Isolating Transformers, The Earth wire connection conundrum

[FlyingCloud1937]

remember I've always said Potential!


With a transformer the output voltage is not referenced to ground - see diagram (a) below. There is no "return path" so you could (stupidly) safely touch the "live " conductor and ground and not received a shock.

I say "stupidly" as, while this arrangement is safer it is not safe unconditionally. This is because, if there is leakage or hard connection from the other side of the transformer to ground then there may still be a return path - as shown in (b) above. In the diagram the return path is shown as either capacitive or direct. If the coupling is capacitive then you may feel a "tickle" or somewhat mild "bite" from the live conductor. If the other conductor is grounded then you are back to the original transformer situation. (Capacitive coupling may occur when an appliance body is connected to a conductor but there is no direct connection from body to ground. The body to ground proximity forms a capacitor.)
SO a transformer makes things safer by providing isolation relative to ground. Murphy / circumstance will work to defeat this isolation.
This is why, ideally, an isolating transformer should be used to protect only one item of equipment at a time. With one item a fault in the equipment will probably not produce a dangerous situation. The transformer has done its job. BUT with N items of equipment - if one has a fault from neutral to case or is wired wrongly this may defeat the transformer such that a second faulty device may then present a hazard to the user. In figure (b) above, the first faulty device provides the link at bottom and the second provides the link at top.

[Saltyhog]

That's a pretty good summation Loyd. I like the drawing. Bear in mind the shock in the right hand picture requires a double fault. If the parasitic leakage components (drawn in dashed) are of low enough impedance to permit a shock, or even tingling, there is a preexisting problem with the installation wiring or equipment.

[FlyingCloud1937]

Originally Posted by Saltyhog

That's a pretty good summation Loyd. I like the drawing. Bear in mind the shock in the right hand picture requires a double fault. If the parasitic leakage components (drawn in dashed) are of low enough impedance to permit a shock, or even tingling, there is a preexisting problem with the installation wiring or equipment.

Yep, that's my point we are on a boat floating in the sea. One day everything is fine and no faults

The next day a fault potential is there.

An ISO on a boat isn't about protecting against faults, it's a magnitude in trying to stop corrosion.

Lloyd

[chala]

Originally Posted by Saltyhog

The thing about these threads that I'm sure is very frustrating to many readers is who do you believe?

They do not have to believe any one they just have to comply with the regulations in force in their own countries. To peddle murderous idea in this forum is irresponsible.

Originally Posted by Saltyhog

To Chala, you are disagreeing with a number of electrical engineers with quite a bit of experience in the field.

Experience in what field? To me they do not look that bright they promote devices that they realize later will offer no protection and do not know how to connect them.

Originally Posted by Saltyhog

Some of us have designed power systems in safety critical medical applications (myself for one).

I hope they are satisfactory too many people have died in hospital out of electrical experiment.

Originally Posted by Saltyhog

For example, if an isolated system yields "tingling" when touched, it's not really isolated (completely). There may be a problem with the transformer, but it's likely a wiring error. There is a leakage path somewhere that is going to require some analysis to nail down.

Someone will say “not really ready for prime time”

Originally Posted by Saltyhog

For us, I think the best, safest method is whole boat RCD, GFCI's on every branch circuit, no ground to seawater. Opinions?

There is nothing new about this method. I note that you are not a proponent of the isolation transformer. I have RCD on my boat and no ground to seawater and that for over ten years.

[pbiJim]

Originally Posted by chala

Here are two GFCI as you may notice each one have 3 wires. How do you connect them to yours two wires floating wiring?

I would be interested to hear the response to this question from this gentleman's most vocal critics. I think that this is a valid & productive question. The correct answer to this question should be useful to anyone with an IT & a GFCI on their boat.

[sailorchic34]

Originally Posted by chala

They do not have to believe any one they just have to comply with the regulations in force in their own countries. To peddle murderous idea in this forum is irresponsible.



Experience in what field? To me they do not look that bright they promote devices that they realize later will offer no protection and do not know how to connect them.




I hope they are satisfactory too many people have died in hospital out of electrical experiment.




Someone will say “not really ready for prime time”



There is nothing new about this method. I note that you are not a proponent of the isolation transformer. I have RCD on my boat and no ground to seawater and that for over ten years.

Hi Chala. I've noticed your quite opinionated with electrical and plumbing issues as well as many other areas too. Would you be a dear and tell us your background . Are you an engineer (EE, ME, CE, PE) or tradesman, doctor, lawyer, etc.

Me I'm just this blonde chic who doesn't know anything and never spent a day in collage in my life. I have however, in the past sat and passed the professional engineers PE exam as well as a few others. Oh I'm not an EE, though I've read the books, and have had lovely discussions with and worked with some of the best in the country.

I do have some small ability with mechanical, plumbing, hydronics and utility plant design though, having been senior project engineer or lead engineer on a number of interesting projects in the $500 million to billion dollar price range, plus software design, Digital electronics and a handful of other boring things.

So your quite right that I know practically nothing and am just this Bimbo

So Chala, whats your background. I really would like to know.

[Saltyhog]

Originally Posted by chala

There is nothing new about this method. I note that you are not a proponent of the isolation transformer. I have RCD on my boat and no ground to seawater and that for over ten years.

Actually, I am a proponent of isolation transformers. I think they are the best solution. I simply am not a proponent of adding the weight for something I seldom use. So, I'm taking a compromise approach. I know it's a compromise. I understand the trade-offs I've made, and accept them. I've sees the HF switched mode isolation transformers -- good idea, but a lot of money and yet more complexity.

[Saltyhog]

Originally Posted by sailorchic34

Hi Chala. I've noticed your quite opinionated with electrical and plumbing issues as well as many other areas too. Would you be a dear and tell us your background . Are you an engineer (EE, ME, CE, PE) or tradesman, doctor, lawyer, etc.

Me I'm just this blonde chic who doesn't know anything and never spent a day in collage in my life. I have however, in the past sat and passed the professional engineers PE exam as well as a few others. Oh I'm not an EE, though I've read the books, and have had lovely discussions with and worked with some of the best in the country.

I do have some small ability with mechanical, plumbing, hydronics and utility plant design though, having been senior project engineer or lead engineer on a number of interesting projects in the $500 million to billion dollar price range, plus software design, Digital electronics and a handful of other boring things.

So your quite right that I know practically nothing and am just this Bimbo

So Chala, whats your background. I really would like to know.

Hey, I like smart blonde chicks. Actually I like smart chicks. I like smart guys too, but not in the same way.

[chala]

Originally Posted by Oceanride007

To Chala
I can see you have a legit concern against IT. Would my floating earth suggestion (above) resolve that. And I think you can still hold on to one leg and jump in the water, but I wouldn't.

I do not have concern against Isolation Transformer, I have concern about how people wire them up and how they may endanger other people. I really did not had the time to analyse and test your suggestion it is maybe a great idea but you will need to convince the Regulatory Authority that it is. You are quite right with your earth lamps but they where already superseded in the 1960 by Ground Fault Indication. I personally feel that in a ship where home appliances are used, RCD’s should be used. It is to late to go and investigate an alarm and find someone dead in the laundry.

[chala]

Originally Posted by sailorchic34

So Chala, whats your background. I really would like to know.

What I am is of no importance. The ones that have to defend themselves by gloating about their titles are always suspect to me. Personally I judge people by their performance not by what they pretend to be. I think you are a bit too hard on you’re self you did a good job in rebuilding that motor I am sure you would be able to wire a GFCI to an Isolation Transformer, more than other can do. Bye
By the way did you find the conundrum?

[chala]

Originally Posted by Saltyhog

Actually, I am a proponent of isolation transformers. I think they are the best solution. I simply am not a proponent of adding the weight for something I seldom use. So, I'm taking a compromise approach. I know it's a compromise. I understand the trade-offs I've made, and accept them. I've sees the HF switched mode isolation transformers -- good idea, but a lot of money and yet more complexity.

I know someone that may say.

Originally Posted by Tantalus

Ya know....you guys are actually agreeing...just using different vocabulary.

[DotDun]

Originally Posted by chala

So you got the clue.
Here are two GFCI as you may notice each one have 3 wires. How do you connect them to yours two wires floating wiring?

Chala,

If you examine your own diagram, you'll notice the ground wire has absolutely nothing to do with the how the gfci works. The gfci looks for an imbalance of current between the wires labeled "L" & "N". If it detects an imbalance of greater than 5ma (in the US), it opens both "L" & "N". The 3rd wire has no affect on the operation. The leakage could be to the case of another appliance plugged into a completely separate circuit.

Now you can answer your own question. "How do you connect them to yours two wires floating wiring?"

[s/v Jedi]

Originally Posted by DotDun

Chala, If you examine your own diagram, you'll notice the ground wire has absolutely nothing to do with the how the gfci works. The gfci looks for an imbalance of current between the wires labeled "L" & "N". If it detects an imbalance of greater than 5ma (in the US), it opens both "L" & "N". The 3rd wire has no affect on the operation. The leakage could be to the case of another appliance plugged into a completely separate circuit. Now you can answer your own question. "How do you connect them to yours two wires floating wiring?"

Another knowledgeable engineer reports with correct factual info, thanks DD

To have to ask the question about three wires or two on a GFCI outlet, while having the diagram. It clearly shows the difference between understanding and being clueless. Also, coming up with BS when asked to state if one was educated on the subject or not should be telling. For me, as an engineer, it is clear who knows and who doesn't in this thread, but I guess for non-engineers it is more difficult. If readers just don't know then it is safest not to trust anything written here. My advice is to call Victron Energy in the Netherlands (they have a good support number there and speak English of-course) and ask them.

There were threads like this one, about IT's before. May be a search can still find them?

[Oceanride007]

I’ll have a stab at it. I’m more mechanical but here goes.

A single circuit supplied by a IT, with a insulation problem that makes a casing live, say on the casing of a refrigerator, although there is a potential there is no risk to any body or discrepancy that will action the individual circuit RCD. There is no danger because we don’t have a return path, yet we have a undiscovered problem. And there really isn’t any need for the RCD in this circuit.


In response to the moon rock scenario, the proposal is multiple RCD on every circuit.
Assume a separate circuit parallel to the first, also has a fault in its insulation, now if that potential is closer to the potential of the other hot leg. And this circuit is also protected by another RCD. The RCD will not give protection for the same reason and we have two faults. However if a hapless person touches both potentials and makes the circuit then we will have imbalance in both circuits that will open a RCD devices and because the threshold is 5ma, then the person has probably had a close call but is safe.

This situation is much the same as a domestic situation, when a shock hazard occurs, the RCD would do its job.

I think some people here believe a regulatory authority would not accept this. Some people say to hell with them, some want the authority to come around.

Some people don’t understand all the implications of a whole of ship approach, we have in water shock hazards and corrosion issues hence the attractiveness of IT.

If you don’t have leakage issues, on your boat, great but how do you know, I think a forum and discussion like this would be helpful, in alerting boat owners to the risk and risk mitigation.

Anyway, no one else has mentioned it but because the first fault could exist for years, wouldn’t a simple mega test help detect it.

[sailorchic34]

Originally Posted by chala

What I am is of no importance. The ones that have to defend themselves by gloating about their titles are always suspect to me. Personally I judge people by their performance not by what they pretend to be. I think you are a bit too hard on you’re self you did a good job in rebuilding that motor I am sure you would be able to wire a GFCI to an Isolation Transformer, more than other can do. Bye
By the way did you find the conundrum?

You say the sweetest things....

Oh sorry, I was not gloating at all. Just fact. You were implying I was just a ditsy blonde, Which Ok I can be sometimes. But not generally.

I've not a title at all at the moment. Other then boat bum-ette. Gee wiring a GFI can be tricky..... thanks for the vote of confidence.

So I'll put you down as a tradesman....