Changing a circuit breaker, step by step

Why replace a circuit breaker?

There are a number of situations that justify replacing a circuit breaker in your electrical installation. Understanding these warning signs allows you to intervene before a more serious problem occurs.

Signs of wear and malfunction

A circuit breaker that trips unexpectedly for no apparent reason is the first indicator of a problem. If there is no overload or short-circuit to explain these repeated trips, the circuit-breaker's internal mechanism may be damaged. Electrical contacts wear out over time, especially if the circuit-breaker has been tripped many times over the years.

Marks of burning or blackening on the circuit-breaker housing indicate abnormal heating. This phenomenon generally results from incorrectly tightened connections or internal component degradation. In this case, replacement becomes urgent to prevent any risk of fire.

A smell of burnt plastic coming from the electrical panel should never be ignored. It indicates severe overheating, which can damage not only the circuit-breaker, but also the conductors and other equipment in the panel.

Upgrading and modernization

Older electrical installations sometimes have circuit breakers whose rating no longer corresponds to today's needs. The addition of power-hungry electrical appliances may require the installation of higher-gauge circuit breakers, provided the cable cross-section allows for this.

The NF C 15-100 standard governing domestic electrical installations in France is regularly updated. During renovation work, it may be necessary to replace old circuit-breakers with models that comply with current requirements, particularly in terms of breaking capacity and tripping characteristics.

Modern earth leakage circuit breakers also offer advanced features, such as overvoltage and arc protection, which significantly enhance the safety of your installation.

Essential safety precautions

Working on an electrical installation involves real risks. Strict adherence to safety rules protects you and those around you.

Complete power failure

Before any work is carried out, the power supply must be cut off at the main circuit breaker. This device is generally located at the head of the switchboard, just after the electricity meter. Set it to "0" or "OFF" to interrupt the power supply completely.

Simply switching off the divisional circuit breaker you wish to replace is not enough. Other circuits in the switchboard remain live, and a handling error could result in accidental contact with an active part.

After switching off the main circuit breaker, systematically check that no voltage is present, using a voltage tester or multimeter. This check is carried out at the upstream and downstream terminals of the circuit-breaker to be replaced. A reliable measuring device represents a minimal investment in relation to the risks involved.

Personal protective equipment

Always wear insulated gloves that comply with electrical standards. These special gloves offer protection against the voltages present in domestic installations. Ordinary gardening or DIY gloves provide no electrical protection.

Protective goggles protect your eyes from splashes when removing connections. Accidental arcing, although rare if you follow the correct procedures, can project incandescent metal particles.

Work in a dry, stable environment. Avoid working barefoot or in socks, preferring shoes with insulating soles. An insulating mat on the floor provides additional safety.

Skills required

Although the replacement of a circuit breaker is technically accessible to an experienced DIYer, it does require some basic electrical knowledge. You need to be able to identify phase, neutral and earth conductors, understand the diagram of your electrical panel and handle the appropriate tools.

If you're not sure of your skills, call in a qualified electrician. The cost of a professional intervention is derisory compared to the risks of electrocution or fire associated with a faulty installation.

Certain situations require the intervention of a professional: major modifications to the electrical panel, doubts about the conformity of the installation, the presence of asbestos in the building, or complex three-phase installations.

Equipment and tools required

Gathering the right equipment before you start ensures a safe and effective intervention.

Choosing a replacement circuit breaker

The new circuit-breaker must have exactly the same characteristics as the one it replaces, unless you are deliberately upgrading it. Check the following parameters:

The rating, expressed in amperes (A), corresponds to the maximum current the circuit-breaker can withstand at all times. Common ratings for domestic installations are 10A, 16A, 20A and 32A. This rating must be adapted to the cable cross-section of the protected circuit: 10A for 1.5 mm², 16A for 2.5 mm², 20A for 4 mm², and 32A for 6 mm².

The tripping curve (B, C or D) determines the circuit-breaker's sensitivity to overcurrents. B curves are suitable for conventional circuits (lighting, sockets), C curves for circuits with inductive loads (motors, transformers), and D curves for specific applications requiring tolerance to current peaks.

Breaking capacity, expressed in kiloamperes (kA), indicates the circuit-breaker's ability to interrupt a large short circuit. For a standard domestic installation, a breaking capacity of 4.5 kA is generally sufficient, but 6 kA or more may be required in some areas.

The number of poles determines the number of protected conductors: unipolar + neutral for a single-phase circuit, bipolar for a single-phase circuit where phase and neutral must be disconnected, tetrapolar for three-phase.

Essential tools

A voltage-testing screwdriver is the safety tool of choice. Choose a reliable model with light and sound indication. Regularly check its operation on a live outlet before use to confirm that no voltage is present.

Insulated screwdrivers in different sizes enable safe handling of the terminals. Flat and Phillips screwdrivers are generally required, depending on the type of circuit-breaker.

A wire stripper makes it easier to prepare conductors if you need to reconnect them. A pair of wire cutters can be used to adjust wire length if necessary.

A digital multimeter, although not mandatory, provides accurate voltage and continuity measurements. It allows you to check with certainty that no voltage is present, and to check the quality of your connections after the work has been completed.

A flashlight or auxiliary light is essential, as you'll be working without power. Electrical panels are often installed in dimly lit areas.

Complementary accessories

Circuit identification markers help you keep your board organized. If your panel is not correctly labeled, take the opportunity to clearly identify each circuit.

Electrical insulation tape is used to secure connections and protect bare conductors.

A camera or your smartphone can document the installation before dismantling. These photos are an invaluable reference during reassembly.

Step 1: Identify and locate the circuit breaker to be replaced

Before any physical intervention, a thorough identification phase is essential.

Locate the right circuit breaker

If your electrical panel has several circuit breakers, make sure you know which one needs replacing. Switch on the devices on the circuit concerned, then trip the circuit breaker presumed to be faulty. If the appliances switch off, you've identified the right circuit breaker.

Note the exact location of the circuit breaker in the panel, its position in the row, and the adjacent circuits. This information makes it easier to find once the power supply has been cut off.

Photograph existing installation

Take several detailed photos of the circuit breaker to be replaced and its wiring. Photograph :

• The whole picture to put the circuit-breaker in context
• The circuit breaker up close, with its terminals visible
• Markings and labels
• Wiring features (wire colors, conductor positions)

These photos serve as a reference during reassembly, to avoid wiring errors.

Identify connections

Clearly mark the conductors connected to the circuit breaker:

• Upstream (incoming): conductors coming from the main power supply or from the upstream earth leakage circuit breaker.
• Downstream (feeder): conductors feeding the protected circuit

Note the color and position of each driver. In standard French installations, phase is red, black or brown, neutral is blue, and earth (if present) is yellow-green. However, some older installations may use different color codes.

If you can't find the conductors, create your own temporary labels with tape and a marker. Indicate "Upstream Phase", "Upstream Neutral", "Downstream Phase", "Downstream Neutral" as appropriate.

Step 2: Switch off the power supply and check that no voltage is present

The safety of this stage determines the rest of the procedure.

Switch off main circuit breaker

Locate the circuit breaker at the head of your installation, usually just after the electricity meter. Switch this circuit breaker to "0" or "OFF". All circuits in your home must be de-energized.

Inform the occupants of the dwelling of the power cut to avoid anyone inadvertently turning the power back on while you are working. You can place a warning sign on the main circuit breaker or use a lockout padlock.

Check for absence of voltage

This is the most important safety measure. Use your voltage tester methodically:

1 First, check that your tester is working properly on an outlet that you know to be de-energized after the general power cut.

2 At the circuit breaker to be replaced, test for the presence of voltage between :

- Upstream phase and earth (or neutral) terminal

- The downstream phase and earth (or neutral) terminal

- Upstream phase terminal and upstream neutral terminal

- Downstream phase terminal and downstream neutral terminal

No voltage should be detected. If your tester indicates the presence of voltage, don't intervene and look for the cause (faulty main circuit breaker, circuit breaker error, power from another source).

Securing the work area

With the power off, set up your auxiliary lighting to work in good conditions. Clear the space around the electrical panel for easy access and to avoid clutter.

If the panel is accessible to children, keep them out of the room for the duration of the work.

Step 3: Remove the old circuit-breaker

Disassembly must be carried out methodically to preserve the integrity of the conductors.

Loosen connection terminals

Modular circuit breakers generally use screw terminals. Using your insulated screwdriver, gradually unscrew each connection screw:

Start with the downstream terminals (feed to the circuit). Unscrew the screws completely and carefully remove the conductors. If a conductor resists, don't force it: unscrew the terminal screw further.

Then proceed in the same way with the upstream terminals (power supply inlet). On some switchboards, upstream connections are made via feeder combs, simplifying disassembly.

Check condition of conductors

Look carefully at the ends of the conductors you have just disconnected. Signs of overheating (blackening, hardening of the copper) indicate a tightening problem or overloading. Damaged conductors must be recut and re-stripped on a sound part.

If the conductors show significant oxidation, clean them with a wire brush or fine sandpaper. An oxidized conductor creates a contact resistance that can lead to overheating.

Measure the length of stripped wire: it should be sufficient for complete insertion into the terminals of the new circuit-breaker (usually 10 to 12 mm). If necessary, strip more wire.

Remove the circuit breaker from the rail

Modular circuit-breakers are mounted on a DIN rail (standardized metal rail). The fastening system generally comprises a clip or pin to be actuated:

Locate the circuit-breaker locking system, often a tab at the bottom of the module. Using a flathead screwdriver, gently pry the lower clip free while tilting the circuit-breaker slightly towards you.

Once the bottom clip has been released, lift the circuit-breaker off the top of the rail. The module must withdraw freely.

Some circuit-breaker models use a different system with a lateral fixing screw. Consult the manufacturer's instructions if the system is not self-evident.

Step 4: Install the new circuit breaker

Installation of the new module follows the reverse procedure of disassembly, with particular attention to the connections.

Mounting the circuit breaker on the rail

Position the new circuit-breaker exactly where the previous one was. The spacing between modules must be constant to maintain a neat layout.

First engage the upper part of the circuit-breaker on the DIN rail. The clip or top lug must snap onto the rail. Then tilt the bottom of the circuit-breaker until you hear or feel the lower fastener click into place.

Check that the circuit-breaker is firmly attached by trying to move it sideways and forwards. No play should be perceptible.

Connecting conductors

Connecting the conductors is the most critical step for the safety and reliability of the installation.

Identify the terminals of the new circuit breaker. On a standard single-pole + neutral circuit-breaker, the upper terminals supply the upstream circuit (incoming feeder), and the lower terminals supply the downstream circuit (outgoing feeder). Check this direction on the front panel of the circuit-breaker, where arrows or "upstream/downstream" indications are usually present.

First insert the upstream conductors :

• Loosen the terminal screw sufficiently to create space for insertion
• Insert the phase conductor into the corresponding terminal (usually on the left or marked "L").
• The conductor must be inserted as far as it will go, only the stripped part enters the terminal, no bare copper must remain visible on the outside.
• Tighten the connecting screw firmly with your screwdriver.
• Check tightness by pulling slightly on the conductor: it must not move.

Repeat the operation for the upstream neutral if your circuit-breaker has a neutral pole.

Proceed in the same way for the downstream connections (to the circuit), carefully observing the conductor markings.

Check tightening quality

Insufficient tightening is the main cause of electrical connection failure. A loose conductor heats up, can cause arcing and damage the circuit-breaker.

After tightening all connections, perform a final check:

• Lightly pull on each conductor to check that it is securely held in place
• Visually check that no stripped part of the conductor is visible outside the terminal.
• Make sure screws are firmly tightened without being overtightened (risk of damaging the thread).

If you have a torque screwdriver (recommended for professional installation), observe the torque specified by the circuit-breaker manufacturer, generally between 2 and 2.5 N.m.

Step 5: Perform pre-power-up checks

Before re-powering the system, a series of preventive checks should be carried out.

Visual inspection of installation

Inspect your work thoroughly:

• Are all conductors correctly connected and tightened?
• Do the colors of the conductors match the markings you made?
• Is any conductor in contact with a metal part other than its connection terminal?
• Is the circuit breaker firmly attached to the rail?
• Are there any tools or metal objects lying around in the painting?
• Can the cover or panel door close without trapping conductors?

Compare your final installation with the photos you took before dismantling. The configuration must be identical, with the exception of the circuit-breaker itself.

Checking the position of the new circuit breaker

Make sure the new circuit breaker is in the "OFF" or "0" position before turning the power back on. This precaution allows you to control the circuit's recharge gradually.

Check for short-circuit

Although you have not modified the circuit downstream of the circuit breaker, a continuity check can be performed if you have a multimeter in ohmmeter mode:

• Measure the resistance between phase and neutral of the circuit: it should be very high (several megohms), indicating the absence of a short-circuit.
• A very low resistance (close to zero) would indicate a definite short-circuit in the circuit, which should be located before power is restored.

Step 6: Switch the system back on

Power-on is gradual and controlled.

Reset main circuit breaker

Return to the circuit breaker at the head of your installation. Switch it to "I" or "ON" to restore power to your entire electrical panel.

If the main circuit breaker doesn't stay on and immediately trips again, there's a fault in the system. Switch off again and look for the cause: poor connection, short-circuit, reversed conductors.

Test the replaced circuit

With the main circuit breaker switched on, your new divisional circuit breaker is always in the "OFF" position. First, use your voltage tester to check that voltage is present at the upstream terminals of the new circuit-breaker. This check confirms that the power supply is operating correctly.

Now switch on the new circuit breaker. Several possible scenarios:

Normal scenario: The circuit breaker trips and remains in the "ON" position. Circuit devices operate normally. Your intervention was a success.

Instant tripping: The circuit-breaker trips again as soon as you try to switch it on. There are two main possible causes:

• A short circuit exists on the downstream circuit (pre-existing fault or fault created during work).
• A wiring problem at the circuit breaker (phase/neutral inversion, poor connection)

Switch off the main circuit breaker again and check your connections. If the problem persists, disconnect the downstream circuit and test the circuit-breaker alone to determine whether the fault comes from the circuit or your installation.

Check equipment operation

Methodically test all equipment in the circuit:

• Turn on light switches and check that fixtures are working
• Connect devices to circuit sockets
• For a specialized circuit (washing machine, oven, etc.)), test the device concerned

During this test phase, keep an eye out for any abnormal signs:

• Unusual odors from the board
• Abnormal heating of circuit breaker (may be slightly warm under load, but not hot)
• Sizzling or crackling noises
• Lamp brightness variations

Common mistakes to avoid

Certain errors are frequently made when replacing a circuit breaker. Knowing what they are enables you to anticipate them.

Calibration and specification errors

It's a serious mistake to install a circuit breaker with a larger rating than that recommended for the cable cross-section. A 20A circuit breaker on a 1.5 mm² circuit will not effectively protect the cable against overloads. The cable can become dangerously hot without the circuit-breaker tripping.

Conversely, an under-calibrated circuit-breaker will cause nuisance tripping as soon as the normal circuit load is reached.

Failure to observe the appropriate trigger curve can also cause problems. A curve D circuit breaker on a lighting circuit will offer insufficient protection, while a curve B on a motor circuit will cause tripping on start-up.

Wiring errors

Phase-neutral reversal at the circuit-breaker may seem of no immediate consequence, but it compromises safety. A single-pole circuit-breaker cuts only the phase: if the phase is reversed with the neutral, the circuit remains partially energized even with the circuit-breaker open.

Mixing different circuits on the same circuit breaker, while technically possible in some cases, does not comply with NF C 15-100, which requires separate circuits for different uses.

Assembly errors

Insufficient tightening of the terminals is the most common fault. Vibrations, temperature variations and load cycles will eventually loosen an initially loose connection even further. The resulting overheating can damage the circuit-breaker and conductors, and even cause a fire.

Excessive tightening is also undesirable: you risk damaging the terminal thread, breaking the conductor (especially the strands of a flexible cable), or deforming the circuit-breaker housing.

If the correct upstream/downstream position is forgotten, the circuit-breaker is fed backwards. Although some models accept this configuration, others only work correctly in a specific connection direction.

Safety errors

Working on live equipment, even when only partially energized, exposes you to the risk of fatal electrocution. Rashness and overconfidence are the main causes of accidents. Take the time to systematically check for tension.

Using uninsulated tools, even on a de-energized installation, is bad practice and can become dangerous if a handling error accidentally causes partial re-energization.

Failure to inform the other occupants of your work could result in accidental power-up while you are handling active parts.

Special cases and situations

Some configurations require special attention.

Replacing a differential circuit breaker

An earth leakage circuit breaker (ELCB) combines the function of overcurrent protection and differential protection against insulation faults. Its replacement follows the same general procedure, but with a few specific features:

Check that the new circuit-breaker has the same differential sensitivity as the old one (usually 30 mA for terminal circuits). Sensitivity is indicated in milliamperes on the front of the circuit breaker.

After installation, make sure the residual current device is working properly by pressing the TEST button on the circuit-breaker. This button simulates an insulation fault: the circuit-breaker should trip immediately. If this is not the case, the circuit breaker is faulty or incorrectly connected.

Installation with feeder comb

Power combs (or connection combs) enable power to be distributed to several circuit-breakers simultaneously, without having to connect each conductor individually. If your board uses this system :

Replacing a circuit-breaker in the middle of a comb means temporarily removing adjacent modules to gain access to the comb. Carefully note the position of each module before disassembly.

Make sure the new circuit breaker is compatible with the comb system used (pin spacing, type of connection). Not all modular circuit breakers accept all types of comb.

When reinstalling, check that the comb pins engage correctly with the terminals on the new circuit-breaker. Partial insertion can create a poor connection.

Old or non-standard electrical panel

Older installations may have special features:

• Obsolete color-coded wiring (black or red phase, gray or white neutral)
• Circuit-breakers with non-standard shapes or mountings
• No earth on some circuits
• Use of fuses instead of circuit breakers

In these situations, a professional assessment of the complete installation may be required. Simply replacing a component does not guarantee the conformity and safety of the whole assembly.

After replacement: care and maintenance

Your intervention doesn't end with a successful power-up.

Initial surveillance

In the days following replacement, carefully monitor the behavior of the new circuit breaker:

• No nuisance tripping
• Normal operating module temperature
• No unusual odors from the board
• Normal operation of all circuit equipment

If the circuit breaker trips repeatedly, don't just reset it. Look for the cause: actual circuit overload, faulty device, installation problem.

Labelling and documentation

Take advantage of this opportunity to improve the labeling of your electrical panel, if you haven't already done so. Clearly indicate on the board :

• The function of each circuit breaker (kitchen sockets, bedroom lighting, etc.) is described below.)
• Circuit breaker rating
• Replacement date

Keep all documents relating to your intervention:

• Before and after photos
• Exact reference of the installed circuit breaker
• Date of intervention
• Manufacturer's instructions for new circuit breaker

This information will facilitate future interventions and provide useful traceability in the event of resale of the property.

Preventive maintenance

An electrical panel requires minimal but regular maintenance:

• Annual check of differential protection devices (TEST button)
• Visual check for signs of overheating or dampness
• Periodic tightening of connections (every 5 to 10 years) to compensate for natural material creep

If your electrical installation is more than 20 years old, consider having a complete diagnosis carried out by a professional. Standards and safety devices have evolved considerably, and upgrading can significantly improve your safety.

When should you call in a professional?

Despite the technical feasibility of replacing a circuit breaker by a competent DIYer, some situations warrant the intervention of a qualified electrician.

Complex installations

Three-phase installations, which are common in large homes or business premises, have technical peculiarities that require in-depth expertise. Phase balancing and differential protection in three-phase systems require specific knowledge.

Secondary switchboards, fed from a main switchboard, can present complex cascade protection configurations. An error in calibration or selectivity can compromise the safety of the entire system.

Doubts about compliance

If you notice any anomalies in your installation (conductors with clearly insufficient cross-sectional area, lack of earthing, home-made wiring, moisture in the switchboard), don't just replace the circuit-breaker. Have a complete electrical diagnosis carried out.

Installations built before 1991 are generally not fitted with residual-current devices. Their addition requires a partial redesign of the table and must be carried out by a professional.

Regulatory obligations

In the case of a rental property, work on the electrical installation must be carried out by a qualified professional who can provide a certificate of conformity. This obligation protects both the owner and the tenant.

When selling a property whose electrical installation is more than 15 years old, an electrical diagnosis is mandatory. If the diagnosis reveals any anomalies, the work to bring the system into compliance must be carried out by a certified electrician.

To qualify for home insurance cover in the event of an electrical claim, you'll need to prove that the installation was compliant and that the work was carried out in accordance with good practice. Invoices from a professional electrician constitute such proof.

Conclusion

Replacing a faulty circuit-breaker is an operation that can be carried out by an experienced and meticulous DIYer, provided that safety rules and technical procedures are scrupulously observed. Prior disconnection of the mains supply, systematic verification of the absence of voltage, and compliance with circuit-breaker specifications are the three pillars of a successful intervention.

More than simply replacing a faulty component, this operation gives you a better understanding of how your electrical installation works, and enables you to detect any anomalies requiring more in-depth intervention. The traceability of your intervention and post-installation monitoring guarantee the longevity and safety of your installation.

Never forget that electricity does not forgive approximations. If you have any doubts about your skills or the conformity of your installation, calling in a professional electrician is the safest and most durable solution. The cost of a professional intervention is modest compared to the risks involved and the potential consequences of a faulty installation.