Both AC fuses (RT18-32) and DC fuses (gPV-32) serve the core function of protecting circuits and electrical equipment from damage caused by overloads or short circuits. However, due to their different technical characteristics, they are used in distinct electrical environments. This article will compare AC fuses and DC fuses to explore their differences. Before doing so, let's first understand these two types of fuses.
What is an AC fuse (RT18-32)?
An AC fuse (RT18-32) is an industrial-grade cylindrical fuse primarily used for overload and short-circuit protection in low-voltage power distribution systems. It consists of two parts: the fuse element (fuse core) and the support (base). Typically, the fuse is rated for AC 380V or 500V, with some models supporting up to 690V. Its maximum current-carrying capacity is 32A. The actual fuse element specifications vary. The standard size of the fuse element is a 10×38 mm cylindrical design.
DC Fuse (gPV-32)
· The DC Fuse (gPV-32) is a DC fuse specifically designed for solar photovoltaic systems. The "g" denotes full-range breaking capacity (i.e., it protects against both short circuits and long-term minor overloads), while "PV" indicates that it is intended for photovoltaic applications. gPV fuses typically have a rated voltage of 1000 V DC or 1500 V DC. These fuses usually feature a cylindrical design with dimensions of 10×38 mm, 10×65 mm, or 10×85 mm. They are designed to handle the low-multiple overcurrent and reverse current conditions specific to photovoltaic systems.
Comparison of AC Fuses (RT18-32) and DC Fuses (gPV-32)
Although AC fuses (RT18-32) and DC fuses (gPV-32) are both protective devices, they differ in terms of application, function, and other characteristics. The following lists these differences and their significance when selecting a fuse type.
Application Differences
AC Fuse (RT18-32): Used in industrial distribution panels, residential circuit breaker panels, and motor control circuits. It delivers stable performance in AC environments.
DC Fuse (gPV-32): Used in solar combiner boxes, DC charging stations, and energy storage battery cabinets.
Functional Protection Scope
The protection scope of the RT18-32 AC fuse is primarily defined within low-voltage AC power distribution systems. Its core function is to provide short-circuit protection, while also offering overload protection under specific conditions.
Depending on the type of fuse element (designated by a letter code) inserted into the RT18-32 base, the protection focus varies:
gG Type: Full-range tripping. Protects against both severe short circuits and prolonged minor overloads. Commonly used in cables and power distribution lines.
aM Type: Partial-range tripping. Specifically designed to protect motor starting circuits. It can withstand the instantaneous high currents during motor startup without tripping, but will trip immediately in the event of a short circuit.
aR Type: Ultra-fast action. Specifically designed to protect precision power electronic devices such as inverters and rectifiers, preventing the destruction of semiconductor components.
The gPV-32 DC fuse offers highly specialized protection, tailored specifically for photovoltaic (PV) systems. Its core protection focuses on three key areas: high-voltage DC, low-multiple overloads, and reverse current.
Reverse current protection of the gPV-32 DC fuse (most critical):
In a photovoltaic array, if a group of solar panels is shaded or damaged, current from other parallel strings may flow back into that group. The gPV-32 is designed to detect and interrupt this dangerous reverse current, preventing the panels from overheating and catching fire.
Sustained Arc Suppression:
Under high-voltage DC conditions, arcs often continue to flicker after a standard fuse blows. The gPV-32's protection capabilities include forcibly extinguishing DC arcs up to 1500 V, ensuring that the fault point is completely de-energized and preventing the distribution panel from catching fire.
Breaking Capacity
The breaking capacity of the AC fuse RT18-32 is typically 100 kA at 500 V AC. This is because the ceramic fuse tube of the RT18-32 is filled with high-purity, treated quartz sand. When a short-circuit current causes the metal fuse element to melt instantly, the quartz sand rapidly absorbs heat and cools the arc, extinguishing it.
·The breaking capacity of the DC fuse (gPV-32) is measured at 20 kA under a DC voltage of 1000 V. Although this value appears lower than that of the AC type (100 kA), safely interrupting 20 kA under high-voltage conditions exceeding 1000 V DC is a very demanding technical requirement, as DC arcs are extremely difficult to extinguish.
When to Use the AC Fuse RT18-32
In practical applications, when dealing with standard municipal power grids or industrial three-phase AC environments, the RT18-32 should be the preferred choice. In low-voltage distribution systems, the RT18-32 is designed to protect branch circuits in distribution panels with rated voltages of AC 380–500 V in factories, shopping malls, or residential buildings. The RT18-32 base supports a maximum current of 32 A.
If your load's operating current ranges from 2A to 32A and you require highly reliable short-circuit interruption, this is the ideal choice.
If you use an aM-type (motor protection) fuse element, it allows the motor to draw several times its rated current during startup without tripping prematurely, yet it will quickly interrupt the circuit in the event of a short circuit.
If you need to quickly identify which circuit has blown, you should choose the RT18-32 base with an indicator light (designated with an "X" suffix); the indicator light will illuminate when a fuse blows.
Never use in high-voltage DC environments, such as on the output side of solar panels. Although the dimensions are the same, the RT18-32 cannot extinguish DC arcs; using it in such conditions may cause a fire.
Do not exceed the rated voltage: Never use in systems exceeding 690 V.
When to Use the gPV-32 DC Fuse
In electrical engineering, the application scenarios for the gPV-32 DC fuse are very specific; it is used exclusively in high-voltage DC environments that require precise overcurrent protection.
The most classic application is when multiple strings of solar panels are connected in parallel; a gPV-32 must be installed at the positive and negative output terminals of each panel group to prevent reverse current caused by faults between strings from burning out the panels. This high-breaking-capacity DC fuse is also used in the auxiliary control circuits of certain DC charging equipment or at the module output terminals.
The system's open-circuit voltage (Voc) must be confirmed. Common gPV-32 models are available in DC 1000V and DC 1500V versions. Guideline: The fuse's rated voltage must be greater than or equal to the system's maximum DC voltage.
gPV stands for "full-range protection." It not only interrupts massive short-circuit currents but also reliably blows when the current is only slightly exceeded (approximately 1.35 times). This is a fundamental difference from ordinary DC fuses (which only protect against major short circuits).
It is strictly prohibited to substitute "AC" for "DC": Never use an RT18-32 in place of a gPV-32.