Cable Knots

[DarSax]

Hey all.

This came up many months ago actually, but I never found an answer and I just thought of it. The answer to this will probably be embarrassing, but I realize my (lack of) knowledge of knots is embarrassing, so here goes!

Let's say you have a batten. (Only one. It's a poor theater.) You approach that batten with a cable straight on (the cable will form a right angle with the batten), on the same level as the batten. The cable is plugged in to the wall behind you, but not affixed to anything else.

Once the cable reaches the batten, it needs to drop straight down, say, exactly 5 feet, so the cable itself will form (as close to as possible) a right angle. What knot do you use to make sure that that the cable doesn't slip down? (While placing the least amount of strain on the cable)


(to red flags: the cable is not holding anything up, it's just reaching a set piece and slack would like to be avoided.)

Thanks all!

 

[gafftapegreenia]

An LD I worked with had a method but I don't know the name of it. It was sort of a half clove hitch.

I usually just use tie line to create a strain relief.

 

[porkchop]

I'm of the opinion that anything involving cable and knots should be avoided at all costs. Wouldn't want to teach it bad habit you know. I have and would again use tie line, double wrapped with whatever knot you please (a can of worms I don't want to reopen at this time) and that should be plenty to keep the cable up.

 

[gafftapegreenia]

I generally agree with you porkchop however the method I witnessed did not appear particularly troubling.

I will say that I do everything in my power to stop people from tying cable ends together. Either gaff it or split the pins! Stop straining the cable.

 

[GreyWyvern]

Doing a clove hitch around the batten will keep the cable securely in place and not put any undue strain on it. It is the method I use and it has always worked. I like it because it doesn't really knot the cable itself.

 

[DarSax]

Just going through my hypotethetical, 5 feet isn't really that much; in reality it was more like 20 feet, enough weight to make the cable want to slip down further. (Though it sounds like these suggestions all still apply)

thanks all!

 

[Reqel]

Doing a clove hitch around the batten will keep the cable securely in place and not put any undue strain on it. It is the method I use and it has always worked. I like it because it doesn't really knot the cable itself.

I'd put a half-hitch over the clove hitch to lock it off and be double sure its not going anywhere

 

[mrb]

I form a 180deg loop in the cable and lash the two parallel runs together with tie line. Then tie the loop to the pipe. This way I can get the drop length accurate, dont have cable swinging all over the place while trying to wrap it around the pipe, and can detach and reattach the cable to the pipe without disturbing anything else. This may not be perfect either, but has saved me alot of trouble a few times.

 

[gafftapegreenia]

I'd put a half-hitch over the clove hitch to lock it off and be double sure its not going anywhere

Again I feel thats to many twists and knots in a short run of cable.

 

[Grog12]

Again I feel thats to many twists and knots in a short run of cable.

GTG...he's talking about using tie-line not the cable itself.

 

[gafftapegreenia]

GTG...he's talking about using tie-line not the cable itself.

OH, well, then that makes sense.

 

[mrb]

OH, well, then that makes sense.

I took it as tying the cable itself around the batten as well

 

[sk8rsdad]

I am of the opinion that you should never ever put a knot in an electrical cable. These things have a minimum bend radius that should not be exceeded. Any knot that is tight enough to hold the cable is damaging to the conductor, the insulation, or both. These things are carrying electricity so any tight loops result in inductance and that translates into heat, which can become fire given the right (wrong?) conditions.

A technique I use for putting a strain relief on a cable is a piece of sash cord attached to the electrical cord with a Prusik knot. It won't slip under tension and it distributes the stress on the cable over a wider surface area. In this picture the electrical cable would be represented by the white rope, and the red cord is the sash cord.

 

[Dionysus]

In a more permanent-ish install you can tie a Kellems Grip to the batten with the Kellems Grip installed on the cable. Only problem is installing the Kellems Grip on the cable itself. You have to remove an end.
Other than that I'd totally go for sk8tersdad's suggestion of a prusik from tie-line.

Do not tie knots in the cable itself, or half-hitch it around the batten. It's not good for the cable.

Edit: Decided to show what a Kellems Grip or 'wiremesh grip' is:

 

[GreyWyvern]

When I suggested the clove hitch, I was talking about the cable itself. It is more than enough the keep it from slipping. A clove hitch tightens itself as it gets pulled on from one side. You could hang on the cable if you do it right, although that would be stupid and potentially damaging to the cable. And I would have to beat you...

Dave

 

[derekleffew]

The only ones who should be allowed to tie knots in cable are the Foy people.

--Bill Sapsis

---------
Spanset and shackle for strain relief. Each has his own intricate method, but all are mere variations on sk8rsdad's prusik.

 

[Grog12]

When I suggested the clove hitch, I was talking about the cable itself. It is more than enough the keep it from slipping. A clove hitch tightens itself as it gets pulled on from one side. You could hang on the cable if you do it right, although that would be stupid and potentially damaging to the cable. And I would have to beat you...

Dave

Wow...really?

Don't do that.

Seriously.

Don't do that

GTG's right its really damaging to the cable to put that many kinks in it.

Go out right now and invest in tie-line.

Knots create kinds in cable and eventually breaks in the S/O. The most you should ever do is put a "loop" in the cable for a little strain relief (think the bow portion of your shoe lace not) and then tie that off with tie line to be safe.

 

[porkchop]

Derek, as usual, has a great point. Although tie-line is commonly used to keep cables up and tidy in the air, this is a hanging situation where there is stress (potentially significant stress if it's heavy cable) on one specific point, that being whatever is holding the cable to the batten right where it drops down. Now you have a load, overhead, with stress. Spansets and Shackles are rated, tie-line is not. Also the Kellems is a good idea too but I always cut myself on those d**m things.

Side Point: Derek why would Foy people be tieing knots in cables?

 

[Dionysus]

Flying by Foy uses a special Knot on their wonderful skinny wire rope. Since any other method doesn't hold very well on such small cable. Thus they use their "secret knot".

I defiantly have to agree on using shackles,etc because of rating over tie-line.
I use the Kellems often enough for various things (mainly permanent install), you get a hang of them. After a while they are easy to use. Plus they hold really well, and the electrical inspector certainly likes them more than tie-line, lol.

 

[GreyWyvern]

If you read the OP, he asked how to keep the cable from slipping down. A clove hitch does exactly that with out any chance of smashing, kinking, flattening, twisting, etc., the cable. The only way that would happen is if the cable itself was holding weight and causing the knot to tighten. Then there are other issues to worry about. I highly doubt that the weight of 20 feet of cable is enough to do any damage. The clove hitch works well because it puts no bends in the cable, the contact is distributed around the larger batten rather than one small point of tie line, and it is extremely easy to adjust to the exact height that you need. I just don't see how it is damaging to the cable.

Dave