ES - Marine Isolation Transformers

ES Marine Hull & Dockside Isolation Transformers    

Hull isolation transformers are the only way to completely eliminate the risk of galvanic corrosion between the ships hull and other metal objects (other ships, pilings etc.).

The problem is caused by an earth loop forming and current flowing through the earth wire on the shore supply. The problems occurs in all boats, although steel & aluminium boats are particularly susceptible. It is important to get advice from a suitably qualified marine surveyor or corrosion specialist before installing shorepower.

The isolation transformer eliminates any electrical continuity between shorepower and the ship. The shorepower is fed to the primary side of the transformer and the ship is connected to the output side (secondary).

Our standard transformer range covers 10, 16, 32, 50, 63 & 100 amp single phase shore capacities at 230v. We offer custom units in single phase, three phase to three phase and three phase to single phase.

In addition to these fixed ratio transformers (normally 1:1) we supply voltage converting transformers. Smaller transformers are offered that will boost 115 volts to 230 volts or visa versa. These are available as manually configured or auto changing.

Hull Isolation Transformers

For more information or to request a quote please contact us.



ABYC Compliant. A metallic shield is fitted between the primary and secondary windings and is electrically isolated from all other portions of the transformer. It is fault tested at 4000 volts for 1 minute. This shield is wired via an insulated lead to the transformer chassis. The shield and its connection are able to carry the full load current of both the primary and secondary windings.

UL Compliant 

Although the transformer does not carry a full UL listing they are built to conform to the necessary standards.

Lloyds Compliant 

The transformer is built to conform to the Lloyds Resister standards.



Iso-Boost transformers

For USA spec boats we offer a replacement for the Charles Industries Iso-Boost transformer. This has two input voltage ranges at 208 volt and 240 volt nominal to allow a boat to connect to 2 legs of a 208 volt three phase supply in the USA or to a 240 volt split phase supply. The transformer automatically selects the appropriate input. This can also be helpful if your 240 volt supply is weak (for instance if you are at the end of the dock).

USA Spec Boats

Shore power in the USA is available in a number of forms.

For small craft you may be offered a 110 volt hook up. This normally is limited to 30 amps of less (3.3 kW). For smaller craft we offer transformers that can be reconfigured in the following ways - 115/115, 115/230, 230/115, 230/230.

For larger, single phase, boats you are normally offered a 'split phase' supply. This consists of two legs of 120 volts and a neutral (which we don't use). The two legs of 120 volts are 180 degrees apart which, in effect, means that they will give you a 240 volt single phase supply. For these applications we offer transformers with a 'European' output (230 volt live and neutral) and a 'USA' output (two legs of 120 volt and a neutral - also referred to as a 120-0-120 or a 120 / 240 type supply. A 240 volt supply is normally available at either 50 amps (12 kW) or 100 amps (24 kW).

For larger craft still you will be offered a three phase supply. Lower power supplies are available at 208 volts and super yacht berths are offered at 440 volt.

For single phase boats we offer a boosting transformer that will take two legs of 208 and boost to 240 volts. We can also build custom transformers that take a three phase supply and output single phase.

We can also supply 3 phase to 3 phase transformers with the input and output voltages that you require.


European Cruising

An isolation transformer can also allow ‘English‘ wired boats to be used on continental shorepower supplies.

Most European countries have a floating neutral where the English system bonds the neutral to earth. This causes polarity problems abroad.

It also means that with single pole switches and circuit breakers there will always be voltage in through the neutral. The hull isolation transformer ‘converts‘ a floating neutral input into an earth bonded output.

The transformer will also ensure that the output polarity is always correct regardless of input polarity.


Standard Insulation

The standard transformer is protected by being immersed in a resin bath. This is done under a vacuum to ensure total coverage. This protects the transformer from air borne moisture and normal corrosion.


Double Dipped Insulation Option

In addition to the standard insulation the transformer receives a second water proof coating. The take off ends of the coil windings are also sealed to prevent water ingress. This additional insulation is suited to transformers that maybe subjected to water contact.


Soft Start

When first connected to the shore supply the hull isolation transformer will draw a very high initial current. This can often trip the shore supply circuit breaker. Energy Solutions are able to install a soft start on the input of the transformer to greatly reduce the inrush current.

Input Configuration

Most of the smaller, single phase, transformer range is offered with a dual wound primary. This allows the transformer to be connected to both 110 volt and 230 volt shore power supplies.

Most three phase transformers are supplied as a Delta input (no neutral connected).


Output Configuration

The output configuration of the transformer can be requested as:

  • 230 volt for European systems
  • 240/120 volt for American systems
  • 208 volts three phase for USA spec boats
  • 400 volts three phase for Europeans spec boats


Custom Transformers

Most of the Energy Solutions range of marine isolation transformers have dual input voltages (120 and 240 volt). This is of particular use on long distance cruising boats that may want to use 110 volt supplies in Caribbean, USA Etc.

They also help to protect swimmers against the risk of electrocution. This is a particular risk on fresh water moorings.

Safety for swimmers

Energy Solutions are able to supply specific transformers for individual applications. These may be single or three phase. We have supplied transformers up to 125 KVA.



Download PDF datasheet

Our standard transformer range covers 10, 16, 32, 50, 63 & 100 amp single phase shore capacities at 230v.


Marine Isolation Transformers

Dockside Transformers

We can also design and build bespoke dockside isolation transformers for use in marinas and boatyards.

Available sizes from 15kVA to 250kVA with special options such as IP54, multi-tapped outputs, integral protection and control gear.