Overhead Power cable from my house to my barn

You may be able to cheer him up by offering to arrange the mountings and the stay wire ends in advance so all he needs to do is clip and slide along - it may be that the working  at height or the risk of pulling bits off the building is the aspect he is not happy with. (It is not unknown for a  rawl-bolted fitting to remove a couple of bricks off  the top course if the forces are not correctly spread, and he may have been caught out by something like that in the past - some folk tend to forget that mortar is not sticky like glue, but is more of a friction fitting due to the sand and the pressure of the layers above. )


(typical low cost parts. 3mm galv wire  Better alternative is larger dia and as you mention the wet, stainless steel   ) Note that for the working load  is not the weight of cable, but the tension  (3mm wires, the working load is 155kilo, for the 4mm s/s the breaking load is 900kgs and the 6mm 2000kg !! - but working and breaking loads are not the same **....)- and that tension depends on the droop - ( and actually it is a surprisingly complex problem )  however, approximately you can get a safe over estimate by pretending that the weight of the cable is at the midpoint of a triangular droop . So if you take my suggested drop of 0.5m over 12.5 (half metre drop at mid span) you get 2.3 degrees, and tension is tangent of (90degrees minus that >> TAN (87.5 deg) is 23  ) times the down force, (half of the total cable weight as the total weight is  held up from both ends) - so about 10-12  times that cable weight as the tension.

Actually  a 6mm SWA would be ~ 18 kilos of cable and by my  noddy rule comes to 180kg of tension. When done slowly with the right formula, it  is more like 125kg force tension, but  even so would be very near or maybe over the limit for the galvanised 3mm cable with a bit of bad weather.  Hence my suggestion to use something bigger, though the best choice depends on your cable size.


Mike.


Edited to clarify the tangent approximation thing applies to half a cable.

PS

**

edited again to suggest SWL (safe working load) should be no more than perhaps 1/4 or a 1/5 of the MBL (minimum breaking load) depending on how serious versus just annoying  it would be if it ever fell down. If there is ever a credible risk to lives, make that ratio more like 1/10 instead. Unless it is an aircraft, where you get things professionally calculated but with much lower safety margins !!

You may be able to cheer him up by offering to arrange the mountings and the stay wire ends in advance so all he needs to do is clip and slide along - it may be that the working  at height or the risk of pulling bits off the building is the aspect he is not happy with. (It is not unknown for a  rawl-bolted fitting to remove a couple of bricks off  the top course if the forces are not correctly spread, and he may have been caught out by something like that in the past - some folk tend to forget that mortar is not sticky like glue, but is more of a friction fitting due to the sand and the pressure of the layers above. )


(typical low cost parts. 3mm galv wire  Better alternative is larger dia and as you mention the wet, stainless steel   ) Note that for the working load  is not the weight of cable, but the tension  (3mm wires, the working load is 155kilo, for the 4mm s/s the breaking load is 900kgs and the 6mm 2000kg !! - but working and breaking loads are not the same **....)- and that tension depends on the droop - ( and actually it is a surprisingly complex problem )  however, approximately you can get a safe over estimate by pretending that the weight of the cable is at the midpoint of a triangular droop . So if you take my suggested drop of 0.5m over 12.5 (half metre drop at mid span) you get 2.3 degrees, and tension is tangent of (90degrees minus that >> TAN (87.5 deg) is 23  ) times the down force, (half of the total cable weight as the total weight is  held up from both ends) - so about 10-12  times that cable weight as the tension.

Actually  a 6mm SWA would be ~ 18 kilos of cable and by my  noddy rule comes to 180kg of tension. When done slowly with the right formula, it  is more like 125kg force tension, but  even so would be very near or maybe over the limit for the galvanised 3mm cable with a bit of bad weather.  Hence my suggestion to use something bigger, though the best choice depends on your cable size.


Mike.


Edited to clarify the tangent approximation thing applies to half a cable.

PS

**

edited again to suggest SWL (safe working load) should be no more than perhaps 1/4 or a 1/5 of the MBL (minimum breaking load) depending on how serious versus just annoying  it would be if it ever fell down. If there is ever a credible risk to lives, make that ratio more like 1/10 instead. Unless it is an aircraft, where you get things professionally calculated but with much lower safety margins !!