Consumer Unit Replacement Procedure

Purpose

To safely replace an existing consumer unit with a new unit, ensuring all circuits are correctly reconnected, protected by the appropriate protective devices, and left in a safe working condition.

Procedure

1. Confirm The Scope Of Work

Identify the existing consumer unit and all outgoing circuits.
Check for signs of damage, overheating, or outdated equipment.
Confirm whether the replacement is like-for-like or an upgrade (e.g. split load to all RCBO).
Take clear photos of the existing setup before any work starts.

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2. Isolate The Supply

Follow the JME Safe Isolation Procedure.
Isolate the incoming supply at the main switch or service cut-out (if authorised).
Lock off and label the supply.
Prove dead at the consumer unit using approved test equipment.
Confirm all circuits are dead before touching any conductors.

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3. Remove Existing Consumer Unit

Remove cover and identify all outgoing circuits.
Label cables clearly if not already identified.
Disconnect outgoing circuits one at a time.
Inspect all conductors for:

 * Damage or overheating
 * Brittle insulation
 * Loose or poor terminations

Remove the old consumer unit once fully disconnected.

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4. Prepare New Consumer Unit

Fix new consumer unit securely in position.
Ensure there is enough space for safe cable routing and termination.
Check incoming tails are suitable for reuse or require replacement.
Prepare all circuit cables for termination.

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5. Device Layout (MCBs vs RCBOs)

MCB (Miniature Circuit Breaker)

Provides protection against:

 * Overload
 * Short circuit

Typically used where circuits share an RCD (e.g. split load boards).
Does not detect earth leakage faults on its own.
Multiple circuits are protected by a single RCD upstream.

RCBO (Residual Current Breaker with Overload Protection)

Provides individual protection for each circuit:

 * Overload protection
 * Short circuit protection
 * Earth leakage protection (RCD function built in)

Each RCBO protects a single circuit independently.
Reduces nuisance tripping affecting multiple circuits.

Neutral Flylead (RCBO Setup)

Most RCBOs require a neutral connection via a flylead.
The flylead connects the RCBO to the neutral bar in the consumer unit.
Each circuit has its own neutral directly associated with its RCBO.
Care must be taken to ensure:

 * Correct neutral pairing per circuit
 * No cross-connected neutrals between circuits

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6. Reconnect Circuits

Reconnect circuits one at a time.
Ensure correct assignment to:

 * MCBs (line protection only)
 * RCBOs (line + neutral protection per circuit)

Tighten all terminals securely.
Keep wiring neat, separated, and under no strain.
Ensure neutrals are correctly paired (especially with RCBOs and flyleads).

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7. Reconnect Supply

Double-check all terminations.
Ensure no exposed conductors remain.
Fit all covers securely.
Remove lock-off devices.
Restore supply and switch on circuits gradually.
Check for immediate faults or tripping.

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8. Testing

Carry out required electrical tests:

 * Polarity
 * Earth continuity
 * Insulation resistance (where applicable)
 * RCD/RCBO trip testing

Confirm correct operation of all protective devices.
Verify each circuit operates independently as expected.
Record test results where required.

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9. Final Checks

Confirm all circuits are correctly labelled.
Ensure consumer unit is tidy, secure, and correctly assembled.
Check for signs of overheating or abnormal operation.
Clean work area and remove all waste.
Explain installation and any changes to the customer.

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Common Issues

Damaged or deteriorated cables during changeover
Incorrect neutral pairing (especially on RCBO boards)
Mixed up circuits due to poor identification
Existing faults causing RCD/RCBO trips
Overcrowded consumer units
Incorrect device selection (MCB vs RCBO mismatch)

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JME Standard

All consumer unit replacements must be safely isolated, correctly terminated, appropriately protected using MCBs or RCBOs as required, fully tested, and left in a safe and compliant condition.