Shore Power Connection Procedure: From Cable Check to Vessel Transfer

Confirm Vessel Data and Operating Roles Before Arrival

The connection procedure begins before the vessel reaches the berth.

The port needs enough information to prepare the shore power system for the actual vessel. At minimum, confirm:

• Vessel name
• Required voltage
• Required frequency
• Expected shore power demand
• Shore connection type
• Connection-point location
• Responsible shipboard contact
• Planned period of shore power use
• Intended transfer method

For a first connection, additional electrical information may be required, including the vessel single-line diagram, neutral arrangement, shore incoming switchboard, onboard transformer and synchronizing arrangement.

In one project procedure, vessel data was submitted 24 hours before arrival. That was an operating rule for that project, not a universal requirement for every port. Each terminal should define a lead time that gives the operating team enough time to review the vessel and prepare the system.

For the electrical information that should be exchanged during early project and vessel compatibility review, see our shore power selection and compatibility guide .

The procedure should also identify who is responsible at each operating location. For many installations, the critical locations are:

• The shore power room
• The berth connection point
• The shipboard switchboard

Each location needs an identified operator and a dependable communication method. Switching commands should be confirmed before action is taken. The procedure also needs to state who can stop the sequence, who authorizes energization and who controls the response after a trip or emergency stop.

A technically correct connection can still become unsafe if different teams are acting on different assumptions.

Inspect Shore, Vessel and Connection Equipment

Do not begin cable connection only because the vessel has the correct plug.

On the shore side, inspect the berth connection box, plug or socket, cable equipment, mechanical supports and the equipment needed for the planned power path.

Look for conditions that can affect the connection:

• Moisture or salt deposits
• Damaged insulation
• Contaminated or damaged contacts
• Loose hardware
• Missing covers or seals
• Abnormal cable condition
• Damage to the cable reel or cable-management equipment

The vessel side also needs to be ready.

For a first connection, one project procedure required the ship to check its high-voltage cable, cable reel, incoming and outgoing switchgear and onboard transformer before the shore connection proceeded.

The vessel shore incoming switchboard and associated equipment should be in the state required by the approved operating procedure.

A connector can be mechanically compatible while the vessel electrical system is still not ready to receive power.

The relationship between the converter, transformers, switchgear and berth connection can be seen in our shore power system architecture and components guide.

Connect the Cable and Prove the Safety Interlocks

Cable reach and mechanical loading should be checked before the connector is inserted.

Vessel position changes with tide, loading and mooring conditions. The cable therefore needs an arrangement that allows the required movement without placing excessive mechanical force on the electrical connector.

Use the intended cable supports and cable-management equipment. The connector should not be used as the main mechanical support for the cable.

Once the cable is connected and secured, the electrical safety conditions still have to be proven.

The protective earth or equipotential connection should be established as required by the connection design before the phase conductors are energized. Pilot contacts and associated safety circuits can then confirm that the connector and required protective conditions are in the correct state.

In one shore power procedure, the operating team performed a safety-interlock circuit test after the berth cable had been connected. Energization was allowed only after the safety circuit was confirmed normal.

Another engineering procedure required the DC resistance of the connected interface to be measured after the ship-to-shore cable was connected. Power could be applied only when the result was within the approved range.

The acceptance value should come from the actual connection equipment and project procedure. A resistance value from another port should not simply be copied into a new project.

For the protective conductor, pilot circuit and equipotential-bonding logic behind this step, see our ship-to-shore equipotential bonding and grounding guide.

Verify Voltage, Frequency and Phase Sequence Before Transfer

After the connection and safety circuits are proven, the shore supply can be prepared according to the approved switching procedure.

Before the vessel accepts the supply, confirm the electrical conditions at the vessel interface.

The required checks include:

• Voltage
• Frequency
• Phase sequence
• Required breaker and interlock status

In one high-voltage vessel connection procedure, shore power was first brought to the incoming side of the vessel main switchboard. The shipboard operators then checked phase sequence, voltage and frequency before allowing the transfer to continue.

If the values are not acceptable, stop the sequence and correct the condition using the approved adjustment method.

In that converter-based system, the shore power converter could be used to adjust phase sequence and output voltage or frequency before transfer. That capability belongs to the specific converter and control arrangement. It should not be assumed for every shore power system.

The marine frequency converter therefore does more than change one nominal frequency into another. Its actual control range, output configuration and permissible adjustment method should be confirmed for the selected system.

For synchronized transfer, matching nominal voltage and frequency is not by itself enough. The synchronization equipment and approved control logic must establish the conditions required before temporary parallel operation is permitted.

Select the Correct Vessel Transfer Method

There are two fundamentally different ways to move a vessel from onboard generation to shore power.

Break-Before-Make Transfer

With break-before-make operation, the existing source is disconnected before the new source supplies the relevant bus.

The sequence avoids intentional parallel operation between the ship generator and shore supply, but it can create an interruption unless critical loads are supported by another approved source.

Whether that interruption is acceptable depends on the vessel and its operating requirements.

Synchronized No-Break Transfer

With synchronized transfer, shore power and the vessel generator are brought into acceptable synchronization before the two sources are temporarily connected in parallel.

The vessel load is then transferred from the onboard generator to shore power before the generator is taken offline.

This requires more than a shore-side breaker command.

The complete transfer can involve:

• Vessel synchronizing equipment
• Generator controls
• Shore power converter control
• Ship and shore breakers
• Protection systems
• Communication between operating teams

Temporary parallel operation also introduces the possibility of reverse power if the two sources or the load transfer are not correctly coordinated.

That issue should be treated as a separate protection and control problem rather than hidden inside the basic connection procedure.

Not every vessel requires no-break transfer. The selected method should follow the vessel electrical arrangement and the agreed operating requirement.

Transfer the Load and Monitor the First Minutes

Closing the required breaker does not mean the transfer is finished.

The operating team should watch the electrical system while the load moves from the vessel generator to shore power.

Useful observations include:

• Shore power voltage
• Current
• Frequency
• Active power
• Breaker status
• Protection status
• Converter alarms
• Vessel load behavior

Large pumps, fans or other significant loads may create changes that were not visible before the vessel began normal operation.

Transfer time depends on the vessel, generator controls, synchronizing system, operating sequence and project requirements.

Before routine connection begins, protection, interlocks and load-related behavior should already have been verified through the agreed commissioning process. Our shore power load testing and acceptance guide explains what should be checked before the first vessel connection.

Disconnect Through an Approved Operating Procedure

Leaving shore power also requires a defined sequence.

The crew and shore operator should first confirm how the vessel will take back its electrical load. If the ship generator has to be returned to service, that transition should follow the approved vessel operating method.

The shore supply should then be removed and placed in the required isolated safe condition before personnel are allowed to release the electrical connection.

The actual switching sequence depends on the switchgear, earthing arrangement, cable equipment and vessel interface.

The procedure should therefore state:

• Who authorizes the transfer away from shore power
• When the shore output is considered isolated
• How the de-energized condition is confirmed
• Which interlocks must return to the safe state
• When the connector may be released
• Who confirms the operation is complete

The project documentation reviewed for this article included separate shore-power energization and de-energization confirmation records and required switching to follow the approved operating procedure.

That is the correct principle to carry into a new project: define the switching boundary and responsibility before routine operation starts.

What Should Be Fixed in the Connection Procedure?

A repeatable shore power connection should not depend on the memory of the operator who handled the previous vessel.

The written procedure should identify:

• Required vessel data before arrival
• Shore and vessel operating responsibilities
• Communication method
• Equipment inspection points
• Cable-handling requirements
• Protective earth and equipotential checks
• Pilot and safety-interlock verification
• Voltage, frequency and phase-sequence checks
• Break-before-make or synchronized transfer method
• Generator and breaker operating responsibility
• Required monitoring during load transfer
• Alarm and emergency-stop response
• Disconnection procedure
• Required operating records
• Reconnection conditions after a trip

For repeat vessels, verified information from previous calls can reduce repeated engineering work.

It should not eliminate the operational checks.

Cable condition, connector condition, vessel equipment status, electrical demand and any changes made since the previous call still need to be confirmed before the next connection.

A vessel profile is useful when it records known information. It becomes dangerous when it is used as a reason to stop checking the actual vessel.

Frequently Asked Questions