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Isolation Transformer

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Just need to confirm my understanding here. Does an isolation transformer on one device such as a preamp that communicates with another device such as a power amp that is not on the isolation transformer guarantee it being impossible to develop a ground loop between these two?

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If the isolation transformer is balanced then ALL your audio equipment needs to be plugged into it so large voltage differentials cannot form across interconnect leads.  The balanced isolation transformers effectively can be used to create a new voltage reference separate to all the other 'normal' circuits in the house. 

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16 minutes ago, acg said:

If the isolation transformer is balanced then ALL your audio equipment needs to be plugged into it so large voltage differentials cannot form across interconnect leads.  The balanced isolation transformers effectively can be used to create a new voltage reference separate to all the other 'normal' circuits in the house. 

I was asking about isolation transformers, not balanced ones per se. But there's no way for voltage to travel between two isolated circuits is there? You'd need a monstrous isolation transformer to be able to put all power amps and electronics on the one circuit if you have high power demans.

Edited by Ittaku

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54 minutes ago, Ittaku said:

But there's no way for voltage to travel between two isolated circuits is there?

 

1 hour ago, Ittaku said:

Does an isolation transformer on one device such as a preamp that communicates with another device such as a power amp that is not on the isolation transformer guarantee it being impossible to develop a ground loop between these two?

 

One problem I have encountered, in a large installation where all the computer equipment was isolated, was when you used a dedicated ground/earth.   This was commonly a stake driven into the ground, literally, with appropriate soil preparation (conductivity and moisture etc).  What happens is that large fault currents, from high current equipment, or lightning, can cause the earth potentials of the dedicated earth to be at a different potential to mains earth/neutral.  This might be the differentials referred to above.   One solution was to tie the two earthing systems together with a high current capable inductor.

 

Other than that, there are some weird setups where neutral is used as a safety ground, or the two are connected. Probably not allowed in Australia, but we import a lot of grey market stuff, especially in Hifi.  Then there's equipment with separated signal and safety grounds. Struck one of them the other day, and the solution was to connect the two (opposite of expected).  Makes looking for ground loops fun anyway.

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@Ittaku, Lucas from Black Art Audio in Melbourne is winding a 7.5kVa balanced isolation transformer for me right now.  Two filters afterwards should limit mains noise to ridiculously low frequencies and levels.  He does not make them very often, but they are the Rolls Royce option, and my relatively high audio system power draw of circa 1kW will not present any trouble whatsoever to this transformer.  

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1 hour ago, Ittaku said:

I was asking about isolation transformers, not balanced ones per se. But there's no way for voltage to travel between two isolated circuits is there? You'd need a monstrous isolation transformer to be able to put all power amps and electronics on the one circuit if you have high power demans.

So there is a difference between iso and balanced transformers?

 

 

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5 minutes ago, pulinap said:

So there is a difference between iso and balanced transformers?

 

 

That article from Tortech that Dave posted earlier briefly explains the difference between balanced and unbalanced isolation transformers.  

 

Isolation transformer simply isolates the active and neutral wires in the mains wiring using a transformer winding:  active = +240V; neutral = 0V.

 

Balanced Isolation Transformer does this as well, but instead has Active = +120V; neutral = -120V and the ground is effectively centre-tapped, or at zero volts.  

 

In both situations your audio gears sees +240V (or whatever the line voltage is at that moment) between active and neutral, but the balanced transformer allows for rejection of common mode noise, just like in a balanced interconnect.

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2 minutes ago, acg said:

Balanced Isolation Transformer does this as well, but instead has Active = +120V; neutral = -120V and the ground is effectively centre-tapped, or at zero volts.  

Interesting.  How is that wired to the equipment and safety ground?  Does the centre tap stay floating, or is it grounded, and if so, how is it isolated any more?  If it floats, how is safety ground for the equipment handled?  

 

I suspect I am missing something :) 

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28 minutes ago, acg said:

@Ittaku, Lucas from Black Art Audio in Melbourne is winding a 7.5kVa balanced isolation transformer for me right now.  Two filters afterwards should limit mains noise to ridiculously low frequencies and levels.  He does not make them very often, but they are the Rolls Royce option, and my relatively high audio system power draw of circa 1kW will not present any trouble whatsoever to this transformer.  

Thanks, that's pretty cool. My system draws 1kW at idle and runs off three separate circuits, one 20A for each power amp and one 16A for the rest.

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27 minutes ago, aussievintage said:

 

 

One problem I have encountered, in a large installation where all the computer equipment was isolated, was when you used a dedicated ground/earth.   This was commonly a stake driven into the ground, literally, with appropriate soil preparation (conductivity and moisture etc).  What happens is that large fault currents, from high current equipment, or lightning, can cause the earth potentials of the dedicated earth to be at a different potential to mains earth/neutral.  This might be the differentials referred to above.   One solution was to tie the two earthing systems together with a high current capable inductor.

 

Other than that, there are some weird setups where neutral is used as a safety ground, or the two are connected. Probably not allowed in Australia, but we import a lot of grey market stuff, especially in Hifi.  Then there's equipment with separated signal and safety grounds. Struck one of them the other day, and the solution was to connect the two (opposite of expected).  Makes looking for ground loops fun anyway.

 

Those are the two issues I was referring to.  The second of which will put 120V potential difference across the interconnect and probably cause smoke to escape from something pretty quickly.

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8 minutes ago, acg said:

That article from Tortech that Dave posted earlier briefly explains the difference between balanced and unbalanced isolation transformers.  

 

Isolation transformer simply isolates the active and neutral wires in the mains wiring using a transformer winding:  active = +240V; neutral = 0V.

 

Balanced Isolation Transformer does this as well, but instead has Active = +120V; neutral = -120V and the ground is effectively centre-tapped, or at zero volts.  

 

In both situations your audio gears sees +240V (or whatever the line voltage is at that moment) between active and neutral, but the balanced transformer allows for rejection of common mode noise, just like in a balanced interconnect.

Thanks....much appreciated.

 

But are they safe...?

 

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13 minutes ago, pulinap said:

Thanks....much appreciated.

 

But are they safe...?

 

 

Yes.  You need the safety switch between the isolation transformer and the load.  Something like the Black-Art Balanced unit I am getting will need installation by a licensed electrician.

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3 minutes ago, acg said:

 

Yes.  You need the safety switch between the isolation transformer and the load.  Something like the Black-Art Balanced unit I am getting will need installation by a licensed electrician.

Can this be retrofitted?

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3 minutes ago, acg said:

 

Yes.  You need the safety switch between the isolation transformer and the load.  Something like the Black-Art Balanced unit I am getting will need installation by a licensed electrician.

Now I am really intrigued.  How can there be earth leakage current with an isolated power source?  Sounds like it is not working as an isolation transformer, but as a common mode filter, like those counter-wound filter transformers in power filters.

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26 minutes ago, aussievintage said:

Now I am really intrigued.  How can there be earth leakage current with an isolated power source?  Sounds like it is not working as an isolation transformer, but as a common mode filter, like those counter-wound filter transformers in power filters.

This is why I raised a whole heap of questions.....being a layman I am not sure what I understand your comment...but what I do understand is that there is a whole heap of confusion....  :)

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45 minutes ago, aussievintage said:

Now I am really intrigued.  How can there be earth leakage current with an isolated power source?  Sounds like it is not working as an isolation transformer, but as a common mode filter, like those counter-wound filter transformers in power filters.

 

I have been talking about Balanced isolation transformers, and as far as I know they all require the safety switch between the transformer and the load.  Here is a quote from Tortech page about their balanced unit:

 

Quote

 

ONE IMPORTANT THING TO NOTE:

RCDs (Safety Switches) are only effective if they are plugged into the supply. Safety switches on your main switchboard will NOT protect equipment connected to the power supply. We recommend you use an appropriate safety switch on the power supplys output socket.

 

 

Talking to Lucas about the unit he is building me, which will have it's own earth rod into the ground separate to that which services the remainder of the house, a safety switch is still required.  No electrician is going to wire one of these things in without the safety switch, so there is no confusion there for me at all.

 

Regarding the unbalanced isolation transformers, the same is true as far as I am aware.  Unless that particular unit that you buy carries the earth through (the few that I have looked at do not carry the earth through and I am pretty sure that by definition an isolation transformer NEVER carries the earth through) you will need a safety switch between the transformer and anything plugged into it.

 

So, it you use an isolation transformer, balanced or unbalanced, you will require a safety switch between it and your gear if you want to keep protective earth operational. 

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19 minutes ago, acg said:

Talking to Lucas about the unit he is building me, which will have it's own earth rod into the ground separate to that which services the remainder of the house, a safety switch is still required.

So, a dedicated earth.  Centre tap probably connected to that, and RCD referenced to that.    With regard to ground loops,  yes all equipment needs to be using the dedicated ground, for safety and noise reasons, however, you can still get a ground loop between individual pieces of equipment.

 

22 minutes ago, acg said:

Regarding the unbalanced isolation transformers, the same is true as far as I am aware.  Unless that particular unit that you buy carries the earth through (the few that I have looked at do not carry the earth through and I am pretty sure that by definition an isolation transformer NEVER carries the earth through) you will need a safety switch between the transformer and anything plugged into it.

I get the impression some people are using an isolation transformer, but connecting the equipment to local non-dedicated ground.

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18 minutes ago, acg said:

I am pretty sure that by definition an isolation transformer NEVER carries the earth through) you will need a safety switch between the transformer and anything plugged into it.

 

The 1kVA isolation transformer that I have - made by Siros, in the back streets of Richmond - has the input earth going through to the 6 output mains sockets (and the traffo's metal case).   "Isolation" (AIUI) refers to the output Active & Neutral being connected to the input Active & Neutral by magnetic coupling - not by being hardwired.

 

Andy

 

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Isolation-Transformer-ISO-ES-Circuit-Ske

 

Here it goes to the case and the transformer input screen only.   The trouble is, what to do with the earth pins on the output sockets.  Yes, a dedicated earth is desirable.  

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6 hours ago, aussievintage said:

Isolation-Transformer-ISO-ES-Circuit-Ske

 

Here it goes to the case and the transformer input screen only.   The trouble is, what to do with the earth pins on the output sockets.  Yes, a dedicated earth is desirable.  

what if one installs a portable RCD to the cable coming out from output socket....?

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17 minutes ago, pulinap said:

what if one installs a portable RCD to the cable coming out from output socket....?

sure, assuming the earth pin is wired to some kind of earth, it will work.  Thing is, even a dedicated earth provides an electrical circuit back to the mains safety earth, even though there may be the extra resistance of the  soil between the two.

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21 minutes ago, aussievintage said:

sure, assuming the earth pin is wired to some kind of earth, it will work.  Thing is, even a dedicated earth provides an electrical circuit back to the mains safety earth, even though there may be the extra resistance of the  soil between the two.

But the secondary (as per the diagram) is not connected to earth/ground...?

 

As mentioned elsewhere...I read a post by John Swenson: (emphasis mine)

 

The basics go like this:

in normal house wiring a dangerous fault is when hot comes in contact with metal chasis, if part of you touches the chassis and some other part of you contacts some ground point, dangerous current can flow through you.

 

The first solution to this was the safety ground wire, when the hot in the device touches the chassis a large current flows through the ground wire, tripping the breaker in the panel. This works if there is a very good short which supports enough current to trip the breaker.

 

If the short is a weak one, you can still have current through you, but there will not be enough current through the breaker to trip it. Thus GFCI. It monitors the current through the two legs (hot and neutral), in normal operation the current is balanced, the same amount on each wire. The GFCI detects a situation where a small amount of current takes a "sneak path", from one of the wires, potentially through you, that goes to ground, thus the current on the hot and neutral are NOT the same. When this happens the GFCI shuts the circuit down.

 

So now lets look at how this works with an isolation transformer. The voltage on the secondary is not connected to the input wire at all, or the ground. They are separate. It's like a battery. You can touch either wire from the secondary (I'll call them Sa and Sb) to the safety ground, any other ground point, either original hot or neutral, a ground rod, ANYTHING, and nothing happens. (not quite strictly speaking true, with the low capacitance ones we are talking about a little bit of leakage current will flow, usually less than a micro amp). This is important, a direct short to ground causes nothing to happen. If you are part of that connection, again, nothing happens.

 

As to a GFCI, it works by detecting differences between current in the two wires going through it. Since connection to anything else will not cause a current to flow, the currents coming out of the secondary will ALWAYS be the same so a GFCI will NEVER trip, so it is completely useless in this system.

 

There is ONE case where you can get injurious current, it takes TWO opposite faults. You have two devices with metal chassis, which are NOT connected to a common safety ground. One has a short from Sa to chassis and the other has a short from Sb to different chassis, if you touch both chassis you will have line voltage between them. If they are connected to a common safety ground, large current will flow through that ground which might trip a breaker.

 

So overall quite safe, GFCIs do absolutely nothing, so you don't need one, period. If no sneak path can exist the current is always balanced so a GFCI will not ever trip, so it is not protecting against anything.

 

I hope that makes some sort of sense. This is a quick response without diagrams which I hope makes some sense.

 

If anyone wants to test this to make sure I'm not blowing wind here, try it with a low voltage transformer. Take say a 1A 120V:6.3V transformer, connect it to a three prong plug, primary wires to the hot and neutral, leave the safety ground unconnected. Tape up one of the secondary wires so you don't accidentally short it, and then measure the voltage between the other secondary wire and safety ground. (AC volts on the meter) You should have extremely close to zero, maybe a few microvolts if you have a really good meter. You can use AC Amps on the meter, again only microamps max. You can try this to a ground rod, anything else you choose and you will get the same results.

 

An isolation transformer is no different, just different voltage ratio, either secondary wire to safety ground or any other ground gives you nothing. You can't get shocked from nothing.

 

John S.

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Ignore my brain fart - separate earth on downstream side of bal isol probably legal under Part 2 of the wiring standard.

 

You'll need to find a sparkie that'll trust what's in the box tho...

 

 

Edited by rmpfyf

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I get my Isolation Transformers from 

https://sklep.toroidy.pl/en_US/producer/Toroidy.pl/6/46

 

They build me beautiful custom balanced or straight primary/secondary Transformers with shields between windings, and are potted in an external shield made of magnetic steel, then polished to mirror.

Have found that it's not worth getting or going balanced transformer.

 

They are always earthed, shields and cases, without exception.

 

Best in World

 

Game over

Edited by Dirkgerman

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23 minutes ago, Dirkgerman said:

I get my Isolation Transformers from 

https://sklep.toroidy.pl/en_US/producer/Toroidy.pl/6/46

 

They build me beautiful custom balanced or straight primary/secondary Transformers with shields between windings, and are potted in an external shield made of magnetic steel, then polished to mirror.

Have found that it's not worth getting or going balanced transformer.

 

They are always earthed, shields and cases, without exception.

 

Best in World

 

Game over

 

Do they add filters?

 

Airlink makes a good 'un too.

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