[Explorer team]

Dear All,

At the moment we are doing on design and production of two 50 meter explorer yacht.
Yachts are under:
a.Classification Society:American Bureau of Shipping
b.Class notation:ABS +A1 (E), Commercial Yacht, Ice Class D0, +AMS
c.Statutory Cod:MCA LY2 > 500GT
d.Flag:Cayman Islands

Hull (steel) and superstructure (Al) are ready for outfitting. To get back to subject.
Past days we had a lot discussions with our contractor for electrical system. Main issue is type of electrical system. Three wire system or four wire system (with grounded neutral)? Talking about voltage of three phase 380V50Hz and single phase 220V50Hz. A lot of devices on board are 220V and made for domestic usage so neutral is required.

If we decide to proceed with three wire system (without neutral) there is a requirement for huge transformers that can provide 220V and neutral. Other wise if we go with four wire system we can get 220V between one phase and neutral so we do not need additional transformers.

Please to advice me about "common practice" for yacht industry in range 40-60 meter vessels regarding type of electrical system, "three or four wires"

In addition to all above here is a cut from RINA rules

[Marmot]

Since it is going to be ABS classed, why not use the ABS guide for steel vessels?

If the boat is really going to do "expeditions" and reliability is a major concern then I would go with an ungrounded neutral system and install transformers for convenience outlets to avoid problems caused by wall warts and surge protectors.

[Explorer team]

We use ABS rules. I had this from RINA but here is cut from ABS.

Can you please explain why do you think three wire system is more reliable?

regards

[Marmot]

Originally Posted by Explorer team

Can you please explain why do you think three wire system is more reliable?

The ungrounded neutral system is more reliable because a ground fault on one phase will not cause a failure of the supply. This means that critical equipment will continue to function until the ground fault can be corrected.

[Garry Hartshorn]

However one could argue that a grounded neutral system is safer

[Marmot]

Some might make a stronger argument that an ungrounded neutral is safer, that's why you can pretty much do it any way you like.

[sharkbait]

here's my 2 cents

when I design any circuit (& that is what you are doing)
I work backwards from the basic question-
what charastics do I want from this circuit and what am I willing to trade to get them- this includes things like:

do I want total safety or systems operating- during fault (single circuit)
(I never recomend this as it can cause electricution fire or other...)
am I running isolated backups for safety (where am I isolating it)
what conditions is it operating in- what is safe

end loads- wire specs- transformer - wire specs - switch/circuit boards breakers, safety/timer switches ect...
main supply to the board can be looked at as a seperate circuit

In Australia we have bush law- it means the following:
you must prove the circuit is safe in the conditions it is exposed to
(now & future).

in essence-
it relises that there are any number of ways to create a circuit
some circuits are safer/better
technology is advancing
the rule book doesn't cover everything

Any monkey can make a curcuit and get it to work
trained peoples understand why it works and if it is safe for the conditions.

My advice is
design the circuit to trip at/before the source when fault occurs
run a backup to a isolation switch at the load
(if load is the fault then you will know instantly and it can be isloated from everything else, if its in the wiring then isolate and run backup circuit)
Don't ever force a crook circuit to perform it will end badly.

maybe this will help.