At a Glance. A Socomec fuse link is not a commodity. The two letters printed on the barrel — gG, aM or uR/aR — decide whether the device protects a cable, a motor feeder or a semiconductor, and the words AVEC PERC / SANS PERC decide whether that fuse can report that it has operated. This guide works through IEC 60269 utilization categories, the body sizes from 10×38 cartridge up to NH3 blade fuse, striker and non-striker versions, breaking capacity, and how FUSERBLOC fuse combination switches, DDMM striker monitoring and SURGYS surge protection fit around them.
1. What a Fuse Protects — and What It Cannot Do
A fuse is the simplest protective device in an electrical assembly and the one most often mis-applied after the original panel has been reworked a few times. Its element heats and melts when current exceeds a defined curve, permanently opening the circuit. That single behaviour gives three strengths and three limits.
The strengths: the fuse is fail-safe, its speed is predictable regardless of how long it has been in service, and it is usually the cheapest way to obtain a very high breaking capacity at a given point in the network. The limits: it is single-use, it does not detect an overload in time to protect a motor winding, and it will not clear a fault that the upstream device has already been coordinated to clear.
The practical consequence for panel builders is that a fuse is almost never a stand-alone decision. It is one half of a pair — fuse plus holder, or fuse plus disconnector — and the pair is only compliant if the two halves are rated for the same duty. A 200 kA fuse fitted into a 50 kA switch does not create a 200 kA assembly; the assembly is rated at the lower figure. That interaction is what Sections 5 and 6 deal with.
2. Utilization Category: gG, aM and uR/aR
IEC 60269 encodes the fuse's job in a two-letter utilization category. The first letter says whether the fuse clears overloads as well as short circuits (g = full-range) or short circuits only (a = partial-range, back-up). The second letter says what it is intended to protect.
| Category | Full or partial range | Protects against | Typical use | Socomec example |
|---|---|---|---|---|
| gG (also marked gL) | Full range | Overload and short circuit | Distribution circuits, control panels, lighting, cable protection | FUS GG 10X38 20A SANS PERC |
| aM | Partial range (back-up) | Short circuit only | Motor feeders, always paired with a thermal overload relay | FUS AM T1 250A AVEC PERC |
| uR / aR | Partial range (back-up) | Short circuit only, ultra-fast | Semiconductor devices: drives, rectifiers, DC links, UPS | FUS UR 22X58 80A AVEC PERC |
The two failure modes you will actually meet in the field are symmetrical. Replace a gG fuse with an aM fuse in a cable feeder and you have removed the overload protection from the cable — the fuse will hold a 150 % overload indefinitely while the insulation cooks. Replace an aM fuse with a gG fuse in a motor feeder and nuisance operation is likely, because the gG curve is not shaped to ride through motor starting current; worse, the gG will eventually open on overload and take the whole feeder down instead of letting the thermal relay trip first.
The uR/aR group is a different world again. Sampled parameters on the FUS UR 22X58 80A show a Fast (F) release characteristic and a utilization category listed as aR to IEC 60269 — these are semiconductor fuses, deliberately not intended to protect cable. They are also rated for both AC and DC at 690 V, which is why they turn up on DC links and rectifier outputs.
3. Body Size: From 10×38 Cartridge to NH3 Blade Fuse
Body size is a mechanical constraint, not an electrical preference: it is fixed by the fuse holder, the terminal spacing and the arc-quenching volume needed at the rated voltage. Socomec uses the standard IEC 60269 families, and the catalogue notation maps cleanly onto the IEC construction type.
| Socomec designation | IEC 60269 construction / size | Body | Example rating in the range | Typical base |
|---|---|---|---|---|
| 10×38 | Cylindrical cartridge | 10.3 mm diameter, 38 mm long | FUS GG 10X38 10A, 20A | Modular fuse holders and carriers |
| 22×58 | Cylindrical cartridge | 22 mm diameter, 58 mm long | FUS GG 22X58 63A, FUS UR 22X58 80A | Fuse holders, FUSERBLOC TS |
| T0 | NH0 / size S0 | Blade fuse, NH body | FUS gG T0 125A | NH fuse base and FUSERBLOC |
| T1 | NH1 / size S1 | Blade fuse, NH body | FUS GG T1 160A, FUS AM T1 250A | NH fuse base and FUSERBLOC |
| T2 | NH2 | Blade fuse, NH body | FUS AM T2 500A | FUSERBLOC T2 |
| T3 | NH3 / size S3 | Blade fuse, NH body | FUS gG T3 E 315A | NH fuse base and FUSERBLOC |
Two details in that table repay attention. First, the Socomec T-numbering and the IEC NH-numbering are the same family — the stored data for the FUS gG T0 125A records both a fuse size of S0 and a construction type of NH0, and the FUS gG T3 E 315A records size S3 with construction type NH3. When a customer sends you an NH2 requirement, you are looking for a T2 part.
Second, the ampacity is not the only consequence of the size. Sampled data on the 10×38 gG parts gives a rated voltage of 500 VAC and a power loss of 1 W at 10 A rising to 2 W at 20 A, whereas the NH-bodied aM parts are rated 690 VAC. In a densely packed enclosure, that dissipated wattage multiplied across dozens of carriers is a thermal budget item, not a footnote.
4. AVEC PERC or SANS PERC: The Striker Decides the Holder
“Percuteur” is French for striker, and it is the single most consequential suffix in the Socomec fuse catalogue. A striker is a small spring-loaded pin that ejects from the fuse body when the element operates.
| Version | Suffix | What it enables | Sample part |
|---|---|---|---|
| Without striker | SANS PERC | Visual indication only; front-access holders; simplest holders with no striker seat | FUS GG 10X38 20A SANS PERC |
| With striker | AVEC PERC | Trips a striker bar to open all three phases, or actuates an auxiliary contact for remote signalling | FUS GG T1 160A, FUS AM T1 250A, FUS UR 22X58 80A |
The selection rule is simple: if the application must know that a fuse has blown — because a motor contactor would otherwise run on two phases, or because a control room needs an alarm — you need AVEC PERC. If the fuse sits behind a transparent cover that an operator opens anyway, SANS PERC is cheaper and mechanically simpler.
The classic mistake is mixing the two on a three-phase circuit. Fit a striker bar across three fuse carriers and populate only one of them with an AVEC PERC fuse, and a single-phase blow will not trip the bar; the motor keeps running on the remaining phases. Either all three fuses carry strikers, or none of them do.
Note also that the two families cross over. The cylinder-bodied gG parts sampled here are SANS PERC, while the NH-sized gG, aM and uR parts are AVEC PERC — so you cannot assume the suffix from the utilization category alone. Read the model code.
5. Breaking Capacity and Coordination With the Switch
Breaking capacity is the maximum prospective short-circuit current the fuse can interrupt without rupturing the holder. Socomec publishes very different figures across the range, and the numbers scale with body volume.
- 10×38 gG: 120 kA at the rated voltage — remarkable for a 38 mm cartridge, and the reason these are trusted in distribution boards fed from large transformers.
- 22×58 uR/aR: 200 kA at 690 V, with a Fast release characteristic for semiconductor duty.
- FUSERBLOC TS 22X58 3X125A: conditioned rated short-circuit current Iq of 100 kA for the complete fuse combination switch.
- FUSERBLOC T2 4X400A: Iq of 50 kA, with a rated operating power of 220 kW at AC-23, 400 V.
The trap is that the fuse's rating and the switch's rating are not independent. The assembly rated short-circuit current is the lower of the two, so a 200 kA fuse in a 50 kA disconnector gives you a 50 kA assembly. Always size the fuse to the prospective fault current at its own point in the network, then confirm the disconnector's Iq is at least that value. This is also why the FUSERBLOC frame size matters: the 22×58 version reaches Iq 100 kA while the NH2 version at 400 A is rated Iq 50 kA.
6. FUSERBLOC: Fuse Combination Switch vs Plain Disconnector
A FUSERBLOC is a fuse combination switch: a load-break switch and a fuse base in one device. It replaces the classic arrangement of a separate switch-disconnector and separate fuses, and it does three jobs at once — isolation, switching under load, and short-circuit protection.
Socomec builds the range with two switching positions, and the difference is worth knowing before you quote:
- I-0 — on and off. The FUSERBLOC T2 4X400A L GA is an I-0 device: four poles, NH2 fuses, 690 VAC, bolt connection on the main circuit, rocker lever, IP20 at the front face.
- I-0-Test — on, off, and a third position in which the fuse can be checked without breaking the main circuit. The FUSERBLOC TS 22X58 3X125A F/L uses this arrangement with a long rotary handle, three poles and 22×58 NFC fuses.
Both sampled devices are documented as usable as a main switch, as a safety switch and as an emergency stop installation, and both offer IP20 front-face protection. If you need more than that, look at the accessories rather than a different switch: external front and side operators, shafts and handles are separate catalogue items, and the FUSERBLOC entry for the 400 A unit states explicitly that the operator is not included.
The alternative to a FUSERBLOC is a non-fused switch-disconnector such as the SIRCO family. That choice is about topology, not quality: a SIRCO device provides isolation and load breaking but no short-circuit protection of its own, so it depends on a fuse or breaker upstream. We compare those options in the switch disconnector guide, which also covers SIRCO versus ATyS — worth reading before you decide whether the fuse belongs inside the switch or somewhere else in the cubicle.
7. Completing the Protection Scheme
Striker monitoring: DDMM
If the fuses are AVEC PERC, something has to read the striker. The DDMM 3P is a three-pole auxiliary contact block for NH1 and NH2 fuse bases that converts the striker's mechanical movement into an electrical signal — one normally-open plus one normally-closed contact — so a blown fuse can trip the control circuit or raise an alarm. Note the fuse-size constraint in its data: it is specified for NH1–NH2 bases, not for the whole NH range.
Surge protection: SURGYS
Fuses and surge protective devices share a cubicle and interact. The PF TYPE1 SURGYS G140-F 2P is a two-pole Type 1+2 device for 230 V networks, suitable for IT and TN systems, with a nominal discharge current of 25 kA and a maximum discharge surge current of 140 kA on the 8/20 µs waveform, a voltage protection level of 1.5 kV and a short-circuit breaking capacity of 50 kA. It carries a remote signalling contact and occupies four modules with IP20 protection. When an SPD and a fuse sit in the same feeder, the fuse has to be selected so that the SPD's backup protection coordinates with the fuse's melting curve — an SPD vendor's maximum fuse rating is not a suggestion.
Accessories and the wider category
Enclosure kits, cage terminals, shafts, handles and striker bars are catalogued separately, and they are the parts that most often delay a retrofit. The full Socomec protection family — 635 catalogued items in this category alone — is listed under Fuses & Circuit Protection, with the manufacturer's full range at Socomec.
8. A Five-Step Selection Routine
- Identify the load. Cable or general distribution → gG. Motor feeder → aM, plus a thermal overload relay. Drive, rectifier, DC link or UPS → uR/aR.
- Read the prospective short-circuit current at the fuse's own point in the network. The fuse breaking capacity must be at least that value — 120 kA for the 10×38 gG parts, 200 kA for the 22×58 semiconductor parts.
- Fix the body size from the holder you already have: 10×38, 22×58, or T0/T1/T2/T3 (NH0–NH3). Ampacity and holder are decided together.
- Decide the striker. AVEC PERC if you need three-phase ganging, a DDMM monitoring contact or remote signalling; SANS PERC otherwise. Be consistent across all three phases.
- Verify the pairing. Confirm the disconnector's conditioned rated short-circuit current Iq is at least the fuse's breaking capacity, and that the fuse physically fits the switch's declared fuse size.
Frequently Asked Questions
What is the difference between a gG and an aM fuse?
gG is a full-range, general-purpose fuse that clears both overloads and short circuits, so it protects cable on its own. aM is a partial-range back-up fuse intended only for short-circuit protection of motor circuits; it must be paired with a thermal overload relay, because it will not clear a sustained overload before the cable is damaged.
What does “AVEC PERC” mean on a Socomec fuse?
“Percuteur” is French for striker. AVEC PERC means the fuse is supplied with a striker, the small pin that ejects when the element operates, so it can trip a striker bar across all three phases or actuate a monitoring contact. SANS PERC means the fuse is supplied without a striker and provides visual indication only.
Can I substitute a 22×58 fuse for an NH fuse?
Only if the holder, terminal spacing and coordination allow it. The 22×58 cartridge and the NH0–NH3 blade fuses are different IEC 60269 body families with different mounting systems, and changing body size changes the assembly's rated short-circuit current and its heat dissipation, so the combination rating has to be re-verified.
How can I tell whether a fuse has operated?
Visually, through a transparent window or the holder cover. Electrically, by fitting an AVEC PERC fuse and a striker-monitoring auxiliary contact such as the DDMM 3P and wiring its one normally-open plus one normally-closed contact into the control circuit.
Does a fuse need its own disconnector?
It needs a means of isolation for safe replacement, which is normally provided by the holder or by the switch it sits in. A FUSERBLOC combines both functions: switching position I-0 or I-0-Test plus an NH or 22×58 fuse base in a single device rated for 690 VAC operation.
Related Products
The parts referenced in this guide, all available from stock or on quotation:
- gG cartridge, 10×38: FUS GG 10X38 10A SANS PERC · FUS GG 10X38 20A SANS PERC
- gG cartridge, 22×58: FUS GG 22X58 63A SANS PERC
- Semiconductor: FUS UR 22X58 80A AVEC PERC
- gG NH blade: FUS gG T0 125A · FUS GG T1 160A AVEC PERC · FUS gG T3 E 315A
- aM motor back-up: FUS AM T1 250A AVEC PERC · FUS AM T2 500A AVEC PERC
- Fuse combination switches: FUSERBLOC T2 4X400A L GA · FUSERBLOC TS 22X58 3X125A F/L
- Monitoring and surge protection: DDMM 3P · PF TYPE1 SURGYS G140-F 2P
- Browse the category: Fuses & Circuit Protection · all Socomec products
Buying Fuses From Glorient
Glorient supplies Socomec fuses, FUSERBLOC fuse combination switches and SURGYS surge protective devices with competitive pricing and worldwide delivery. Send us the fuse size, the utilization category, the rated current and whether you need a striker, and we will confirm the exact order number within 24 hours. Start from the quotation form, or read the companion guide to current transformer and power monitoring selection if your project also covers measurement.
A fuse is the last line of defence in an electrical assembly, and it is chosen in minutes. Getting the utilization category, the body size and the striker version right takes only slightly longer — and it is the difference between a panel that protects its cable and one that merely contains it.