Electrical Shore supply

Shore supply is generally required in dry dock, to supply the vessel with power when the onboard generator and auxiliary system goes offline for maintenance. There must be a suitable connection box conveniently located at the entrance of accommodation or the emergency generator room to connect the shore supply.

The connectin box may have the following

1. Circuit breaker or a switch and fuse to protect the cable linking the connection box
2. Data plate depicting the ships electrical system(voltage and frequency)
3. Voltmeter to indicate the voltage
4. Frequency meter to indicate the frequency
5. Phase sequence indicator usually a lamp to indicate that the shore power is available for connection to the bus bar
6. An interlock with the MSB to ensure the breaker is not closed when the ship's generator is connected.

Problems with higher frequency and voltage

• A higher frequency will cause the motor to run faster and overheat.]
• A higher voltage may generally cause equipment to draw higher current and overheat and may cause a motor to accelerate more rapidly and this may over stress-driven load

If the shore supply frequency differs

If the shore supply frequency differs with the ship's normal frequency then ideally the shore supply voltage should be different in the same proportions.

If the ships normal supply is 3phase,440V,60Hz, then the available supply should be chosen as 380V and 50hz

Checks and Test

• Ensure the circuit breaker of ships alternator is kept open
• Interlock provided should not enable the shore circuit breaker to close if the ships alternator circuit breaker is kept close
• Ensure correct voltage and frequency are supplied (as asked by C/E)
• Ensure the phase sequence is OKAY
• Earth connection to the shore should be made before connecting the shore supply
• Insulation of incoming cables should be tested

IF the ship-shore connection box is not supplied with phase okay indicator

Check the physical rotation of the smallest motor onboard keeping all the other motor breaker open, if the rotation of the motor is the reverse direction, interchange any two leads of the shore supply cable at the connection box