How to Wire a 3-Phase Distribution Board

I am going to walk you through the complete process of wiring a 3-phase distribution board from start to finish. This will allow you to fully understand all aspects of the wiring and have the confidence to wire your own 3-phase distribution board.

Planning the 3-Phase Distribution Board

The first step is planning out the 3-phase distribution board. This involves several key aspects:

• Determining the size of the distribution board - Consider the number of circuits and load requirements to determine the appropriate size enclosure and din rail space needed. Common sizes are 8-way, 12-way, 24-way etc.

• Choose disconnector and RCCB - A disconnector switch isolates the distribution board from the main supply. The RCCB (residual current circuit breaker) detects earth faults and disconnects power. Choose appropriately rated units.

• Select circuit breakers - MCBs (miniature circuit breakers) protect each circuit. Choose breakers of the correct amperage based on cable size and load.

• Calculate total load - Add up the total expected load in amps that the distribution board will need to supply. This determines the size of the main cable and supply breaker.

• Choose enclosure - Consider a metal enclosure for safety and durability. Check the IP rating suits the environment (IP65 or higher is typical).

• Labeling - Plan a labeling system to clearly identify each circuit and record on the circuit chart.

Cables and Wiring

The next stage is preparing the cables, din rail and accessories ready for installation.

• Cut cables to length - Measure and cut the incoming supply cable, distribution cables and circuit cables to the required lengths.

• Strip cables - Strip back the insulation on all the cable ends ready for connection.

• Din rail - Cut and install din rail strips on the backboard for mounting the components.

• Insert grommets - Insert rubber cable grommets into the enclosure gland plates ready for the cables to be fed through.

Mounting the Components

Now we can start mounting the various components:

• Disconnector - Mount the disconnector switch on the din rail with a small gap between it and the supply gland.

• RCCB - Install the RCCB next in line, connecting to the disconnector.

• Circuit breakers - Mount the MCBs along the din rail in order, leaving a small gap between each one.

• Cable entries - Position the cable glands where required and feed the cables into the enclosure.

• Supply terminals - Install and connect the incoming supply terminals near the disconnector.

• Neutral and earth bars - Securely mount the neutral and earth bars in an accessible position.

Wiring up the Distribution Board

We can now start wiring up the components:

• Main supply - Connect the supply cable first between the gland, disconnector and supply terminals.

• RCCB connections - Wire the RCCB between the disconnector and circuit breakers. Follow the connection diagram.

• Circuit breakers - Connect each MCB between the RCCB and the outgoing circuit cables.

• Neutral and earth - Terminate all neutral conductors on the neutral bar and earth conductors on the earth bar.

• Cable management - Use ties to neatly route and secure the cables inside the enclosure. Avoid tight bends.

• Labels - Affix circuit labels for each breaker corresponding to the circuit chart.

Testing and Commissioning

The final vital stage is testing and commissioning:

• Visual inspection - Carry out thorough visual checks of all wiring against circuit schematics.

• Insulation test - Use a megger to test insulation resistance phase-to-phase and phase-to-earth.

• Polarity test - Verify correct polarity of all connections.

• RCCB test - Push the "Test" button to confirm the RCCB trips properly.

• MCB test - Push the "Test" button on each MCB to check they trip.

• Full power test - Energize the board and systematically test each circuit under load to confirm correct operation.

The distribution board is now fully installed, tested and ready to be permanently energized. Following the steps outlined will result in a safe, compliant and reliable distribution board installation. Let me know if you have any other questions!