Buy Switch Fuse Units (SFU) Online at Electrihub

A Switch Fuse Unit (SFU) — also referred to as a Switch Disconnector Fuse (SDF), Fuse Switch Disconnector (FSD), or fused isolator — is a manually operated switching device that combines a load-break isolating switch with HRC (High Rupturing Capacity) fuse protection in a single integrated unit. The switch provides a visible, lockable isolation point for safe maintenance and the HRC fuses provide high-speed fault current limitation and short-circuit protection that a plain switch or isolator cannot offer.

Switch Fuse Units are rated and tested to IEC 60947-3 (low-voltage switches, disconnectors, switch-disconnectors, and fuse combination units) and, for Indian market products, to IS 13947-3. Key specifications include rated current (A), rated operational voltage (up to 690 V AC), number of poles (2P/DP, 3P/TPN, 4P/TPN+N), fuse type and size (DIN NH / BS / HRC cylindrical), execution (open / enclosed), and utilisation category (AC-23A for motor switching duty, AC-22A for mixed resistive-inductive loads).

At Electrihub we stock Switch Fuse Units from the world's leading manufacturers — ABB, Siemens, Schneider Electric, Lauritz Knudsen (L&T), and Eaton (Bussmann series) — covering complete current ranges from 32 A to 1250 A, in open and enclosed executions, for every distribution board, motor control centre (MCC), sub-main panel, and industrial switchboard application.

Switch Fuse Unit (SFU) vs Switch Disconnector Fuse Unit (SDFU) — What's the Difference?

In common industry usage in India, the terms SFU (Switch Fuse Unit) and SDFU (Switch Disconnector Fuse Unit) are often used interchangeably. However, there is a precise technical distinction defined in IEC 60947-3:

A switch-fuse is a switch combined with fuses in series, where the switch is not certified as a disconnector — it may not guarantee full visible isolation with defined isolation gaps. A switch-disconnector-fuse (the more modern and more commonly specified product) is a switch-disconnector combined with fuses in series, where the switch-disconnector meets all the requirements of IEC 60947-3 for a disconnector — providing a visible, lockable off position with a confirmed isolation gap that is verifiable by the operator. For all safety-critical isolation applications — maintenance isolation, work-permit lockout/tagout (LOTO) procedures, and panel isolation — always specify a switch-disconnector-fuse (SDFU/SDF), not merely a switch-fuse.

All major manufacturers marketed under the SFU name today — ABB OS, Siemens 3KL8/3NP1, Schneider TeSys GS, L&T FN, and Eaton Bussmann EBH/EBV — are technically switch-disconnector-fuses meeting IEC 60947-3 disconnector requirements.

Types of Switch Fuse Units

Open Execution (DIN Rail / Panel Mounting)

Open execution Switch Fuse Units are mounted directly on a back-plate or DIN rail inside a switchboard enclosure. Live parts are exposed (protected by the panel enclosure itself) and the operator interacts with the unit via a direct or external handle extending through the panel door. Open execution units are compact, cost-effective, and by far the most common type used in Indian MCCs, distribution boards, and industrial panels. All major series — Siemens 3KL8 open, Schneider TeSys GS open, ABB OS open, L&T FN open — are open execution.

Enclosed Execution (IP-rated Housing)

Enclosed execution Switch Fuse Units have an integral enclosure (typically IP54 or IP65) housing the switch mechanism and fuses. They are used for wall mounting in locations without a dedicated panel — such as motor isolation points on factory floors, outdoor pump houses, and agricultural feeders. The integral enclosure protects against dust, water ingress, and accidental contact with live parts without requiring an additional switchboard cabinet.

2-Pole (DP) Switch Fuse Units

2-pole (Double Pole / DP) Switch Fuse Units switch and fuse both line conductors simultaneously in single-phase circuits. They are used for single-phase motor and feeder isolation, lighting sub-distribution, and control circuit isolation where both line and neutral must be broken for maintenance safety.

3-Pole (TPN / TP) Switch Fuse Units

3-pole (Triple Pole / TP or TPN) Switch Fuse Units are the standard for three-phase power distribution and motor circuit isolation. They switch all three line conductors simultaneously. TPN (Triple Pole and Neutral) variants include a switched neutral in addition to the three line poles, providing four-pole simultaneous isolation — essential for TN-S earthing systems and IT network installations where neutral isolation is required during maintenance.

4-Pole (TPNC / TPSN) Switch Fuse Units

4-pole Switch Fuse Units switch three lines and the neutral conductor simultaneously. In some variants the neutral pole is a solid (non-fused) link that disconnects mechanically with the three fused line poles. They are specified for installations where neutral isolation during maintenance is a safety or code requirement, for bi-directional feeders, and for automatic transfer switch (ATS) applications.

Bus-Bar Mounting (Vertical / Horizontal) Switch Fuse Units

Bus-bar mounting SFUs — such as the Eaton Bussmann EBH and EBV series and the Siemens 3NP1 — are designed for direct mounting onto the busbars of a panel, eliminating cable connections between the busbar and the switch. They are used in large distribution boards, capacitor bank panels, and sub-distribution switchgear where space efficiency and direct busbar interface are priorities.

Switch Fuse Unit Brands and Series – Technical Comparison

The table below covers every Switch Fuse Unit brand and series stocked by Electrihub. Use the current range, pole configuration, fuse type, and execution columns to shortlist the right product for your application, then follow the series link to browse available stock.

All Switch Fuse Units are certified to IEC 60947-3. Indian manufactured products also comply with IS 13947-3. Current ratings shown are maximum rated thermal current (Ith). Refer to individual product datasheets for AC-23A motor duty ratings, conditional short-circuit current ratings, and fuse size compatibility.

About the Switch Fuse Unit Brands We Stock

ABB — OS Series Switch Fuse Units

ABB's OS (Operating Switch) series is one of the most comprehensive switch-disconnector-fuse ranges in the world, covering current ratings from 16 A (OS Mini) up to 1250 A (OS1250), in 3-pole and 4-pole configurations, for DIN, BS, NFC, and UL/CSA fuse types. All OS series units comply with IEC 60947-3 and are rated for AC-23A motor switching duty. The OS handle mechanism provides IP65 protection in the OFF position and can be padlocked in the OFF position for LOTO (lockout/tagout) safety procedures — a standard requirement for maintenance isolation in industrial facilities. A door-interlock mechanism prevents the panel door from being opened while the handle is in the ON position, protecting maintenance personnel.

OS Mini (16–63 A) units use protected tunnel IP20 terminals as standard. OS100–OS160 units include a terminal bolt kit. OS200–OS1250 units are designed for high cable cross-sections with threaded rod or bus-bar terminals. Available accessories include auxiliary contacts (early-break and position-indicating), blown-fuse indicator contacts, phase barriers, and terminal shrouds for IP20 maintenance. The ABB OS series has a mechanical endurance of 20,000 operating cycles, making it exceptionally long-lived in high-use distribution applications.

Browse All ABB Switch Fuse Units →

Siemens — Superswitch 3KL8 and SENTRON 3NP1 Series

Siemens offers two key Switch Fuse Unit platforms for the Indian and global market. The Superswitch 3KL8 is Siemens' flagship switch-disconnector-fuse for the Indian sub-continent, available in current ratings from 20 A to 800 A in 2-pole, 3-pole (TPN), and 4-pole (TPSN) configurations, with DIN HRC type fuses. The 3KL8 is specifically designed for high-ambient-temperature environments and requires no derating up to 60 °C — a critical advantage for Indian industrial and infrastructure applications. It features self-cleaning rolling contacts for high short-circuit withstand capacity, fuse monitoring capability (via optional microswitch accessories), and is available in open and enclosed executions suitable for use in corrosive environments. The 3KL8 supports both motor control (AC-23A) and distribution (AC-22A) duty applications.

The SENTRON 3NP1 is Siemens' global NH fuse switch-disconnector for panel and busbar mounting applications, rated from NH000 (up to 160 A) to NH3 (up to 630 A) in 1-pole and 3-pole versions, compliant with IEC 60947-1 and IEC 60947-3. The 3NP1 supports optional electronic fuse monitoring modules (EFM) for blown-fuse detection and signalling — enabling integration with building management systems and SCADA panels.

Browse All Siemens Switch Fuse Units →

Schneider Electric — TeSys GS and NX Series

Schneider Electric's TeSys GS series is the IEC global standard switch-disconnector-fuse, covering 30 A to 630 A in 3-pole and 4-pole configurations with DIN NH blade fuse sizes 000 to 3, rated at up to 1,000 V AC. The TeSys GS is a highly modular system: the switch body (GS1 with direct handle; GS2 with external panel-mount handle) is equipped with add-on auxiliary contact modules — front-mount GS1AM (early-break and position signalling), side-mount GS1AN (position signalling, reversible NO/NC), and top-mount GS1AF (blown-fuse signalling contact for striker-type fuses). GS2 series units provide a short-circuit withstand of up to 100 kA at 400 V, among the highest in the industry. All TeSys GS products are Green Premium (RoHS/REACh) certified and multi-standard certified (IEC and Marine).

The NX series (sold under Schneider India/Meher branding) provides TPN and TPNC switch-disconnector-fuses for DIN and BS HRC fuse types, specifically optimised for the Indian market distribution panel and MCC requirements at 415 V. The NX series includes models such as NX063TPNBS, NX125TPNDI, NX160TPNDI, NX315TPNDI, NX630TPNDI, and NX630TPXDI, with open and enclosed execution options for direct and feeder-circuit applications.

Browse All Schneider Electric Switch Fuse Units →

Lauritz Knudsen (L&T) — FN Series Switch Fuse Units

Lauritz Knudsen Electrical & Automation (formerly L&T Switchgear) manufactures the FN series Switch Fuse Units, ISI-marked to IS 13947-3 and IEC 60947-3, built specifically for Indian distribution networks, MCCs, and industrial switchgear. The FN series covers current ratings from 63 A to 630 A in DP (Double Pole), TPN (Triple Pole and Neutral), and TPNC (Triple Pole with Neutral Changeover) configurations, for both DIN HRC and BS HRC type fuses, in open and enclosed executions.

FN series SFUs are widely specified for sub-distribution feeders, motor isolation points, MCC incomer isolation, agricultural feeder panels, and infrastructure switchboards across India where ISI-marked, BIS-certified products are mandatory for government and utility tenders. Key models include FN 63, FN 100, FN 125, FN 200, FN 315, FN 400, and FN 630 series with DP, TPN, and TPNC pole configurations in both DIN and BS fuse variants. Accessories include auxiliary contact modules, padlock attachments, door-coupling handles, and phase barriers.

Browse All L&T Switch Fuse Units →

Eaton (Bussmann Series) — EBH and EBV Switch Fuse Disconnectors

Eaton's Bussmann series EBH (Horizontal) and EBV (Vertical) NH fuse switch-disconnectors are designed specifically for installation on busbar systems in large distribution panels, sub-station LT boards, and industrial distribution switchgear. The EBH horizontal series covers NH000 (up to 160 A), NH00 (up to 160 A), NH1 (up to 250 A), NH2 (up to 400 A), NH3 (up to 630 A), and NH4 (up to 1,250 A on request) fuse sizes at up to 690 V AC. The EBV vertical series is available for NH1/NH2 (160–400 A) and NH3 (up to 630 A) fuses.

Thermoplastic parts of Eaton EBH/EBV units are made from fibre-glass reinforced halogen-free polyamide with V0 flame-retardant classification — the highest possible flammability class. Silver-plated contacts ensure low power loss and stable contact resistance over the product's operating life. The EBH/EBV series is IEC 60947-3 compliant and supports direct busbar mounting (60 mm, 100 mm, or 185 mm busbar systems), making them the preferred choice for OEM switchgear builders and sub-station engineers who need compact, direct busbar interface fuse isolation in LT distribution applications.

Browse All Eaton Switch Fuse Units →

Where Are Switch Fuse Units Used?

Incomer and Feeder Protection in MCCs and Distribution Boards — SFUs are widely used as incomer devices on Motor Control Centre (MCC) sections and sub-distribution boards, providing simultaneous isolation and HRC fuse protection for feeder circuits. The high short-circuit current handling capacity of NH HRC fuses (up to 120 kA breaking capacity) combined with the isolation function of the switch-disconnector makes SFUs the preferred choice for incomer protection at high prospective fault current locations.

Motor Isolation and Protection — In motor starter circuits, a Switch Fuse Unit mounted upstream of the contactor and overload relay provides both the short-circuit protection (via HRC fuses, typically aM type for motor starting) and the maintenance isolation point. AC-23A rated SFUs are specifically designed for inductive motor switching duty. A padlockable SFU in the OFF position forms the first element of a safe isolation and LOTO (lockout/tagout) procedure for motor maintenance.

Transformer LV Incomer Isolation — Switch Fuse Units are installed as the LV incomer device on distribution transformers (100 kVA to 2,500 kVA) to provide both short-circuit protection on the LV side (using gG/gL type HRC fuses) and a lockable isolation point for transformer maintenance and replacement. The SFU is typically the first switching device on the LV side of the transformer before the main distribution busbar.

Sub-Main Distribution in Buildings and Infrastructure — In large commercial buildings, data centres, hospitals, and infrastructure projects, Switch Fuse Units are used at sub-main distribution points — between the main LT panel and floor-level DBs or section boards — providing discriminative fuse protection at each distribution tier and isolation for safe maintenance work on sub-circuits without shutting down the main panel.

Capacitor Bank Isolation — SFUs rated for AC-23B duty (capacitor switching) are used as the isolation and protection device for power factor correction capacitor banks and capacitor duty contactor panels. They withstand the high inrush currents associated with capacitor energisation and provide a lockable isolation point for capacitor bank maintenance (a critical safety requirement given the stored energy in large capacitor banks).

Busbar Sectioning and Ring Main Distribution — In large industrial plants with ring-main LT distribution networks, Switch Fuse Units mounted directly on main busbars (Eaton EBV/EBH, Siemens 3NP1) serve as tie-switches and feeder disconnect points, allowing individual bus sections and feeders to be isolated for maintenance without interrupting the full plant supply.

How to Select the Right Switch Fuse Unit

Step 1 — Determine the rated current

Select the SFU current rating at or above the full-load current of the circuit it will protect and isolate. For motor circuits, select the SFU based on the motor full-load current and the required aM or gG fuse size from the manufacturer's coordination tables. For distribution feeders, select based on the design current of the feeder cable, not exceeding the cable's current-carrying capacity.

Step 2 — Select the number of poles

For three-phase circuits: use 3P (TPN) as standard. Use 4P (TPNC) where neutral isolation is required during maintenance — such as in TN-S earthing systems, IT networks, or where work-permit procedures require full 4-conductor isolation. For single-phase circuits: use 2P (DP).

Step 3 — Select the fuse type

For Indian LV systems (415 V), DIN HRC (NH type) fuses are the standard. BS HRC fuses are used in older installations and some OEM equipment. Fuse type selection also determines which SFU series is compatible — DIN NH and BS fuse holders are physically different and not interchangeable. For motor circuits, specify aM (motor protection) type fuses, which have a higher let-through current characteristic to allow motor starting. For feeder and general distribution circuits, specify gG (general purpose) type fuses for full overload and short-circuit protection.

Step 4 — Choose execution (open or enclosed)

If the SFU will be installed inside a metal enclosure or switchboard panel: choose open execution. If the SFU will be wall-mounted or floor-mounted without a surrounding panel enclosure: choose enclosed execution with an IP54 or IP65 rated integral housing. For direct busbar mounting inside large distribution switchgear, choose busbar-mount type (Eaton EBH/EBV, Siemens 3NP1).

Step 5 — Verify short-circuit withstand and discrimination

Confirm that the SFU's rated conditional short-circuit current (Inc) — the maximum prospective short-circuit current the unit can withstand safely when protected by its specified HRC fuse — exceeds the prospective fault current at the point of installation. This is typically calculated from the upstream transformer impedance and cable impedance. Check the manufacturer's fuse-SFU coordination table for the specific fuse size to confirm compliance. Also verify selective discrimination with upstream and downstream devices to ensure the correct fuse (and only the fuse directly upstream of the fault) clears on a fault event.

Key Technical Terms — Switch Fuse Units

AC-22A and AC-23A Utilisation Categories

IEC 60947-3 defines utilisation categories that specify the type of load the SFU is rated to make and break. AC-22A covers switching of mixed resistive and inductive loads including moderate overloads — used for feeder and sub-distribution switching. AC-23A covers switching of motor loads and other highly inductive loads — this is the correct category for SFUs used as motor isolators. Always verify that the SFU selected is rated to AC-23A if it will be used for motor isolation duty. AC-23B covers capacitor bank switching duty.

HRC Fuse (High Rupturing Capacity)

HRC (High Rupturing Capacity) fuses — also called HBC (High Breaking Capacity) fuses — are ceramic-bodied fuses filled with silica sand that quench the arc during a fault clearance. Unlike rewirable fuses, HRC fuses have a precisely defined time-current characteristic and a rated breaking capacity of up to 120 kA, enabling them to safely interrupt very high fault currents. NH type (DIN) and BS type are the two common HRC formats used in Indian LV switchgear.

NH Fuse (DIN Fuse)

NH (Niederspannungs-Hochleistungs) fuses are the German DIN-standard blade-type HRC fuses used in NH fuse switch-disconnectors across Europe and India. They are available in sizes NH000 (up to 160 A), NH00 (up to 160 A), NH1 (up to 250 A), NH2 (up to 400 A), NH3 (up to 630 A), and NH4 (up to 1,250 A). NH fuses are physically non-interchangeable between sizes, preventing insertion of an incorrect rating. All Siemens 3KL8, Schneider TeSys GS2, ABB OS (DIN range), and Eaton EBH/EBV series SFUs use NH DIN fuses.

gG and aM Fuse Types

gG (general purpose) fuses provide full-range protection — both overload and short-circuit protection — and are used for feeder cables and distribution circuits. aM (motor protection) fuses provide short-circuit protection only (no overload protection) and are designed to withstand motor starting inrush currents (typically 6–8× FLC) without blowing. aM fuses must always be used with a separate overload relay in motor circuits. For motor isolator SFUs, specify aM fuses. For feeder SFUs, specify gG fuses.

Positive Isolation / Visible Isolation

A switch-disconnector certified to IEC 60947-3 provides positive isolation — meaning the switching element is confirmed to be in the open position by a mechanical indicator directly linked to the contact mechanism (not just the handle position). This positive isolation confirmation is mandatory for safety isolation — it is the key distinction between a disconnector-grade SFU and a plain switch-fuse that may not guarantee an open contact gap when the handle indicates OFF.

Lockout/Tagout (LOTO) Capability

All IEC 60947-3 certified SFUs include a padlockable OFF position — the handle can be padlocked in the OFF position so the device cannot be accidentally or unauthorised re-energised during maintenance. This LOTO capability is a mandatory requirement under Indian factory safety regulations, IEC 60364 electrical installation standards, and ISO 14118 (prevention of unexpected energisation) for maintenance work on electrical equipment.

Rated Conditional Short-Circuit Current (Inc)

The rated conditional short-circuit current (Inc) is the maximum prospective symmetrical fault current (in kA r.m.s.) that an SFU can withstand without damage when protected by its specified HRC fuse. This is different from the SFU's own breaking capacity — the fuse clears the fault and limits the let-through energy; the SFU body only needs to withstand the mechanical and thermal stress until the fuse clears. Typical Inc values for modern SFUs with appropriate NH fuses range from 50 kA to 120 kA at 415 V.

Frequently Asked Questions — Switch Fuse Units

What is the difference between an SFU and an MCCB?
A Switch Fuse Unit (SFU) uses replaceable HRC fuses for overcurrent and short-circuit protection combined with a switch-disconnector for isolation. An MCCB (Moulded Case Circuit Breaker) uses a self-contained tripping mechanism (thermal-magnetic or electronic) that can be reset after tripping without replacing any component. SFUs offer higher fault current limiting capability (via current-limiting HRC fuses), lower overall let-through energy at high fault levels, and selective discrimination advantages in tiered fuse-protection systems. MCCBs offer the convenience of resetting without fuse replacement and adjustable overload settings. SFUs are generally preferred for transformer incomer protection and high-energy fault-current environments; MCCBs for motor feeders and final circuits where frequent resetting is expected.

Can I use a 415 V rated SFU on a 440 V system?
No. Always select an SFU rated at or above the system voltage. A unit rated 415 V should not be used on a 440 V system. Both the SFU and the HRC fuses must be rated for the actual system voltage. For 440 V systems, select SFUs with a rated voltage of 500 V or 690 V. Check that the fuses are also rated at the correct voltage — using 415 V rated fuses on a 440 V system will result in incorrect clearance behaviour.

What is the difference between a TP and TPN Switch Fuse Unit?
A TP (Triple Pole) SFU has three switching poles — one for each phase — but the neutral is connected as a solid link and is not switched. A TPN (Triple Pole and Neutral) SFU has three fused line poles plus a switched neutral pole, providing four-pole simultaneous isolation of all line and neutral conductors. TPN is required when the neutral must be isolated during maintenance — as required by some earthing system standards (TN-S, IT systems) and certain regulatory environments.

What does "open execution" mean on an SFU?
Open execution means the SFU body itself does not have an integral enclosure — live parts are accessible from the front unless protected by the switchboard panel in which it is mounted. Open execution SFUs are mounted inside a metallic enclosure (MCC, distribution board, industrial panel) and are operated via a handle extending through the panel door. They must not be used in open, unprotected locations. Enclosed execution SFUs have an integral IP54/IP65 housing and can be wall-mounted or floor-mounted without a surrounding enclosure.

What is a door-coupled (door interlock) handle on an SFU?
A door-coupled operating handle is an external handle mechanism that attaches to the SFU shaft and mounts through the panel door, allowing the SFU to be operated (ON/OFF) without opening the panel door. The door interlock mechanism physically prevents the panel door from being opened when the handle is in the ON position, protecting operators from accidental contact with live parts. In the OFF position, the handle can typically be padlocked for LOTO compliance. Door-coupled handles are standard accessories for all major SFU series — ABB OS, Siemens 3KL8, Schneider TeSys GS2, and L&T FN.

What type of fuse should I use for a motor circuit SFU — gG or aM?
For motor isolation and protection, always use aM (motor protection) type HRC fuses. aM fuses are designed to withstand motor starting inrush currents (typically 6–8× FLC for 5–10 seconds) without nuisance blowing. They provide short-circuit protection only — not overload protection — so a separate overload relay (bimetallic or electronic) must always be fitted downstream. gG fuses provide full-range protection including overload, but their characteristics may cause nuisance operation on motor starting inrush if sized for the full-load current. For feeder cables and distribution circuits where there is no motor starting, use gG fuses.

Are Electrihub's Switch Fuse Units original and genuine?
Yes. Electrihub sources all Switch Fuse Units exclusively through authorised distribution channels directly from manufacturers. All products are supplied in original manufacturer packaging with full traceability. Manufacturer certificates of conformity are available on request for project and tender documentation requirements.

Buy Schneider Switch Disconnector Fuse Unit - NX063TPNBS, NX125TPNDI, NX160TPNDI, NX630TPXDI, NX630TPNDI, NX315TPNDI, NX100TPNBS

Buy L&T Switch Disconnector Fuse Unit - SK90482, SK90481, SK90491, SK90496, SK90487

Buy Siemens Switch Disconnector Fuse Unit - 3KL8431-2UJ00, 3KL8431-4UJ10, 3KL8171-4TA00, 3KL8121-4TJ10, 3KL8221-2TJ00

Buy ABB Switch Disconnector Fuse Unit - 1SCA107932R1001, 1SCA114051R1001, 1SCA105248R1001, 1SCA022759R9220, 1SCA022813R7220, 1SCA105475R1001

Popular Brands in FSU

ABB FSU, Eaton FSU, L&T FSU, Siemens FSU, Schneider FSU

Categories in Low Voltage Breakers

ACB | ACB Accessories | Angle Adapter | Fuse Base | GFCI | HRC Fuse | HRC Fuse Accessories | MCCB | MCCB Accessories | Pin and Sleeve | Switch Fuse Unit | Switch Fuse Unit Accessories