Pointwork

Points and Crossovers

 

As modellers we like to be able to change the direction our trains are going.  Even modern layouts tend to be well off for point work. Our electric trains need to have the overhead above them when changing direction.

 

Crossovers

 

I will deal with these first.  Mk1 and Mk3 equipment differed slightly but the principal is the same. The crossover wire has a fixed end and a balanced end if automatic tensioned equipment. Fixed tension has two fixed ends. These terminating mast are the outer two. The next masts are those that are positioned over the toe of the points. This mast has two registration arms or on portal have registration arms with a hinge where one of the contact wires runs.  They are set up with opposite staggers so the mainline contact wire is in the pull off position and the crossover wire in the pull off. The crossover wire goes over the top of the mainline wire where they cross. With Mark 1 equipment there is a central mast supporting the cross over wire above the centre of the crossover track.

 

Crossovers with Mk3 equipment do not have the cental mast.

To maintain the independence of electrical supply of both main lines there is an isolator on the crossover wire. There have been several designs of these over the years and differing designs depending on the speeds of the trains.
 

 

Sidings

 

These are wired similar to crossovers. Normally at the buffer end of the siding is the fixed terminating mast. The balance weights are found on a mast on the running line. The mast carrying the two registration arms is the opposite way round to a crossover. The siding wire is supported in the pull off position and the running line in the push off. Like with a crossover the siding wire goes over the main line wire.  Some sidings can be isolated, these will have an isolator close to a registration arm and the mast supporting that arm will have the switchgear to isolate the siding.  Where there is a series of sidings the wires for these may be carried as out of running wires until they are above the point relating to their siding when they become contact wires. In some locations they are registered before the point on the hinged registration arms. There is not always the need to electrically isolate siding wires from each other so there will be no insulators between the wires of adjacent tracks. 

 

The terminating points for the wires are not always on mast supporting catenary wires. Both balance weights and fixed terminal points are found on independent mast. Fixed terminal mast may have several wires on them. In some locations, mainly Mk1 or converted 1500dc equipment the wires are terminated on heavy portal mast.

 

On 1500v dc systems knuckle spacers seem to have been used rather than the wires crossing each other above the point. When converted to 6.25v ac the Shenfield equipment retained this feature. It was changed when the mast were rewired for 25Kv ac.

 

Diamond crossings and slips.

 

There seem to be no hard and fast rules about these when it comes to how the contact wire runs over diamond crossings and slips. In some locations the two wires cross over each other in others there is a knuckle spacer and the wires changes direction.