Tie Knots In Low-Voltage Cable?

How many people are aware of the "cable knot as lightning protector" theory?

This post on LinkedIn recommends installers be in the habit of tying knots in cables for the purpose of lighting surge prevention.

I've heard this stated many times over the years, and many arguments about why it does, or doesn't, work for an actual lightning strike.

How many people here tie knots in power cables or any kind of low voltage cable? Has anyone ever see a cable that was damaged at/near a knot, but otherwise protected the equipment connected?

I'm skeptical this would do anything useful, if that were the case it would seem that electronics companies would use this technique all the time as cheap insurance against equipment damage and return/repair issues.


I'm skeptical as well. After all there is no new ground path provided.

I suppose the resistance may be increased slightly by deforming the cable, but what about the other 1000 Amps that make it thru?

I have never done this , I think I heard of it once and dismissed it as junk knowledge, which I will do again, there is nothing electrically that I can imagine that would benefit from this. I do sometimes tie a knot in the common side of a transformer tail when I meter it , maybe I have been preventing damage unwittingly over the years..

Everyone knows their fuse box is just a fancy name for knot holders, right?

To be blunt: this is stupid advice. At best, it is a waste of time. At worst, you violate bend radii and can create transmission flaws in cable types like UTP. (See: Cable Strapping IP Camera Networks for just how picky the restrictions can be.)

I don't know about quality issues with simple power conductors with knots, but I have seen firsthand lightning vaporize portions of rigid conduit. Like *poof* disappear. Knots won't even slow down lightning, much less stop it.

Anybody want to go in on a Kickstarter project with me?

Lightning bolt cable with pre-made lightning bolt knot. $19.99*

I mean how often is somebody gonna be disappointed? 1 out of 100,000 cables?

ok, sorry sir, here's your new computer...

I was told a while back by an old timer alarm installer to tie knots in my cable 3 or 4 feet before the device you want to protect.

His theory was that lightning doesn't like to make sharp turns and that he actually saw a knot blown apart one time from lightning.

So he thought that the actual lightning was traveling through the cable? As far as lightning not liking to take sharp turns I have never seen a straight lightning bolt... I have seen door contacts damaged during lightning storms, the reed inside would get stuck in the closed position, essentially fused.

His theory was that lightning doesn't like to make sharp turns...

The theory has a lot of potential...

Well, in feng shui philosophy, right angles are considered bad. They're called 'poison arrows' (warning: clicking on that link will cause your brain to explode. IPVM takes no responsibility for raised blood pressure, facial tics, or exploded brains). So I guess Thor is a big believer in feng shui, according to this guy.

This response is an example of why Ari is a legend...

Call the author of the LinkedIn post. John Pecore is very friendly, and I understand him to be an authority on the subject matter. That being said, I do believe you need to understand the low-voltage comm. for your application. Ex. A knot or two in an outdoor copper Network Camera connection that is only using about 10% of BW connectivity on a 100MB connection should not be a problem... Unless it's an Avigilon 30MP or Any Arecont 180 Camera, etc.. Chance of Packet Loss has probably increased, lost video even (maybe), never cared to try to investigate. I would think almost any integrator in FLA would have a better idea. John is in FLA.

(Lightning Capital of the US)

Well, I'm convinced now.

Florida really is the lightning capital of the world North America after all!

Point is Protection against direct strike from my experience as Security Professional is less a concern compared to In-direct (Static Surge through Atmosphere). Direct or In-Direct surge suppression for the AC Grid is responsibility of the EC and the Owner. Mitigation for protection against effects of lightning are case-specific and involve shielding, bonding, grounding and suppression. This is particularly true when it comes to lightning protection against indirect effects. Knots or No knots, this effects what I do but is not my core competency. I would advise to simply consult a trusted expert.

I now will now bow out to your sarcasm and superior wisdom... And wish you well at the Kite Flying Convention in Tampa! :)

From the LinkedIn article:

It is an important part of every job a technician should tie knots in wires. It is like a signature of good workmanship. Failure to do so, could cost the end user a lot of money. However the bigger company is the less likely they are inclined to use this simple concept that does not cost anything accept a little time.

If you are the end user, do a simple quality control inspection of your current systems and if this concept is not deployed, have your service provider come out and correct it according to your specifications...

Question to Integrators: You get a call from a client after the fact asking you to correct your work by creating lightning loops, do you

  1. Do it for free, because you now know better?
  2. Do it for fee, because a buck is a buck?
  3. Refuse to do it on principle?
  4. Look in to getting your Feng Shui certification?
  5. Tell him what he really needs is to redo the whole place in Audio Quest 99.999% oxygen free copper:

If my client asked me to come back out and do this, I would happily refer them to my competitor for future work.

Ok, perhaps drastic. But if I really wasn't able to educate my client, I would still refuse. As the installer, I'm responsible for the integrity of my work and its code-compliance. While this may not be a code violation, it certainly goes against the cable manufacturer's recommended best practices (bend radius) and so I would be liable for any future damages. No thanks.

This advice has been around forever, yet IEEE, BICSI, and the NEC do not advise wire knots at all. I'll stick with the lightning guidelines that were created by professional engineers vs. some guy making claims with no backup.

If (and it's a big `if`) this actually works, no one can actually recommend it because it requires you to exceed the bend radius of whatever cable or wire you are using. So it *might* protect against the effect of a nearby lightning strike, but at the cost of the cable integrity.

I learned this trick many years ago at an ISC conference. I took a whole day course on lighting protection and I was told about the knot. You are correct about lighting strikes, nothing will survive a direct hit; but I do recall the speaker made a pretty good case for doing the knot thing. Theory is, that the protection is not from direct strikes, but from near strikes and things that will conduct the HV to your equipment. The HV takes the path of least resistance; but the knot will work ONLY if there is an easier path to ground that occurs BEFORE the knot. I also noted that the "easier path" is not always apparent. A kink in the ground wire, a bend in the grounding conductor less than 6" were also extolled as potentially problematic

In today's world of effective surge protection and more tolerant electronics, I wonder if knot is relevant...

The HV takes the path of least resistance...

One thing to mention, sure the HV will take the path of least resistance, but it also takes the path of more resistance also.

Meaning that just because one path is an Ohm or two less doesn't mean that ALL the current will suddenly switch over to that path and abandon the others completely. Rather, each path will get a greater or lesser portion inversely proportional to its resistance.

So unless the added resistance of the knot is substantial, the current reduction won't be either.

And if the resistance of the knot IS significant, then that means that you are wasting power the rest of the time since that resistance will be part of your load.

Jim, do you remember who was espousing the knot? Was it a vendor or just an expert?

One thing to mention, sure the HV will take the path of least resistance, but it also takes the path of more resistance also.

Meaning that just because one path is an Ohm or two less doesn't mean that ALL the current will suddenly switch over to that path and abandon the others completely. Rather, each path will get a greater or lesser portion inversely proportional to its resistance.

Kirchhoff - not just a good idea, it's the law!

Kirchhoff - not just a good idea, it's the law!

Couldn't agree more. Ken really knows the law, and not just contracts. We use him for everything, now.

Jim, do you remember who was espousing the knot? Was it a vendor or just an expert?

As i recall the guy was a engineer who -- at least at the time -- had a lot of credentials. Don't recall if he was with a manufacturer or "knot". This was a long (really long) time ago, maybe even in the 70's.

Someone really needs to ask this question in the ADI parking lot...

I have heard of this before when a sales engineer was referring to "some consultant" he worked with. I always assumed it was an urban legend being relayed as a joke.

Well, the author of the linked article is an idiot. I wish there was a nicer way to say it. There is a very good reason that this practice is no longer used. It's very bad for the cable integrity. It's impossible to tie a knot without exceeding the cable's bend radius and much of today's low voltage cabling is twisted pair which is especially susceptible to bend-related degradation. Of course, this whole theory assumes a direct lightning strike, yet most lightning related damage is the result of indirect effects such as current induction caused by a lightning strike in near proximity to a conductor. The amount of induced current is relative to the strength of the lightning strike and its distance away from your conductor. Since most lightning strikes don't occur directly on top of your house or building, it's likely that the induced current is small enough to ride the roller coaster around your knot while still happily frying whatever devices may be attached to it. This theory also doesn't speak to the far more common indirect effect that occurs when lightning strikes the earth sending an overvoltage rising up through the earth ground into your system rendering the knots in your cords completely useless.

Final conclusion: The guy is a quack.