cables & poles

[FunnyFellow]

at christmas time my school is doing a variety show type thing and I have to string cables between posts about 38 feet apart. Should I wrap the cables around a length of rope or just string them without reinforcements?

[SHARYNF]

I would string them and support them via a rope with loop ties holding the mic cables up to the rope. This way the Rope can be securely attached to the two poles and you are not trying to tie a not in a mic cable and you don't have to wrap the mic cable, just tie it up

Sharyn

[Chris15]

If you have a 11.5 metre span, a catenary wire is essential.

Cable ties would be the normal means of attachment to the rope or steel cable, leaving them loose enough not to damage your cables.

If this involves coming through a wall, tent or building, you would be well advised to put a drip loop on the outside of any wall to keep the water outside...

How high are these poles and what's holding them up?

[FunnyFellow]

One pole is on the side of a balcony about 3 metres up and the other one is holding up a rotunda which is about 3.2 metres high.

[Chris15]

One pole is on the side of a balcony about 3 metres up and the other one is holding up a rotunda which is about 3.2 metres high.

If this spans a vehicle way, then the relevant standards require it traverse that with no point lower than 4.5m above the ground, ie. the ends will need to be higher than that. Where a truck can be expected, that increases to 6m.

While you are unlikely to run into issues with the lateral loading with the structures (assuming you aren't putting in too much multicore or 3 phase here), you do need to be careful when you install the catenary that you aren't going to leave marks on the poles, so things like synthetic rope around the poles and possibly cardboard or moving blankets under that depending on the surface and how much people care about it...

[ajb]

Regarding lateral loading, remember that the lateral load increases dramatically as the amount of sag you allow decreases--in fact if you graph it, you'll see that you'll see that tension approaches infinity as sag approaches zero. So you're better off supporting the cables higher on the poles and allowing them to sag more in the middle versus supporting them low and pulling them very taut if there's any significant weight to your bundle.

[SHARYNF]

you can balance the effect of the lateral load from a taut line if you then provide a line from the pole to the floor. This has the effect of transfer a portion of the lateral load to vertical

Sharyn

[FunnyFellow]

the cable does not span a vehicleway, only an unofficial walkway.