The central section of the main switchboard is used for the control of the main generators.
The switchgear cubicles on either side of the generator panels are used for essential services and flanking these are the grouped motor starter panels.
Handles for opening the doors on switchboard cubicles are usually linked (or interlocked) to an isolating-switch.
This ensures that supplies to components in the cubicle are switched off before the door can be opened.
Fused isolators are isolating switches that incorporate fuses. The action of opening the switch isolates the fuses so that they can be replaced safely.
Fused isolators can also be interlocked with the cubicle door handle. Motor starters frequently incorporate this arrangement.
One type of interlocked fused isolator can be completely withdrawn and removed to ensure complete safety when carrying out maintenance on equipment.
Maintenance on fused isolators consists of periodically checking the operating mechanism. Contacts must be inspected for damage and lightly greased with an electrical lubricant.
The interlock mechanism (if fitted) should also be examined for correct and safe operation.
A separate section switches the three phase 220V a.c. low power and lighting services. Check your own switchboard and particularly note the controls and instruments on the generator panels;
the link to the emergency switchboard;
steering gear supplies (duplicated);
other essential services to the engine-room;
navigation equipment supplies and section board feeders.
Note the alarms and insulation resistance (earth fault) monitors on both the 440 V and the 220V sections.
Lighting transformers may be located inside the main switchboard or, more likely, will be separately mounted nearby.
The main generator supply cables are connected directly to their respective circuit-breakers. Short copper bars from each generator circuit breaker connect it to the three ships bus-bars which run through the length of the switchboard.
The ship bus-bars maybe seen if the rear doors of the switchboard cubicle are opened, but they may be in a special enclosed bus-bar duct acting as an internal fire barrier.
Take care when opening doors on switchboards, live parts are exposed
you are in danger
The ship’s electrical diagrams will include drawings of the front, and perhaps the rear, of the main switchboard showing the as-fitted equipment.
The electrical distribution diagrams will follow the physical arrangement of the main switchboard layout.
You should study the electrical circuit and layout diagrams for your ship to identify, locate and appreciate the role of each key component in the scheme.
Efficient fault-finding on a ship distribution network can only be achieved by a thorough understanding of the scheme and its normal operation.
Switchboard instruments and controls for particular functions are grouped together.
For example, the generator synchronising panel has all the instruments, relays and switches necessary for generator paralleling.
Each generator panel has all the instruments, relays, switches, controls and status lamps necessary for control of the generators.
The instruments on panels of outgoing circuits are usually limited to an ammeter, status lamps, function switches (e.g. manual/off/auto) and push buttons.
Low power control and instrument wiring is of relatively small cross-section, with multi coloured plastic insulation which is clearly identified against the larger main power cables.
The instrumentation and control wiring is supplied from fuses which are located behind the appropriate panel.
Green and yellow striped earth wiring from instruments and panel doors etc., is connected to a common copper earth-bonding bar running the length of the switchboard at its rear.
This earth bar is electrically bonded to the ship’s steel hull.
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