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True or False: Tying a knot in a power cord "provides protection against lightning"

kolek

kolek

Inventor of the Electron
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There are articles online claiming that typing a knot in a power cord will provide protection against lightning. For example, this one.


Could tying PV cables in a knot provide any lightning protection? These are 400V 12A DC lines. Or alternatively, could a coil like this reduce solar production? In my case, I'm tying off my PV cables to my rack to isolate them during earthquakes from being jerked out of their connections to my inverter.

Personally, I'm skeptical of the "lightning protection" claim, but I'd like to hear what the experts here have to say. I specifically interested in hearing from people who have tested this or can provide sound electrical engineering arguments why or why not this is legit.

"If it worked, everyone would be doing it and nobody would sell lighting suppression equipment." Sure, we all know that. But that's not scientific proof, so I'm still curious if anyone here knows the actual science.

loop-knot.jpg
 
knots.jpg

"When you see these round things on cables, sometimes all that’s inside is a knot, sometimes it’s a metal sleeve (ferrite core)."
 
Not submitting this as evidence either way, just what I'm seeing on this topic.

How do you calculate energy dissipated in a coil?

The formula to calculate the power dissipated in the coil's resistance is P = I 2 R , where 'P' is power measured in watts (W), 'I' is the current, and 'R' is the resistance.
 
The knot is supposedly acting as a coil but in theory a single knot will only prevent a tiny surge the main reason for it on ferrite core is simply to stop the core from moving.
physics.stackexchange.com

Tying knots in power cables to prevent power surge from lightning strikes

There are plenty of references to this claim on the internet that tying knots in power cables will prevent a piece of equipment e.g. television or computer from a power surge. How can this be debu...
physics.stackexchange.com physics.stackexchange.com
Will give you a better understanding of the science
 
"What Do You Do With a Static Drain Coil?"

"c. A high-impedance coil usually attached from the antenna input to ground to drain off static charges caused mainly by lightning or wind-driven dust."

www.radioworld.com

What Do You Do With a Static Drain Coil?

The problem we have before us is to attenuate in intensity the static charges, either around the tower before a discharge or after high voltage is induced into the system when lightning strikes, and in unique cases where a static charge build-up is developed by wind driven dust or sand.
www.radioworld.com www.radioworld.com
 
Pasting from that reference:

"The surge impedance of any line is the square root of its inductance divided by its capacitance, and electromagnetic waves travel most readily down a line where that surge impedance doesn't change. A point of changing impedance is a discontinuity that causes a partial reflection of the wave back towards its source. As an example, the end of the line is a surge impedance jump to infinity and the whole wave is reflected back (which means the wave voltage at the open end doubles!) This is also the reason why you want to use terminators on the ends of coaxial cables. Open-ended cables will reflect back the signal causing poorer picture quality and ghosting (and similar things happen for poorly made connections that have higher impedances than the surge impedance of the coax).

Knotting the line gives that part of it a higher inductance (think of the knot as a coil with a couple of turns). That means two surge impedance discontinuities (from line to knot, and from knot back to line). It seems to me (too lazy to resort to doing the math) that this is bound to reduce the magnitude (voltage and current) of a surge passing through the knot because some will be reflected back. However, I'd guess that the reduction would be small."
 
So the ferrite core and not will prevent static and interference on small levels but 0.3GV and 30KA of a lightning strike will just fry everything in it's path
 
A choke resists sudden changes in current; a capacitor resists sudden changes in voltage. Trying to reduce current flow from a lightning strike by increasing impedance... is not going to work. You need to provide a lower impedance path to ground for the lightning energy first and foremost, and then you can do things to manage extraneous voltages that make it through. It is all about defense in depth at that point.
 
So could putting a loop like that attenuate solar generation to any measurable degree? I'm assuming again, virtually no effect.
 
kolek said:
So if these are real lightning suppressors, 1 knot in a wire doesn't look like it's gonna do much.
Click to expand...
Personally I think messing about with lighting is idiotic(no offence to any sparks here I'm sure you do good work) but adding anything to do with lightning to your regular residential home apart from a typical SPD seems to be inviting trouble, I see it regularly here in Thailand some medium sized house with lightning rods on the roof likely fitted by a farmer who works in the off season as an electrician thinking that's going to protect them rather than just invite lightning to hit them.
Hell I've never seen lightning even touch land here, it tends to be sheet lightning in clouds. Our farm has a concrete tile roof and plenty of surrounding trees and giant bamboo that in theory should get hit first I'll just leave it to nature and if we buy chance did get hit so be it.
 
I think a more interesting question would be to any properly qualified electricians actually fitting lightning protection "has any system you've fitted actually been hit? What happened? Did the conductor even hold up?"
@Hedges @timselectric you've likely been around these systems in places that actually need it have you seen any strikes? What happened? I've worked at plenty of old British churches with lightning conductors (normally an 1"x1/4";or so copper strip running the side of the stonework) but I've never seen one actually take a hit would that copper even take the power or being copper would it just burn up?
 
kolek said:
More pictures of actual legit lightning suppressors:

View attachment 227910

View attachment 227911
Click to expand...
these lighting arrestors are spark gap arrestors only useful for high voltage lines. They contain a series of isolated metal washers or disks providing an ark value 3-20k or so volts higher than the nominal line voltage the fancy outer architecture is just to prevent surface tracking they are very robust and will shunt many lighting strikes throughout their life. a 7620v line gets 10k arrestor, a 13.2k line gets a 18k arrestor and so on.
when they take a hit usually results in an off on blink of your lights/power from the ark shunt I'm sure you've seen this during an electrical storm.
 
Daddy Tanuki said:
Nothing of value to offer though I do know that I have had no issues since I installed my midnite solar SPD's
Click to expand...
Yeah I considered those but they are so darn expensive. The price for 4 of them is almost the same as the cost of the inverter I'm using, which kinda almost defeats the purpose. You using one on each PV string?
 
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