I also use an isolation transformer. I specially ordered the transformer from a transformer maker. It really helps my service work because I work in repairing switching power supplies. It may have saved my life countless times because the line here is 220v.
I got a new Fluke Model 12 still in the factory package while searching eBay months back, they even had an original Fluke holster for it. Works great and the $60 price I thought a good deal for a nice compact meter. Now if I can learn the slide switch and button arrangement without fumbling all will be good. 😉
I think your distinction between "isolating" and "isolation" transformers is a useful one, in that there are different setups for different use cases. I think it borders on criminal when a manufacturer calls their piece of equipment an "isolation transformer," when it does not actually have a complete galvanic isolation. Using different terminology such as isolating vs isolation, as you have suggested, would be a very good start. I want to thank you for spending the time to make the three videos on these transformers - they have been a good part of my deep dive into isolation transformers over the last couple of days and I have found them to be quite helpful. As an aside, I looked up isolation transformers at Hammond, thinking I would like to buy a nice Canadian made piece of equipment. While the secondary outputs appear to be floating, the secondary ground looks to be connected through to ground. :( *Edit:* I am referring specifically to the Hammond Manufacturing 171 series isolation transformers.
I've always been a bit confused on whether it makes sense to put an earth ground on the output ground of an isolation transformer. The actual output hot and neutral (which are both floating and therefore neither is really hot or neutral, they are just two ends of a wire) are still not referenced to earth ground in that configuration. In your medical isolation transformer drawing, that'd be only cutting the "output neutral to ground" connection you have in the drawing. The danger of doing that I suppose would be polarized equipment that within the device bonds neutral to ground within it, though I can't say that I've sen a device like that because I think it'd trip GFCI breakers immediately. Another way to look at it would be that what an isolation transformer needs to do that an isolating transformer doesn't is isolate earth ground from neutral. You being grounded while touching any single of the three wires (earth ground, and the two floating H/N output wires) should not shock you if there is no neutral to ground connection on the output side - in my mind anyway, could be wrong though. The advantage I suppose of keeping the earth bound is for dissipation of static electricity which could kill sensitive electronics equipment when there is no easy path to earth ground. I feel like that's why oscilloscopes have ground connections to begin with? On the same token, I think you could connect a regularly-earthed oscilloscope to any two points on a device that has an earth ground and your two floating H/N wires - you just can't have a connection from neutral to earth ground anywhere on the output side for the device under test.
Thanks for this overview! It will save some bad surprises (shocks). Just an FYI: There is one more VERY important reason for isolation, which I didn't catch in this video, and THAT is for the safety of your test equipment, especially an oscilloscope. For instance, if you want to test a "delta" signal within the equipment under test, rather than a signal relative to ground, you will use the ground wire on the probe to something other than unit's ground. Doing this could destroy at least your o-scope's input channel, if not the whole unit.
Awesome video!! You always have such great information. I have something called a ONEAC Condition One. I've done some research and it's used in the audio recording industry and as you say in the beginning of the video it gets rid of garbage. Also, in reference to your video, I took a resistance reading from input plug (ground pin) and the output sockets (ground pins) of this device and I get close to zero ohms. Therefore top left diagram on your paper. I wanted to use this device to isolate my oscilloscope. Could it just cut the ground wire going the outlets of the device and that would isolate my oscilloscope. I've been watching you for years. Thank you for the education. Appreciate all you do.
I have always read that it is dangerous to lift the ground on an oscilloscope, but I think you said that it is better to have the oscilloscope floating so that earth ground is not re-established. So, would I be correct to think that for most service needs, it is better to float the oscilloscope all the time? Seems like using one of those ground-lifter adapters is not good enough for this task. Seems like you MUST plug the scope into an isolation transformer in order to isolate the neutral? So I am now thinking that you HAVE to plug the scope into an isolation transformer because just lifting its ground doesnt accomplish anything because its neutral grounded back at the electrical box.
Just to confuse the situation about the bonded earth further. In Norway we use the IT-system (Insulated Terra) system, so there is no bonding between N and Earth. Everything is floating. Not sure the history about it, but in new buildings N and earth are bonded, but older and rural areas not. It causes some problems for imported equipment that expect N and E to be connected. How the GCF crcuit breakers work, no idea, but my mains tester shows faults on all our plugs. Anycase, your video explains the isolation-transformer problem very well. On a side note, I assume you also use a switcable light bulb in series with the DUT. If so, do you preceed it with a NTC to further limit the current in case of a short when the filament of the lightbulb is quite cold? Somehow people never think about that, nor have I seen anybody else doing it.
I do have a switchable light bulb in series on a separate outlet. Even when the filament is cold it will limit the current if a unit has a fault which will protect other components and even the new fuse from blowing as the max current a device can draw with a 100 watt bulb at 120v is .9 amps.
It's confusing. They say neutral and ground is not the same. I have a hard time understanding. I was told by a utility worker that the neutral was connected to the supplier of the power. Ground went to a stake in the earth. I will watch and see if I can understand.
Here in North America there are 2 types of grid. Common neutral and earth return. In BC its all common neutral where the entire grid is tied to a common neutral that is bonded to ground electrodes at every pole or underground transformer and every 300 meters in betweem. Alberta uses earth return so in that province the neutral is connected to a ground rod at the pole with the transformer and again at the next span back. Your house ground is bonded to an electrode at your service entrance and this is also bonded to neutral at the service entrance. Neutral is NOT ground. It is close to ground but at outlets it will rise above ground by a few milli volts to a few volts depending on the load. If I were to say fire up my electric heater the difference at the plug is 0.98 volts. Remember when I checked in in the video it was 0.2 volts. Why? because of internal resistance of the cable as all the power being drawn by the heater is returning on the neutral, and there is nothing flowing on the ground wire, or shouldn't be unless there is a fault.
This is a great video. Thanks man. A quick question on an old video... "dim bulb protection for vintage rdios". My radio is rated at 30 amps. Can I get by with a 60 watt bulb just to cut down on the annoying light show?
Both my isolation transformer and variac have pass thru ground on their sockets. Neither was found to be part of the circuit upon inspection. Variac is a TDCG-2KM and isolation transformer is a model PHC ISO-300. Always check out the stuff you buy first before using them, make no assumptions. One should look for videos on how to go about checking each out so you know what you are getting into.
@richard. Careful with that PR57. The secondary is connected to earth on the schematic. This is not true isolation. I use a 3 to 2 prong adapter for my DUT.
I also use an isolation transformer. I specially ordered the transformer from a transformer maker. It really helps my service work because I work in repairing switching power supplies. It may have saved my life countless times because the line here is 220v.
Absolutely. Mandatory piece of safety equipment
I got a new Fluke Model 12 still in the factory package while searching eBay months back, they even had an original Fluke holster for it. Works great and the $60 price I thought a good deal for a nice compact meter. Now if I can learn the slide switch and button arrangement without fumbling all will be good. 😉
That's a pretty good deal.
I think your distinction between "isolating" and "isolation" transformers is a useful one, in that there are different setups for different use cases. I think it borders on criminal when a manufacturer calls their piece of equipment an "isolation transformer," when it does not actually have a complete galvanic isolation. Using different terminology such as isolating vs isolation, as you have suggested, would be a very good start.
I want to thank you for spending the time to make the three videos on these transformers - they have been a good part of my deep dive into isolation transformers over the last couple of days and I have found them to be quite helpful.
As an aside, I looked up isolation transformers at Hammond, thinking I would like to buy a nice Canadian made piece of equipment. While the secondary outputs appear to be floating, the secondary ground looks to be connected through to ground. :( *Edit:* I am referring specifically to the Hammond Manufacturing 171 series isolation transformers.
I paid 12 for this one back in 93 at a hamfest
Thanks for this. I have been shopping for one. Most of them are the noise filtering type. That I have seen used.
Most need to be modified. I did a video showing how to do it.
When I was a wee young lad, there was a song: "Transformers! More than meets the eye!," and I'm like, ya think?
Your video i remember I understand the difference isolating Vs isolation, Video was helpful
I've always been a bit confused on whether it makes sense to put an earth ground on the output ground of an isolation transformer. The actual output hot and neutral (which are both floating and therefore neither is really hot or neutral, they are just two ends of a wire) are still not referenced to earth ground in that configuration. In your medical isolation transformer drawing, that'd be only cutting the "output neutral to ground" connection you have in the drawing. The danger of doing that I suppose would be polarized equipment that within the device bonds neutral to ground within it, though I can't say that I've sen a device like that because I think it'd trip GFCI breakers immediately.
Another way to look at it would be that what an isolation transformer needs to do that an isolating transformer doesn't is isolate earth ground from neutral. You being grounded while touching any single of the three wires (earth ground, and the two floating H/N output wires) should not shock you if there is no neutral to ground connection on the output side - in my mind anyway, could be wrong though.
The advantage I suppose of keeping the earth bound is for dissipation of static electricity which could kill sensitive electronics equipment when there is no easy path to earth ground. I feel like that's why oscilloscopes have ground connections to begin with? On the same token, I think you could connect a regularly-earthed oscilloscope to any two points on a device that has an earth ground and your two floating H/N wires - you just can't have a connection from neutral to earth ground anywhere on the output side for the device under test.
Thanks for this overview! It will save some bad surprises (shocks).
Just an FYI: There is one more VERY important reason for isolation, which I didn't catch in this video, and THAT is for the safety of your test equipment, especially an oscilloscope.
For instance, if you want to test a "delta" signal within the equipment under test, rather than a signal relative to ground, you will use the ground wire on the probe to something other than unit's ground. Doing this could destroy at least your o-scope's input channel, if not the whole unit.
Awesome video!! You always have such great information. I have something called a ONEAC Condition One. I've done some research and it's used in the audio recording industry and as you say in the beginning of the video it gets rid of garbage. Also, in reference to your video, I took a resistance reading from input plug (ground pin) and the output sockets (ground pins) of this device and I get close to zero ohms. Therefore top left diagram on your paper. I wanted to use this device to isolate my oscilloscope. Could it just cut the ground wire going the outlets of the device and that would isolate my oscilloscope. I've been watching you for years. Thank you for the education. Appreciate all you do.
Great video as always. Been following you for years now. Thank you for all you do. Keep up the good work. VE6RFL
Very well explained great video 🔌💡thanks
I have always read that it is dangerous to lift the ground on an oscilloscope, but I think you said that it is better to have the oscilloscope floating so that earth ground is not re-established.
So, would I be correct to think that for most service needs, it is better to float the oscilloscope all the time? Seems like using one of those ground-lifter adapters is not good enough for this task. Seems like you MUST plug the scope into an isolation transformer in order to isolate the neutral? So I am now thinking that you HAVE to plug the scope into an isolation transformer because just lifting its ground doesnt accomplish anything because its neutral grounded back at the electrical box.
Your scope has a travafirner that will isolate it from the bonded neutral so lifting the ground will isolate the scope.
Just to confuse the situation about the bonded earth further. In Norway we use the IT-system (Insulated Terra) system, so there is no bonding between N and Earth. Everything is floating. Not sure the history about it, but in new buildings N and earth are bonded, but older and rural areas not. It causes some problems for imported equipment that expect N and E to be connected. How the GCF crcuit breakers work, no idea, but my mains tester shows faults on all our plugs. Anycase, your video explains the isolation-transformer problem very well. On a side note, I assume you also use a switcable light bulb in series with the DUT. If so, do you preceed it with a NTC to further limit the current in case of a short when the filament of the lightbulb is quite cold? Somehow people never think about that, nor have I seen anybody else doing it.
I do have a switchable light bulb in series on a separate outlet. Even when the filament is cold it will limit the current if a unit has a fault which will protect other components and even the new fuse from blowing as the max current a device can draw with a 100 watt bulb at 120v is .9 amps.
It's confusing. They say neutral and ground is not the same. I have a hard time understanding. I was told by a utility worker that the neutral was connected to the supplier of the power. Ground went to a stake in the earth. I will watch and see if I can understand.
Here in North America there are 2 types of grid. Common neutral and earth return.
In BC its all common neutral where the entire grid is tied to a common neutral that is bonded to ground electrodes at every pole or underground transformer and every 300 meters in betweem. Alberta uses earth return so in that province the neutral is connected to a ground rod at the pole with the transformer and again at the next span back. Your house ground is bonded to an electrode at your service entrance and this is also bonded to neutral at the service entrance. Neutral is NOT ground. It is close to ground but at outlets it will rise above ground by a few milli volts to a few volts depending on the load. If I were to say fire up my electric heater the difference at the plug is 0.98 volts. Remember when I checked in in the video it was 0.2 volts. Why? because of internal resistance of the cable as all the power being drawn by the heater is returning on the neutral, and there is nothing flowing on the ground wire, or shouldn't be unless there is a fault.
This is a great video. Thanks man. A quick question on an old video... "dim bulb protection for vintage rdios". My radio is rated at 30 amps. Can I get by with a 60 watt bulb just to cut down on the annoying light show?
You mean 3 amps. Go bigger wattage. A 100 watt at 120v is good for 0.8 amps. 1 100 on parallel will give more current and the bulbs would be dimmer.
@@12voltvids Thanks for the reply. I meant to say 30 watts so if I = P/E then, 30/125 = 0.24 amps, right
Do you recommend putting the dim bulb on the primary or secondary side of the isolation transformer? Does it matter?
It goes on the secondary side, just in line with what you are testing
Both my isolation transformer and variac have pass thru ground on their sockets. Neither was found to be part of the
circuit upon inspection. Variac is a TDCG-2KM and isolation transformer is a model PHC ISO-300. Always check out the
stuff you buy first before using them, make no assumptions. One should look for videos on how to go about checking
each out so you know what you are getting into.
I have a video showing how to mod the transformer to make it safe.
I have medical type with my computer and a sencore P57 for my equipment being repaired!
I use a Bluetti EB3 with my computer. Full time UPS, not a standby ups.
@richard. Careful with that PR57. The secondary is connected to earth on the schematic. This is not true isolation. I use a 3 to 2 prong adapter for my DUT.