Aerial wiring

[jksmith82]

Good morning All,
Would someone kindly refresh my memory as to adding the extra wire to an aerial. It’s 75’ and I am installing a messenger cable. The wire is 12-5 tray cable. To account for the sag.

Thanks.
Jim

 

[kwired]

Are you asking how much extra length is needed to account for sag?

 

[jksmith82]

Hi kwired,
That is what I am asking. Any help would certainly be appreciated.
Jim


Sent from my iPhone using Tapatalk

 

[kwired]

Well there is formulas on how to determine the length of the arc but you still need to know how to figure out the radius of the arc and the arc's central angle to use that formula.

I'd probably just make sure to have plenty of extra cable. 75' run with minimal sag probably isn't going to be much more than 5 extra feed to allow for sag. I'd still get 85-90 feet of cable minimum.

 

[jksmith82]

Thank you very much for the info. Have a great weekend.

Jim

 

[wwhitney]

Well there is formulas on how to determine the length of the arc but you still need to know how to figure out the radius of the arc and the arc's central angle to use that formula.

Except a cable suspended at both ends doesn't create a segment of a circle, it creates a catenary: https://en.wikipedia.org/wiki/Catenary

Cheers, Wayne

 

[electrofelon]

Except a cable suspended at both ends doesn't create a segment of a circle, it creates a catenary: https://en.wikipedia.org/wiki/Catenary

Cheers, Wayne

Yes, but if we are being REAL picky, its not a perfectly flexible cable thus it doesnt really conform to a catenary either.

 

[kwired]

The tighter one makes it (less sag) the closer it gets to being same length as a straight line.

Often aerial cables are desired to be relatively tight with little sag.

If ends are not at same elevation then lowest point is not going to be center of the span (it won't be symmetrical).