eastanglianrailways.myfreeforum.org

nebulaman · Site Admin Joined: 29 Jan 2007 Posts: 188

Made up of the following equipment:

Stanchion: The upright posts that hold everything off the ground.
Registration arm: Holds the wires over the track and away from the stanchion.
Catenary wire: Top wire.
Dropper: Holds the Contact wire to the Catenary wire.
Contact wire: The wire the train's pantograph is in contact with.
Red Bond: A small wire that Earths the stanchion to the running rail.
Return wire: The wire that runs along the outside of the stanchion parallel to the contact and catenary wires. This basically provides a closed circuit.
Insulators: The glass or porcelain disks that insulate the live equipment from the stanchions.

OHLE MUST BE CONCIDERED LIVE AT ALL TIMES!!! Do not touch any detached equipment of anything in contact with or near to the overheads. The equipment is live at 25,000Vac and will cook you in seconds.

The return conductor is live only when a train is in section but must be treated as live at all times. The voltage here is around 1000v but the amperage is the same as the main wires, again it WILL kill.

Due to voltage drops sections of OHLE must be provided. As they can be powered by different power stations the AC voltage would be out of phase. If they were joined up it would cause a loud bang. Therfore the sections are separted by a neutral section. It consists of a dead bit of wire that trains coast through.

Even when the OHLE is turned off the Earth's magnetic field induces a current in the wire. It is of the order of 200V. The current is not of killer proportions but would give a nasty tickle if touched. The section must be Earthed if being worked upon. It is earthed by placing bonds at areas signed by DEP (Designated Earthing Points). It also acts as a safety precaution in case the juice is turned on while being worked upon. It would trip the circuit breakers at the Electrical Control Operator's desk (ECO).

If you see a person or object in contact or near to the OHLE NEVER TOUCH OR APPROACH AS 25KV DOES JUMP!!! Intstead call the emergency services or advise rail staff who will arrange the assistance.

memorex · Joined: 31 Jan 2007 Posts: 50

Aye. At St Pancras I was told ALL power cables were LIVE with 25kv.... scared the shit out of me to see someone reaching up to one with a metal pole to one on PF18!

nebulaman · Site Admin Joined: 29 Jan 2007 Posts: 188

At Crown Point we had contractors working on the roof. They were lowering scaffolding poles down. One of them swung out and hit the OHLE! Fortunatley the cleaners in the shed had taken an Isolation and so the line was dead. The contractors had not asked for one so had it been another day there would have been a rather crispy scaffolder.