Any ship electrical drawing representing an ship electrical installation or ship circuit uses specific symbols to represent the various ship electrical devices in shorthand.
This provides the electrical engineer with an overview of the circuit or installation and is particularly useful for troubleshooting onboard. It is important to be familiar with the various ship electrical symbols.
Some of the commonly used ship electrical diagram symbols are.
Line or ladder diagrams are used to portray control symbols , and these are made up of two circuits: the control circuit and power circuit.
In this diagram lines represent ship electrical wires with control circuit wiring shown by lighter weight lines, power circuit wiring is shown by heavier weight lines. A small dot or node at the intersection of wires indicates a ship connection.
Contact symbols on ship electrical diagram
These are used to indicate open or closed paths of current flow In the ship power system. Contacts are shown as normally open (NO) or normally closed (NC). Relay contacts shown by this symbol require another device to actuate them, normally electrical coils.
The standard way to represent contact is to indicate the circuit condition that is produced when the actuating device is in the de-energised state (DIN 40900). For example, relay -K1 Is used as the actuating device for the motor starter. The contacts -K1/13-14; 23-24 are shown as normally open, indicating that the contacts are open when the relay coil is de-energised and a completed current path does not exist.
Normally open contact on ship electrical diagram
Ship circuit is first shown in the de-energised state. The contacts of relay -K1 are shown in their normal state (NO). When the -K1 relay becomes energised, contact -K1 /23-24 closes, completing the circuit for the contactor coil -K2. The motor starts as a result.
Normally closed contact on ship electrical diagram
Ship overload relay -F2 contact 95-96 is shown as normally closed (NC), this means the contact is closed when the relay is not tripped due to an overload. A complete ship electrical circuit exists as soon as the start button is pressed and so relay -K1 energises.
Input contacts are either normally open or closed, indicate the binary state of the condition:
On or Off (true or false)
Variations of simple control circuits are used to represent common logical conditions.
Ship diagram a) is called an’AND’operation circuit.
The circuit would be completed, ie the actuator -KM1 energises, If the Input conditions of-K1 and -K2 become true (both contacts are closed).
Ship diagram b) represents a circuit called an ‘OR’ operation circuit.
The circuit would be completed if either of the inputs -K3 or -K4 becomes true.
Ship diagram c) represents a circuit called a ‘NAND’ operation circuit.
The circuit would be completed If either or both of the input conditions remain false.
Ship diagram d) represents a circuit called a’NOR’ operation circuit.
The circuit would remain completed if neither of the two input statuses change.
