Cathodic protection

[NickNap]

I'm moving from a swinging mooring to a pontoon with mains. At the moment I have no shore power fittings, and current bonding connects engine inlet seacock, propshaft & rudder stock. Two questions:
If I onlyuse one of those power leads with trip included for mains, do I need to add anything to existing arrangements?
If I fit a consumer unit, couple of sockets etc, do I simply connect mains earth (inc GI) to existing bonding at one point(adding engine as well)? If I do, do I need to worry about keels?
thanks

 

[VicS]

If you just use a lead and an RCD then you need nothing further, but be sure it is fused appropriately.

If you fit a consumer unit (with RCD and MCBs) but do not connect the earth to the "ship's earth"/12volt negative then there are no further worries. You should not need a galvanic isolator.

If you opt to connect the earth to the ship's earth and 12volt negative in accordance with ISO 13297 and ABYC and CE standards then you would be strongly advised to fit a galvanic isolator, especially if shorepower will be left connected (in use or not).

The whole subject of connecting the mains earth to the ship's earth is highly debatable and until recently I argued strongly in favour of it.

Nothing different should be necessary regarding the keels.

Some useful info about the use of GIs HERE on Sterling's website

 

[NickNap]

Thanks Vic, much appreciated

 

[davidwf]

I bonded my mains earth to -ve 12V as per ISO 13297 and although I used a Gavanic Isolator I ended up with a badly corroded shaft. Have just read ISO 13297 and found that para 4.2 allows for the mains earth to not be connected to boat -ve if an RCD is fitted. See para below. I will be disconnecting my earth before it goes back in the water as a result.


From ISO 13297
4.2 The protective conductor shall be connected to the craft's d.c. negative ground (earth) as close as
practicable to the battery (d.c.) negative terminal.
NOTE If an RCD (whole-craft residual current device) or an isolation transformer is installed in the main supply circuit of the a.c. system (see 8.2), the negative ground terminal of the d.c. system need not be connected to the a.c. shore ground
(protective conductor).

Para 8.2 describes the RCD.

 

[VicS]

Useful info. Did you find ISO 13297 on line. i have never manged to find it. Plenty of offers to sell it to me though.

 

[davidwf]

Yes found it online took me ages though because as you said everybody wants to sell you it. Got it here PDF here

 

[rogerthebodger]

As you know Vic I have been saying this for some time. The one thing I would add is 2 neons between the live and earth and the neutral and earth to show if the shore power earth is intact and the live and neutral's are connected correctly.

 

[claudio]

How would you connect the neons ?
Would you use a 'push to test' type switch, or do you leave the neons permanently connected ?
I would be concerned about leakage current from live to earth finding its way back via some underwater gear.

 

[VicS]

I'll leave Roger to explain although i know what he means.

An alternative is to buy one of those "polarity" tester plugs from a DIY store and plug that in to a socket permanently. As Roger is building his own panels incorporating the neons is an obvious thing to do.

 

[claudio]

I understand how the neons work, but sending the current through the earth wire ?
Won't that bypass even galvanic isolators ?

see here neons

The polarity tester type plugs will produce the same results

I have a huge isolation transformer. It doesn't matter which way the shore power is connected because it goes into the primary circuit only. The secondary windings are'always correct' polarity because they are wired that way.
Also the shore earth does not make it past the consumer unit. The boat has it's own independent safety earth. The consumer unit has an RCD device to protect against leakage currents on the primary side.