Tying knots in a power cord will protect against lightning surges

[snopes]

Comment: Rumor:
Tying five knots in your computer's power cord will protect it from power
surges caused by lightning. In the event of a surge, the cord's
insulation will be fried up to the third or fourth knot and the computer
will feel no effect.

Explanation:
Lightning has a fantastically high frequency. Since inductive impedance
increases as frequency increases, the tiny inductance of the knots will
have an enormous impedance against the lightning and little effect on the
60Hz AC power supply.

When I think:
Lightning is a DC arc. That means the current flows in a bunch of pulses
in quick succession, but always in the same direction. Therefor, it has
both an AC and a DC component. The knots might dampen the AC component,
but will have little effect on the DC part. Since the computer has an
internal power transformer which also won't respond to DC, it's plausible
that the computer's sensitive parts might escape damage.

However, the bit where the cord is cooked to the third knot is quite
suspect. The current has to go in AND out through each knot, and the
current is uniform throughout the cable even though it may vary with time.
Assuming the knots are identical, they'll all have the same impedance.
They'll take the same current, and therefor respond the same way: by
creating a voltage. The voltage across each knot will be the same,
therefor the power each inductance releases/absorbs will be the same.
Therefor, any damage to the cord would be equal at each knot.

The voltage *drops* will be the same, but your theory assumes a parallel circuit with equal resistors. I agree it's still suspect, but if could happen you would have to have the knots *in series* to get the effect, which is the case with this arrangement.

[Singing in the Drizzle]

Looking into this a couple of sites say it seems to work, but they are relying on other people claiming it saved them. They acknowledge that they have not tested and it is only other people claiming it does.

[purpleiguana]

Why am I having an image of a cartoon power cord swelling up from the excess power of a lightning strike, forcing its way through the first four knots, before just giving up and the cord swelling goes down?

[ganzfeld]

I just wrap all of them in a maze. There's no way in hell a surge is going to make it through that mess.

[Arriah]

Originally Posted by AsForMe

The voltage *drops* will be the same, but your theory assumes a parallel circuit with equal resistors. I agree it's still suspect, but if could happen you would have to have the knots *in series* to get the effect, which is the case with this arrangement.

If there are 5 knots tied in the power cord, they will be in series.

I know a really cool way to protect your computer from a surge: Plug it into a high-quality surge protector! Works (nearly) every time.


ETA: DH points out that with 5 knots in your power cord, you'll be unable to plug it into both the computer and the wall. I guess the OP would work!

[Troberg]

Pure bullshit. There is no way a know will provide any protection against surges. It just doesn't make sense in any of the laws of physics which control electricity.

Besides, most of the damages does not come from direct strikes anyway. Most damage comes from small spikes due to the electric fields in the air during a thunderstorm, which nibble away at the sensitive electronics.

Most important advice: Do not unplug stuff if there is a thunderstorm. Yes, your stuff will be more exposed. You have an insurance to handle that. However, the last thing you want to do if there is a direct strike is to hold a wire. You might very well have an insurance that covers getting burned to a crisp by Thor, but you'll still probably not find it worth the compensation you'll get.

I know many people recommend unplugging stuff. Don't. It's wrong, and it can kill you.

[Squirt]

Tying a knot confuses the sky-demons who try to travel through your wires into your television. You can also prevent damage by placating them - try leaving old televisions in your garden so they can feed off them easily.

[chocolate kisses]

Originally Posted by purpleiguana

Why am I having an image of a cartoon power cord swelling up from the excess power of a lightning strike, forcing its way through the first four knots, before just giving up and the cord swelling goes down?

(Because you watch too many cartoons, like me!! )

Originally Posted by snopes

Comment: Rumor:
Tying five knots in your computer's power cord will protect it from power
surges caused by lightning.

Which is why tying knots in a TV cable completely cuts off the much higher frequency and so much weaker TV signals.