Engineering Standards For Electrical Safety

Breakers or fuses? Why many VFD manufacturers, specially European, are reluctant to accept breakers only as the sole protection of drives? Just had this question asked today by an OEM. The reasoning comes down to both technical and standards-compliance aspects: 1. Speed of Protection • IGBTs in VFDs are very sensitive: they can be destroyed in a matter of microseconds under short-circuit or fault conditions. • Circuit breakers, even modern MCCBs or IEC-rated motor breakers, have response times in the milliseconds range. That’s often too slow to protect semiconductors. • Ultra-fast fuses (aR/gR type) are designed to clear faults in the microsecond range, limiting peak let-through current (I²t) and energy stress on the drive’s power semiconductors. 2. Selectivity & Coordination • European standards (IEC 61800-5-1 for adjustable speed drives) require tested coordination between the protective device and the drive. • Drive makers test their VFDs with specific fuse types, publish them in manuals, and guarantee that protection works as intended. • Breakers are not predictable enough in terms of let-through energy, so manufacturers can’t guarantee semiconductor survival unless fuses are used. 3. Standards and Certification • Under IEC 60269 and IEC 60947, fuse-based protection for power electronics is the norm. • Many EU notified bodies certify drives only with the recommended fuses. Using breakers risks losing CE-mark conformity or voiding warranty. • UL/NEMA practice in North America is different (breakers more accepted), but IEC culture is fuse-oriented for semiconductor protection. 4. Practical Concerns • Breakers are excellent for protecting wiring and for disconnect/isolation, but not for semiconductor protection. • Fuses are smaller, faster, and cheaper for high-fault currents. • Breakers can still be used upstream for line protection and isolation, but manufacturers want fuse protection directly on the drive input. #vfd #protection #fuses

The National Electrical Code (NEC) 2023 has highlighted the critical importance of surge protection in emergency circuits within buildings. As per the NEC 2023: Section 760.33 requires the installation of an approved surge-protective device (SPD) on the supply side of a fire alarm control panel, in line with Part II of Article 242. It's essential to recognize that surges are not solely caused by lightning. A common misconception among contractors, especially in the western region of the US, is to disregard surge protection due to the infrequency of lightning. Surges can originate from various sources: 1. Direct Lightning Strikes: Typically have catastrophic effects. 2. Proximity Lightning Strikes: Lightning impacts several miles away can induce major voltage surges along transmission lines. 3. Utility Grid Switching: This happens when utility companies switch between different power systems. 4. Brownouts/Blackouts: Characterized by under-voltage or voltage drops, usually followed by a surge or spike. 5. Inductive Loads: The activation or deactivation of electrical motors in facilities, affecting systems such as HVAC, refrigeration, pumps, CNC machines, and office equipment. 6. Mechanical Failures: Breakdowns within the electrical distribution system. 7. Human Error: Accidental introduction of AC power into low-voltage system circuits. Given these varied sources of surges, electrical contractors should consider the Space Age E120V-GT model. This model not only meets surge protection requirements but also includes the ELock FA device. The ELock FA effectively locks out the breaker, enhancing safety and compliance. Furthermore, the model comes with red labels for panel identification. This feature aligns with the requirements specified in NFPA 72, Chapter 10.6, ensuring that emergency circuits are clearly marked and identifiable. Choosing the Space Age SSU00468 model shown here thus ensures both compliance with current codes and enhanced safety for emergency circuits.

Understanding Exposed-Conductive Parts (ECP) of equipment in Electrical Systems According to IEC standards, metal parts of electrical equipment that carry no active components and are connected to ECPs are not classified as ECPs themselves. An example is the door of an electrical panelboard without live components. Defining such doors as non-ECP implies that no bonding jumper should be applied between the door and the panel's frame. Why? Because grounding the door could actually reduce safety by making the door conductive during a fault. On the other hand, if live parts are exposed when the door is opened, the door must be bonded, as it is an integral part of the basic insulation system. This distinction is critical for safety in electrical panelboard design, ensuring user protection in the event of a fault. M. Mitolo, "Protective Bonding Conductors: An IEC Point of View," in IEEE Transactions on Industry Applications, vol. 44, no. 5, pp. 1317-1321, Sept.-Oct. 2008, doi: 10.1109/TIA.2008.2002272. #ElectricalSafety #IECStandards #Engineering #PanelboardSafety #Grounding