In addition to ensuring safety, the correct installation of a lightning arrester significantly impacts its performance and efficiency. As shown in the general connection diagram, practical measurements have confirmed that the length of the connecting cables, the number of connections, and their configuration all influence the voltage drop. This is primarily due to the inductance of the connecting lines, which directly affects the induced voltage. To minimize this inductive voltage in parallel lightning arresters, the following four strategies are effective:
1) The shorter the connecting line, the lower the inductance, resulting in reduced inductive voltage. Therefore, it is recommended that the cable length be kept under 25 cm.
2) When current flows through two connecting lines, opposing magnetic fields are created. If these lines are tightly bundled together, the magnetic fields cancel each other out, significantly reducing the inductive voltage.
3) If the cable length exceeds 25 cm, using two sets of connecting lines can help. By splitting the current between the two sets, the magnetic field strength is halved, thereby lowering the induced voltage to an acceptable level (less than 700V).
4) Since grounding wires are often longer than other cables—especially when installed above or inside the distribution box—it’s advisable to use two ground wires. One wire connects to the metal casing of the distribution box, while the other provides grounding. In some cases, series surge arresters can also be used to further reduce inductive voltage.
According to CCITT, BS, and IEC standards, the transient overvoltage and current on signal and data lines are typically lower (around 5kV and 125kA) compared to power lines. Therefore, it's recommended that the grounding cable be no longer than 1 meter, and if possible, as short as possible. For longer grounding cables (e.g., 2m, 3m, or 4m), multiple cables can be used, provided they are spaced at least 5 cm apart.
| Resistive Voltage Drop | Inductive Voltage Drop | Cable Size (mm²) | Voltage Drop (V/m) | Cable Size (mm²) | Inductance (H/m) | Voltage Drop (V/m) |
|------------------------|------------------------|------------------|--------------------|------------------|------------------|--------------------|
| 51.6 | 1 | 1 | 1.2 | 450 | 2.5 | 20.6 |
| 376 | 2.5 | 2.5 | 1.1 | 376 | 4 | 12.9 |
| 342 | 4 | 4 | 1.1 | 342 | 6 | 8.6 |
| 342 | 6 | 6 | 1 | 239 | 10 | 5.16 |
| 239 | 10 | 10 | 1 | 239 | 100 | 0.516 |
Can a thicker cable reduce inductive voltage? While a thicker cable may slightly improve the voltage drop, the transient inductive voltage is usually much higher—often more than ten times greater than the resistive drop. Therefore, increasing the cable thickness has limited effectiveness in addressing the main issue.
Other installation considerations:
1. For loads up to 63A with 4mm² cables, or up to 100A with 10mm² cables, fuses may not be necessary. However, if the load is too high, a fuse or
Circuit Breaker should be used—not to protect the arrester itself, but to prevent the cable from melting during a short circuit.
2. Most manufacturers recommend installing the first load output of the power distribution panel as shown. Additionally, if the load could generate transient overvoltage and send it back to the power supply, an extra protection device is required.
3. If the three-phase power supply lacks a neutral line, the neutral terminal of the surge protector must be connected to the power supply's ground.
4. In the presence of a residual current circuit breaker (RCCB), the surge arrester must be installed before it. The layout of input and output lines in a series arrester greatly affects its performance. If the output line is too close to the input line, it may pick up transient overvoltage from the input side.
Finally, the grounding method plays a crucial role in the proper functioning of the surge arrester. Using a "relative" grounding system allows the device to work effectively. However, if an "absolute" grounding method is used—such as independent grounding with a resistance of 10 ohms or more—an inrush current of 100A could cause a voltage spike of at least 1000V, potentially damaging the arrester and the equipment it's meant to protect.
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