In addition to ensuring safety, the correct installation of a lightning arrester plays a crucial role in its overall performance and efficiency. As illustrated in the general connection diagram for surge arresters, practical measurements have shown that the length of the connecting cables, the number of connections, and their configuration all significantly impact the voltage drop. This is primarily due to the inductance of the connecting lines, which directly influences the induced voltage. The following four methods can effectively reduce the inductive voltage in parallel surge arresters:
1. **Shorter Connection Lines**: The inductance of a cable increases with its length. Therefore, shorter cables result in lower inductive voltage. It is recommended that the cable length should not exceed 25 cm.
2. **Tight Bundle of Cables**: When current flows through two parallel cables, opposing magnetic fields are generated. By tightly bundling the cables together, these magnetic fields cancel each other out, significantly reducing the induced voltage.
3. **Use of Dual Cables for Longer Connections**: If the cable length exceeds 25 cm, using two sets of cables can help. The current is split between the two sets, reducing the magnetic field strength by half, which in turn lowers the induced voltage to an acceptable level (below 700V).
4. **Grounding Considerations**: Since grounding wires are often longer than other connection lines (typically more than 25 cm), it's advisable to use two ground wires—one connected to the distribution box’s metal casing and another for direct grounding. Additionally, series-type surge arresters can also be used to further reduce inductive voltage.
According to standards such as CCITT, BS, and IEC, the transient overvoltage and current on signal and data lines are generally lower than those on power lines (around 5kV and 125kA). Therefore, it is recommended that the grounding cable should not exceed 1 meter in length. If longer grounding is necessary, the cables should be separated by at least 5 cm to minimize interference.
| 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?**
Although a thicker cable can slightly reduce resistive voltage, the transient inductive voltage is typically ten times higher. Therefore, increasing the cable thickness has limited effectiveness in reducing inductive voltage.
**Other Installation Tips:**
1. For loads up to 63A with 4mm² cables or up to 100A with 10mm² cables, fuses may not be required. However, if the load is too high, a fuse or
Circuit Breaker should be installed to prevent cable melting during short circuits—not to protect the surge arrester itself.
2. Most manufacturers recommend installing the first output from the power distribution panel as shown. If the load might generate transient overvoltages that could feed back into the system, additional protection is needed.
3. In three-phase systems without a neutral line, the neutral terminal of the surge arrester must be grounded to the power supply’s ground.
4. When using a residual current device (RCD), 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, an overvoltage from the input may be transferred to the output.
Finally, the grounding method is critical to the proper functioning of the surge arrester. Using a "relative" grounding method ensures the desired protection. However, an "absolute" grounding approach—where the ground is independent and has a resistance of 10 ohms or more—can lead to dangerous voltage spikes. For example, a 100A transient current could cause a 1000V spike, potentially damaging the arrester and the equipment it is meant to protect.
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