This type of Ship’s Diagram includes basic circuit logic.
Electrical components are confined by ‘series and parallel’ rules. These rules are essential in the understanding of the electrical diagram.
To place the series and parallel rules into perspective, it is necessary to re-examine the line diagram approach.
Voltage drop on Ship Power System
Every resistor, motor, coil, or indicating lamp is designed to operate at a specific voltage. If all these loads require 24 volts d.c. and they are connected in parallel, then the power supply unit can properly provide 24 volts to each device.
If as few as two 24-volt components are connected in series, the 24-volt power supply will not provide enough voltage to operate them properly. This is due to the basic voltage division rule.
It is based upon the individual values of resistance, where the larger resistance causes a higher voltage drop across it;
however the current through both components would remain the same.
Thus loads are generally restricted to one load per line. Each component is provided with access to a positive potential and a negative potential. In alternating current circuits, this is still true.
AC provides alternating differences in potential 120 times a second at 60 hertz.
Ship Circuit Diagram
A circuit diagram shows in full, the functioning of a circuit.
All essential parts and connections are depicted by means of symbols arranged to show the operation as clearly as possible but without regard to the physical layout of the various items, their parts or connections.
For example, as required by some classification societies, the circuit diagrams of an electrical propulsion system (where fitted) will also provide details of the following;
- Ratings of electrical machines, transformers, etc
- Cable information such as insulation-type, size and current carrying capacity
- Details of circuit breakers and fuses, etc.
- Instrumentation and protection devices
- Earth-fault indication and protection
The electrical connections of the motor starter are clearly shown in the simplest possible way.
No attempt is made to show the moving contacts of a relay or Contactor alongside the coil that operates them (where they are physically located). Instead, a common number or letter identifies the coil and its related contacts.
How to read Ship Circuit Diagram
For example, main contactor coil ‘KM’ also controls two auxiliary contacts identified as ‘KM-4’ and ‘KM-5’ in addition to the main contacts identified as ‘KM-1, KM-2 and KM-3
In a regular circuit, each wire connection will be identified by a number, which may be found on a numbered sleeve on each wire at its termination, on a component in the actual starter.
International agreements for electrical components
Although there are International agreements as to the symbol to be used to represent electrical components, you must be prepared to meet various symbols representing the same component.
The use of a circuit diagram is to enable the reader to understand the operation of the circuit, to follow each sequence from the moment of initiating the operation (e.g. by pressing a ‘start’ button) to the final act (e.g. starting of the motor).
How to locate fault on ship diagram
If the equipment fails to operate correctly, the reader can follow the sequence of operations until he comes to the stage that has failed. He can then examine all the components involved in that faulty operation. This helps one to locate the faulty component.
He has no need to examine the other components that are known to function correctly and have no influence on the fault; his work is simplified.
A circuit diagram is thus an essential tool in troubleshooting.
