The power surge from the electrical line has taken out electrical appliances from many houses not sure if it's a power sub station fault or primary lightning strike on power pole.

But some of the houses had SDP installed indeed on their main distribution panel. but nonetheless electronic appliances has been impacted like TV , AC main circuit board are all fried.

One of the house owners told me that the SDP that they installed caused frequent tripping and it didn't serve them any good and they have lost appliances due to voltage surge anyways.

A Month back, I got to know there was a lightning strike on a tree and that caused some kind of secondary lightning effects i.e induced power surge in the residential electrical line or ground potential rise and somehow the power voltage surge entered into the building through ground rod or something because their plumbing lines are plastic and the earth rod is the only thing that's buried in earth and have connection to building electrical line and again this house also had SDP category 1 and 2 installed in their building.

So I enquired the electrician from power station , he told me that SDP is just a fancy thing that rich people have in their home and it never works and it's just a nuisance with constant tripping.

I don't know how much I can take this professional's word , may be they bought a good for nothing SDP or the person who installed the SDP didn't wire it as it should be.

So why does an SDP not work correctly?

  • I removed "how do we buy, because that's a shopping question, which is off-topic. I also removed "How do we install" because that's been answered several times, which can be searchable, try "whole-house surge protector", has many how to install questions and answers. Nov 27, 2023 at 14:56
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    They usually have a limit on how much of a surge they can handle. The power of a full on lighting strike will destroy most devices. Most SPDs are made to protect against indirect surges or surges caused by the power coming back on.
    – crip659
    Nov 27, 2023 at 14:57
  • @crip659 - If not direct lightning strike , can it protect accidental high voltage that comes from electrical substation.
    – CuriousMan
    Nov 27, 2023 at 16:02
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    Up to it's limit. The answer provide does answer most of this, but you can search and get more of the theory and find what the limits are.
    – crip659
    Nov 27, 2023 at 16:12

1 Answer 1


A whole-house surge protector, or surge protection device (SPD), is designed to pass extra electricity higher than a certain voltage limit. In fact it is always passing electricity, since the MOV devices that provide the surge protection are not on/off devices, but more like resistors that reduce their resistance as the voltage across them increases. Thus they non-linearly pass more electricity at high voltages than they do at low voltages. (The SPD on my house panel draws 50 watts of power all the time.)

The higher the voltage, the more electricity passes through, until the device burns out and fails. Then it cannot pass any more surges. Also, the more surges it has to pass over time can degrade its functionality each time.

If a high-enough surge comes through, the device could burn out all at once and not complete the passing of the surge or handle the next surge. If many surges come over a long time, cumulative damage could occur that does not leave enough room to stop the next surge.

Additionally, the SPD requires an excellent passageway to ground to disperse the surges. If the ground connection is bad, the surge protector will not pass surges and may be damaged. (This requirement was stated as a serious consideration for installing my panel's SPD.)

Finally, lightning is at a high enough voltage that all bets are off. Things that would never conduct electricity at normal house voltages or even industrial voltages become conductors at lightning voltages.

The best choice of SPD to limit these degrading and higher surges is to get an SPD with higher "joule" ratings, or a higher surge capacity amp rating. "Joules" refers to how much work the SPD can do suppressing surges, and amp capacity is how many amps it can dump into ground.

Also, surge protection is defense in depth: multiple surge protectors along the line to your devices. A whole-house protector, then a decent plug-in surge protector, then a UPS for the computer or entertainment system, etc.

However, if a car crashes into a power pole and the 13kV distribution line lays firmly down on your house's 240V line, or lightning strikes nearby, the power may be beyond any surge protector to stop.

  • Other than doing whole house surge protection , when we do Point-of-use surge protectors . Would there be MOV or just fuse to protect the voltage surge ? Could you share me your insights into this please ?
    – CuriousMan
    Nov 27, 2023 at 17:08
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    Point of use protectors would also have to be MOV-based. Surges are voltage overloads, but fuses protect against current overloads. (Though a voltage overload will probably also overload the current too, so maybe they could work together.) Nov 27, 2023 at 17:52
  • Thanks, I will buy a power strip which has MOV and if it has Fuse then it's extra safety.
    – CuriousMan
    Nov 28, 2023 at 11:48
  • Wow, taking 50W continuous sounds like a terrible SPD. A European SPD has Ipe of 0.45mA or 5uA, which is a quiescent power of 100mW or 1mW respectively. Nov 29, 2023 at 16:57
  • I may have measured it wrong. One of these days I'll pop open the panel and measure again. Nov 29, 2023 at 21:35

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