How to Choose a Disconnect Switch? | 5-Criteria Selection Guide

Lucas Moreau Electrical Engineer · Low-Voltage Installation Specialist · 15 Years' Experience

At a Glance

To choose a disconnect switch (switch-disconnector), evaluate 5 criteria: the rated voltage (Ue) matching your network (230 V, 400 V, up to 1,500 V DC for solar), the rated current (In) above the total circuit current, the number of poles (1P to 4P depending on the network type), the breaking capacity (Icu) for applications at risk of short-circuit, and the operating environment (IP65 minimum for outdoor use). A disconnect switch isolates a circuit for maintenance — it does not protect against overloads like a circuit breaker.

What Is a Disconnect Switch?

A disconnect switch — also called a switch-disconnector or isolator — is a mechanical switching device that electrically isolates a circuit to allow safe maintenance or repair work.

Its operation is straightforward: in the closed position, current flows normally. In the open position, it interrupts the current and physically separates the contacts, providing total and visible isolation. This visible break is the fundamental characteristic that distinguishes it from a simple switch.

It is found in:

Industrial installations: at the head of switchboards, to isolate motor feeders and production lines.
Commercial and tertiary buildings: as main disconnectors for distribution boards.
Photovoltaic installations: to disconnect DC current on the panel or inverter side.
Some residential applications: as emergency disconnects or for specific circuit isolation.

⚠️ Fundamental Distinction

A disconnect switch is not a circuit breaker. A circuit breaker automatically protects against overloads and short-circuits. A disconnect switch manually isolates a circuit without any active protection. The two are complementary and are often combined in the same installation.

Key takeaway Disconnect switches are mandatory under regulations (NF C 15-100 in France, IEC 60364 internationally) to allow manual isolation of electrical circuits and ensure maintenance safety. They must comply with IEC 60947-3.

Types of Disconnect Switches

Disconnect Switch Types and Applications
Type	Voltage	Format	Main Application
AC disconnect switch	Up to 690 V AC	DIN-rail modular or panel-mount	Industrial, commercial, distribution boards
DC disconnect switch	Up to 1,500 V DC	DIN-rail modular or enclosed	Photovoltaic, energy storage, battery circuits
Enclosed disconnect switch	AC or DC	Plastic or metal enclosure IP65/IP66	Outdoor emergency disconnects, harsh environments
DIN-rail modular	AC or DC	Compact, DIN rail	Electrical cabinets, distribution boards
Fuse-disconnect switch	AC	Panel-mount	Combined isolation + fuse protection

Key takeaway In photovoltaic systems, a DC disconnect switch is essential because direct current is harder to break than alternating current (no natural zero crossing). DC disconnect switches are specifically designed with arc-quenching chambers for high-voltage DC.

5 Selection Criteria for a Disconnect Switch

1Rated voltage (Ue)

The maximum voltage the switch can handle under normal operation. It must be equal to or greater than the network voltage.

Single-phase residential: 230 V AC
Three-phase industrial: 400 V AC (or 690 V for some applications)
Photovoltaic: 600 V to 1,500 V DC depending on string configuration

2Rated current (In)

The maximum current the switch can carry continuously without overheating or damage. It must exceed the total current of all connected devices.

Common Disconnect Switch Ratings
Rating (In)	Typical Application
16 – 32 A	Residential circuits, small commercial feeders
40 – 63 A	Medium feeders, sub-distribution boards
100 – 125 A	Main board disconnectors, small industry
160 – 630 A	Main switchboards, industrial cabinets
800 – 3,200 A	Head of industrial installations, transformer substations

3Number of poles

Determines how many active conductors the switch can break simultaneously:

1 pole (1P): simple single-phase circuit (phase only).
2 poles (2P): single-phase with neutral, or bipolar DC circuit (photovoltaic).
3 poles (3P): three-phase without neutral — most common in industry.
4 poles (4P): three-phase with neutral — required when the neutral must be disconnected (TN-S system, certain public buildings).

Key takeaway In DC photovoltaic systems, 2-pole (single string) to 10-pole (multi-string) disconnect switches are used. The number of poles depends directly on the solar installation's architecture.

4Breaking capacity (Icu)

The maximum current the switch can interrupt without damage. This is critical in installations where high short-circuit currents are possible (near a transformer, high-power networks).

For standard applications, the switch's breaking capacity is sufficient. For installations with high fault currents, a fuse-disconnect switch provides additional protection.

5Operating environment and IP rating

Indoor (panel, cabinet): IP20 sufficient — DIN-rail modular or panel-mount.
Outdoor or damp environment: IP65 or IP66 required — enclosed switch with sealing gaskets.
Harsh industrial environment: vibration resistance, UV resistance, reinforced mechanical robustness.

Application Example: Photovoltaic Installation

For a 10 kW solar installation at 400 V with a 25 A current:

Disconnect Switch Sizing for a 10 kW PV System
Criterion	Requirement	Selection
Rated voltage	≥ 400 V DC (string voltage)	DC disconnect switch 600 V or 1,000 V
Rated current	≥ 25 A	32 A DC disconnect switch
Number of poles	2P minimum per string	2P or 4P depending on number of strings
IP rating	Outdoor installation	IP65 minimum
Standard	IEC 60947-3, DC compatible	PV-specific disconnect switch

Key takeaway Never use an AC disconnect switch to break DC current. DC disconnect switches are specifically designed with arc-quenching chambers suited to direct current, where there is no natural zero crossing to extinguish the arc.

Key Brands and Ranges

Disconnect Switch Brands — Ranges and Specifications
Brand	Range	Specificity	Ratings
Socomec	SIRCO M	Compact modular, 1 to 4 poles	16 – 125 A
Socomec	SIRCO	Panel-mount, robust industrial	125 – 3,200 A
Socomec	SIRCO PV	Optimised for PV DC	100 – 3,200 A
Telergon	S3 Series AC	IP66 enclosure, lockable	Up to 20 A / 690 V
Telergon	F1 Series DC	DC up to 1,500 V, DIN rail or door-mount	Up to 32 A
Telergon	F7 Series DC	Modular 2 to 10 poles, IP66	Up to 55 A

Frequently Asked Questions — Disconnect Switches

What is the difference between a disconnect switch and a circuit breaker?

A circuit breaker automatically trips to protect against overloads and short-circuits (active protection). A disconnect switch provides manual isolation of a circuit for maintenance work, without any overcurrent protection. The two are complementary in any installation.

What is the difference between a switch, a disconnector and a circuit breaker?

A switch simply opens or closes a circuit under load. A disconnector isolates a circuit with a visible break, guaranteeing operator safety. A circuit breaker automatically protects against overloads and short-circuits. A switch-disconnector combines the first two functions: load-breaking + visible isolation.

Is a disconnect switch mandatory?

Yes. Standards such as NF C 15-100 (France) and IEC 60364 (international) require a means of isolation to allow manual disconnection of electrical circuits during maintenance. In photovoltaic installations, a DC disconnect switch is also mandatory on the generator side.

Can a disconnect switch be used instead of a circuit breaker?

No. A disconnect switch provides no protection against overloads or short-circuits. It must always be paired with protective devices (circuit breakers, fuses) downstream. Using them interchangeably would put the installation at risk.

Why can't an AC disconnect switch be used for DC current?

In alternating current, the electrical arc naturally extinguishes at each zero crossing of the sine wave (100 times per second at 50 Hz). In direct current, there is no zero crossing: the arc persists and can damage the switch or even cause a fire. DC disconnect switches incorporate specific arc-quenching chambers designed to force arc extinction.

What is the difference between an RCD and an RCBO?

An RCD (Residual Current Device) detects only earth leakage currents (electrocution protection) but does not protect against overloads or short-circuits. An RCBO (Residual Current Circuit Breaker with Overcurrent protection) combines both functions: residual current protection + thermomagnetic protection against overloads and short-circuits.

What is a visible break and why does it matter?

A visible break means you can visually verify (directly or via a mechanical indicator) that the switch contacts are open and the circuit is genuinely isolated. This is a fundamental safety requirement for maintenance: it guarantees technicians that the circuit is de-energised before any work begins.

What is a lockable disconnect switch (LOTO)?

A lockable disconnect switch can be locked in the open position with a padlock (LOTO — Lock Out / Tag Out procedure). This prevents accidental re-energisation while a technician is working on the circuit. This feature is mandatory in many industrial installations and recommended in public-access buildings.

Key Takeaways

A disconnect switch isolates a circuit for maintenance — it does not replace a circuit breaker.
Choose a rated voltage (Ue) ≥ the network voltage and a rated current (In) ≥ the total circuit current.
The number of poles depends on the network: 2P for single-phase, 3P or 4P for three-phase, 2P to 10P for DC photovoltaic.
For outdoor or damp environments, require an IP65 or IP66 protection rating.
Never use an AC disconnect switch to break DC current — DC switches have specific arc-quenching chambers.
Visible break and lockout capability (LOTO) are fundamental safety requirements.
Verify compliance with IEC 60947-3 and local installation standards.