The distribution system shall be insulated against hull throughout the vessel except for ground detecting circuits, secondary circuits of potential and current transformers will be earthed at switchboard or control panel. The voltage for some portable equipment such as portable control box for turning gear motor and traveling crane and so on should be lower than AC 50 V using two (2) windings type transformer of which the secondary winding shall not be earthed. The metal frame or body for portable equipment shall be earthed by the earth connection, if the voltage for portable equipment is AC 220 V