Why Galvanic Isolators?
Recent interest in damage done to boats due to the 230V shore mains has highlighted the need to fit a galvanic isolator to your boat.
In order for modern boat builders to comply with modern CE standards such as EN ISO 13297 they must fit the shore earth wire to your boat’s bonding system which is also connected to the hull / anodes / fuel tanks / engine blocks / shafts / propellers / stern tubes / rudders / rudder glands / water intakes / etc. This ensures that any 230V mains faults will operate the R.C.B on the boat in order to save your life.
The downside from these standards is that electrically speaking your boat is now connected to the rest of the boats in the marina and any other metal structures in the area. Electrically speaking they become one and the same. If you follow the earth line you can see everything bonded to the earth, this includes your boat, the one next to you, metal work etc.
This results in two main problems.
Any earth problem on any boat or shore earth will increase the earth voltage cable and so dissolve your boat and anodes at an alarming rate (this could result in the total loss of all the metal on the boat below the waterline).
Because all the boats are now one, if you have a zinc anode on your boat, but no one else has or the marina has not put anodes on its structures (metal pontoons etc) then your boat's zinc (or aluminium / magnesium) will protect all the structures and boats around you, resulting in dramatic zinc loss and expensive lift-outs to replace the zinc. For boats on inland waterways, if you have a magnesium anode and everyone else has zinc or no anodes at all, your magnesium anode will protect all.
The trick is to maintain the continuity with the earth to ensure the safety of your life but remove the continuity with the shore power for the safety of your boat. The solution is very simple. By installing a Galvanic Isolator / Zinc Saver we maintain a good earth link with the shore, but prevent any stray currents coming up the earth line and damaging the boat. The isolator is a simple bridge rectifier but built to the latest ABYC standards. This means in a major fault condition it can carry its rated current for 24 hours without exceeding 90 C on the heat sink. Plus it is forward compatible to meet the new ABYC standards due to be introduced in July of 2002.
The Galvanic Isolator has the following extra features:
- A 4-pin molex connection to enable the latest monitoring system to be connected either as a optional extra (in Europe) or a mandatory installation (for new boats going to the USA)
- 24kt gold plated connectors to prevent corrosion on the earth terminals in the future.
Recent upgrades in the new ABYC recognises the vital importance of the earth wire on the boat. You may have the earth wire connected correctly on your boat but has the marina connected the earth correctly on the shore?
If a fault occurs on the live or neutral cable then the appliances on the boat will stop. This may annoy you but the bottom line is that you can ''live with it''. However the extremely boring, non functional, apparently useless earth wire can be disconnected with no effect on your appliances or without you knowing about it. The difference is that in the event of a fault you may live with the live disconnected but you could die if the earth is disconnected.
If the earth wire is disconnected or has a bad contact, this will not stop the live side from working as normal, with you unaware of a pending disaster.
The new ABYC regulations insist on two new main features.
- The shore earth must be checked to ensure it is connected.
- Anything in the earth system must check itself.
In order to do this there is the Motoring System. The solution to the two main features are archived by the following.
Checking the shore earth
If you look at the wiring diagram you can see that at the power station / local transformer the neutral and the earth are jointed together. So, if we send a signal up the neutral wire then we would expect to receive it back down the earth wire. This is what the monitoring system does: every 'x' minutes it fires a signal up the neutral and monitors its return down the earth, failure for the signal to return to the monitor means there is a fault on the shore earth and an alarm will sound. Also with any type of isolator it is subject to extreme conditions, for example, if a lightning strike hits the boat it is possible to destroy the isolator or any other isolating device such as a transformer. However the new monitor also checks the isolator circuits themselves ensuring the device is in full working order.