Running 35mm armoured overhead

[Robertbaker63]

A farmer wants me to run a new supply to a building, it's to be run in 35mm armoured, part of the route is a 25m overhead span between buildings, is this okay for the cable or should I be getting an extra pole in the middle put in to take the weight

 

[telectrix]

is going underground out of the question?

 

[Pete999]

25 of 35mm SWA is going to be heavy, very heavy, as Tel asked why can't you take it underground between the two buildings? I expect like most Farmers they want a cheap job and b--ger the safety aspect. The regulations tell you the spacing for horizontal and vertical clipping etc, I would of thought that experience would tell you that the method you are talking about is IMO a no no.

 

[Sintra]

How many cores in this cable? I'm asking this so that you think about the weight of the cable across the span. For example a 3 core 35mm weighs approximately 2Kg/M so this would be 50Kg. Imo this should be supported across the full length of the span using an appropriate catenary system.

 

[Darkwood]

A cable of that size run overhead should be fully supported and usually with heavy duty cable ladder, this would also require frequent support poles as you have to account for the weight of the ladder too and its max unsupported recommendations (at a guess every 5m) and been a farm then at a suitable height for farm plant to cross under even with any folks etc raised.

I would be seriously looking into burying this given the cost and obvious hazards having a overhead system with multiple supports would present on a farm.

 

[Robertbaker63]

Yes it's 3 core armoured, the overhead part is not in a.through vehicle route and not possible to go underground as it's over a few smaller sheds

 

[Darkwood]

Can a ladder system be fixed to the existing sheds, plus what stops you going around the sheds - a straight line isn't always possible .... just shots in the dark of course but info for us is lacking.

 

[atm84]

What about using a catenary wire. You can then cable tie it to that but like already said, try to work out the weight of the cable first.

 

[Deleted member 72666]

is going underground out of the question?

Dunno! Ask Paul Weller!

 

[atm84]

What's the supply for, have you carried out cable calcs. Is 35mm2 required.

 

[ImpededLoop]

What are the 3 cores for? If one is cpc you could consider omitting that and use the armouring or TT the new installation.

 

[davesparks]

Would it not be better off run in hard drawn overhead cable?

 

[nickblake]

What about using a catenary wire. You can then cable tie it to that but like already said, try to work out the weight of the cable first.

35mm SWA on a catenary wire cable tied ,imagin that in the wind would last 5 mins , only real method for that enviroment is under ground in ducting

 

[Brightspark2]

35mm SWA on a catenary wire cable tied ,imagin that in the wind would last 5 mins , only real method for that enviroment is under ground in ducting

I've seen a lot bigger than 35mm on a catenary wire!!!...still hanging on in there lol

 

[shanky887614]

I've seen a lot bigger than 35mm on a catenary wire!!!...still hanging on in there lol

unsupported over 25m?

 

[Brightspark2]

unsupported over 25m?

Oops missed that bit!!...ha ha

 

[shanky887614]

Oops missed that bit!!...ha ha

if there are no supports over the 25m i recon it might dislodge a brick before landing on the ground

thats only my opinion i have never used catinery wire so i honestly don't know but i recon the manufacturer's will have the recommended support distances with loadings in there paperwork

 

[nickblake]

used cateenary wire loads of times normally over short distances but not over that distance and with that size cable

 

[Guest77]

Yes it's 3 core armoured, the overhead part is not in a.through vehicle route and not possible to go underground as it's over a few smaller sheds

You need to completely redesign the whole job, it is not possible to support a cable that size on cateenery wire over that distance, a rethink, no point trying to continue down the cateenery route, just pointless.

 

[Guest77]

A cable of that size run overhead should be fully supported and usually with heavy duty cable ladder, this would also require frequent support poles as you have to account for the weight of the ladder too and its max unsupported recommendations (at a guess every 5m) and been a farm then at a suitable height for farm plant to cross under even with any folks etc raised.

I would be seriously looking into burying this given the cost and obvious hazards having a overhead system with multiple supports would present on a farm.

Good advice, I agree a ladder with supports or get it in the ground.

 

[Dcf]

What about abc type cable or the old fashioned method of type 8 overhead channel iron and insulators at each end?
whatever method you decide the fixings will need to be rock solid at each end

 

[Darkwood]

I think the sheer cost of Ladder, post digging, bare or insulated singles wires overhead method all come with large costs, although burying it would in no doubt increase the CSA requirement you should still cost it up and ask the farmer to do the digging work if he can to keep costs low.

All methods are going to be a pain and a knock in his pocket but if that's the power he needs then he has to accept its going to be expensive.

 

[benji]

RS do a 30mtr catenary kit that seems to carry 130kg ? and the dia. is only 3.0mm ??.Today i was looking at a catenary suspended between poles for street lighting approx 25mtr apart total run about 200mtr cable looked about a 25mm swa ? (i was driving at the time ) very little sag between poles and its been there for years.

 

[shanky887614]

RS do a 30mtr catenary kit that seems to carry 130kg ? and the dia. is only 3.0mm ??.Today i was looking at a catenary suspended between poles for street lighting approx 25mtr apart total run about 200mtr cable looked about a 25mm swa ? (i was driving at the time ) very little sag between poles and its been there for years.

might do it. 100m of 35mm 4c is 240kg so should work.


the problem isnt the cable but the fixings either end.

those supports have cable supports as well to keep them up usually and you will need a concrete base etc for them.

it might be cheaper to find a longer route and use a bigger cable, quick search online and 35mm 4c is £9ish a M

so thats £280 just on cable (30m)

70mm is £13pm = £390 (30m)

i bet the cost of poles and everything else will add upto a lot more than installing a bigger cable and going underground or a longer distance

 

[benji]

Correct but if distance is only 25mtr pole might not be required but the fixing of the catenary at each end needs to be paramount

 

[shanky887614]

Correct but if distance is only 25mtr pole might not be required but the fixing of the catenary at each end needs to be paramount

thats the problem.

how many farmers look after there buildings etc? there among the worst for bodges

 

[Guest77]

RS do a 30mtr catenary kit that seems to carry 130kg ? and the dia. is only 3.0mm ??.Today i was looking at a catenary suspended between poles for street lighting approx 25mtr apart total run about 200mtr cable looked about a 25mm swa ? (i was driving at the time ) very little sag between poles and its been there for years.

An experienced Time served Electrician wouldn't consider it :icon12:

 

[D Skelton]

Catenary is possible, but you'd need to sink two proper telegraph poles, plus counter anchoring. He's gonna need deep pockets!

If you're going overhead, I'd also ditch the SWA and go for HO7RNF.

 

[shanky887614]

An experienced Time served Electrician wouldn't consider it :icon12:

Catenary is possible, but you'd need to sink two proper telegraph poles, plus counter anchoring. He's gonna need deep pockets!

If you're going overhead, I'd also ditch the SWA and go for HO7RNF.

thats the thing it soon gets expensive, one of the biggest reasons the dno goes above surface is its cheaper than burying and making good in certain cases.

if you think about the logistics of it, it makes sence.

 

[D Skelton]

I've suspended 5 core 70mm HO7 over a gap of 20m before, but I was securing the catenery to solid concrete on one side, and a metallic ship hull on the other. It is easily doable, but if you're doing it at height, which I wasn't, it needs to be done properly!

 

[Darkwood]

SWA is not a constant flexing cable designed for suspension, the steel armour can work harden very quickly thus breaking or even the cores so anywhere its subject to wind or repeated movement will effect the structural integrity of the cable. You can get away with it to a certain extent with small cables over small gaps but the larger sizes need support fully along the run.

I fit energy cabling (control and power) to machine wiring looms where the cables are specifically designed to repeatedly move with little structural deteriation or core twisting, its a complex calculation but I can usually tell the customer that a cable I have installed is good for 10million flexes and will last x amount of years, a normal flex can only withstand a few hundred to a thousand flexes of a similar nature before it fails.... its from this angle I would advise you don't use SWA suspended free or to a catinery set-up. If you have ever run cable in when its freezing weather you know how stiff the plastics/pvc become so I wouldn't want the wind swinging any such cable against its anchor points as the sheath would just crack and split.

 

[davesparks]

Go old school on it, insulators and hard drawn singles