Isolating Transformers, The Earth wire connection conundrum

[sailorchic34]

Originally Posted by pbiJim

I think that there may also be some local codes that need to be adhered to in some places, in addition to NEC. NYC comes to mind.

Oh true, NYC does have its own electrical code, well building codes, as does Chicago and I think Philly. Most of that is union written to increase the cost of installation. By Union written, I mean the original code was written by building officials who were tied to the electrical union. By adding cost I mean like requiring 10 gauge minimum wire size for branch circuits. Chicago requires all electrical to be in hard conduit That adds a bit to every house. That sort of thing.

The old uniform plumbing code was written by union plumbers who became building officials. Though local inspectors still prefer the older UPC. Much of the code is there to increase cost of installation. Least as it related to waste and vent design, for example. The newer international plumbing code (which is not quite international in scope) does resolve that to some extent. That is allow other options in waste and vent design, for example.

[FlyingCloud1937]

It seems everyone wants to take bits and pieces of each system they favor and combine them into their own preference.

What we have is:

Earth Ground
Ships Ground
DC Ground
Bonding Ground
Radio Ground
Lighting Ground
Plus a number of inter related grounds. ie: inverter/generator/IT/Shore...it goes on.

Each is its own system, each requires they be fully autonomous, but each requires relation of inter-connecting, whether by bond or switching.

So you can't get to point Z from point A, unless you understand why you make each connection.

I don't believe a novice can get to point Z properly from the recommendations from any posting here.



Lloyd

[DotDun]

Originally Posted by Oceanride007

I really don't think a IT will help out with Harmonic distortion issues.

I'm at a loss trying to figure out this statement. Do you not understand how inductive reaction affects AC?

[sailorchic34]

Originally Posted by FlyingCloud1937

It seems everyone wants to take bits and pieces of each system they favor and combine them into their own preference.

What we have is:

Earth Ground
Ships Ground
DC Ground
Bonding Ground
Radio Ground
Lighting Ground
Plus a number of inter related grounds. ie: inverter/generator/IT/Shore...it goes on.

Each is its own system, each requires they be fully autonomous, but each requires relation of inter-connecting, whether by bond or switching.

So you can't get to point Z from point A, unless you understand why you make each connection.

I don't believe a novice can get to point Z properly from the recommendations from any posting here.



Lloyd

Luckily we're talking recreational boats and not ships. So its not that complicated. Where a IT is used for boat power, such as Jedi has, Shore ground/earth is 100 percent isolated from the boat. There is no ground loop from the IT secondary to earth or shore ground. This is per the NEC and ABYC. So at least in the USA, shore earth does not connect through a IT and where an IT is used shore earth is not connected to boat ground. Pretty basic and not complicated at all..

DC ground is really DC- and not a separate ground, least ways on a small boat. RF ground is generally separate, though can be earthed via through hull. Generally its capacitance coupled to earth in a small boat. On a small boat bonding and lightning is normally the same thing. Different on ships though.

Without an IT, THEN the shore ground/ earth is also the boats a/c ground when connected to shore power. Which creates lots of issues with ground loops and mis-wired boats.

Throw in a IT on the boat after the shore plug and look the boat side is decoupled from shore A/C. No ground loops.

[transmitterdan]

Originally Posted by DotDun

I'm at a loss trying to figure out this statement. Do you not understand how inductive reaction affects AC?

An IT is not really useful as a harmonic filter. Harmonic distortion will just be replicated by most ITs available. Specially designed high leakage transformers can reduce distortion. However, you will not like the voltage regulation of these setups unless you integrate the high leakage transformer into the voltage feedback system. Few small generators can deal with this complication.

[transmitterdan]

I agree with SC. It's not complicated and it can be done with no "ground" which has many benefits to both safety and corrosion prevention.

[Saltyhog]

Originally Posted by transmitterdan

An IT is not really useful as a harmonic filter. Harmonic distortion will just be replicated by most ITs available. Specially designed high leakage transformers can reduce distortion. However, you will not like the voltage regulation of these setups unless you integrate the high leakage transformer into the voltage feedback system. Few small generators can deal with this complication.

You beat me to it Dan. If your IT has enough leakage inductance to filter harmonics, your IT will be pretty inefficient. Even if the leakage inductance was high enough to matter, depending on your load, it can make things worse.

[Oceanride007]

So is this where we are at:

Earths not required after the IT. Although Jedi tied them together and called it boat ground.
IT not required for Harmonic distortion issues.
Size of IT optional
RCD is optional.

Have I missed something.

My thoughts:
Double pole, not consensus, but on a metal vessel I suggest mandatory.

To FC I sympathize with your remark about a free for all. It should not be, and Cowboys (do you use that term in US) should not be encouraged, yet on this forum we are all looking for answers or discovering safety issues on our own system.

I still think that a fault from L1 to Frame on non-double insulated equipment, especially on a metal boat, is a concern. Double pole switch would help, but is it enough?.

I have a big problem on a yacht (Swan 65’) because of so called professionals haven’t done it neatly, provided wire numbers or supplied drawings, yet its safe and they say complies with the rules. Can we get neatness, provide drawings and wire numbers on a refit regulated? I’m not serious, but you see my point.

[s/v Jedi]

Originally Posted by Oceanride007

So is this where we are at: Earths not required after the IT. Although Jedi tied them together and called it boat ground.

Almost. When on the hard, I install a jumper and have ground at every outlet and device like code requires. Also, I have several (!!) bonding and grounding systems to seawater aboard and could choose to connect to that if I want for some reason.

In fact, I have a total of four grounding systems:

1. Shore power ground, runs from shorepower cord to inlet to input of isolation transformer. This ground protects against failures of the shorepower cord or inlet, which is where 99% of all problems start.

2. Bonding system to cope with lightning strikes. Under each keelstepped mast is a bronze plate connected to the mast and almost all metal parts on deck, including all cleats, winches, padeyes etc.

3. AC boat ground. Every outlet and permanent connection has the ground wire, incl. the output of the isolation transformer, where I can jumper it to the shore power ground.

4. HF ground, which is a copper mesh that is laminated into the aft section of the hull. Contrary to what many suggest, it has no direct connection to the seawater, but it is capacitively coupled to it for HF frequencies.

Now here is something important to check for anybody who has a bonding system and spends time at anchor: your windlass should NOT be grounded/bonded. The metal housing should not be connected to ground. The motor should have an isolated negative terminal so that no contact with the housing exists. No green bonding wires either. Also. With the anchor deployed, the chain should not touch any bonded metal parts on deck.

The reason is that the anchor into the seabed is at another potential than the bonding plate under the hull, which means a current will flow when one of the connections described above exists. This can eat up anchor chains very quickly; I have seen it happen in 2-3 weeks time.

[transmitterdan]

Nick,

I don't believe you have to connect AC boat common (third wire) to shore ground to comply with codes. In fact it might violate NEC in US because your IT secondary is not referenced to shore ground. If you found a code requirement on this I would like to look it up. All the NEC references I find about IT usage says earth ground should not be associated with the secondary circuit of an IT which means the third wire of any outlets should not be earth ground. I believe it is ok to connect third wire to one IT secondary in single phase systems. I haven't found a code reference that says not to. If you know of one please tell me about it too.

[DotDun]

Originally Posted by transmitterdan

An IT is not really useful as a harmonic filter. Harmonic distortion will just be replicated by most ITs available. Specially designed high leakage transformers can reduce distortion. However, you will not like the voltage regulation of these setups unless you integrate the high leakage transformer into the voltage feedback system. Few small generators can deal with this complication.

It handles the high freq, I'll take shots from a scope.

[pbiJim]

Please pardon 2 nagging questions.

1) Does SV Jedi use GFCI outlets anywhere on board?
2) If so, what do you connect the green ground screw on the GFCI to?

I understand that my question 2 might be redundant to your last point #3. I am just seeking clarity.

Thanks,
Jim

[chala]

Originally Posted by s/v Jedi

Almost.

1. Shore power ground, runs from shorepower cord to inlet to input of isolation transformer. This ground protects against failures of the shorepower cord or inlet,

I agree and I would ad: transformer to the list. (This ground protects against failures of the shorepower cord or inlet,) and transformer.

Originally Posted by s/v Jedi

3. Every outlet and permanent connection has the ground wire, incl. the output of the isolation transformer

Fine

Originally Posted by s/v Jedi

where I can jumper it to the shore power ground.

Not recommended will defeat the purpose of having an Isolation Transformer.

Originally Posted by s/v Jedi

Now here is something important to check for anybody who has a bonding system and spends time at anchor: your windlass should NOT be grounded/bonded. The metal housing should not be connected to ground. The motor should have an isolated negative terminal so that no contact with the housing exists. No green bonding wires either. Also. With the anchor deployed, the chain should not touch any bonded metal parts on deck.

The reason is that the anchor into the seabed is at another potential than the bonding plate under the hull, which means a current will flow when one of the connections described above exists. This can eat up anchor chains very quickly; I have seen it happen in 2-3 weeks time.

The above is more about galvanic corrosion and as little to do with a correctly wired Isolation Transformer. It is rare to see a boat connected to shore power with its anchor deployed.
I have a metal boat in which it would be very difficult to effectively isolate the chain from the metal hull. In the many years that I have been sailing this and a previous metal boat, I never had problem as described above.

[pbiJim]

Originally Posted by chala

It is rare to see a boat connected to shore power with its anchor deployed.

In some areas, you nose into the dock to pick up shore power & drop a stern anchor. to keep from swinging around. People who do not have a good stern anchor rig will sometimes reverse the boat direction at those nose-in docks.

[pbiJim]

Originally Posted by transmitterdan

An IT is not really useful as a harmonic filter.

It depends what you are trying to filter. If you have high amplitude spikes, an IT will often clip them. Very high frequency hash will usually get bucked. Signal distortions that do not exceed the flux saturation capacity of the transformer generally do pass right on through though.