BC Electrical Techniques

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Isolation Transformers for the prevention of corrosion

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Marine Isolation Transformer

When a boat is connected to a shore supply of mains electricity, it is vulnerable to certain sources of corrosive damage not faced by boats that have no shore connection. This is because safely wired boats will be connected to the mains Earth, and this can create a corrosion risk in one of the following ways:

Corrosion with other boats in the marina.

All the boats in a marina that have a mains electricity connection will effectively share a physical connection with each other via the Earth wire of the supply cable. They also share a physical connection through the water, and this can lead to a flow of electrons from the metal parts of one boat, (usually the sacrificial anodes) to the metal parts of another. A process similar to electro-plating takes place, corroding the anode and severely shortening its life. If a boat does not have sacrificial anodes fitted, or if they corrode away completely, then the hull, rudder or other metal parts will begin to corrode, with potentially disastrous consequences.

Isolation Transformer

Corrosion caused by difference in potential between earths

A secondary corrosion risk exists in the difference between the Electrical Earth, which is the potential of Earth at the hook up point, and the

True Earth, which is the potential of the water that the boat floats in. The boat creates a circuit between the two potentials. At the electricity power station, the potential of Electrical Earth is the same as True Earth. However, as the power cables make their way across the country, the Earth can pick up an electrical charge from stray currents in the cable. This can lead to a difference at the mooring power point between the two Earths, causing current to flow from the boat, through the hull and into the water. At the points where the current flows, there is a risk of corrosion.

Isolation Transformer

How an Isolation Transformer Prevents Corrosion

An Isolation Transformer has no physical connection between its Primary and Secondary coils. This means that it can sever connection between moored boats whilst they are still able to draw power and be safely connected to earth

A simple wiring diagram showing an Isolation Transformer

Isolation transformer

The above diagram shows the path of the Earth wire from shore to boat. The Earth wire does not physically cross between the two coils of the Transformer, preventing stray currents from flowing to the boat via the Earth.

Isolation Transformers for Voltage Conversion

An Isolation Transformer can be made to change the shore supply to suit your craft. For example, you may wish to take your yacht to the USA, but it is wired for 240V and in America the Voltage is 115V. We can build a Transformer that will allow you use both types of power supply. We can supply a system that simply requires a visit from an electrician to change input voltages, or for an extra charge we can fit the Transformer with a switch-over device, allowing you to adapt your craft to another country’s electrical supply in seconds.


Galvanic Isolators

Transformers for Galvanic Isolation

Further Reading

Corrosion in Marinas – "The Hot Dock"