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Johnsboat
Johnsboat

Posted: Mon Jan 20, 2014 1:46pm

Post Subject: 230v Earth Bond.

I've just brought my first boat and had a BSS examination at the same time as the survey. I've been advised to bond the 230v protective earth to the steel hull. Talking to the surveyor he said to take an earth lead from the 230v consumer unit and fix it to an engine bearer. Is it necessary to use the bearer, or could I fix it to the cabin/engine bay bulkhead? If I do have to fix it to the bearer what thickness should the cable be for a distance of about 8 feet? Thanks in advance for your advice. John

230v Earth Bond.
Tony-B
Tony-B

Posted: Mon Jan 20, 2014 3:03pm

Post Subject: 230v Earth Bond.

Before I even attempt to answer your direct question there is another vital conversation the surveyor should have had with you concerning hull corrosion. If you will never use a shoreline so the 230V supply is ALWAYS from an inverter or onboard generator then there is no corrosion issue but once a shoreline is involved there is a potential problem because your boat's hull will be connected to many other boats via the shoreline earth. This means that shore side wiring inadequacies or faults on other boats might cause your hull to be eaten away by stray currents. If a shoreline is involved I would advise you to fit an isolation transformer, if funds permit, or otherwise a galvanic isolator before making that hull connection. The next point concerns any inverter you may have. Some have a center tapped "earth" which means that the normal line and neutral are running at +115 volts and -115 volts giving 230v rather than the domestic situation where it is +230 volts and 0V. If you blithe connect a center tapped inverter "earth" to the hull you cold well short out one half of the inverter with the inevitable results. You must investigate any inverter you ensure it is safe to do as you have been advised. Now to your direct question assuming such a connection is safe. I suppose 10mm conductor cross sectional area cable is indicated by domestic practice but I am equally sure in this case 4 or 6mm CSA MULTI-STRAND cable will be fine. Stick with the yellow/green colour coding so others know its a mains earth bond. Best practice dictaes that the mains earth bond should be close to the 12V negative hull bond but NOT on the same bolt. This more or less indicates whichever engine bed the 12V is bonded to. However although I can not advise anything other than best practise I would observe that the bulkhead is welded to the hull, as are the engine beds, so it should still have a perfectly adequate low resistance path for fault currents. Tony Brooks

Johnsboat
Johnsboat

Posted: Tue Jan 21, 2014 11:31am

Post Subject: 230v Earth Bond.

Hi Tony, Thank you for your quick response. The 230v is via a shoreline and the surveyor did suggest a galvanic isolator, which I have brought and am about to install. There is no inverter on board yet, it's on the wishlist, but depends on how we use the boat. Thanks again for the advice. John.

hmorse
hmorse

Posted: Sat Aug 08, 2015 10:35am

Post Subject: 230v Earth Bond.

Hi - I have a question related to this topic, if I may. Since lifting a boat out of the water for blacking I see it has corrosion that appears to be from 230v power. My boat has never, to my knowledge, been in a marina, and has no mains inlet. Could you help me understand how this might happen - would it be another boat using mains power close to me on the canal?

Tony-B
Tony-B

Posted: Sat Aug 08, 2015 3:27pm

Post Subject: 230v Earth Bond.

The first thing to question is why you think the pitting is caused by 230 volt electricity. All galvanic corrosion is likely to result in silver pits so it could just as well be a 12/24 volt problem or, if your boat is in any way in electrical contact with adjacent metal piling or walkways , it could be simple galvanic corrosion caused by two dissimilar metals in water. By and large our anodes only protect to about a 6ft or so radius so if the conductive contact between your boat and the shore based metal was near the middle the anodes would not be so likely to protect and wear. If your boat is in no way connected to the earth or adjacent metalwork then with one boat close by one side with a mains earth fault and another on the other with no galvanic isolation then your boat may provide the easiest path for the fault current to get back to the substation. This means electrons will be joining your boat on one side and leaving them on the other, hence corrosion.

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