Supply of temporary Electrical Power Supply Process

Determination of Electrical Demand

Prior to connection of a temporary power supply the Vessel electrical, with Vessel Chief Engineer and other parties shall agree necessary electrical demand.

Each vessel has a Load Distribution plan and this, along with common knowledge may be used in determining this.

Any equipment which not needed during the period of  temporary supply should be isolated . This should be in sympathy with knowledge of difficulties of re-start when re-establishing normal power supplies

Starting Currents

Shoreside connections are typically limited in their ability to sustain large starting currents. Loads such as the start up of galley equipment in the morning may be sufficient to overload the system and cause  overload protection devices to operate.

Direct driven generators may be more tolerant of this effect and should therefore be considered over Shore Connections where such large start up loads are an inevitability such as for  Cranes.

As part of pre planning , start up of services should be considered to minimise these transients.

Sensitive equipment.

Shoreside supplies tend to be more variable in terms of voltage and frequency than  vessels supply. Additionally there can be excessive ‘noise’ all of which can cause damage to sensitive equipment which does not have  in place adequate protection.

Before enabling shore side supplies the Vessel electrician shall review all equipment that will be supplied and determine  

Identification of Supply Connection Points

As part of the pre planning  the potential Connection points shall be identified and agreed. Preference should always be given to connecting using the  installed Ship/Shore connection facility. Where this is not practical then direct connection to Switchboards may be considered.

Where no other  practical  alternative exists, or where in doing so  other risks are reduced such that associated to   Cable routeing,  then consideration may be given to  direct connection to Local Start boxes. In doing this special attention should be  

Effort should be made to limit the number of connection points to a minimum.

Cable Routeing

Prior to installation of temporary Supply cabling the Vessel Electrician shall agree with the Vessel Chief  Engineer necessary electrical demand. The supply points shall be agreed and the method of transiting cables to those supply points agreed

Where practical cables should only be routed through established Temporary supply  ports and/or transits.

To prevent unnecessary cable length and transit  then consideration should be given for the addition of new permanent or temporary ports

Routing of cable through Accommodation areas

Routeing of cables through Accommodation areas shall be avoided as far as is practical.

Where it is essential  then suitable protection shall be in place to prevent unnecessary contact and trip hazards. Such cables shall be well identified with  suitable signage an example of which is shown below .

Determination of Electrical Equipment Segregation

Where multiple supply sources exists, or where there is a requirement to carryout distribution system maintenance there is a risk of back feed supplies making sections live despite actions believed to have led to isolation.

As part of Planning the Vessel electrician shall assess the potential  of extraneous and circuitous electrical paths.

System isolation should not breach those described in OMS9 042 Maintenance Management of Electrical Equipment and other regulatory requirements including that described in the Code of Safe Working Practices.

Determining a suitable  Temporary Electrical Source

These are considered to be

Preference whilst vessel is in repair shall be for supply of electrical power through Shore Connection via the established Ship/Shore connection breaker box backed up where necessary using the ships Emergency Generator. The caveat would be where such supply is through Yard Generator which may not provide a reliable  stable supply.

Where there is a requirement for continuous supply or where the stability of shore supply is questionable it may be advantageous to utilise a diesel driven Generator of limited size mounted in close proximity to the vessel.

Where large starting loads are expected then it may  require the use of a diesel driven Generator to  cope with the load transients.

Differing supplies  should only be  feed to Boards or Local Starters  which are isolated from systems which are powered by  existing vessel supplies by a breaker capable of being locked out or with removable links


In no circumstances shall temporary power supplies , from  any source, be synchronised with existing vessels supplies .

In no circumstances shall differing supply source types  supplies  be synchronised with existing vessels supplies .

Determination of Maintenance of Discrimination

Discrimination should be maintained. The Fault tolerance of electrical supplies should not be less than the expected fault levels of consumers. Where this is in doubt then advice should be sort from the supplier.

Supplies from temporary sources shall be  via Fuses with a suitable rating able to protect the  cabling from over load. Where Fuses are replaced with other means of breaking fault current the correct setting of these should be assured.

Special attention should be given where temporary supplies are fed directly to  Local starters so that overload and fault tolerance at point of connection is maintained.

The following example  arrangement should be avoided due to the potential of supplying overload currents for which the connection arrangement is insufficient to withstand.

Inspection of Installed Cables


Cables should be of suitable design, free of defects and sized to suit expected current draw by the consumer.

The use of multiple cables per phase should be avoided but may be acceptable and for phase currents greater than 100A may be a more practical solution due to the radial stiffness of the cable.

Inspection of cables

Prior to hook up the vessels Electrician shall inspect over full length  any temporary cables to ensure free from defect. Limited damage to outer sheath which does not perform any insulation function may be accepted. For armoured cable damage to the wire wrapping shall be considered unacceptable.

Damage or degradation of  sheathing providing insulation in any form shall be considered unacceptable.

Before hook the Vessel electrician shall test insulation properties with suitable test equipment cable of creating potentials not less than those described below.

Acceptable Insulation reading

Voltage RMS

Max Test Voltage

Min Insulation Reading



25M ohm



100 M ohm



100 M ohm



1 T ohm

Where insulation readings are less than this then  representation must be made to the cable supplier to explain and rectify.

Cable segregation, 3 phase power supplies

Where multiple cables are used  in the transfer supply cables must NEVER be segregated into phase bundles.

Instead the wires should be grouped into bundles of three containing each of the Phases

Inspection of Connections

Final Connection

Final connection shall be carried out by a competent person only. Connection means shall be suitable for supply requirements and compatible with the connectors. The connection arrangement shall not  demonstrate an unprotected  live electrical risk

 The Vessel electrician shall inspect  on completion before power is supplied.

Testing of Electrical supply Properties

Before vessels equipment is  supplied from temporary source the properties of the electrical supply shall be tested

 Frequency of supply

Using supplies at a lower frequency can cause equipment to run hot due to reduced inductance and loss of performance. Running equipment with too high a frequency can cause equipment to run hot due to overload.

A frequency range of 55 to 62 Hz shall be considered acceptable with transients in normal operation of no greater than 10 %.

Where these values are exceeded then representation should be made to the supplier of the source. Consideration  should be given to running on Emergency Generator supply only

It should be noted that for yards with their own generator supplying the shore connection it is not unusual for them to operate at lower frequency’s for their commercial benefit

Voltage Supply

Supply voltage should be stable  and of fundamentally sinusoidal waveform. Square wave and truncated supplies shall not be considered satisfactory.

Where supply is not of fundamental Sinusoidal form, is too high or too low equipment damage may occur.

Normal voltage  deviation up to +/- 5 % may be considered satisfactory with voltage dips of upto 20 %  through transient loading may be considered where equipment damage would not be expected.

On transient loads return to acceptable stable supply shall be expected within 1.5 cycles once the transient has passed.

Phase Rotation

Prior to enabling equipment using temporary supplies  up phase rotation must be checked. For supplies using the ship shore connection the in built phase rotation meter may be used. In other cases a portable Phase rotation of type similar to below  shall be used.

Periodic Inspection of  temporary electrical Supply Properties

The properties of electrical supply shall be tested prior to first connection, or following reconnection,

The Vessel electrician shall monitor the properties of the electrical supply not less than once per day and more frequent where it is considered that the stability of supply is questionable