Are there any adverse effects from isolating the AC power supply on my electronics bench?

I have not been able to keep up with this but one thing I noted (That im not sure was addressed) was that the secondary side had a ground connection through the GFCB (Ground Fault Circuit Breaker)  this would then present the same shock ability if you touched something on the secondary side of the transformer and effectively negates the need for the transformer.

The isolation provided by the transformer is designed to allow such things as a grounded scope to be attached to a "Live wire" without frying your scope, as there is a now common ground you have not achieved this

The ground fault protector will not work of course if there is no ground as there is no alternate route to close the circuit of the secondary side if it is not grounded

When this is on the Mains side of the transformer it is working by measuring the difference between the two legs of the mains wires (Live and Neutral) this does not matter if in the UK or Canada, 240 or 110, we all share a common theme, the neutral is connected to ground at the transformer and sometimes also at the fuse panel, the idea behind the GFCB is that id the current is passing through the ground wire instead of the neutral back to the panel ground it will trip the breaker as the neutral line is not balanced with the live anymore

this is the Canada / USA kind of wiring to show my point

and this is the UK version (Or one possible version) I think this also applies to Australia and parts of Europe

So what is common is that for an GFCB to work it needs a path back to its source so adding an isolating transformer provides the isolation to allow you to break that return path and provide a some what level of protection to you as the unit is now isolated. But if you add a GFCB back in and ground it (Required to make it work) you loose the point of the isolating transformer unless you start constructing a "FLOATING EARTH" for the purpose of the GFCB but that's kinda defeating the point.

This is a simplified circuit of a GFCB and as you can see, it needs the ground return to work

I think in summary, if your after personal protection, then you dont need the transformer but do need the breaker (The lower current device (5mA) would be the less painful but either will save your life in a crunch )

If you want to isolate equipment so you can safely probe around with your scope etc then you need an isolating transformer but you sill need to be aware that the scope or other equipment is also connected to mains ground still so you need to think about what your grounding and the possible current loops you may be setting up.

The idea of a high power and value resistor (A MEG or more) to ground will prevent the drifting up of the isolated side but again if you connect the GFCB it negates that resistor as it will be shorting it out

I have not been able to keep up with this but one thing I noted (That im not sure was addressed) was that the secondary side had a ground connection through the GFCB (Ground Fault Circuit Breaker)  this would then present the same shock ability if you touched something on the secondary side of the transformer and effectively negates the need for the transformer.

The isolation provided by the transformer is designed to allow such things as a grounded scope to be attached to a "Live wire" without frying your scope, as there is a now common ground you have not achieved this

The ground fault protector will not work of course if there is no ground as there is no alternate route to close the circuit of the secondary side if it is not grounded

When this is on the Mains side of the transformer it is working by measuring the difference between the two legs of the mains wires (Live and Neutral) this does not matter if in the UK or Canada, 240 or 110, we all share a common theme, the neutral is connected to ground at the transformer and sometimes also at the fuse panel, the idea behind the GFCB is that id the current is passing through the ground wire instead of the neutral back to the panel ground it will trip the breaker as the neutral line is not balanced with the live anymore

this is the Canada / USA kind of wiring to show my point

and this is the UK version (Or one possible version) I think this also applies to Australia and parts of Europe

So what is common is that for an GFCB to work it needs a path back to its source so adding an isolating transformer provides the isolation to allow you to break that return path and provide a some what level of protection to you as the unit is now isolated. But if you add a GFCB back in and ground it (Required to make it work) you loose the point of the isolating transformer unless you start constructing a "FLOATING EARTH" for the purpose of the GFCB but that's kinda defeating the point.

This is a simplified circuit of a GFCB and as you can see, it needs the ground return to work

I think in summary, if your after personal protection, then you dont need the transformer but do need the breaker (The lower current device (5mA) would be the less painful but either will save your life in a crunch )

If you want to isolate equipment so you can safely probe around with your scope etc then you need an isolating transformer but you sill need to be aware that the scope or other equipment is also connected to mains ground still so you need to think about what your grounding and the possible current loops you may be setting up.

The idea of a high power and value resistor (A MEG or more) to ground will prevent the drifting up of the isolated side but again if you connect the GFCB it negates that resistor as it will be shorting it out

the secondary side had a ground connection through the GFCB

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/gfi3.html#c1

The ground is where the inbalance occurs, ie if the phase an neutral currents are different then it must be going to earth (or another phase as some have discovered).

http://www.siemens.com/download?BTLV_40730

The only ground I see is the ground wire on the load side, not the GFCB.

Mark

BTW we don't switch neutral on this side of the world ... that just leads to big problems.

I agree but it was shown in this image which is why i mention it

also both sides of the transformer are grounded, it is  defeating the purpose of the isolating transformer, as it is a 1:1 transformer  there is still 110V or 240V AC depending on region on the output and now you can still shock yourself to ground or a grounded part of the equipment under test.

Without the transformer being grounded, the GFCB will not work which is why I say it is not needed in a truly isolate situation. GFCB's are for personal protection and as such needs the ground to provide an alternate route back to the transformer to cause the in-balance. If there was no alternate return path, there could never be an in-balance. there could be over 1000V on the isolated side of the transformer and a person could technically hold on to either side (ONE AT A TIME) and never get a shock (I DON'T RECOMMEND TESTING THAT THEORY THOUGH AS A MISTAKE WILL BE FATAL) but if either side is grounded as in this diagram then all bets are off without the GFCB to provide a safety valve.

I agree with you all that having two GFCB's is pointless and that one should go with the single 5mA version

But I have yet to see how the transformer will provide protection if both sides are grounded , that's not what there used for.

Peter

Yes the sketch that Mike provided does 'appear' to have two grounds ...but does it ground the transformer?

The first is a monitored resistor and he did not include the value, which if it was 25M ohms would not be much of a ground.

I don't know why you would have this, since you could just use a meter between ground and one leg of the transformer ... if it goes above zero then something is not 100%.

The second ground only connects to the GFCB, and every GFCB drawing I've seen with an earth also had two 3 pin outlets.

The earth was connected to the 3rd pin on the sockets.

Without the transformer being grounded, the GFCB will not work

You continue to say this and I think the problem is with the name.

The examples of GFCB I showed above from Siemens (a very well respected company) have no earth and operate the same as our RCD.

Yes in order for the inbalance to occur there must be leakage, and unless it leaks to a higher voltage, then by elimination it must be ground ...

The GFCB doesn't need a ground to work, it just needs the inbalance.

I do admit to seeing on TV an example where they also supply surge protection which requires the earth ...

Mark

The drawing with the monitored ground resistor and the GFCI was someone elses that I posted just for ideas.  It was NOT my intention to use the resistor.  I did think that I could get away with the GFCI though because my understanding was that the GFCI would just detect a current imbalance between either of the legs and if there was an imbalance it would break the circuit.  I went looking for a schematic of the internals of a GFCI and came up with this:

The earth ground appears to be carried through, but there are no connections between the GFCI and ground.  So, Peter, are you telling me that the GFCI will not work unless it is connected to a Neutral that is grounded as would be the case in our normal home power distribution in the US?  So, are you saying that if the P and N were the secondary leads of my isolation transformer and neither of them were grounded that the GFCI would not work?  I think I can't wait for my isolation transformer to arrive so that I can test this.

There are a few earthing systems applicable to the UK. A requirement during installation is to determine the type of supply you have (or will be receiving), as this can affect the protective devices required.

More information can be found here: EARTHING: YOUR QUESTIONS ANSWERED - IET Electrical

Ignoring the Breaker for a moment

simple electronics

if you want a current to flow, it MUST have a return path, there will be a positive and a negative and current will flow from one to the other

If this is completely isolated as with the transformer or just take a 240V battery (Without grounding) then how will you get 5mA or any leakage for that matter if there is no return path other than the two wires directly connected to the source.

going back to the breaker now

even though it is not implicitly connecting a ground to anything, both the power wires run through the sense windings (Keeping them in balance). if this is the only possible paths between the source then it can NEVER be unbalanced.

It will become unbalanced if an alternate return path is provided that bypasses the common sense coil in the breaker, this is the return path typically via ground or some other wire that may not be part of the main circuit and if say a human touches one wire and ground it will trip the breaker

if your not grounded and you touch both wires flowing through the coil of the breaker and there is no alternate path, you will simply electrocute yourself and the breaker will happily let you as all the current is still flowing through the breaker sense coil keeping it in perfect balance.

For the breaker to trip there MUST be an alternate path back to the source that bypasses one of the wires in the breaker

the Ground ensures this will happen by providing a low impedance path back to the source

Every domestic household mains wiring example I found searching Google had some form of ground connected to the neutral wire either at the electric company transformer or at the house and in some cases both. The example I showed above included US/Canada and the UK, the US/Can working on 110V ish and a 2 phase system, the UK based on three phase with the centre of the star connected to ground

Of course there are other variants but they will all have the same basic concept... provide a reliable return path that is not expected to conduct electricity under normal operation that in a fault condition (Human short or mechanical / electrical failure) will cause an imbalance in the circuit and trip the breaker

simple electronics

 

if you want a current to flow, it MUST have a return path, there will be a positive and a negative and current will flow from one to the other

 

If this is completely isolated as with the transformer or just take a 240V battery (Without grounding) then how will you get 5mA or any leakage for that matter if there is no return path other than the two wires directly connected to the source.

Oh, man, face palm! Thanks, Peter!  LOL!  I was looking at this thinking that the GFCI would work and that a leakage to ground on either secondary lead would produce a current difference and the GFCI would trip out.  I was not even thinking about the "5mA leak" needing to make the ground loop and that with an isolation transformer with no grounding on the secondary, that there essentially is no return.  The leak circuit would be open, so there should be no leak, so the GFI shouldn't trip.  If the secondary wires were truly perfectly isolated and there isn't a ground loop, I should also be able to grab any individual wire and not be affected though either, correct?

if your not grounded and you touch both wires flowing through the coil of the breaker and there is no alternate path, you will simply electrocute yourself and the breaker will happily let you as all the current is still flowing through the breaker sense coil keeping it in perfect balance.

Grabbing both wires obviously just makes you the load, a crispy fried load, but a load none-the-less.

Oh, and in case anyone asks, I'm still alive because I ask questions.

Your'e still alive because you take advice, and tales of woe (experience).

Sorry I took so long to jump in but I've been very busy the last few weeks, at least I got there before your cooked yourself

I think there has been a few situations recently where members have been lets say not 100% on the implications of safety so I try to take these subjects seriously and may not weigh in unless I feel there is someone's safety at risk, a bit Like Mark and co re a certain mains relay board. This is by no means in the same category but I felt I had to say something based on my understanding of the solution

If I got something wrong here guys, please let me know, I have as much to learn as the rest of us and you have all been kinda quiet since I responded ?

you have all been kinda quiet since I responded

I think you simply filled in the last part .... we had earlier discussed using mixed isolated/non-isolated and eventually got the plan 'more refined'.

Mike is still playing with XRay machines and if we add microwaves he might have the opportunity to 'cook' himself.

Mark