Connecting multiple aerosol generators from one panel is simple in theory, but traditional wiring methods can create real challenges. Series wiring risks single-point failures, while parallel wiring can overload your panel’s circuit capacity. Both can compromise system reliability and compliance.

That’s why DSPA developed the SCR Interface, a solution that allows you to safely connect and trigger up to 15 DSPA Aerosol generators from a single panel output, without stressing your FACP or introducing wiring vulnerabilities.

Aerosol fire suppression systems offer a modular and scalable solution for fire protection. Each generator contains a solid agent that, when activated, produces a finely divided cloud of extinguishing particles. The system's effectiveness relies on achieving a specific density of this aerosol, which means all generators within a protected area must activate.

A key advantage of DSPA systems is their ability to interconnect generators, allowing for greater volumetric coverage. These generators, equipped with an electrical starter, connect directly to a Fire Alarm Control Panel (FACP). The starter contains a resistance that, upon receiving an electrical current, heats up and initiates a self-sustaining chemical reaction inside the metal canister of the generator. This process generates the extinguishing aerosol.

The Electrical Challenge: Series vs. Parallel Connections

When multiple generators are required in the same protected volume, two wiring methods are most commonly used: in-series and in-parallel.

In-Series Connection

• Pros: The total resistance is the sum of the individual resistances, which keeps the current at a safe level for the FACP. The formula for total resistance in a series circuit is:

Req =R1 +R2 +...+Rn

• Example: The same 10 generators connected in series would have an equivalent resistance of 8 Ω (Req =10×0.8Ω). This limits the current to a safe 3 Amperes (I=24V/8Ω).
• Cons: This method is vulnerable to a single point of failure. If one generator's resistance breaks, the circuit is interrupted, and all subsequent generators will not activate. This could lead to a critical failure in a fire suppression scenario.

In-Parallel Connection

• Pros: This connection method offers redundancy. If one generator fails, the others will still receive current and activate.

• Cons: The equivalent resistance (Req ) of the circuit decreases as you add more generators. The formula for total resistance in a parallel circuit is:

1/Req =1/R1 +1/R2 +...+1/Rn

This low resistance creates a significant problem. According to Ohm's Law (I=V/R), a low resistance leads to a high current. This can easily damage the FACP, as most panels are not built to handle the high current demands of multiple generators in parallel.

• Example: A 24V FACP connected to 10 generators (each with a resistance of 0.8 Ω) in parallel would have an equivalent resistance of just 0.08 Ω. This would demand a current of 300 Amperes (I=24V/0.08Ω), far exceeding the typical 3-ampere limit of most FACP outputs.

How the SCR Interface Ensures Reliable Multi-Generator Activation

To overcome the single-point-of-failure issue in a series circuit, each generator needs a diode to maintain current flow even if a resistance breaks. However, a manual installation of individual diodes is complex and inefficient (see the enclosed wiring scheme).

In fact, each diode causes a voltage drop (approximately 1-1.5V), which limits the number of generators to around 10 before the voltage becomes too low for reliable activation.

The SCR Interface is the definitive solution to these challenges.  It uses a single SCR controller to regulate current across the entire circuit, while separate SCR forwarders—one for each generator—handle the distribution from individual generators.

• Simplified Installation: It replaces the need for complex, manual diode installations with a single, efficient device.

• Increased Capacity: The SCR Interface maximizes the current, allowing you to activate up to 15 DSPA generators from a single FACP*.

• Enhanced Safety: The SCR forwarders, which come with junction boxes, have labelled terminals for easy and safe connections, including those for the diodes and the End-of-Line resistor.

The SCR Interface provides a robust, simple, and scalable solution that ensures your DSPA fire suppression system is both technically sound and highly reliable.

*Note: The FACP must have a minimum output of 500mA and 20.5Vdc.

Ready to see how the SCR Interface can fit into your next project?

📩 Contact DSPA for full technical specifications and integration guidance.

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