Earth

[pvb]

Don\'t bond it...

Unfortunately, textbook writers are certainly not always right. You shouldn't bond AC earth to battery negative. But you should ensure that your AC installation is properly protected by a sensitive RCD.

 

[Gunfleet]

Re: Don\'t bond it...

That seems to be the consensus and goes with my own logic. I couldn't see what problem wouldn't be solved by connecting a simple shore side power supply with a very short cable run on board to an RCD. But I'd be willing to be convinced different by a qualified electrician!

 

[jfkal]

Exactly. Use diodes with ample amperage to make sure they support a short and trip the breakers

---|<----|<--- in parallel with ---->|----->|-----

 

[AlanPound]

The way to do it (the galvanic isolator) is to use a fairly beefy bridge rectifier, connect the + and - together, and connect one ~ (AC) connection to the shore-side earth, and the other ~ to the boat earth. In addition, it would be worth putting a non-polarised 0.1 uF capacitor straight across the ~ pins, as this will provide a low-impedance path to shore-side ground for any high-frequency signals (voltage rating probably doesn't matter, as it will only see just over a volt across it, but any cap that small is likely to have a reasonable voltage rating).

.... Or just buy a commercial galvanic isolator, which is basically the same thing...

 

[Trevethan]

Re: Don\'t bond it...

Good job I logged on this morning.

Been in London all week and not looked in here. Back in Devon now and was about to nip down and do the bonding job. seems like it is not requires and I should install a polarity testy thing. Wonder if I could just wire in volt metre with some kind of diode in it that would block live current fromthe neutral terminal?

Or am I talking rubbish? still don't get ac electrics really!

regards Nick

 

[ean_p]

for our part (and its a steel boat!) we had an isolating transformer wound that is 'centre tapped'....that is to say that you feed 240 volts in at one side and at the other side you have 3 wires...one at -110v one at -0v and another at -110v there in you can pick off 240 volts from the two outside ones and connect your rcd to the centre tapping(as rcd's work on imbalance) to give what is in effect a virtual earth....into this transformer we feed what ever source of 240 v that we have be it shore...genny or inverter all by using a selector switch that breaks before making...hench we import no connection to the shore supply at all(even an earth link to shore can be a problem....) yet retain the very important use of the rcd.....well thats how we do it anyway.....no perfect answer or we'd all be doing it that way.....

 

[tome]

With a transformer you will isolate both live and neutral which has some advantages but also some dangers. If either tap comes into contact with the hull the other becomes lethal so this is one case where I would deliberately bond to DC earth (hull) and label it neutral so that you enjoy Live protection from the other conductor.

Wouldn't want to connect an RCD to the centre tap as this imbalances any protection. Connect it to the outer taps only. Centre tap is most definitely not a virtual earth.

Please leave a flourescent lamp in your rigging so I can steer well clear. You won't need to connect it!