What Is a Modular Switch? DIN Rail Switch-Disconnector Selection Criteria
A modular switch is a DIN rail switch-disconnector that mounts beside circuit breakers, switches a circuit manually under load and isolates it when open.
A modular switch (modular switch-disconnector) is a switch that mounts on the same DIN rail as miniature circuit breakers, can open and close a circuit manually under load, and isolates the line from the supply in the open position. It does not open by itself on overload or short circuit; protection is provided by the fuse or circuit breaker upstream. It is used in distribution boards as the main incoming switch or to isolate a group of circuits for maintenance. The catalog models are from the Schneider Electric Acti9 iSW series.
iSW models in the catalog
| Poles | Circuit | 63 A | 125 A | Width (9 mm pitches) |
|---|---|---|---|---|
| 1P | Single-phase, phase only isolated | A9S65163 | A9S65192 | 2 (18 mm) |
| 2P | Single-phase, phase and neutral isolated | A9S65263 | A9S65292 | 4 (36 mm) |
| 3P | Three-phase, no neutral | A9S65363 | A9S65392 | 6 (54 mm) |
| 4P | Three-phase with neutral | A9S65463 | A9S65492 | 8 (72 mm) |
The 2P, 3P and 4P models have a rated operational voltage of 415 V AC.
What the technical values mean
- Utilisation category AC-22A: Suitable for frequent switching of mixed resistive and inductive loads, including moderate overloads. Highly inductive loads such as direct-on-line motor starting require category AC-23.
- Icw (rated short-time withstand current): The current the switch can carry while closed, without damage, until the upstream protective device opens. The catalog gives 1260 A for the 63 A models and 1500 A for the 125 A models.
- Icm (rated short-circuit making capacity): 5 kA for the switch-disconnector alone. The conditional short-circuit current it withstands together with its upstream protective device is in the manufacturer's coordination table.
- Uimp (rated impulse withstand voltage): 6 kV.
- Ui (rated insulation voltage): 500 V AC on the 2P–4P models.
Selection criteria
- Number of poles: Choose 2P or 4P where the neutral must also be isolated; 3P is enough for a three-phase load without neutral.
- Rated current: The switch-disconnector's rated current must be equal to or greater than the rated current of the upstream protective device. A 63 A switch-disconnector does not go behind an 80 A circuit breaker.
- Short-circuit coordination: Compare the prospective short-circuit current in the board with the value given for the switch-disconnector together with its upstream protective device.
- Board width: Allow 18 mm per pole; a 4P model takes 72 mm.
Common mistakes
- Using a modular switch instead of a circuit breaker: A switch-disconnector does not open on overcurrent, so the line is left unprotected.
- Choosing a switch-disconnector rated lower than the upstream protective device: An overload heats the switch-disconnector without tripping the breaker.
- Switching a motor directly: Category AC-22A is not made for motor starting currents; use a contactor or a motor protection circuit breaker for motors.
Standards
- IEC 60947-3: Low-voltage switches, disconnectors, switch-disconnectors and fuse-combination units. The iSW series is listed to this standard and is suitable for isolation.
Brands in the catalog
The modular switches category has 8 active products, all Schneider Electric Acti9 iSW. Other types of switch-disconnector (compact INS, TeSys VARIO, fused, horizontal and vertical) are in the Load Break Switches category (114 active products: Schneider Electric 79, Siemens 32, Tibcon 2, Sigma 1).
Frequently asked questions
What is the difference between a modular switch and a miniature circuit breaker?
A miniature circuit breaker opens by itself on overcurrent and short circuit. A modular switch is only opened and closed by hand and isolates the line when open; it does not protect.
Does a switch-disconnector open on a short circuit?
No. The upstream fuse or circuit breaker clears the short circuit; during that time the switch-disconnector must be able to carry the current up to its Icw value.
Should I choose 1P or 2P?
Choose 1P if isolating only the phase is enough on a single-phase line, and 2P if phase and neutral must be isolated together.
What does AC-22A mean?
It is a utilisation category in IEC 60947-3: frequent switching of mixed resistive and inductive loads, including moderate overloads. The final letter A indicates frequent operation.