I Have Old Wiring in the Walls. Are RCD Safety Devices a Good Idea?

Yes. RCD safety devices can be a valuable improvement in a home with older wiring because they can quickly disconnect the electricity when current leaks to earth.

However, an RCD does not repair deteriorated wiring or correct an unsafe installation. The wiring and switchboard should be assessed first so the right protection can be added in the right way.

What does an RCD protect against?

A residual current device constantly compares the electricity flowing into and out of a circuit. If it detects that some current is escaping, possibly through damaged equipment or a person, it disconnects the supply very quickly.

This provides a layer of protection that traditional fuses and circuit breakers do not provide on their own. WorkSafe describes RCDs as protection against the risks of electrocution and fire caused by earth faults. However, an RCD cannot protect against every possible type of electrical contact or fault. WorkSafe New Zealand

Old wiring is not automatically unsafe

The age of the wiring is only one part of the picture.

Some older wiring may remain serviceable if it was installed properly, has not been damaged and continues to test satisfactorily. Other wiring may have deteriorated insulation, poor connections, missing or ineffective earthing, or alterations completed at different times and to different standards.

WorkSafe has also confirmed that existing New Zealand installations do not need to be comprehensively upgraded simply because electrical standards have changed, provided the installation is not unsafe. WorkSafe’s guidance on existing installations

This means the important question is not simply, “How old is the wiring?” It is, “What condition is it in, and how is it currently protected?”

An RCD will not fix damaged wiring

Adding RCD protection should not be treated as a substitute for addressing wiring that has reached the end of its serviceable life.

An RCD cannot:

• Restore deteriorated cable insulation

• Provide an earth conductor where one is missing

• Repair loose or overheating connections

• Correct poor-quality alterations

• Increase the capacity of an overloaded circuit

• Replace the overload protection provided by a fuse or circuit breaker

If testing identifies a wiring defect, that issue may need to be repaired before RCD protection can be installed or relied upon.

New protection can reveal existing problems

Older wiring and appliances can sometimes have small amounts of existing earth leakage. Shared neutrals, incorrect connections or deterioration may also have gone unnoticed under older fuse or circuit-breaker protection.

When RCD protection is added, these conditions may cause the device to trip.

That does not necessarily mean the RCD is faulty or “too sensitive.” It may be revealing a condition that was already present. Proper testing helps identify whether the leakage comes from the fixed wiring, an appliance, or the way circuits have been arranged.

Consider how the circuits are divided

The type and arrangement of the protection matter too.

A traditional RCD may protect several circuits together. If a fault occurs on one of them, multiple circuits can lose power at the same time. This can make fault-finding more difficult and may unnecessarily turn off lighting, refrigeration or other unaffected circuits.

An RCBO combines residual-current protection and circuit-breaker protection for an individual circuit. Where the switchboard has sufficient space and the installation is suitable, individual RCBOs can provide clearer separation. A fault on one circuit is less likely to affect the rest of the home.

The best arrangement will depend on the wiring condition, circuit layout, switchboard capacity and what the home may need to support next.

What should be checked first?

Before deciding on an RCD or RCBO upgrade, a licensed electrician should consider:

• The type, age and visible condition of the wiring

• Insulation resistance and existing earth leakage

• Earthing and polarity

• The condition of switches, sockets and connection points

• How the circuits are divided and labelled

• The condition and available space within the switchboard

• Any future plans for heating, induction cooking, EV charging, solar or renovations

This is especially useful in older Dunedin homes where the electrical system may have been extended gradually over several decades.

When should you seek advice promptly?

Arrange an electrical assessment if you notice repeated tripping, warm or discoloured fittings, buzzing, crackling, burning smells, damaged accessories, electric tingles, or uncertainty about previous electrical work.

You should also review the electrical foundation before renovating or adding a significant new load. It is better to understand the existing wiring and protection before new work is connected to it.

The takeaway

RCD safety devices are often a good idea in a home with old wiring, but they should be part of a considered protection upgrade rather than treated as a complete solution.

Review the wiring first. Confirm what remains serviceable, address anything unsafe, and choose a protection layout that provides clearer separation and room for future needs.

The goal is safer circuits and a more dependable electrical foundation for what comes next.