Need or Necessity: Electrical Switchgear Risk Assessment in New Zealand | Carelabs

Switchgear is the part of an electrical installation that receives the least attention relative to the consequence of its failure. It sits in a room nobody enters, performs no visible function during normal operation, and gives very little indication of deteriorating until it does not operate when required — or fails destructively.

A great deal of New Zealand industrial and commercial switchgear is now well beyond the age at which its designers expected it to be assessed.

What actually deteriorates

Terminations and busbar joints. The dominant failure path. A bolted joint relaxes over thermal cycles, contact resistance rises, the joint heats, oxidation accelerates and resistance rises further. It is a self-reinforcing process that ends in a fault at the joint, and it is entirely detectable well beforehand.

Insulation. Tracking across surfaces where dust, moisture and salt accumulate. Coastal installations, which in New Zealand is a large proportion of them, deal with airborne salt that is aggressive to both insulation surfaces and metalwork.

Mechanisms. Circuit breakers are mechanical devices with springs, latches and lubricant. A breaker that has not operated in fifteen years may not operate when called on, and lubricant that has hardened is a common cause. This failure mode is invisible to any amount of electrical testing.

Protection relays. Electromechanical relays drift. Early electronic relays age and their settings may no longer be readable, let alone verifiable.

Spares availability. Not deterioration, but decisive. Switchgear whose manufacturer no longer supports it can turn a component failure into a board replacement with a long lead time.

What an assessment involves

Thermographic survey under load. Infrared imaging of energised equipment locates high-resistance joints by their thermal signature. It is non-invasive, requires no outage, and finds the dominant failure mode before it develops. It must be done under representative load, since an unloaded board reveals nothing.

Partial discharge measurement. For MV switchgear, PD testing detects insulation breakdown activity before it progresses to failure. Both transient earth voltage and ultrasonic methods can be applied to energised equipment.

Contact resistance testing. Micro-ohm measurement across closed contacts and bolted joints, which quantifies what thermography indicates qualitatively. Requires isolation.

Insulation resistance and dielectric testing. Establishes the condition of insulation between phases and to earth.

Mechanical operation and timing. Verifies the breaker actually operates, and does so within its rated time. On MV breakers, travel analysis characterises the mechanism's condition in detail.

Protection verification. Secondary injection confirms relays operate at their set values, which is the only way to know that a relay that has never been tested will do what its settings claim.

Visual and physical inspection. Corrosion, moisture ingress, dust loading, evidence of overheating, condition of seals, and whether documentation matches the installation.

When an assessment is warranted

• Switchgear over about twenty-five years old that has not been assessed
• Any equipment whose manufacturer support or spares availability has ended
• Coastal, dairy, food processing or other corrosive environments
• Boards that have been extended, where additions may not match original ratings
• After a through-fault, since fault current imposes both thermal and magnetic stress on everything it passes through
• Where the supply fault level has increased following lines company reinforcement
• Before an acquisition, where switchgear condition is a genuine liability and rarely examined
• Where an arc flash or protection study has identified the board as a high-consequence location

The decision the assessment supports

The output is not simply a condition grade. It is the basis for deciding between continued operation with defined monitoring, refurbishment, or replacement — and for timing that decision rather than having it made by a failure.

That distinction has real financial weight. Planned switchgear replacement is a capital project with a chosen date, a procurement process and an outage arranged around production. Unplanned replacement follows a failure, with emergency procurement, an outage of whatever length the lead time dictates, and in the worst case damage extending beyond the switchgear itself.

Related reading: electrical safety inspection covers the routine regime that runs between deeper assessments, and arc flash analysis quantifies the energy present at the boards concerned.