A switchboard is a component of an electrical distribution system which divides an electrical power feed into branch circuits while providing a protective circuit breaker or fuse for each circuit in a common enclosure. These points ensure a secure and proper electrical connection, allowing the flow of current to pass safely through to the circuits. Outgoing feeders from a primary distribution substa-tion are typically feeding secondary distribution substations and bigger, most often industrial type, consumers. GM Rewards members can earn 1785 points for an eligible purchase. The Accessory Power Distribution Box from GMC Accessories is an add-on module that mounts under the hood and allows you to conveniently control up to four external accessories using auxiliary switches. STEP3: The ransmission Substation, increases the step-up voltage transformer from 69,000 to 765,000 volts.