Lightning and Surge Protection: Why the Router Dies

An applied extra to Cobler's Electricity Fundamentals course.

The storm passes in twenty minutes. The lights never even flickered. The kettle still boils, the fridge still hums, the fan still turns. But the router sits there dark, and when you unplug it and plug it back in, nothing. Maybe the TV as well, or the Astro box, or the modem. Almost every Malaysian household has buried one small electronic casualty of a thunderstorm, quietly replaced and never really explained.

So here is the question nobody bothers to ask, the kind you feel but never look up: why does lightning always kill the cleverest thing in the house and leave the dumbest things untouched? Get the answer and surge protection stops being a mystery printed on a plug label. It becomes something you can actually reason about, at home and across a whole facility.

Why does lightning kill the router but spare the kettle?

Because the two devices are built completely differently inside, and a surge destroys one kind while the other shrugs it off. Start there, because it explains everything else.

Malaysia earns this problem. The Klang Valley averages around 240 thunderstorm days a year, against roughly 10 for London, and Subang ranks among the most lightning-prone spots on the planet (Daily Express). We sit in one of the most lightning-dense regions on Earth. So the storms are not rare events to plan around once a year. They are a standing condition of living here.

The surprise is that a strike does not have to hit your house to kill your router, or even hit close. In Part 1 of the course we saw that a lightning bolt is the same physics as the spark off a car door, just scaled up past reason: a storm cloud separates charge until the voltage reaches hundreds of millions of volts and the sky finally breaks the air down. When that much energy dumps into the ground or a power line a few streets away, it induces a sudden overvoltage, a surge, onto every conductor nearby. Your power cable picks it up. So does the phone line, the TV aerial, the coax. The surge arrives through the wiring, not through the roof.

That is why the classic victims are always the devices plugged into more than one cable. A router has power plus a phone or network line. A TV has power plus coax plus HDMI. Each cable is a separate doorway a surge can walk in through. The kettle has exactly one cable and no brain waiting at the end of it.

What makes a chip so fragile and a heating element so tough?

A router is full of microscopic semiconductor junctions (the tiny switches inside every chip) that fail tens of volts over their rating; a kettle is a lump of metal that does not care.

Inside every chip, power supply and network port are those junctions, thinner than a wavelength of light, with almost no thermal mass. A surge dumps energy into that tiny structure faster than it can carry the heat away, and the junction melts itself in microseconds (Alpine Intel). These parts are engineered to work on a few volts. A surge of hundreds or thousands of volts vaporises them.

A kettle element is the opposite of delicate. It is a coil of resistance wire designed to glow red-hot and survive it, a heavy lump with enormous thermal mass. A surge is a brief splash of extra heat that it barely notices. There is no fragile junction to destroy. The same is true of the iron, the water heater, the old incandescent bulb. Think of the surge as a splash of boiling water: it instantly destroys a spider's web and barely warms a cast-iron pan. The router is the web. The kettle is the pan.

What actually stops a surge? The surge protection chain, roof to socket

A coordinated chain, where each stage knocks the surge down further before handing what is left to the next. Real surge protection is never one device. It is a cascade.

It starts outside the building. An air terminal, the lightning rod on the roof, intercepts a direct strike. A down conductor carries that current down the outside of the structure, and an earthing electrode dissipates it safely into the ground. This is the same earthing logic that keeps you alive indoors, covered in Part 20 of the course, Earthing and RCDs: give the energy a deliberate low-resistance path so it does not choose a worse one. But note the limit. That external system protects the building from fire and structural damage. It does nothing for the induced surge already travelling down your power cables. For that you need surge protective devices, and they come in tiers. Malaysia adopts the international lightning-protection standard as MS IEC 62305, endorsed in 2007, with SPDs governed by MS IEC 61643 (TAKO).

- Type 1 sits at the main incoming switchboard. It takes the brutal, high-energy hit from a direct or near strike and clips the worst of it.
- Type 2 sits at your distribution boards. It is the workhorse, catching the overvoltage that the Type 1 let through and stopping it spreading to your loads.
- Type 3 sits right at the socket, inside that "surge protected" power strip. It is the last and weakest stage, and it is only ever a supplement to a Type 2 upstream, never a standalone defence.

Each tier assumes the one before it did its job. A Type 3 strip alone, with no SPDs at the board, is a screen door on a submarine.

What is really inside a "surge protected" power strip?

Usually one component: a metal-oxide varistor, or MOV. Normally it behaves like an insulator. The instant the voltage climbs past its threshold it snaps to low resistance and diverts the excess to ground, holding the voltage down to a safe clamping level.

Two things about it matter, and neither is printed in big letters on the box. The first is the joule rating, its lifetime energy budget. A strip rated at 1,000 joules can absorb roughly that much surge energy across its whole life, and every hit spends some of it. The MOV degrades cumulatively, so a thousand small everyday spikes wear it out just as surely as a few big ones (Americord).

The second is the trap. When the joules are gone, the strip keeps delivering power exactly as before, with no warning that its protection is spent (MakeUseOf). It is now an ordinary power strip wearing a surge-protector label. Better units have a status LED, but many do not, and some only confirm the MOV is present, not that it is still healthy. A surge strip is a consumable. Replace it every few years, and always after a known big surge.

Why unplugging during a storm is still the only sure thing

Because the only protection no surge can defeat is an air gap. Every SPD has a rating a big enough strike can exceed. A physical disconnection has no rating to exceed.

If you genuinely care about one irreplaceable device, pull it out of the wall during a severe storm, and pull the signal cables too: the aerial, the coax, the phone line, any Ethernet from an outdoor run. A surge enters through any connected conductor, so a router unplugged from power but still joined to the phone line is still exposed. It is inconvenient, and it is the one method that is 100 percent.

And do not expect insurance to soften the loss. A standard Houseowner policy covers the building, and lightning is a listed peril, so the structure is protected. But that policy covers the structure, not the contents. A fried TV or router is contents, which needs a separate Householder policy (Tokio Marine). Even then, whether a pure surge with no fire actually pays out depends on the exact policy wording, so confirm yours rather than assuming. Prevention is cheaper than the argument.

What a facility should actually check

The household version of this is a dead router. The building version is a dead PLC, a reset controller, or a data-line card that quietly failed, and the same induced surge that stops a router is one of the causes of the voltage sags that halt a production line. The checks are unglamorous and they are the ones that matter.

Walk the switchboard and distribution boards and read the SPD status windows. Most Type 1 and Type 2 devices show a green-to-red indicator that flips when the module has worn out, and a red window means the protection is already gone even though everything still runs. Confirm the earthing is intact and low-resistance, because an SPD with a poor earth has nowhere to send the surge. And keep a record of when each device was installed, because like the power strip at home, an SPD is a consumable that fails silently and looks identical to a working one right up to the storm that finds it out.

This is an applied extra to Cobler's Electricity Fundamentals course. It builds on Part 1: What Is Electricity for the physics of the strike, Part 20, Earthing and RCDs for where the energy goes, and Voltage Sags and Swells for what the same surge does to a plant.

A dead SPD looks exactly like a working one until the storm arrives. CobiNeural monitors your building's power quality in real time and logs surge and sag events with a timestamp, so the record exists before anyone starts guessing. Talk to us.