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Effectiveness of Surge Protective Device to Protect a critical equipment

Surge Protection Devices are used to Protect electrical & electronics equipment from the overvoltage transients and Surges generated due to Lightning or Switching. In order to achieve optimal overvoltage protection Connecting conductors of SPDs shall be as low as possible, Connecting conductors are the conductors connecting the Line conductor to the surge protective device and from the surge protective device to the main earthing terminal or to the protective conductor. Long Lead Length will degrade the Protection Offered by the SPD. The residual voltage transferred to the equipment or the effective Voltage protection Level for the equipment will be sum of residual voltage of SPD and the induced voltage drop along the connecting lead length.


As a general rule, lead inductance can be assumed to be 1 µH/m. This inductive voltage drop when caused due the impulse with minimum rate of current rise(di/dt) 1 kA/µs will be approx. 1 KV/M of lead length. Also, if di/dt is more, this voltage drop with be further more.


Hence overvoltage protection is achieved when all connecting conductors of SPDs are as short as possible (preferably not exceeding 0.5 m for the total lead length) and without any loops.

Fig a.




Fig b.



If it is not possible to reduce the conductor length to the desired value, Busbar Mounted SPDs shall be used as shown in Fig b. which are connected as shown in Figure b. in this type of connection effect of the inductance can be considerably reduced.


The webinar will explain you more insights about the importance of the length of connecting wires for SPDs and outlines alternative methods for protecting sensitive and critical electrical and electronic installations, as well as modern solutions



Surge Protective Device: Connecting wire length and Conventional SPD’s



(Q&A) Surge Protective Device: Connecting wire length and Conventional SPD’s


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