Modern LED lighting systems are highly energy-efficient, yet they present a significant challenge: extreme inrush currents. When an LED driver is switched on, its internal input capacitors charge instantaneously, generating a brief current surge (lasting milliseconds) that can exceed the nominal operating current by a factor of 20 to 60.

This surge poses a critical risk to Triac dimmers, smart switches, controllers, and circuit breakers, often leading to burnt contacts or nuisance tripping of protection devices. To address this issue, specialized limiters are employed—notable examples being the S1-S and S1-SX models. These devices feature fundamentally different internal architectures and are designed for distinct applications.

1. Model S1-S: Compact NTC Solution for Localized Zones

The core of the S1-S device is a semiconductor element — an NTC thermistor (a thermistor with a negative temperature coefficient).

  • Operating Principle: In a cold state (at room temperature), the NTC element has a relatively high internal resistance. When the circuit is energized, this resistance acts as a physical barrier, smoothly regulating the initial flow of current. As the current passes through the thermistor, it heats up. As the temperature rises, the element's resistance drops sharply — approaching near-zero — and the device enters a "pass-through" mode, effectively allowing the system to operate without obstruction while consuming minimal energy.
  • Technological Limitations: NTC thermistors require a cooling-down period (ranging from 30 seconds to 2 minutes) after the power is turned off. If the light is switched off and immediately turned back on, the thermistor — still hot — will not have had time to recover its resistance, meaning the protection mechanism will not be active.
  • Technical Specifications: The device is rated for a maximum operating current of 2 A (corresponding to a load of approximately 200–480 W on a 220 V mains supply). Thanks to its ultra-compact dimensions and flexible leads — suitable for soldering or quick-connect installation — it is ideally suited for placement directly inside a wall box (alongside a TRIAC-based dimmer) or for installation ahead of individual chandeliers and track lighting fixtures..

 




2. Model S1-SX: Powerful Relay-Based Limiter for Automation Systems

The S1-SX device is designed for high-load systems and commercial lighting. Instead of a thermistor, it utilizes a significantly more stable active-relay circuit.

  • Operating Principle: When power is applied, the current is directed through built-in, high-power, fixed-value ceramic resistors (for example, two 7.5-ohm resistors). These effectively limit the inrush current amplitude to safe levels (typically 15–20 A). After 40 milliseconds, an internal microcontroller triggers a mechanical bypass relay to close. The current then flows directly through the relay contacts, bypassing the resistors.
  • Technology Advantages: Since the resistors operate for only 40 ms, they do not have time to heat up. The device is ready to provide protection again immediately after being switched off. The unit ensures stable operation regardless of how frequently the switch is toggled.
  • Technical Specifications: This model supports a continuous operating current of up to 8 A and can switch loads of up to 2000 W. It is equipped with reliable screw terminal blocks for connecting standard-gauge cables.

    Comparison Table of Characteristics

Parameter

S1-S (Base)

S1-SX (Professional)

Maximum operating current

2 А

8 А

Maximum load capacity

to 450–480 W

to 1760–2000 W

Constraint element

Thermistor (NTC)

Powerful resistors

Bypass mechanism (Bypass)

Self-heating of the element

Built-in electromechanical relay

Time to readiness for restart

Requires cooling (~1–2 min)

Instantly (ready in <1 sec)

Primary purpose

Local protection for a single dimmer/switch

Protection of main lines and panel automation



     Example of a connection diagram:



Summary for the Engineer and Installer

  • The S1-S is suitable for residential use to protect a specific, sensitive dimmer when the total power load of the LED fixtures in a room is low.
  • The S1-SX is the essential solution for circuits involving a large number of LED drivers (such as those found in magnetic track lighting systems or commercial LED panels). Installing one such device downstream of a B10 or B16 circuit breaker completely eliminates the issue of the breaker tripping, allowing the full rated capacity of the circuit breaker to be utilized.