How to Determine if a Low-Voltage Switchgear Has Expired

Determining whether a low-voltage switchgear has expired requires systematic testing and key indicator evaluation. The core is to comprehensively analyze the equipment's operating years (usually 15-20 years), usage environment, maintenance records, and measured data, avoiding a "one-size-fits-all" approach based solely on age.

 

Key Testing Items, Standard Values, and Judgment Basis

Table: Testing Item | Standard Value | Judgment Basis

Insulation Resistance | ≥1 MΩ (phase-to-phase and to ground) Below 1 MΩ indicates insulation aging or moisture absorption, posing a risk of leakage or short circuit, requiring immediate attention.

Temperature Rise | Busbar connection point temperature rise ≤70K, casing surface temperature rise ≤20K. Infrared thermal imaging detecting localized temperature anomalies (e.g., exceeding 80℃) indicates poor contact or overload, potentially leading to fire.

Mechanical Operation Performance | Circuit breakers and disconnectors should operate smoothly and without jamming after three manual opening and closing operations. Difficulty, jamming, or incomplete operation indicates wear or deformation of transmission components, affecting the reliability of emergency disconnection. **Electrical Clearance and Creepage Distance: ≥20 mm (between live parts of different polarities in the main circuit). Measured values ​​less than the standard are prone to arcing, especially dangerous in humid environments.

Grounding Continuity: Grounding resistance ≤4 Ω. Values ​​exceeding 4 Ω indicate grounding protection failure, preventing effective current conduction during faults and endangering personal safety.

Protection Device Operating Characteristics: Tripping current error ≤±10%. Excessive deviation of the test value from the set value may lead to failure to trip or maloperation (frequent tripping), rendering the protection meaningless.

Appearance and Structural Integrity: No deformation, corrosion, coating peeling, or uniform door gaps. Severe cabinet corrosion or frame deformation indicates prolonged exposure to harsh environments, resulting in decreased overall structural strength and potential safety hazards.

 

Comprehensive Judgment Logic:

Operating Life: ≥20 years. The design lifespan has been reached. Even if the surface appears normal, internal components (such as circuit breaker contacts and capacitors) may be nearing the end of their mechanical or electrical lifespan.

If two or more test items fail to meet standards, even if the cabinet is not yet due for its intended lifespan, it should be considered "functionally expired," and a replacement assessment process should be initiated.

If the cabinet has experienced multiple malfunctions or has excessively high repair costs, such as requiring repairs more than three times within a year, or a single repair cost exceeding 40% of the price of a new cabinet, it is no longer economically viable.

If load demand fluctuates significantly, and the original cabinet capacity is insufficient, and the current load consistently exceeds 80% of the rated capacity, it is considered overloaded operation, accelerating aging, and should be upgraded.

If the cabinet fails to meet current safety standards, such as lacking arc fault protection, not being equipped with intelligent monitoring, or not complying with the latest GB7251.1 requirements, there are compliance risks.