Impulse relay (stroomstootrelais) — switching from many locations without two-way/intermediate switches

The reading a single-line diagram guide and the electrical switching symbols guide cover how to recognize switching components on a diagram. This article covers a specific component that is often overlooked on that diagram: the impulse relay, the standard solution once a circuit needs to be operated from more than two locations.

The problem it solves

With two switching points, a two-way switch pair (also called a "hotel switching" arrangement) is enough. With a third point, an intermediate ("crossover") switch is needed between the two two-way switches — and for every additional point after that, another intermediate switch, each with its own four-core connection. In a stairwell with five or six floors, this wiring quickly becomes impractically heavy and fault-prone.

An impulse relay (also called a latching relay or teleruptor) solves this differently: every switching point is simply wired in parallel on the control coil of the same relay, using light bell-wire (typically 0.5–1.5 mm²), regardless of whether there are two or twenty switching points.

Operation: bistable, not monostable

An impulse relay is a bistable relay: it has two fixed states and toggles on every short voltage pulse to the control coil — from on to off, or vice versa — and holds that new state until the next pulse, without the coil needing to stay continuously energized. This distinguishes it from an ordinary (monostable) relay, which stays on only as long as the coil is energized.

Electromechanical impulse relays built to IEC/EN 61095 (electro mechanical contactors for household and similar use) typically have a switching capacity of up to 16 A per contact at a 230 V AC control voltage; heavier models with higher switching capacity or multiple contacts are also available — exact values differ per manufacturer and model and must be read from the nameplate or datasheet, not assumed.

Note: an impulse relay is operated with a momentary push-button (a button that only makes contact while pressed), not with an ordinary on/off switch. If an on/off switch is accidentally wired into the same control circuit, the coil stays energized as long as that switch is "on" — which makes the relay's response to the next pulse from another location unpredictable.

Practical use

Stairwells and corridors: lighting that must be operable from every floor or entrance, often combined with a delayed shut-off (stairwell timer) or a presence detector.
Central-off function: some models offer a separate input that forces the relay into the off state regardless of its current state — for example linked to a main switch when leaving a building.
LED loads: the switching capacity of an impulse relay is typically specified for a resistive or incandescent load; with a large number of parallel LED drivers, the combined inrush current of those drivers can load the contacts more heavily than the wattage alone suggests — when in doubt, consult the manufacturer's LED-specific load rating rather than simply adding up wattages.

Why this is not an isolation device

As the §537 classification guide covers: an impulse relay performs the function of functional switching, not isolation. The relay contact typically does not break all poles, has no lockable off position, and offers no guaranteed, visible isolating distance — safe work on the circuit still requires the installation's own isolating device (breaker or switch in the distribution board), not the impulse relay itself.

Practical relevance

When designing a circuit with more than two switching points, an impulse relay is almost always the simpler and cheaper solution compared to an extended intermediate-switch arrangement — mainly because each extra switching point only requires an extra momentary push-button with light wiring, instead of an extra intermediate switch with heavier cabling.

Common mistakes

Wiring an ordinary on/off switch into the control circuit instead of a momentary push-button — this keeps the coil continuously energized and disrupts the bistable switching behavior from other locations.
Judging switching capacity by wattage alone for a large number of parallel LED drivers, without checking the combined inrush current of the load.
Mistaking the impulse relay for an isolating device — it performs the function of functional switching (§537), not isolation, and offers no lockable, guaranteed absence of voltage.