Brackets to support cable.

[damduck-egg]

I wish to run an overhead cable supported from a stronger steel wire to an out building. Probably because I am looking in entirely the wrong places or using the wrong terminology I cannot find a supplier for the type of bracket/hook I wish to use to support the steel wire. To get a little more head room I need to raise the height over the eave of the out building so am looking for something shaped like an upside down J with an eye on the end. The Post office/BT use something shaped just right for attaching the phone line on many buildings. Probably has a name such PO hook 43 or something.

Anybody give me any pointers in the right direction?

G.Harman

[Cicero]

========================================= The support wire is called 'catenary wire' so a bit of googling might help. Screwfix sell some bits and pieces for straining wires so a look there might give you some ideas. One item listed is a 'turnbuckle' which is about the shape you're looking for but might be a bit too elaborate for your purpose.

Cic.

[John Rumm]

as someone else suggested, screwfix do the basic fixings)

[Dave Osborne]

Nah, you're thinking of a PO Extended Bracket 32

see

258

[Bill]

Many electrical wholesalers sell kits, wire fixings etc. Look for catenary wire kits. Getting the tension as high as possible, without pulling one end or the other down is important, turnbuckles / barrel strainers, as shown on the following web page make this easy.

?hl=en&q=catenary+wire+kit&btnG=Search&meta=cr%3DcountryUK|countryGB

[damduck-egg]

Many thanks ,that is exactly it.

Thanks to other posters that pointed out catenary parts but I have those, it is the Extended Bracket I need. Wonder if a mate I only see occasionally is A .Still working for Openreach B Able to get that part from stores still.

G.Harman

[SJP]

Sometimes called a "swan neck" bracket

[Andy Dingley]

It's pretty much impossible to use a turnbuckle on a catenary wire [*], but that's what Screwfix list them under. They're OK for typical "across the driveway" runs, but they're expensive and their other range of similar fittings is cheaper. For most domestic catenaries, you're OK with just galv wire rope.

I can't remember what a PO Hook 43 was really called, but I still have a few. They were a spiral of solid wire, coated in PVC. Great for phone dropwires, not really for T&E or anything thicker. BT's own catenary wire was two copper cores and a steel strength member, all in an overall sheath.

A "catenary" is the shape that a wire or chain will form when only tensioned by its own weight. A turnbuckle applies additional tension to pull it straight(er) than this. A turnbuckle is appropriate for short runs, but only if the extra force added is less than the weight and the tensile strength of the cable. Trying to pull a long cable die- straight is just a recipe for over-tensioning it and snapping something.

[Andrew Mawson]

weight

Surely if you apply tension the curve is still a catenary with different parameters (with a flatter curve) - you cannot entirely eliminate the droop?

AWEM

[John]

We used to call them pigs tails when I sold them a few years ago.

John

[Frank Erskine]

Electrified railways seem to use a catenary tensioned by concrete (?) weights every so far, suspending the actual pickup conductor. The exact height above the track isn't all that critical since the "engine's" collector is spring-loaded. Obviously there'll be some variation with the ambient temperature and coefficient of expansion.

[David Hansen]

On Fri, 23 Jan 2009 11:25:42 +0000 someone who may be [e-mail] wrote this:-

Television/radio brackets could be used to make what you are after.

What is the outbuilding made of and how high do you want to put the end of the wire?

[David Hansen]

On Sat, 24 Jan 2009 00:23:04 +0000 someone who may be Frank Erskine wrote this:-

Concrete blocks which are fitted onto a holder.

For some value of "all that". The contact wire height is raised and lowered depending on the locality. It is highest at level crossings and lowest in restricted locations, like bridges and tunnels. However, changes between different heights need to be made at a rate which the pantograph can cope with as, depending on the direction of the slope, the pantograph will either part company with the contact wire or put excessive force on it if it cannot follow the contact wire properly.

It is more complicated than that however. If the contact wire was level between the supports then as the pantograph moves between two supports it will push up the contact wire by a variable amount, a minimum amount at each support and a maximum amount half-way between them. As a result the pantograph would bounce along the contact wire, with bad current collection at speed. The much maligned British Rail looked into this and came up with a sagged contact wire. Generally this is lower half-way between the supports and the sag is carefully designed and built so that when pushed up by a pantograph the contact wire "seen" by the pantograph is level between the supports.

There is a huge amount of engineering in the seemingly simple arrangement. Modern pantographs even have small aerofoils, shows the prototype, to equalise the performance in both directions.

shows it under test.

One of the reasons for using weights is to provide the same force no matter what the temperature and thus the expansion/contraction of the wire. Obviously this is only true within the limits the weights can move.

[damduck-egg]

Have got a section of aerial mast in the right shape with an attached mounting ,obviously it is bulkier but painting it a dark colour will tone its appearance down. May well do till I get the type I wanted. The ali mast won't be as strong but the cable span is only 6ft. I'm actually mounting a satellite dish on the garden shed and running the coax to the house. This will let me align with the satellite without having it on the front of the house or high up on the chimney which would mean getting ladders etc.

Brick, enough clearance to let most people pass underneath without ducking so about 7ft. I only need another 6" and in truth there are various ways to achieve it but the tidiest would be the phone wire extended bracket.

G.Harman

[Andy Dingley]

No, it will start to approximate a parabola, more than a catenary (which you'd need to measure to tell apart anyway, but...)

As you rightly say though, nothing is going to pull perfectly straight unless you use Mathematician's Light Inextensible String. This is why attempts to achieve it are doomed - to get anywhere near it requires ridiculous tensions, quite likely to break stuff. That's before you worry about thermal expansion too.

[Andy Dingley]

Wasn't this one of the problems with the TGV? A power car at each end of the train runs into problems because the first pantograph shakes a wave into the cable and the second powercar's pantograph has a terrible time trying to maintain contact with it. The TGV solution was to only use a single pantograph, which then requires power cabling the length of the train.

[David Hansen]

On Sat, 24 Jan 2009 16:48:03 -0800 (PST) someone who may be Andy Dingley wrote this:-

A pantograph does set up waves in the overhead, which need to be damped if a second pantograph is to make good contact. This depends on the speed, amongst other things, so there is no great problem with two locomotives at 75mph or two or more multiple units at

100mph (the pantographs are further apart with these so there is time for the damping to take place). At higher speeds a more stable contact wire is necessary and even having a pantograph at each end of the train gives rise to the problem.

There are three solutions:

1) brute force. This was the Japanese approach with the first generations of Shinkansen.

2) put the pantograph and power cars in the middle of the train, with a bus connection between them, or put the power car/locomotive at one end of the train. This was the British approach, largely due to 25kV bus lines being banned between passenger vehicles.

3) put the power cars at both ends, or distribute the power throughout the train and feed them from one pantograph via a bus line. The most well known example is the TGV, but the ban in Britain has now been withdrawn and Pendolino trains have this.

[David Hansen]

On Sat, 24 Jan 2009 17:21:08 +0000 someone who may be [e-mail] wrote this:-

That's good, things can be mounted on it firmly.

For a small distance that sounds by far the best solution. I wondered whether the required height was nearer a metre.