Isolating Transformers, The Earth wire connection conundrum

[goboatingnow]

And PBIJim yes you cannot have a hazard to ground if ground is not in the circuit as is the case of a floating IT

And Chala , merely quoting regulations is nonsense, what has the force of law in major jurisdictions , do you know and even then look at the unconscionable delay abyc took in mandating whole boat RCDs, when the EU had them in its code for neatly 25 years.


To remind people this thread is a debate about earth referenced or floating secondary outputs from ITs. ( which are NOT auto transforners under any circumstances )

[pbiJim]

Originally Posted by sailorchic34

Not possible in a residential location. You have a hot and neutral as the two wires. Neutral and ground are at the same potential. So you never get balanced flow in the two wires and shock. Only from hot through a ground loop..

The IT has two hots at opposite ends of phase. No ground loop is available to conduct so no ground loop current flow happens.

GUY's this is BASIC electrical, not even electrical 101.

Like transmitterdan. I to am SO done.

In the case of an older house, wired before the grounded neutral standard was in place, this is very much possible.

In the case where someone has grounded a center tap, as some have suggested in some scenarios, this actually becomes more likely, & therefore more relevant in this discussion.

[pbiJim]

3'd wire on a GFCI...

I just took a brand new Leviton brand GFCI & wired it with the ground terminal open. I then placed a 10KΩ resistor from L1 to S2, inducing about a 11-12ma imbalance in the legs. The device tripped.

When I put the resistor from L1 to the green ground connection screw, nothing happened. The device did not trip.

The people who have said that A GFCI will trip due to a leg current imbalance, regardless of grounding, are correct.

The shortcoming of not wiring the ground is not isolated to removing the ability for a breaker to trip out on over-current though. If a faulty appliance had an electrical leak to it's case & the case was wired to the ground pin on a 3 prong plug, a GFCI outlet with a floating ground would not see that. A GFCI with it's ground screw wired would see that problem & trip as soon as 5ma was drawn through the ground pin.

I am not trying to imply that this means you should ground an IT secondary. I am just saying that this is an example of something that someone may wish to consider when deciding what to do with that pesky extra little green ground-connection terminal on the GFCI outlet, since those outlets are recommended in wet areas of a boat, like the galley, the head & top side.

[goboatingnow]

Originally Posted by pbiJim

3'd wire on a GFCI...

I just took a brand new Leviton brand GFCI & wired it with the ground terminal open. I then placed a 10K ohm resistor from L1 to S2, inducing about a 11-12ma imbalance in the legs. The device tripped. The people who have said that A GFCI will trip due to an imbalance regardless of grounding are correct.

The shortcoming of not wiring the ground is not isolated to removing the ability for a breaker to trip out on over current though. If a faulty appliance had an electrical leak to it's case & the case was wired to the ground pin on a 3 prong plug, a GFCI outlet with a floating ground might not see that. A GFCI with it's ground wired would see that problem as soon a 5ma was drawn through the ground pin.

I am not trying to imply that this means you should ground an IT secondary. I am just saying that this is an example of something that might be considered when deciding what to do with that pesky extra little green terminal on the GFCI outlet that is recommended in wet areas like the galley & on deck.

Middle paragraph is wired pbiJim , whether the imbalance flows via the earth wire or via the earth itself , the RCD will trip. Note GFCI is really a redacted term as its suggests the ground is the only fault path that can trip such devices in Europe GFCI has long been replaced by RCD , which is a more correct term

Dave

[pbiJim]

Originally Posted by goboatingnow

Middle paragraph is wired pbiJim , whether the imbalance flows via the earth wire or via the earth itself , the RCD will trip. Note GFCI is really a redacted term as its suggests the ground is the only fault path that can trip such devices in Europe GFCI has long been replaced by RCD , which is a more correct term

Dave

Can you please comment as to what you suggest a person does with the green ground-connection screw on a GFCI outlet on a boat with an IT that is installed as per your instructions?

I'm not looking to set up an intellectual ambush here. I'm really not sure what I would want to do with that connection in a system with a floating secondary IT.

[transmitterdan]

Originally Posted by pbiJim

Can you please comment as to what you suggest a person does with the green ground-connection screw on a GFCI outlet on a boat with an IT that is installed as per your instructions? I'm not looking to set up an intellectual ambush here. I'm really not sure what I would want to do with that connection in a system with a floating secondary IT.

Ok, I'll try one more time. The ground terminal on a GFCI or RCD does not impact the ability of the device to work. It does not have to be connected to anything for the device to work.

The purpose of the ground wire in a US house is for something that predates GFCI or RCD. Before these devices came along safety was improved by making a low resistance path to earth that hopefully was less than a human body. If an appliance developed a short from hot to the case the ground wire would hopefully trip the breaker. If the current was lower leakage then at least the current would likely flow in the ground wire and not in your hand when you touched it.

The ground wire has nothing whatsoever to do with the function of a RCD. If you don't believe or understand this statement then we may be unable to communicate.

[pbiJim]

Originally Posted by transmitterdan

Ok, I'll try one more time. The ground terminal on a GFCI or RCD does not impact the ability of the device to work. It does not have to be connected to anything for the device to work.

Hi Dan & thank you for the response.

The quick little test that I documented a few posts back (post #244) confirms that you are correct in saying that an imbalance in the current between L1 & L2 will trip a GFCI regardless if the green screw on the outlet is wired or not.

I am still left to wonder though, in the case of a boat with a floating secondary IT, & a GFCI outlet, what is the best thing to do with the ground-connection screw on the GFCI outlet. Should it be left open? Should it be tied to the hull? Should it be tied to the box that the GFCI is in but isolated from everything else? Should something else be done with it?

If that 3'd connection on the outlet can be used to improve safety in some way, I think that the option should be explored. I think that this is a genuine practical question.

[goboatingnow]

Originally Posted by pbiJim

Hi Dan & thank you for the response.

The quick little test that I documented a few posts back (post #244) confirms that you are correct in saying that an imbalance in the current between L1 & L2 will trip a GFCI regardless if the green screw on the outlet is wired or not.

I am still left to wonder though, in the case of a boat with a floating secondary IT, & a GFCI outlet, what is the best thing to do with the ground-connection screw on the GFCI outlet. Should it be left open? Should it be tied to the hull? Should it be tied to the box that the GFCI is in but isolated from everything else? Should something else be done with it?

If that 3'd connection on the outlet can be used to improve safety in some way, I think that the option should be explored. I think that this is a genuine practical question.

Actually that's really what we are discussing.

If the IT is floating , then connecting the green terminal on the GFCI outlet does nothing. In fact other then protecting you from the wired dual live to two appliance faults , the GFCI in a floating system actually has virtually nothing to cause it to trip.

If the IT is truest floating then the earth connection can be ignored.

If the IT has a local earth wire , then that should be connected to the earth terminal of the outlet

Dave

[chala]

Originally Posted by transmitterdan

Ok, I'll try one more time. The ground terminal on a GFCI or RCD does not impact the ability of the device to work. It does not have to be connected to anything for the device to work.

The device still requires 3 paths to work.

[chala]

Originally Posted by goboatingnow

In fact other then protecting you from the wired dual live to two appliance faults

Which is in fact not of a small importance.

[goboatingnow]

Originally Posted by chala

Which is in fact not of a small importance.

It's a fairly far fetch fault.

Dave

[chala]

Originally Posted by pbiJim

If that 3'd connection on the outlet can be used to improve safety in some way

Yes it does. If an appliance is faulty, why waiting for a person to trip the RCD? Why having a person subjected to a fault current? The 3’ connection will make the RCD to trip as soon that the appliance become faulty.

[Oceanride007]

To FC, Gobo, Jedi and others not preoccupied talking about RCD.
Well, compelling arguments but I worry that you have moved to the area of dueling qualification and dueling ego and using these as suedo trump cards. The amount of jargon has escalated as well.

I got on to this thread because I want to understand the limitations of my play boats electrical system better, to me it’s a given, I want to understand it better and with my improved knowledge apply test tools to understand what leakage I have, inside and outside the hull.

I like the idea of IT , but with the qualifier that testing should occur to ensure insulation has not broken down and do it before a second fault occurs. I also mentioned double pole switching on each circuit, nobody apart from Jedi picked up on the importance of that. (I suspect my other idea earth lamps won’t fly, but you may consider it.).

Our best solutions to problems were done at a time when there were little regs to get around, best solution is to encourage experiments outside the norm but done safely and knowledgably and get pear review somewhere otherwise the evolutionary process will not deliver the best system.

At sea on a vessel usually with isolated neutral (therefore no hull/earth current), a fault is allowable to be created, so long as you have a method of detecting it. Isolated neutral and floating IT share a lot of advantages in that with a single fault it is still safe and no voltage differences around the hull to cause you the hull/fitting corrosion. The problem occurs cose you tie up and connect with a shore supply and have to comply with a reg/code that is rigid. Hence, I think the purpose of this thread.

Could we have more talk on solution to satisfy the neigh sayers, especially around the area of AC equipment like chargers inverters that may inadvertently connect AC earth to DC neg and my prop shaft.

[transmitterdan]

Originally Posted by Oceanride007

Could we have more talk on solution to satisfy the neigh sayers, especially around the area of AC equipment like chargers inverters that may inadvertently connect AC earth to DC neg and my prop shaft.

I would be curious to know of any charger or inverter that internally connects AC ground (green/yellow wire) to DC minus. Can anyone provide a manufacturer's model that does this?

[s/v Jedi]

Originally Posted by transmitterdan

I would be curious to know of any charger or inverter that internally connects AC ground (green/yellow wire) to DC minus. Can anyone provide a manufacturer's model that does this?

Inverter/chargers often do that when they switch to invert mode. On the Victron unit I have, you can re-program this. The inverter is a power source, so it needs to create a grounded neutral for installations that require one.