Protective Device

Defects

Probable causes for the defect

Design for Maintainability (DfM) Guidelines

Thermal image of an overheated circuit breaker

Corroded circuit breaker (CB)

• Damaged by dirt, corrosion or mishandling.
• Contacts are burnt if they are loosely fitted.
• Improper design rating or wrong installation – should be tested.Fuse of wrong rating or non-calibrated CB –usually from careless maintenance GFCI-deformed or missing pins, damaged insulation, incorrect wiring.
• Interlock is worn with time or key missing for mechanical type. As a result CBs can’t function properly.

• Comply with the requirements of electrical installations as per BS 7671:2008+A3:2015, SS CP 5:1998, NFPA 70 [5]; including the location and number of power points.
• Ensure switchboards have adequate space and access for operation and maintenance.
• Specify suitable switch closets with regard to moisture exposure conditions.
• Refer to the definition of types and functionality of RCCBs and specifications for RCBOs as per SS 480:2016 (IEC 61009-1:2010+AMD1:2012+AMD2:2013 CSV BS EN 61009-2-1:1995).
• Provide sub-metering system with remote measurement capability and link to BMS/EMS to track energy consumption data trends [6].

Construction

• Conform to the guidelines for construction and compliance inspection of electrical connections and earthing thereof (BS 1363-4:2016, SS 403:2013).
• Refer to BS 8512:2008 for storage, handling and installation of power cables on wooden drums.
• Install sub-metering system with remote measurement capability and link to BMS/EMS to track energy consumption data trends [6].
• All accessible metal parts of connection units should be in electrical contact with the earthing terminal(s) (BS 1363-4:2016, SS 403:2013).

Maintenance

• Conform to the maintenance of electrical installations as per BS 6423:2014, BS 6626:2010, SS 538: 2008, [3;7].
• Check for insulation damages (e.g. cracks, blisters, warping) caused by overheating, physical impact or by spillage of cleaning chemicals.
• Check for potential short circuits or ground faults. Ensure that switchboards are not exposed to direct sunlight or alternative heat sources.
• Conduct annual shutdown to eradicate hot spots along the distribution network as witnessed by the owner and certified by a Licensed Electrical Worker (LEW).
• Provide necessary warning notices/labels at switchboards (e.g. shock hazard warnings).

• Poor contact in control circuit.
• Low voltage causes chatter – rating mismatch with supply.