Stations
Stations present a problem if using standard cantilever mast. The insulators are at the mast ends of the arms. Making the arms live. In this situation it would mean live equipment over platforms if standard masts were used. For passenger safety there are several solutions. With Mk1 systems the usual method is to use portal mast and where necessary a special type of fixing on the end of the insulator holding the registration arm.
On some lines the use of negative stagger registration arms keeps the live equipment away from the platform.
Where Mk3 has been employed there have been different approaches on differing lines. The Great Northern Suburban electrification used some very tall cantilevers.
Other overhead projects have produced other designs, including several special cantilevers. In many places where Mk3 is system employed twin track headspan is used. When headspan is employed there are insulators in line with the platform edge, this ensures that there are no live wires above the platforms.
Stations often have footbridges linking one platform to the other, this means that the catenery and contact wire have to be lowered to fit under the bridge. Causing the mast to be combination of station type mast and reduced encumbrance designs.
The Glasgow suburban lines have at many of the older stations used the platform canopies to fix the registration arms on.
Bay and loop platforms sometimes produce some differing types of mast.
The combination of curved tracks going through a station and an over bridge appears frequently on model railways and the prototype.
On the Liverpool Street to Shenfield line the contact wire was raised to 20ft in stations where steam locomotives would be likely to take on water. I have quite a bit of personal experience travelling on this line and cannot find any location, which suggest that this higher level for the contact wire is still in place except Ilford EMU sheds. I think when the older 1500v dc was converted to 6.25Kv ac it was lowered.
It is very rare to have wires terminating on platform masts; I cannot find a location where there are balance weights on a platform. Sometimes a mast will be used to terminate a fixed tension wire there will be an insulator between the last supporting mast and where the wire crosses the platform edge, like with headspan the wire there is no live wire over the platform.
Normally if there is a siding point or crossover at the end of the platform where the wire could not be terminated before the start of the platform, the wire is taken trough the station as an out of running wire on the structures supporting registration. It is then terminated the other end of the station clear of the platform. Heavy weight portals are used to terminate fixed tension wires in some stations where Mk1 equipment is used. Combinations of lower encumbrance and out of running wire supports are more common in station areas and appear very complicated.
At larger stations on the Euston to Liverpool and Manchester system where the speed of the trains is slower a different type of arm is to be found on the portals. Heavier portals also seem to be used.
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