Multiple tracks

 

On main lines the overhead for each track is isolated from the others. This is not normally a problem for twin track where cantilevers are used, as they do not touch each other. Where more than 2 tracks are in use then the structure the overhead is supported on needs maintain that isolation for each contact wire above its respective track. Cantilever mast with arms on both sides are used were the loading is light, examples being sidings and slow speed areas. Normally transverse structure is used on mainlines.

 

With Mk 1 OHLE this would take the form of a lattice portal frame, different sizes of frame were used depending on the loading. The width of the portal depends on the number of tracks and trackside obstacles or services, they normally span no more than six tracks without an additional upright support.

 

Mk 3 equipment mainly uses headspan on multiple tracks, this is less unsightly than Mk 1 portal. Portal supports are used in places of high loadings, there are many variations on portal designs but they all use the same support arms that are found on headspans. Headspan like portal is variable in width and does not span more than six tracks.

 

With both designs of equipment the same rules as with cantilevers apply regarding contact wire length, mast spacing, stagger, wire height etc.

 

Portal and to a lesser extent headspan can be found on twin track. Areas like station platforms, viaducts and overbridges are examples where they are to be found. It is also common to use portal equipment for specialist mast.

 

With curved multiple track, like twin track the stagger is set to the outside of the curve and can be up to 380mm (15inches).