Quick answer: Fuse class letters indicate the time-current characteristic and intended application. gG = full-range general-purpose (overload + short-circuit) for cable and circuit protection. aR = partial-range semiconductor protection (short-circuit only) for VFDs and rectifiers. gPV = full-range photovoltaic fuse specifically designed for solar DC systems with low fault currents. Choose based on what you are protecting and the fault current characteristics of your system.

Understanding the IEC Fuse Class Coding System

IEC 60269 defines a two-part code for fuse time-current characteristics. The first letter (lowercase) indicates the breaking range, and the second letter (uppercase) indicates the application category:

gG: General-Purpose Full-Range Fuses

gG fuses are the most common type, providing full-range protection against both sustained overloads and short-circuit currents. They are used for general cable and circuit protection in industrial and commercial installations.

• Opens on both overload (1.25×-2× rated current) and short-circuit
• Standardized time-current curves for selectivity coordination
• Available in cylindrical (10×38, 14×51, 22×58) and NH sizes
• Typical applications: distribution panels, lighting circuits, motor branch circuits

Limitation: gG fuses are not suitable for semiconductor protection (too slow) or PV DC systems (may not detect low fault currents).

aR: High-Speed Semiconductor Protection Fuses

aR fuses are ultra-fast fuses designed to protect sensitive semiconductor devices (IGBTs, diodes, thyristors, MOSFETs) from short-circuit damage. They provide only partial-range protection — they do NOT protect against overloads, which must be handled by a separate device (contactor, breaker, or gG fuse in series).

• Ultra-fast opening (typically < 1ms at 10× rated current)
• Very low I²t (let-through energy) to protect semiconductors
• High breaking capacity (up to 200kA)
• Typical applications: VFDs, UPS, rectifiers, welding equipment, EV inverters

Products from DC Fuse Link and GFEFuse offer aR class high-speed fuses for industrial and renewable energy applications.

gPV: Photovoltaic DC Fuses

gPV fuses are specifically designed for solar photovoltaic DC systems. PV systems have unique fault characteristics: fault currents can be very low (as low as 1.5× rated current) due to the current-limiting nature of solar panels, and standard gG fuses may not detect these faults.

• Designed to interrupt low DC fault currents (1.25×-2× rated)
• DC voltage ratings up to 1500V DC
• Full-range protection (overload + short-circuit)
• Typical applications: string combiner boxes, re-combiner boxes, PV inverter DC input

Using a gG fuse in a PV string can result in failure to clear a fault, leading to panel damage or fire. Always use gPV-rated fuses for solar DC circuits.

Which Fuse Class for Your Application?

For fuse selection assistance, contact EssFuse engineering or explore our product catalog. Visit EssFuse.com for additional technical resources.