main circuits

The provisions of this section of Part 3 in the 2002 BSS Standards are mandatory for non-private boats where applicable.

You can help the examiner identify whether your 12 or 24 volt distribution cables are adequate to carry the current they are intended for, and that the fuses feeding each of the cables is suitable for the circuits. Why not label each fuse with the identity of the circuit it feeds? By turning the power off you can safely disconnect each fuse in turn, before switching the main power source back on and investigating which circuit is affected. This will also help you if you have to replace a fuse in the future. Always have a cover over the fuse mounting box. [3.3]

To minimise the risk of damage to cables, and to allow a visual inspection of the installation, main circuits must be installed above bilge water level. Bilge water level can usually be determined by the presence of a 'tidemark', the position of the bilge pump or its inlet, or the level at which the float switch is set. All main circuits, other than starter circuits, must be protected by circuit breakers or fuses of the appropriate rating and of a suitable design. This means that the fuse or circuit breaker must have a rating which is lower than the current that would cause damage to the circuit. The safe operation of these devices must not be compromised by the use of thicker fuse wire or by using tape to keep the contacts closed.

If your boat has a 240V supply it's strongly recommended that you fit a residual current device (RCD) to automatically disconnect the supply. This will prevent an earth leakage current flowing through a faulty appliance, and protects someone inadvertently touching a live circuit and getting an electric shock. [3.3]