I’ve seen quite a few threads about having to isolate TPWS because of a dodgy signal and usually members will throw out a few different ideas on how to isolate TPWS. I thought I’d describe the ways here with an explanation of what situations you’d use each type of isolation for those who are curious to know and want extra immersion. I’ve used the Class 377 for pictures. This is the TPWS panel in its normal state. This is where the temporary and permanent isolations are. There are 3 ways to isolate the TPWS system. Train Stop Overide button on the TPWS panel The TPWS panel is usually right in front you and consists of 3 buttons. The yellow square* button is Train Stop Override. When pressed, the yellow square will illuminate and this will prevent a TPWS activation from happening for 20 seconds. On freight, it lasts for 60 seconds instead of 20 seconds. Once 20 seconds is over or once you’ve gone over the active TPWS grid, depending on which happens first, the light will extinguish and return to its normal state of being unlit. Scenario: You’re stopped at a red signal and the signaller tells you that you need to pass it at danger. If there is a TPWS grid on the ground by the signal, you need to press the Train Stop Override button just before you pass it. Once you’ve gone past the signal, TPWS will continue to function normally. *Ive just realised it’s a yellow circle on electrostars but it’s usually a square Train Stop Override light lit on TPWS panel Temporarily isolate TPWS This is a rocker switch usually on the backwall or secondman’s side of the cab near the isolation switches/MCBs. This is used if TPWS needs to be temporarily isolated because you’ll be performing an operational move which requires it to be isolated. Note that AWS will still continue to function normally. The rocker switch is usually secured with a cable tie which needs to be cut in order to move the rocker switch. When you’ve temporarily isolated TPWS, the yellow circle labelled “TPWS temp isolate/fault” on the TPWS panel will be lit steady yellow. In order to reinstate TPWS, move the rocker switch to Normal and the yellow light should extinguish. Scenario 1: You’ve stopped at a red signal and the signaller informs you that you need to pass multiple consecutive signals at danger because there has been a signalling failure. (This is known as Emergency Special Working or Temporary Block Working which is essentially one very long section). In this case, temporarily isolate the TPWS before you enter the affected area. Remember to reinstate TPWS when you leave the affected area. Scenario 2: You’re propelling a failed train (meaning you’re driving from the middle cab). Obviously as you’re driving 4//5/however many coaches from the front, by the time your cab goes past a signal, it will have already turned back to red which will cause a TPWS activation when your cab goes over the TPWS grids associated with the signal. Therefore, temporarily isolate TPWS. Remember to reinstate TPWS when you have finished doing the move. TPWS Temporarily isolate/fault light lit on TPWS panel Permanent isolation of TPWS This is an isolation switch and is usually located on the backwall or secondmans side of the cab. This would be used if there is a fault with the TPWS system and so it needs to be permanently isolated. To know if TPWS is faulty, the yellow circle labelled “TPWS temp isolate/fault” on the TPWS panel will be lit flashing yellow. On a lot of traction, the TPWS and AWS are connected so isolating the TPWS will also cause the AWS to be isolated. Isolating the AWS/TPWS is a big deal which is subject to speed restrictions as well as going out of service at the first available opportunity. To isolate, use the master key to turn the AWS/TPWS switch to isolate by rotating the key 90degrees clockwise. The TPWS panel would remain unlit as normal but the Safety Systems isolated button will be lit yellow which informs you that a safety system has been isolated. Red ‘safety systems isolated’ light lit In the game, you can unisolate by using the master key to rotate 90 degrees anti-clockwise to return the switch to the Normal position. However, this cannot be done in real life. Once you’ve isolated it, it’s not possible to unisolate as it requires a special key which only maintenance staff have. There is a very small hole on the bottom right of each isolation switch (you can see it in the second image) which is where this “special” key would be inserted in order to unisolate it. Scenario: Pretty straightforward really, it needs to be isolated if there is a fault with the system. This wouldn’t be done lightly though- you’d be on the call to maintenance and they would instruct you to do so if necessary.
Has anyone managed to find the rocker switch to temporarily isolate the TPWS on the Midland Mainline HST? I can’t see it anywhere. Probably looking right past it…
