Fuses Selection Guide
A fuse is a device that protects the cable and equipment by interrupting the circuit on overcurrent and short circuit. Types of miniature circuit breakers, blade fuses and cartridge fuses, and how to choose.
What is a fuse? A fuse is a device that protects the cable and equipment by interrupting the circuit when overcurrent or a short circuit occurs in the circuit it is connected to. In fusible types such as blade fuses and cylindrical cartridge fuses, the internal fusing conductor melts and breaks and the fuse is replaced; miniature circuit breakers, on the other hand, open the circuit with a thermal and magnetic tripping mechanism and can be reset.
This guide explains what to look at when choosing products in the Fuses category.
Types of fuses
- Miniature Circuit Breakers: resettable miniature circuit breakers with thermal and magnetic tripping. 1-, 2-, 3- and 4-pole models with B and C curves are listed; solar DC miniature circuit breakers for photovoltaic systems are also in this group.
- Miniature Circuit Breakers with Residual Current Protection: combine overcurrent and residual current protection in a single housing; models with rated residual current of 30 mA and 300 mA are listed. For separate residual current protection, see the Residual Current Devices category.
- Blade Fuses: NH fuse links fitted in a base or a fuse switch disconnector; used in main distribution and power factor correction panels and at drive inputs.
- Cylindrical Cartridge Fuses: fuse links with 8x31, 10x38, 14x51 and 22x58 mm bodies, and gPV cartridges for photovoltaic strings.
Curve and breaking capacity of a miniature circuit breaker
The notation "C16" or "B10" in the product name gives the tripping curve and the rated current together. The curve letter determines the magnetic tripping threshold: the B curve trips instantaneously at 3-5 times the rated current, the C curve at 5-10 times and the D curve at 10-20 times. The B curve is used for general line protection, and the C curve for loads that draw high current when switched on, such as machines and lamp groups; B and C curve models are listed in this category.
The breaking capacity is the 4.5 kA, 6 kA or 10 kA value written in the product name, and it must not be lower than the prospective short-circuit current at the point where the breaker is installed. The miniature circuit breaker standard IEC 60898-1 covers devices with a rated current of up to 125 A and a breaking capacity not exceeding 25 kA. Some models are also declared according to the industrial circuit breaker standard IEC 60947-2, and the product card then shows two separate breaking capacities; make the comparison using the value of the same standard.
Size and utilization class of fusible fuses
For blade and cartridge fuses, the body size must match first: the frame size for an NH fuse link (such as NH00, NH1, NH2), and the diameter and length for a cartridge fuse. Then the two-letter utilization class is checked: gG is a full-range fuse for cable and line protection, aM breaks only on short circuit and is made for motor circuits, and gPV is made for photovoltaic strings. Next to an aM fuse, a separate protection such as a thermal overload relay must be provided for overload.
How to determine the rated current
A fuse primarily protects the cable: its rated current is not chosen below the line's load current or above the cable's current carrying capacity. You can find the load current with the Current and Fuse Calculation from Active Power tool and the current the cable can carry with the Cable Current Carrying Capacity Calculation tool; the steps of cross-section selection are in the article How to choose a cable?.
The thermal threshold of a miniature circuit breaker cannot be adjusted. For motor feeders, Motor Protection Circuit Breakers are used, and for distribution feeders that need adjustment and high current, Molded Case Circuit Breakers are used.
Brands in this category
- ABB: S 200, SH 200 and FMS series miniature circuit breakers, S804PV solar DC miniature circuit breakers, DS201 and DS203NC miniature circuit breakers with residual current protection, OFAF blade fuses, E 9F solar cartridge fuses.
- Schneider Electric: Acti9 iC60N, Easy9 and Easy9 Pro miniature circuit breakers, iDPN Vigi miniature circuit breakers with residual current protection, DF2 cartridge fuses.
- Siemens: 5SL and 5SY miniature circuit breakers, 5SU1 miniature circuit breakers with residual current protection, 3NO and 3NE blade fuses.
- Chint: NXB-63 and DZ-158 series miniature circuit breakers.
Order notes
Fuses are sold by the piece; a three-phase circuit needs three blade or cartridge fuse links and one multi-pole miniature circuit breaker. For products with a lead time, confirmation of the delivery time is obtained before ordering. You can reach a product directly by typing the manufacturer code, such as 5SY5203-7 or EZ9F57216, into the search.
Fuse and miniature circuit breaker comparison table
| Protection Device | Standard | Typical Ratings | Application Area | Category Link |
|---|---|---|---|---|
| Miniature circuit breaker (MCB) | EN 60898-1 / IEC 60947-2 | 0.5 A – 125 A (4.5 / 6 / 10 kA) | Resettable protection for lighting, socket, and machine branch circuits | Miniature Circuit Breakers |
| NH blade fuse | IEC 60269-2 (gG / aM) | 16 A – 1250 A (100–120 kA) | Main distribution feeders and high short-circuit current limitation | Blade Fuses |
| Cylindrical and glass cartridge fuse | IEC 60269 / IEC 60127 | 100 mA – 100 A | Control circuits, PLC/SMPS inputs, and electronic board protection | Glass Fuses |
| Automotive blade fuse | ISO 8820 | 2 A – 100 A | 12 V / 24 V DC vehicle and mobile equipment circuits | Automotive Fuses |
Frequently asked questions
What is the difference between a B-type and a C-type miniature circuit breaker?
The difference is in the threshold of magnetic, that is, instantaneous, tripping. A B curve breaker trips at 3-5 times the rated current, a C curve at 5-10 times and a D curve at 10-20 times. The B curve is for general line protection; the C curve is chosen for loads that draw high current at the first instant, such as machines and lamp groups, so that it does not trip during start-up. On long lines the short-circuit current can remain low, so the curve is selected according to the project calculation.
What do the 4.5 kA, 6 kA and 10 kA values on a miniature circuit breaker mean?
This value is the highest short-circuit current the breaker can interrupt. The short-circuit current that can occur at the point where the breaker is installed must not exceed this value; close to the transformer and on feeders with a thick cross-section, the short-circuit current is higher. The miniature circuit breaker standard IEC 60898-1 covers breaking capacities up to 25 kA. For some models a second value according to IEC 60947-2 is also given; make the comparison using the value of the same standard.
Is a miniature circuit breaker still needed when there is a residual current relay?
Yes. A residual current relay detects only current leaking to ground; it does not detect overload or a phase-neutral or phase-phase short circuit, so the line is also protected with a fuse. A miniature circuit breaker with residual current protection combines both functions in a single device. Devices with a rated residual current of 30 mA are used for personal protection, and devices of medium sensitivity such as 300 mA for fire protection.
If the fuse trips often, can a higher amp rating be installed?
The rated current of a fuse is determined by the current the cable can carry; simply increasing the fuse leaves the cable unprotected. First the cause of the tripping must be identified: thermal tripping is seen if too much load is connected to the line, and magnetic tripping if a device is faulty or the inrush current is high. If the load has really increased, the cable cross-section and the fuse are recalculated together; the calculation and the change must be done by a qualified electrician.
Can an AC miniature circuit breaker be used in the DC circuit on the solar panel side?
The values declared for AC are not valid in a DC circuit. IEC 60898-1 covers only miniature circuit breakers operating on alternating current; AC and DC operation is addressed separately in IEC 60898-2. In photovoltaic strings, solar DC miniature circuit breakers for which the manufacturer declares a DC rated voltage and gPV cartridge fuses made according to IEC 60269-6 are used; the string voltage must not exceed the DC rated voltage of the device.
What is the difference between gG and aM fuses?
Both are utilization classes of fusible fuses. gG is full-range: it interrupts all overcurrents from overload to short circuit and is used for cable and line protection. aM is partial-range: it interrupts only on short circuit, is intended for motor circuits and is used together with a separate device such as a thermal overload relay for overload protection. A gG and an aM fuse link of the same size and current are not interchangeable.