Overhead outside supply - fastening to catenary?

[MickBee]

The existing supply to my domestic garage uses 2.5 T & E suspended from a catenary. 10 years ago, electricians replaced the fastenings with cable ties, which were not pulled tight; some of these ties have broken and others have slid along together, leaving the cable hanging in big loops.

What should be used to hang the cable? It seems to me that the fastening needs to be tight on the catenary to prevent movement along it, but it should hold the cable away from the catenary to avoid chafing in the wind.

I think that the basic set-up is correct; in the house, earthing is TN-S with a 30 mA RCCD supplying a separate CU with 16A MCB; the catenary is at least 3.5m high throughout its (20m) length; in the garage a CU has separate fuse for lights and sockets; sockets only used for power & garden tools; garage is brick & tile with a concrete floor and steel roller door.

I have looked at previous threads but have not found the info I need; I would be grateful for constructive advice.

 

[Steve]

T&E should not be used exposed outdoors. It breaks down with exposure to UV light.

Split concentric is much more suitable.

 

[MickBee]

I appreciate that T&E would not be used in a new set-up. I need to know how to make the best of the existing situation.

 

[Steve]

cable ties. tighter.

They should be sufficient. Dont be scared of chafing - the correct cable type wont chafe.

 

[grahamderek]

Good quality cable ties will not break (proper Ty-Wraps)Use 1 round the support wire pulled tight, and another through the first and round the cable

 

[holmslaw]

..

 

[aptsys]

Leather Suspenders eh? Got me worried for a sec there when I clicked that link...

 

[MickBee]

Thank you all for your replies. I think I'll try the double ties method.

Is there a recommended minimum thickness for ties for them to be durable? Maplin have "weather resistant self-locking cable ties" with thicknesses ranging from 2.5mm to 4.8mm. I'd rather spend a couple of quid more on the ties, and only hire a tower frame to do this job once.

 

[TicklyT]

Telephone cables used to be hung from a catenary wire between poles with a series of rings lashed to a smaller wire. The cable was laid out, and the rings pulled along the catenary using the smaller wire like drawing a curtain. The wire was finally fixed at both ends to keep the rings in position. Almost everything could all be assembled at ground level, then hoisted up the poles, and there was no need for a 'cherry picker' to fix the cable along the catenary.

 

[JohnD]

what about the question of PVC T&E exposed to sunlight?

 

[MickBee]

At the risk of repetition, I appreciate that UPVC T&E would not be used in a new set-up; I am dealing with the existing situation. (The NICEIC professionals who replaced the ties 10 years ago made no comment about the cable - although from reading other posts about competence, that is nothing to go by.)

If the cable sheathing were to break down through degradation of the UPVC, is the result likely to be dangerous/life-threatening, or just inconvenient (i.e. earth-tripping)?

 

[RF Lighting]

Both

 

[Lectrician]

It is common to leave the ties loose, as the steel catenary will expand and contract at different rates to the cable. They shouldn't be loose enought to all 'pool' at the lowest cable point though!

Suspended T+E is not good.

Couple reasons.

Degradation of the PVC Plasticiser in the sunlight. Cable becomes brittle and crackes due to movement.

If it is 2.5 or below, the cable will be single strand soft drawn copper which will work harden due to movement and eventually fail.

 

[MickBee]

Thanks again for all your comments