I was using an outdoor outlet (must be GFCI to meet code) with a metal conduit (buried to 6-inches) and two-wire cable to a shed to power an electric fence (which has its own ground rod). However, many fence energizers, including mine, cause a GFCI outlet to trip if an animal touches the wire. This should not happen, as the energizer output should be isolated, but unfortunately it does. I fixed the issue by using an isolation transformer (at the shed) to power the energizer. This solved the GFCI trip problem very nicely.
I had never heard of that happening! So the fence engerzier must somehow connects its high voltage pulse circuit to either the 120V line or hopefully neutral to cause a current imbalance. It hardly seems safe to be setup that way. Or maybe they are isolated, but after a while a fault has developed between the HV and 120V side. Could easily happen with some moisture getting in, and for the zapping voltage would need to be anywhere close to a short. Glad you solved it!
@krslavin For some reason I am notified of you reply "Thanks! It could be some sort of inductive coupling due to the high rate of change of current and the fence energizer being separately grounded." but can see it here. Your right! Those sharp edged pulses have so much high frequency energy they can leak though the slightest capacitances. Thats probably it.
There is an option to combine a Isolation Transformer and a GFCI. Because a Isolation Transformer doesn't have a return path to ground, and a GFCI needs a return path to ground for detecting the unbalance between Live and Neutral, you can solve this by connecting the earthpin of the outlet socket to one of the 2 Hot wires of the isolation transformer where this Hot wire enters the GFCI. That way, when there is leakage from the second Hot wire to the ground/earth chassis of the device connected to the output, a inbalance is created inside the GFCI, and it trips when the leakage exceed the treshold of the GFCI. Another modification you can do to a isolation transformer, is to connect the connection of the one Hot wire of the output and ground/earth pin of the output socket, to the ground/earth of the primary (mains earth) through a 2 Mohm 2a3 watt resistor. Each isolation transformer has a leakage voltage, this leakage voltage between the floating output and the ground/earth of the mains grid, this leakage voltage can go above 100V with a current in the µA range. With a 2 Mohm connecton, this leakage voltage is reduced to a very safe voltage, and with a maximum current of arround 120µA when using 240V on the output socket. If you then connect a device to this output, and you accidentally connect your ground clip of your scope probe to the Hot wire inside this device, a maximum current of only 120µA will flow, and this wil not harm your device/scope probe and scope itself. This mod create a "High impedance" grounding of the isolation transformer with enough safety margin for human and device.
I have often though about way to add a GFCI to the isolation transformer and I think in some situations your approach would be great, such as catching leakage current. I have been thinking a lot about your comment since you posted it yesterday - I do think the merits of a GFCI as an addition may be quite situation dependent : if one was to touch the metal device case as well as something at higher voltage inside a device under test, is it better to have the device's metal case floating/isolated so there there is no return path (or at the most a few uA) or risk brief burst of current while the GFCI disconnects? I'm assuming a North American GFCI only cuts the live connection, while neutral remains on. so potentially with the connected ground you always now have a path from ground/case to neutral and could get a severe shock if there are large capacitors holding a charge inside. So in perhaps a tube radio with a metal case the GFCI may not be a good idea. But in other cases - say maybe a incandescent lamp (to make the example simple) with no charge storage, shutting down power in case of any stray leak would help. I really appreciate your thoughtful comment!
@@ElectromagneticVideos , i don't know how the American GFCI works, but here in Belgium equivalent devices Earth Leakage Switch or Differential Current Switch interrupts all live and neutral wires. Even the portable Earth Leakage Switch interrupts live and neutral.
Great video. When I picked up my first isolation transformer I saw 'medical' and assumed (yep...) that it meant made better. Fortunately it was made by Toroid and only took minor rewiring. Regardless, that could have been very bad. You mentioned making a follow up video to test how isolated your isolation transformer is. I just did a quick search here and I wasn't able to find anyone covering that very important part. Thanks again!
That could be added protection to catch a problem if a fault developed in the transformer - say the secondary somehow shorted to ground and now was no longer isolating. I have never seen that done - but a very good thought. Great thing about your suggestion is that a fault like that would not be caught by a GFCI providing power to the isolation transformer. Could be particularly useful if one was powering a device that generates such high voltage that if the device under test faulted, it could raise the isolation transformer's secondary to the point where its insulation failed. For that type of situation i have used an GFCI without an isolation transformer, since the device had its own transformer. But you really got me thinking - might add that to my setup! Thanks!
@@ElectromagneticVideos , when you add a GFCI to the secondary side, a GFCI won't trip because there is no path for leakage current. A GFCI trips if there is unbalance between the Hot and Neutral, but because the secondary side is not referenced to ground (and also not to neutral), there is no leakage path if you touch the secondary side. But a trick to use a GFCI combined with a isolation transformer can be done, when you tie the ground pin and the neutral pin together in the outlet socket. The only downside to this trick is that there will be a "Ghost" voltage on the metal case of the device that is connected to the isolation transformer. This "Ghost" voltage can be as high as 50% (or more) of the output voltage, but is very low current (in µA range). A second trick to lower this "Ghost" voltage, is to connect the previous made connection of the earth pin/neutral pin of the outlet socket with a 2 Mohm resistor to the earthpin/wire of the mains grid. This 2 Mohm resistor needs to be a 2 or 3Watt type for getting the 240V voltage rating. A 1/8 Watt resistor is not rated for mains voltage use. With these 2 tricks, you can use a GFCI AND have a very low "Ghost" voltage (arround 30a40V at µA current). When doing scope measurings on the device connected to the isolation transformer, and when connecting accidentally the ground clip to the hot wire of the secundary, will only allow a current of 240µA (with 240V mains voltage, 120µA with 120V mains voltage) through the scope probe and scope itself. This will not harm the scope, while this fault without a isolation transformer, will blow up your scope probe and your scope. The grounding of the secondary side to the earthpin/wire or ground of the mains grid with a 2 Mohm is also called a "High impedance grounding".
@@BjornV78 Really like your two tricks! So much so I will add them to my unit. They would certainly be a great way of catching inadvertent human contact in some situations and shut the system down adding one more line of protection beyond the isolation transformer. To clarify my comments above, a gfci (with or without your tricks) could in some circumstances catch unbalanced currents as a result of and issue in the transformer where the transformer becomes no longer isolating.
Agreed it's a must. Unfortunately, proper "lab" Isolation transformers are pretty pricey but, your life should be worth much more to you. I run all my DUT (devices under test) through an Isolation transformer, a current limiting light bulb, and a Variac. I definitely recommend anyone working with high voltage and current to make a setup of all 3 next to each other and use it as your life may depend on it.
Completely agree!!! And to add to your comment. I have seen some ads for isolation transformers that arnt isolating - they have their neutrals connected with an intended purpose of noise reduction for high end equipment and studios. I hope than people using the transformers for safety are knowledgeable enough to understand this and check their transformer after purchasing to ensure its really isolating!
@@ElectromagneticVideos I picked up a Hammond isolation transformer a while back. Similar to the one referenced in the video and I was shocked at how badly? the enclosure was grounded. I had to add serrated lock washers to properly ground the enclosure.
@@stevenspmd That's a bit surprising - I have always thought of Hammond a quality brand, but maybe these days like everything else it isn't what it used to be :(
@@ElectromagneticVideos Maybe I'm being picky? but the grounding of the enclosure on the secondary side didn't seem that great; just single wire passed through a bolt hole of the transformer body from the primary side. I put serrated lock washers on both sides of all four bolt holes and now the enclosure ground/resistance is the same all around.
All very good suggestions! The MOV particularly for use when dealing with semiconductor devices that might be damaged by spikes particularity if the power to the transformer is cut and the remaining magnetic field in the transformer produces a surge. As far as fusing goes, my preference would be a switchable dim bulb current limiter as part of the whole setup. But maybe a slow-blow fuse on the transformer output as well for safety. I wouldnt put one on the input of the transformer as that might cause surge reasons.
@@ElectromagneticVideos Simply cutting the input causes a spike? MOV across secondary? Then we needn't trust a sensitive DUT to protect itself. Yes my box has a switchable dim bulb. I will need to move my 2A fuse. I had thought it belongs on the input/power cord. I selected Triad FD8-120 which does not tie the neutrals and has low cost 38 CAD. 100 VA. Hipot 2500 V.
@@d46512 Consider the transformer connected to the AC supply but not to a load. The transformer draws lagging current because of the inductive nature of the primary coil. Now you flip the AC switch at the instant when the current though the inductor (=transformer) is at its peak. So the magnetic field in the transformer is also at its peak and holds a lot of energy. By their nature inductors want to keep the current though them flowing constant (I did a video on this a while back) so the inductor forces its voltage to rise enough to keep the current flowing at the same amount it was before. This usually results in a nice spark across the switch. The high voltage generated is also seen on the secondary by transformer action. So there is your spike. It dissipates quickly as the energy in the magnetic filed that powers it is used up, but can easily be 1000s of volts. So a MOV on the output is a good idea. Now if you had a big load connected the current across the small resistance of the load would result in a much smaller spike - maybe less than the normal operating AC peak. The transformer looks like good value for a nice small isolation transformer. I would leave the fuse where you have it, and put a smaller one on the secondary. That way there is protection if the transformer is damaged somehow ....
Theoretically, let's say I plugged an isolation transformer into a gfci then touched the live wire on the secondary side of the transformer, using my body as the return path for the current. Would the gfci still trip or would the isolation transformer essentially "bypass" the gfci protection? Not that I would ever try this, just curious
The GFCI won't trip because the secondary side is not ground referenced, so there is no return/leakage path. That's also the reason that you don't feel anything if you touch 1 wire of the secondary side. That's also the reason that a isolation transformer is used, but If you touch both output wires at the same time, then you will get a shock offcourse.
Thank you, thank you for this marvelous video. Someday this might save my life!
!
I was using an outdoor outlet (must be GFCI to meet code) with a metal conduit (buried to 6-inches) and two-wire cable to a shed to power an electric fence (which has its own ground rod). However, many fence energizers, including mine, cause a GFCI outlet to trip if an animal touches the wire. This should not happen, as the energizer output should be isolated, but unfortunately it does. I fixed the issue by using an isolation transformer (at the shed) to power the energizer. This solved the GFCI trip problem very nicely.
I had never heard of that happening! So the fence engerzier must somehow connects its high voltage pulse circuit to either the 120V line or hopefully neutral to cause a current imbalance. It hardly seems safe to be setup that way. Or maybe they are isolated, but after a while a fault has developed between the HV and 120V side. Could easily happen with some moisture getting in, and for the zapping voltage would need to be anywhere close to a short.
Glad you solved it!
@krslavin For some reason I am notified of you reply "Thanks! It could be some sort of inductive coupling due to the high rate of change of current and the fence energizer being separately grounded." but can see it here. Your right! Those sharp edged pulses have so much high frequency energy they can leak though the slightest capacitances. Thats probably it.
There is an option to combine a Isolation Transformer and a GFCI.
Because a Isolation Transformer doesn't have a return path to ground, and a GFCI needs a return path to ground for detecting the unbalance between Live and Neutral,
you can solve this by connecting the earthpin of the outlet socket to one of the 2 Hot wires of the isolation transformer where this Hot wire enters the GFCI.
That way, when there is leakage from the second Hot wire to the ground/earth chassis of the device connected to the output, a inbalance is created inside the GFCI, and it trips when the leakage exceed the treshold of the GFCI.
Another modification you can do to a isolation transformer, is to connect the connection of the one Hot wire of the output and ground/earth pin of the output socket, to the ground/earth of the primary (mains earth) through a 2 Mohm 2a3 watt resistor. Each isolation transformer has a leakage voltage, this leakage voltage between the floating output and the ground/earth of the mains grid, this leakage voltage can go above 100V with a current in the µA range. With a 2 Mohm connecton, this leakage voltage is reduced to a very safe voltage, and with a maximum current of arround 120µA when using 240V on the output socket. If you then connect a device to this output, and you accidentally connect your ground clip of your scope probe to the Hot wire inside this device, a maximum current of only 120µA will flow, and this wil not harm your device/scope probe and scope itself. This mod create a "High impedance" grounding of the isolation transformer with enough safety margin for human and device.
I have often though about way to add a GFCI to the isolation transformer and I think in some situations your approach would be great, such as catching leakage current.
I have been thinking a lot about your comment since you posted it yesterday - I do think the merits of a GFCI as an addition may be quite situation dependent : if one was to touch the metal device case as well as something at higher voltage inside a device under test, is it better to have the device's metal case floating/isolated so there there is no return path (or at the most a few uA) or risk brief burst of current while the GFCI disconnects? I'm assuming a North American GFCI only cuts the live connection, while neutral remains on. so potentially with the connected ground you always now have a path from ground/case to neutral and could get a severe shock if there are large capacitors holding a charge inside. So in perhaps a tube radio with a metal case the GFCI may not be a good idea. But in other cases - say maybe a incandescent lamp (to make the example simple) with no charge storage, shutting down power in case of any stray leak would help.
I really appreciate your thoughtful comment!
@@ElectromagneticVideos , i don't know how the American GFCI works, but here in Belgium equivalent devices Earth Leakage Switch or Differential Current Switch interrupts all live and neutral wires. Even the portable Earth Leakage Switch interrupts live and neutral.
Great video. When I picked up my first isolation transformer I saw 'medical' and assumed (yep...) that it meant made better. Fortunately it was made by Toroid and only took minor rewiring. Regardless, that could have been very bad. You mentioned making a follow up video to test how isolated your isolation transformer is. I just did a quick search here and I wasn't able to find anyone covering that very important part. Thanks again!
Oops! I still have to make that video! Sorry!
@@ElectromagneticVideos Your videos are very informative and highly apprecaited. I'm glad you popped up in my suggestions. Thanks!
@@SilvaD702 Thanks you so much! Glad you liked the videos!
What about putting a GFCI on the isolated side of the transformer?
That could be added protection to catch a problem if a fault developed in the transformer - say the secondary somehow shorted to ground and now was no longer isolating. I have never seen that done - but a very good thought. Great thing about your suggestion is that a fault like that would not be caught by a GFCI providing power to the isolation transformer. Could be particularly useful if one was powering a device that generates such high voltage that if the device under test faulted, it could raise the isolation transformer's secondary to the point where its insulation failed. For that type of situation i have used an GFCI without an isolation transformer, since the device had its own transformer. But you really got me thinking - might add that to my setup! Thanks!
@@ElectromagneticVideos , when you add a GFCI to the secondary side, a GFCI won't trip because there is no path for leakage current. A GFCI trips if there is unbalance between the Hot and Neutral, but because the secondary side is not referenced to ground (and also not to neutral), there is no leakage path if you touch the secondary side. But a trick to use a GFCI combined with a isolation transformer can be done, when you tie the ground pin and the neutral pin together in the outlet socket. The only downside to this trick is that there will be a "Ghost" voltage on the metal case of the device that is connected to the isolation transformer. This "Ghost" voltage can be as high as 50% (or more) of the output voltage, but is very low current (in µA range). A second trick to lower this "Ghost" voltage, is to connect the previous made connection of the earth pin/neutral pin of the outlet socket with a 2 Mohm resistor to the earthpin/wire of the mains grid. This 2 Mohm resistor needs to be a 2 or 3Watt type for getting the 240V voltage rating. A 1/8 Watt resistor is not rated for mains voltage use.
With these 2 tricks, you can use a GFCI AND have a very low "Ghost" voltage (arround 30a40V at µA current).
When doing scope measurings on the device connected to the isolation transformer, and when connecting accidentally the ground clip to the hot wire of the secundary, will only allow a current of 240µA (with 240V mains voltage, 120µA with 120V mains voltage) through the scope probe and scope itself.
This will not harm the scope, while this fault without a isolation transformer, will blow up your scope probe and your scope.
The grounding of the secondary side to the earthpin/wire or ground of the mains grid with a 2 Mohm is also called a "High impedance grounding".
@@BjornV78 Really like your two tricks! So much so I will add them to my unit. They would certainly be a great way of catching inadvertent human contact in some situations and shut the system down adding one more line of protection beyond the isolation transformer. To clarify my comments above, a gfci (with or without your tricks) could in some circumstances catch unbalanced currents as a result of and issue in the transformer where the transformer becomes no longer isolating.
Agreed it's a must. Unfortunately, proper "lab" Isolation transformers are pretty pricey but, your life should be worth much more to you. I run all my DUT (devices under test) through an Isolation transformer, a current limiting light bulb, and a Variac. I definitely recommend anyone working with high voltage and current to make a setup of all 3 next to each other and use it as your life may depend on it.
Completely agree!!! And to add to your comment. I have seen some ads for isolation transformers that arnt isolating - they have their neutrals connected with an intended purpose of noise reduction for high end equipment and studios. I hope than people using the transformers for safety are knowledgeable enough to understand this and check their transformer after purchasing to ensure its really isolating!
@@ElectromagneticVideos I picked up a Hammond isolation transformer a while back. Similar to the one referenced in the video and I was shocked at how badly? the enclosure was grounded. I had to add serrated lock washers to properly ground the enclosure.
@@stevenspmd That's a bit surprising - I have always thought of Hammond a quality brand, but maybe these days like everything else it isn't what it used to be :(
@@ElectromagneticVideos Maybe I'm being picky? but the grounding of the enclosure on the secondary side didn't seem that great; just single wire passed through a bolt hole of the transformer body from the primary side. I put serrated lock washers on both sides of all four bolt holes and now the enclosure ground/resistance is the same all around.
@@stevenspmd Well it sure sounds better the way you did it!
Should we add a MOV for overvoltage surge suppression? Should we fuse one or both windings to match the transformer's VA rating?
All very good suggestions! The MOV particularly for use when dealing with semiconductor devices that might be damaged by spikes particularity if the power to the transformer is cut and the remaining magnetic field in the transformer produces a surge.
As far as fusing goes, my preference would be a switchable dim bulb current limiter as part of the whole setup. But maybe a slow-blow fuse on the transformer output as well for safety. I wouldnt put one on the input of the transformer as that might cause surge reasons.
@@ElectromagneticVideos Simply cutting the input causes a spike? MOV across secondary? Then we needn't trust a sensitive DUT to protect itself.
Yes my box has a switchable dim bulb. I will need to move my 2A fuse. I had thought it belongs on the input/power cord.
I selected Triad FD8-120 which does not tie the neutrals and has low cost 38 CAD. 100 VA. Hipot 2500 V.
@@d46512 Consider the transformer connected to the AC supply but not to a load. The transformer draws lagging current because of the inductive nature of the primary coil. Now you flip the AC switch at the instant when the current though the inductor (=transformer) is at its peak. So the magnetic field in the transformer is also at its peak and holds a lot of energy. By their nature inductors want to keep the current though them flowing constant (I did a video on this a while back) so the inductor forces its voltage to rise enough to keep the current flowing at the same amount it was before. This usually results in a nice spark across the switch. The high voltage generated is also seen on the secondary by transformer action. So there is your spike. It dissipates quickly as the energy in the magnetic filed that powers it is used up, but can easily be 1000s of volts. So a MOV on the output is a good idea. Now if you had a big load connected the current across the small resistance of the load would result in a much smaller spike - maybe less than the normal operating AC peak.
The transformer looks like good value for a nice small isolation transformer. I would leave the fuse where you have it, and put a smaller one on the secondary. That way there is protection if the transformer is damaged somehow ....
Theoretically, let's say I plugged an isolation transformer into a gfci then touched the live wire on the secondary side of the transformer, using my body as the return path for the current. Would the gfci still trip or would the isolation transformer essentially "bypass" the gfci protection? Not that I would ever try this, just curious
The GFCI won't trip because the secondary side is not ground referenced, so there is no return/leakage path. That's also the reason that you don't feel anything if you touch 1 wire of the secondary side. That's also the reason that a isolation transformer is used, but If you touch both output wires at the same time, then you will get a shock offcourse.
At 0:30 it should be noted that "turn everything off" does NOT apply to the operation of nuclear power plants. IJS