Blade Fuses Selection Guide
For a blade fuse, the frame size determines the base the fuse link fits; the size, rated current and duty class must be read correctly when choosing.
This guide explains what to look at when choosing products in the Blade Fuses category.
Frame size and rated current
The frame size determines which base or fuse switch disconnector the fuse link fits into; when ordering, look at the size before the current. The rated current of the base depends on the size: the Siemens 3NH bases in the Blade Fuse Bases category are for 160 A in size 000/00, 250 A in size 1, 400 A in size 2, 630 A in size 3 and 1250 A in size 4.
The same current is available in more than one size, and this varies from manufacturer to manufacturer: 125 A and 160 A fuse links are listed in size 00 in the ABB OFAF series and in size 000 in the Siemens 3NO series; Tibcon offers its 160 A fuse link in both size 00 and size 1. The NH000 body is narrower than NH00. The two sizes fit the same base, but a 00 fuse link does not fit narrow fuse switch disconnectors made only for size 000. Some series go above the usual upper current of a size (such as 800 A in size 3 in ABB OFAF); for these fuse links, verify the rated current of the base or disconnector separately.
On the product card of ABB OFAF fuse links, the maximum breaking capacity is given as 120 kA; the reason the NH system is used at main distribution points with high short-circuit current is a breaking capacity at this level.
How to read the duty class
The two-letter code on the fuse link tells you what it protects. The first letter is the breaking range: g is a full-range fuse that breaks all overcurrents from overload up to short circuit, and a is a partial-range fuse that breaks only above a certain multiple of the rated current. The second letter indicates the protected circuit.
- gG: general purpose; cable and line protection. The ABB OFAF fuse links in the category are in this class.
- aM: short-circuit protection in motor circuits. It does not break on overload; it is used together with a separate overload protection such as a thermal overload relay.
- gR, gS and aR: very fast fuses for semiconductor protection; used at the inputs of drives, soft starters and rectifiers. gS protects the cable and line together with the semiconductor, while aR breaks only on a short circuit. In the category, the Siemens 3NE1 series is class gS and the 3NE3 series is class aR.
For drives and soft starters, the device manufacturer specifies the type and current of the fuse; a gG fuse link cannot replace a semiconductor fuse.
Base, fuse switch disconnector and rated voltage
A fuse link is not used on its own: in fixed mounting it is fitted into a base, and if three fuse links are to be opened and closed together with a handle, into a fuse switch disconnector. The products in this list with Siemens 3NP1 codes are not fuse links but fuse switch disconnectors that take NH fuse links, and their parts; other disconnectors are in the Load Break Switches category.
The rated voltage of the fuse link and the base must not be lower than the circuit voltage. In the category, ABB OFAF fuse links are listed with a rated voltage of 500 V and Siemens 3NE1 fuse links with a rated voltage of 690 V AC; a 500 V fuse link is not used on a 690 V network. The AC rated voltage does not apply to a direct current circuit; in a DC circuit, only a product with a declared DC value is used. For low-current control and photovoltaic string circuits, see Cylindrical Cartridge Fuses, and for adjustable and resettable protection, see the Molded Case Circuit Breakers category.
Brands in this category
- Siemens: fuse links with 3NO codes, 3NE1 (gS) and 3NE3 (aR) semiconductor protection fuses, and 3NP1 fuse switch disconnectors; the rated current is written in the product name. Bases with 3NH codes are in the subcategory.
- ABB: OFAF series 500 V gG fuse links; in sizes NH000, NH00, NH1, NH2, NH3, NH4 and NH4a. The code gives size and current together: OFAF000H25 is a 25 A fuse link in size 000; OFAF1H250 is a 250 A fuse link in size 1.
- Tibcon: size 00 and 1 fuse links; the size is read from the stock code (TB-NH00-63 is size 00, TB-NH01-250 is size 1).
Order notes
Blade fuses are sold by the piece; a three-phase outlet needs three fuse links, and all three must be of the same size, class and current. You can reach the product directly by typing a manufacturer or stock code such as 3NE1225-0, OFAF000H25 or TB-NH00-63 into the search. When determining the fuse link current, you can calculate the load current of the line with the Calculating Current and Fuse from Active Power tool.
Comparison and selection table
| Selection Criterion | NH000 / NH00 Blade Fuse Link | NH1 / NH2 Blade Fuse Link | NH3 / NH4 High-Current Fuse Link |
|---|---|---|---|
| Rated Current Range | 6 A – 160 A | 35 A – 400 A | 315 A – 1250 A |
| Breaking Capacity | 100 kA / 120 kA (500 V / 690 V AC) | 100 kA / 120 kA (500 V / 690 V AC) | 100 kA / 120 kA (main busbar protection) |
| Utilization Class | gG (full-range cable/line) or aM (motor short-circuit) | gG (general feeder) or aM (motor switchgear) | gG (transformer & heavy riser protection) |
| Fuse Base / Switch | NH00 fuse base or fuse-switch disconnector | NH1 / NH2 base or vertical fuse disconnector | NH3 / NH4 busbar fuse base (puller handle) |
Frequently asked questions
What is the difference between NH00 and NH000 fuses?
The two sizes fit the same base; the NH000 body is narrower and takes up less space. Which current is made in which size varies by manufacturer: in this category, in the ABB OFAF series the 100 A fuse link is size 000 and the 125 A and 160 A fuse links are size 00; in the Siemens 3NO series, 125 A and 160 A fuse links are listed in size 000. A 00 fuse link does not fit narrow fuse switch disconnectors made only for size 000; when replacing, check the size marking on the old fuse link and the disconnector.
Why is a semiconductor fuse required instead of gG at a drive input?
Semiconductors such as thyristors, diodes and IGBTs heat up very quickly on overcurrent. Class gR, gS and aR fuses are made to melt very fast to protect these elements; a gG fuse link is for cable protection and does not provide this speed. Because class aR breaks only on a short circuit, overload protection is installed separately. Take the type and current of the fuse from the table in the drive manufacturer's manual.
How can I tell a blade fuse has blown, and how is it replaced?
NH fuse links have an indicator that changes position when the melting element breaks; the definitive check is made by measurement with the circuit isolated from the supply. The fuse link is removed from the base with an NH fuse puller (an insertion and extraction handle). The NH system is defined for use by authorized persons; replacement should be done by qualified personnel with personal protective equipment. The new fuse link must have the same size, class, current and voltage values, and the cause of the blowing must be eliminated first.
Should I use a blade fuse or a molded case circuit breaker?
An NH fuse provides high breaking capacity in a small volume and limits the short-circuit current; on the other hand, the fuse link is replaced on every blow, and when a single fuse link blows the load may be left on two phases. A molded case circuit breaker opens all three poles together, can be reset, is adjustable and can be tripped remotely. Which one to use depends on the short-circuit and selectivity calculation in the project; at drive and soft starter inputs, the fuse type required by the device manufacturer is the basis.
Can a 500 V blade fuse be used on a 690 V or DC circuit?
A fuse link is not used in a circuit with a voltage higher than the rated voltage written on it; a 690 V network needs a fuse link with a 690 V rated voltage. The AC rated voltage does not apply to direct current: in a DC circuit, only fuse links for which the manufacturer declares a DC rated voltage are used. The voltage rating of the base is also checked separately; for the bases in the category, 250 V or 440 V DC values are stated along with 690 V AC.