformer. I simply noticed that Dave's outlet at his workbench area is not GFGI protected. I always plug DUT into an isolation transformer. But transformer is plugged into an outlet that is on a GFCI breaker. And all my instruments, tools, music equipment - anything I touch is on that GFCI circuit breaker.

Bc best place in the country to live. Expensive yes but look at what we have. Have a friend in Ontario and the doctor and niece shortage is even worse so I guess we have it pretty good.

You weren't watching. I removed the ground from the chassis as well. You do not want any reference to ground. Primary is connected to hot and neutral and secondary is connected to output receotical. No connection to ground. My isolation transformer has a 2 prong cord and 2 prong outlet. As there is no bonding to ground you can't get shocked by accidental contact between a live source and earth ground. You will get a shock if you get connected between the secondary winding but not secondary and earth.

Nothing is grounded on isolation transformer. 2 wires in, hot and neutral and 2 wires out. Since the secondary is floating there is no neutral and no hot. Either one can be hot or neutral. That's what protects you and test gear. You make contact with anything while standing on a wet floor with bare feet and nothing happens as the potential is isolated from ground. Now grab onto both secondary wires and yes you will get a shock but not from accudantal contact with earth ground and anything live on the chassis.

⁠@@12voltvids thanks for the reply! What about if there was a short on the primary side inside the IT, wouldn’t you want to ground the IT chassis to earth’s ground (and still have no ground on the secondary side)?

@@jimkluka39 when is the last time you saw a transformer short to the core? Like never. If a winding shorts there will be smoke and the winding will pop.

Well that is how they work. Perhaps tomorrow I will do a demo of a GFCI in a fault condition.

Yes. Neutral is grounded. Isolation transformer isolates device from both live and neutral.

so in the US and Europe neutral is always grounded? Despite having different connection methodology and ofcourse voltages.@@12voltvids

I completely agree that grounding equipment is the best practice for safety. Here's my take on isolation transformers for lab use, excluding situations with vintage two-prong equipment. The ideal isolation transformer for this scenario would maintain the ground connection. Its primary function would be to act as a current limiter. If excessive current is drawn, it would automatically trip a circuit breaker or blow a fuse. This allows you to protect sensitive equipment, like a valve amplifier, from drawing too much current (e.g., exceeding 10 amps). In such cases, the isolation transformer's fuse would blow before the amplifier suffers damage.

The whole point of using an isolation transformer is to eliminate that touch potential. Even if the live side did touch the chassis it is not connected to line. It is connected to the floating winding. Therefore eliminating a path through you or your test equipment. If your device is floating you can't be shocked. You can still be shocked if you touch 2 points in the device that have a potential across them but not from any potential to ground because the unit is not grounded. It's essential as a service tool to protect you and any devices such as scopes that may be grounded. I recommend removing the ground on a scope (by plugging into iso tranny) when testing as well as the grounded chassis on the scope will restore the path to ground and negate the safety an isolation transformer provides. Suggesting replacing old equipment with modern? What would be the point of restoring vintage equipment then. Also much if this you can't buy. They no longer manufacture much if this. Try buying a new VCR for example. You can't. So your only option is to repair the old stuff and that requires an isolation transformer for your protection. There is also a reason that most gear does not have a 3 prong grounded plug. Ground loops. You know that low level ac hum caused when equipment is connected to a ground that is different than the outlet the device is connected. Think cable TV ground connection which is distant from the house ground as it's grounded at the pole. We used to have to make isolators for that problem for years.

@@12voltvids While I certainly wouldn't claim to be the expert here (you clearly are!), I remain unconvinced that isolation transformers are always beneficial. Here's my perspective: Risk of Blowing Up an Oscilloscope: Knowledge and experience are crucial in preventing harm. With proper care, you can avoid creating a short circuit with the voltmeter's black lead. Checking voltage differences between ground or the voltmeter and the device's ground point can be done safely. Differential probes offer another safe option for grounded scopes, making them as safe as multimeters for this task. Essentially, there are two ways to prevent damaging the scope: through caution and proper equipment. Isolation Transformer and Ground Loops: You're right; using a grounded scope with an isolation transformer can defeat its purpose by creating an unintentional ground path for the device. Scopes are just one example of this potential hazard. Musician Analogy: The example of musicians with ungrounded vintage amps is a good illustration. Touching a grounded microphone while the amp chassis is hot can lead to a shock. Isolation Transformer Safety Concerns: An isolation transformer can indeed create a false sense of security for someone unaware of grounding risks. Such a person might believe they are safe from shock but could be exposed if they touch a grounded device unexpectedly. My Approach: While I lack extensive experience in repairing electrical devices, I believe the safest approach for vintage equipment is to ensure proper grounding before use. Modern equipment is already grounded, and there are ways to minimize hum and noise without resorting to lifting the ground.

Once again If your device is isolated on an isolation transformer it doesn't matter if a short to the chassis occurs. It is isolated from ground. Think bird on a wire. No path to ground means no possibility of electrical shock. You can touch either side of the line cord while grounded and you will not get a shock. If you were to measure either side with your high impedence meter between earth and the secondary you would indeed measure voltage due to the meter being high impedence but no current would flow because any form of conductor (your body) for exqmple would pull that floating voltage to ground. It's really not a hard concept to follow. You want to use isolation before connecting test equipment because even if you are careful when happens if your scope probe falls off and drops on the line or b+ rail. Instant sparks. Same situation chassis on isolation tranny and your scope ground drops and lands on line or b+ and nothing happens. No sparks no equipment damage no blown fuse. That rail becomes grounded and the potential shifts to the other side of the line. ( Which would create a shock Hazzard at this point and that is why it is also important to have a non grounded scope unless it is necessary for specific measurements. I've been in this game a long time and i have had my share of jokts over the years always when no isolation transformer was available. Got the shock of my live on a tube tv in a customer's house. Had the back off and a cheater cord. Asshole customer made me take off my insulated boots. Some how i made contact with line on chassis. (hot chassis very common) and my foot was touching the heat register. I was lit up good. The jolt made me jump and that broke connection. Had a had an isolation transformer with me that would not have happened. It was that job that I told my boss I would not go on any more service calls unless he bought me a transformer. That transformer incidentally is the one i use on my bench. I stole it from the shop when we stopped doing in home service. Argue all you want, they are the most important safety device you can have on your bench. Any argument is pointless. Every professional service person knows this and we will not work on anything is it's not isolated especially switch mode power supply.

@@12voltvids Thanks for your valuable input. You do agree however that you hot isolated equipment will jolt you the very moment you get into contact with any other piece of equipment that has a proper short to ground? Like the musician illustration where the guitarist touches his lips to the microphone. The isolation is not perfect. You get to be of the same potential of the chassis might not realize you are now 120 volts and ready to discharge if you touch a different piece of equipment. You would agree with this? I am sure you do. This is because in the scenario that you constructed before with you touching a hot point and then touching ground and nothing happening, the catch is that you are not yet closing the circuit, so the ground acts as a conductor but it has no path back to circle to. But on my scenario of touching a grounded piece of equipment a circuit with ground does exist and is complete. That is the hole point of grounding equipment after all. In short, you become a new AC power source and the equipment is a circuit you are supplying AC to. This is a very real risk. this world scenario i am depicting is also ever present, things are grounded all over the place. And in grounded systems current that touches a grounded point flows through. You could acknowledge that this much happens to be a real risk. So try to repeat the video where you have a second metal lamp that is grounded and has a metal case. Turn that light on, now that light represents a grounded closed circuit. Touch the metal casing once your isolation transformer was supposedly making you safe. That will not end well. Your isolation transformer has just officially become grounded and there is a catch now. If the equipment had been grounded in the very first place the equipment would have an ultra low resistance back to the power grid, effectively a short to the mains and you would represent a high impedance parallel leg. But with your isolation transformer you are really in a spot because you now are a parallel leg of the circuit but the only single path that happens to exist to ground . So entire 120 volts will drop through you. in short equipment that is not grounded is terribly dangerous. it might be the safest thing you can do if the equipment has a two prong power cably to have it floating but you must be well aware that the protection from discharging to ground is not a certainty, the environment around you could destroy that illusion. so people need to understand that as well and not just hear it is going to be on there is no catch here. that is the problem for me of the video it almost advertises that normal grounding of a circuit is just bad , but it is best practice. you float your circuit and will be well. you are safe. No you are at 120 volt potential and all it takes is closing a circuit any circuit somehow. And it does not take all that much to get in contact withwith grounded closed circuits, they are literally everywhere. The microphone for the musician is just an example of an infinite number of death traps. So be careful when floating your device.

As has been stated before only outlets in wet areas, that would be the crapper and outdoor outlets require GFCI. GFCI are a pain in the ass. They trip for no reason. I ended up removing one in a bathroom that I have a timer and plant light plugged into. Wife keeps her house plants in there. Have to keep them locked up because cats like to eat them and some are toxic to them. So we have an led plant light on a timer. When it kicked off it would trip the GFCI almost every day. So it was removed as it was annoying me almost every day. Same thing happened to my aquarium that I had a GFCI on. The inductive ballast for the metal halide lights caused it to trip killing power to the pump which resulted in about 1000 in dead fish and corals.

@@12voltvids I have the same problem with the ceiling fan kicking off the GFCI in my bathroom when the power switch is shut off. Also the stereo makes a pop through the speakers. Need to quench the EMF back current from the induction in the circuit. I was thinking of a capacitor in series with the power switch, maybe 0.1 uf XY cap?

@@zulumax1 every time a light is turned on or off the picture on my tv goes our for 1/2 second as the induced voltage causes errors on the extra long HDMI over cat5 cable as my amplifier is about 40 feet away from the TV.

Whilst that does help make it safer, it is NOT the same protection as an Isolation transformer. An RCD or GFCI is kind of like relying on your car's airbag to prevent death, rather than getting your brakes repaired.

@@johncoops6897 Just to clarify my earlier comment. I am NOT implying that GFCI is a replacement for an isolation transformer. I simply noticed that Dave's outlet at his workbench area is not GFGI protected. I always plug DUT into an isolation transformer. But transformer is plugged into an outlet that is on a GFCI breaker. And all my instruments, tools, music equipment - anything I touch is on that GFCI circuit breaker. You are right, GFGI is an airbag.... but Dave doesn't have it at his bench. That was the point of my comment.

@@astaltsev - Yes, that makes sense. However in the context of this video, your comment came across like you were suggesting an RCD instead of an Isolation transformer. In Australia having an RCD is mandatory for the power circuits, and the past 2 houses I've lived in have one RCD per individual circuit. I trip them quite often, since I do all manner of dubiously unsafe things LOL, but at least it only takes down one circuit rather than the entire house!

@@johncoops6897 definitely wasn't my intention and I thought my comment to Dave was quite clear, I referred to the minute and second in the video where he connected a bulb between hot and house ground and the bulb came and stayed on instead of tripping an RCD breaker. When I wired my garage in Sydney, I made sure to have a separate RCD so I don't affect anyone with my activities. The rest of outlets were all on the same RCD :(

@@astaltsev - ​ You just wrote _"I referred to the minute and second in the video where he connected a bulb between hot and..."_ ... If you go up and take a look at your original comment, you will see that you didn't include any such timestamp or reference [wink] . Even stranger, why have you changed IDs from "Hugo Sauerstein" to "Dmitri Astaltsev" ? Anyway, neither of you included a timestamp, however I didn't notice the ID change and thought I was replying to the same person... now I am just confused LOL

Well with floating power there won't be any ground faukt now will there.

@@12voltvids The whole bench and equipment hooked up will need to be all floating together then.