Hi, I just got myself a 1:1 transformer and watched several videos suggesting what NOT to do regarding the neutral connection.
Since neutral and earth are joined at the distribution panel it makes sense that the transformer secondary neutral should be isolated from the primary neutral.
Question 1: does the socket on the secondary get a ground connection at all? Or do i just wire Live and neutral to it?
Question 2: if I wanted to have this setup on a separate breaker box, How and where in the circuit would I wire an RCD?
Since it is isolated from mains how is it supposed to measure the residual current leaking to ground if there is no ground?
I understand that one needs to touch both sides of the secondary to get shocked but it still sounds sketchh and potentially dangerous. So is there a way to trip a breaker on the transformer secondary for extra safety?
Since neutral and earth are joined at the distribution panel it makes sense that the transformer secondary neutral should be isolated from the primary neutral.
Question 1: does the socket on the secondary get a ground connection at all? Or do i just wire Live and neutral to it?
Question 2: if I wanted to have this setup on a separate breaker box, How and where in the circuit would I wire an RCD?
Since it is isolated from mains how is it supposed to measure the residual current leaking to ground if there is no ground?
I understand that one needs to touch both sides of the secondary to get shocked but it still sounds sketchh and potentially dangerous. So is there a way to trip a breaker on the transformer secondary for extra safety?
Most countries have their own conventions, so check locally.
If possible, always use a licensed electrician to do the work.
If possible, always use a licensed electrician to do the work.
I would stronly recomment a GFCI on the output of the isolation transformer. It doesn't need a ground connection and will sense if any power is going astray.
An isolaton transformer can help in some situations but is not instant safety. Treat anything connected to mains, isolated or not as dangerious.
An isolaton transformer can help in some situations but is not instant safety. Treat anything connected to mains, isolated or not as dangerious.
On my isolation transformer I have the primary side grounded.The secondary I used isolated ground receptacles so I could plug 3 prong equipment in. Some outlets ground to the chassis through the mounting screws but these isolated don't.
Which is a safety hazard in itself should something go bang and startle you into falling backwards - one hand behind the back is perhaps safer, or maybe use an electrician's glove on one hand.
And very important: use small amp fuses for the workbench - any short will be stopped without major problem. I use 3A / 127V. When more power is needed, I feed the equipment from another outlet.
Another thing is to have an outlet in series with an incandescent lamp (60W) for testing circuits. First power up with the lamp in series. If it is ok, than you short the lamp with a switch. That will save you a lot of hw.
Another thing is to have an outlet in series with an incandescent lamp (60W) for testing circuits. First power up with the lamp in series. If it is ok, than you short the lamp with a switch. That will save you a lot of hw.
If there is no continuity from the ground of your output outlet and ground of your input power wire they are isolated. In my case the ground on my output outlet were grounded to the case and the case was also grounded to the input power cord so I cut it from the output outlet. This would mean your dut (device under test) case is no longer going to be safety grounded, and you treat it as such.
Isolating the output ground may still expose the user to a hazard. A gfci on both the input and the output would be pretty good protection as is a smaller fuse. Still safe is BOTH hands in your pockets. Just because its isolated doesn't mean contacting the secondary side is safe in any way.
Isolation transfromers were essential working on all amarticcan 5 radios that had no power transformer. today they are helpful for 1) problems like insulation breakdown in the primary circuit and 2) conducted noise reduction. Noise reduction is rarely need when troubleshooting.
Isolation transfromers were essential working on all amarticcan 5 radios that had no power transformer. today they are helpful for 1) problems like insulation breakdown in the primary circuit and 2) conducted noise reduction. Noise reduction is rarely need when troubleshooting.
The issue with isolation is to prevent your oscilloscope probes ground from shorting out anything above ground potential you contact with it. When you work on a piece of equipment you assume it is hazardous until you finally are done testing and put everything back together.
Rod Elliott - ''Is An Isolation Transformer A Safety Measure Or Death Trap?'':
https://sound-au.com/articles/iso-xfmr.htm
https://sound-au.com/articles/iso-xfmr.htm
Great article. Something so simple can be so dangerous. Now I have to figure out what is the safest way to go with my bench setup. Maybe GFI on my whole bench? Let's share how other's are doing it.
Think first why touching the live conductor is dangerous. It is dangerous only because in the distribution system the neutral is grounded. So the reasoning is this:
The reason that equipment has an earth connection is:
This also induces that an safety earth connection (the third pin) in the outlets is useless for protection in the insulation transformer secondary circuit.
So key point is that you do not connect the neutral of your insulation transformer to the primary neutral or primary earth. Or for that matter to primary anything.
Installing a GFCI is totally useless. GFCI devices are designed so that an unequal current in neutral and live can be detected. That current difference is exactly the current which runs through your body to earth. Since your secondary does not have any connection to earth and should not have under any circumstance, a GFCI device is useless.
Rod Elliot points out a very important point. If you connect the ground of your measuring equipment powered from the ordinary mains to the device connected to the secondary of your insulation transformer, you have a connection between primary and secondary of your insulation transformer. Lethal!
So summarizing,
I worked for years in a lab where the complete room was separated from the mains with an insulation transformer. All outlet grounds (the third conductor) were connected to ground and to the metal shielding of the room. That only was for shielding, not for protection. Had this not been a Faraday cage, I would not have connected the ground pins at all.
Unfortunately in that same room someone installed a non-insulated three-phase 400V test outlet. So that is the last recommendation. Do not mix insulated and non-insulated outlets on your bench. Don't ask how I know this.
- The neutral is grounded
- The live wire has voltage with respect to the neutral
- You (person) is grounded. (Feet on the ground)
- If you touch the live wire, then voltage is across your body
The reason that equipment has an earth connection is:
- To keep the equipment on ground potential
- When you touch said equipment when it has an earth fault, no voltage difference exists between the equipment and your feet.
This also induces that an safety earth connection (the third pin) in the outlets is useless for protection in the insulation transformer secondary circuit.
So key point is that you do not connect the neutral of your insulation transformer to the primary neutral or primary earth. Or for that matter to primary anything.
Installing a GFCI is totally useless. GFCI devices are designed so that an unequal current in neutral and live can be detected. That current difference is exactly the current which runs through your body to earth. Since your secondary does not have any connection to earth and should not have under any circumstance, a GFCI device is useless.
Rod Elliot points out a very important point. If you connect the ground of your measuring equipment powered from the ordinary mains to the device connected to the secondary of your insulation transformer, you have a connection between primary and secondary of your insulation transformer. Lethal!
So summarizing,
- Connect the output of your insulation transformer to the two pins of the outlet(s). And to nothing more.
- Power everything else on your bench which might touch anything connected to the secondary circuit of the insulation transformer to the insulated outlets as well.
I worked for years in a lab where the complete room was separated from the mains with an insulation transformer. All outlet grounds (the third conductor) were connected to ground and to the metal shielding of the room. That only was for shielding, not for protection. Had this not been a Faraday cage, I would not have connected the ground pins at all.
Unfortunately in that same room someone installed a non-insulated three-phase 400V test outlet. So that is the last recommendation. Do not mix insulated and non-insulated outlets on your bench. Don't ask how I know this.
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I did go back and forth with the ground on the outlet on the isolation transformer, it is a darned if you and darned if you don’t. I did end up breaking down and buying a isolation probe set for the osilliscope, takes a little of the pressure off where you place your ground wire.