Choosing the best NH fuse depends on your application requirements. NH fuses—also known as high rupturing capacity (HRC) fuse—are common in industrial and commercial applications. You need to understand which of the NH fuse types to use – gG, aM, gR, or aR? Read on to see what each type of fuse is and how to select each of them.

NH Fuses: What Are They?

NH fuses are low voltage fuses designed to protect electrical systems from conditions where the current may flow at a dangerously high level. They typically conform to the IEC 60269 standard and are CE certified. Different sizes of fuse are required for different settings and sizes of electrical circuits; they may be NH00, NH1, NH2, NH3 or NH4, depending on their rated current and breaking capacity. NHs are common in industrial panels as well as in electrical motor control centres.
The commonest types of NH fuses are gG, aM, gR and aR but knowing the difference in requirements between each of them is the key to preventing equipment damage through improper protection.

NH Fuse gG: General Purpose Protection of Equipment

The gG NH fuse is a general-purpose fuse – it gives full-range protection against overload and short-circuit. gG fuses use is general in distribution, transformer protection, and industrial use. If in doubt as to the size, and when it’s required for protection of cables and equipment, you’re fine with this, it’s rated to IEC 60269 specificationsAnd if you don’t know what you’re looking for, gG is generally a good fuse to fall back on.
NH Fuse aM: Motor Protection
This NH fuse protects motors, but doesn’t interrupt small overloads. That’s important if you want to fuse motors, as motors can have a temporary overload at startup. Using an aM means you protect your motor from that heavy short-circuit event and let it ride through your normal operational overloads. That’s how it’s standard in motor control centers and Industrial Automation.
NH fuse gR and aR: Semiconductor Protection
gR and aR are for providing the protection for all kind of rectifying, diode and power module applications. The gR are a full range of fuses similar to the gGen type but have a high speed characteristic curve for semiconductor use. aR are like the aM, only mean for use protecting semiconductors and only on short-circuits, not otherwise.
Semiconductors are sensitive to overcurrent and heat, if you haven’t already noticed. You need to choose the right gR or aR or you stand to lose your precious semiconductors, and a lot of time.
How to Choose the Right NH fuse
Choosing your NH fuse involves understanding your application and what kind of load you are protecting.This is mainly the magnitude of the working current, and the fuse should be rated slightly above the ordinary load. The magnitude of the current flowing through the fuse under normal working conditions must be known, and a fuse chosen which on the curve is slightly higher than the normal load. The current rating must be determined at the maximum permanent working temperature.
The nature of the circuit to be protected will also help to determine the appropriate fuse. If it is for apparatus having an inductive reactance, such as a motor, then we should use an aM fuse for such apparatus. If the fuse determines the operating time of the device to which it is attached so as to potentially injure the apparatus protected, then an aR or alternatively a well-dimensioned gR fuse should be chosen. In other instances, however, it is quite safe to use either gG or gL.
Another matter to watch is the breaking capacity of the fuse.
It is essential that the current carried by each part of the system should be not greater than its rating, and that the fuses shall not blow (except in the event of a serious fault) at any fault, influence or stranded current actually occurring in the installation.
The standard for fuses, i.e. IEC 60269 is recommended, and for Europe, a CE certification is most welcome. You need to ascertain whether the fuse you are buying will comply with these standards (also on its packaging), and in case of doubt, you can contact your NH fuse supplier, who will clarify and settle your doubt.
These fuses are referred to as “NH.” Fuses are not only available in various styles but also forming an integral part of SQ – (Switchgear) arrangement. The SQ2 with a 50kA breaking capacity is highly suitable for use in the electrical protection of large busbars and to protect transformers from overload, short-circuits etc. The fuses are also conveniently mounted on low uniform bases. Then there are also the intermediate meets, etc.
The sizes are: NH00, NH01, NH02, NH03, NH04.