12V DC or 240V AC generator

[Ships_Cat]

For the same safety reasons as applies to the 3 wire polarised system in your house's AC supply (assuming you are in the UK or similar) where AC sources have their neutral bonded to ground (as at the house switchboard) so that the house wiring's earth conductor then provides a return path in the case of fault on an appliance or cabling.

For on a boat most (all?) codes require, to achieve the same thing, that all AC sources have their neutral grounded at the source. So, for example, an installed generator, which is an AC source in the same way as a house's switchboard is an AC source, has its neutral bonded to earth at the generator and same for an invertor.

If the boat has an isolating transformer then the shore neutral (and its earthing) is, of course, isolated from the boat side of the transformer so it cannot be "seen" from the boat's point of view, so the transformer is regarded as an AC source in the same way as an invertor or generator is and the neutral on the output side earthed to again give a 3 wire polarized system on board.

For a portable generator with floating neutral the effect is similar to not correctly bonding to earth an on board transformer's neutral. However, as explained before, if it is plugged into the boat's shorepower connection, as they usually are, then the whole of the boat's AC distribution will be floating neutral (as for other safety reasons the neutral on the boat is lifted from the boat's earth when the AC supply is switched to the shore power connection).

Now one could possibly provide a special switched connection for a portable generator seperate from the shore power one such that the generator's neutral is earthed but I suspect no one does or is likely to do that. Furthermore, while the generators have fault protection built in, I suspect that this will in most (all?) cases enable preventing generation if the neutral is earthed and the generator chassis is also earthed, as it should be, or leaks to earth if it is not (I have not and never will have a need to see if this is so).

From time to time I hear some say that if there is an isolating transformer (or small floating neutral generator) you don't need to earth the neutral on the output side, just as when they are used on land. However, in the land case they are thinking of only a single appliance being normally connected to an isolating transformer, so no other AC distribution/appliances are able to be implicated in a fault situation to cause a shock hazard.

Obviously, people get away with ignoring all of these things, just as in a house incorrect wiring may last the life of the house without the circumstances arising where an accident occurs.

Hope that is clear.

John

 

[Anonymous]

[ QUOTE ]
For the same safety reasons as applies to the 3 wire polarised system in your house's AC supply (assuming you are in the UK or similar) where AC sources have their neutral bonded to ground (as at the house switchboard) so that the house wiring's earth conductor then provides a return path in the case of fault on an appliance or cabling.

[/ QUOTE ]You are dreadfully out of date - at least in the UK. Since the mid 1970s houses have been wired with Protected Multiple Earthing (PME) where the neutral is NOT bonded to local ground and can rise many volts - even to phase volts - with respect to local earth. This is why bonding of all metal pipes, etc., in modern homes is so vital. It is perfectly valid technically for a boat to be wired in the same way. I am not familiar with all the boat standards and had assumed that you are current on them but if you didn't know about PME I question that. Exactly which regulations or standards have you been quoting in this thread?

David

 

[Ships_Cat]

Oh my goodness Lemain here you are at it again off down another tack that does not show anything. I live many thousands of miles away from the UK so cannot profess to be exactly correct as to the specific point at which the earth and neutral is bonded there for the electrical distribution to houses. But in effect what I say is still correct, the neutral and earth are bonded.

You are very strangely picky, I suspect trying to prove some sort of superiority of marine knowledge by confounding with irrelevant tangents.

In what I said the neutral is bonded outside of the installation at the point of service which in many places is actually at the switchboard. That is also essentially so with PME albeit the neutral to earth bond is down the wires a bit from the installation rather that at the switchboard.

It is still as I describe so one can only imagine that you are making an attempt to unravel what I say by irrelevant comment.

If anyone has any questions they wish to ask specifically of me, would you please just send me a PM and I would be happy to try and answer if I am able. I think it is clear that it is pointless me trying to make any comment or provide any responses on here as it only leads to time wasting for all.

So have your last say Lemain, I am sure it will be pathetically picky and confounding - however, I will not be reading it. Seems though that you ran out of criticisms of the generator and marine bit - it took some time.

Many thanks to everyone else.

John

 

[Anonymous]

It is sad that you have sunk to personal attacks - indeed almost from the outset. Having sent you two polite PMs and received rude replies I really give up all hope of having any reasonable discussion with you.

Clearly you don't understand basic electricity - it seems inconceivable to me that you actually hold any sort of formal electrical qualification. Do you?

 

[Ships_Cat]

The answer to your question is "Yes" at university level.

I can add that I am in New Zealand and work in the marine industry, among other things, managing the design and construction of high quality boats (built in various countries) for clients as far away as the East Coast of USA. They seem to say that I know what I am talking about (but I am too modest to claim that they are correct /forums/images/graemlins/blush.gif) and I suspect that they also know what they are talking about.

John