Fuses are required by the Boat Safety Scheme to be fitted in all connections to the domestic battery.  This is in order to protect the associated wiring not the equipment connected.  The fuse must not be a higher rating than the cable.  It can be lower than the cable rating to match the connected equipment.

Our fuses should be installed with our holder.  This should be bolted to an insulated base (or with insulation material underneath) and the supplied cover securely fitted.