Here is how it works (I sign 171s):
The conductor's panels on a 4-coach 171 (/8) are arranged like this:
Code:
<=== Vehicle 1 === === Vehicle 2 === === Vehicle 3 === === Vehicle 4 ===>
Cab(P) - V1 - V2(P) V1 - V2(P) V1(P) - V2 V1(P) - V2 - Cab(P)
Vestibule = V - number is indicative only
(P) = Panel in this location
For a 2-coach 171/7, then you just need to remove Vehicles 2 & 3 from the above diagram; the end coaches remain the same from this perspective.
By vehicle we mean coach; in this case, per the technical manuals, "vehicle" is mostly used.
The conductor's panels are arranged around a single vestibule in each vehicle. As you can see, the formation is symmetrical, so there are panels in both cabs, at the furthest end from the cab on those vehicles, and in the middle vehicles (where applicable) they are both towards the middle of the train.
The correct way of putting it is that the doors will open on any vehicle if the "release" buttons are pushed and the panel is powered up (conductor's key in). However, if the Door Deselect button is pushed [when the train is under 4mph] then the Door Deselect light will activate on the panels on both sides of the vehicle in which it is pushed. This indication shows that the door release buttons on the appropriate side will either:
1. Release the doors on that
vehicle only, if there is no "active cab" with a driver's key on.
Or:
2. Release all the doors on that
vehicle and all other vehicles through to the one in which there is an active cab.
Door Deselect should be named Vehicle Deselect. It isn't. This is probably to try to add a visual reminder on the control panel that this is effectively a form of Selective Door Operation, which is what this sort of thing is called in the classroom training.
(Mysterious and terrible things happen if you try to activate 2 cabs, if you try to move without reaching 4mph and then select different vehicles to deselect, or in other strange scenarios which we won't look at here.)
Therefore, assuming normal operations, say we arrive at Crowborough in six-coach formation. This can be 3x 171/7s or, more likely, 1x 171/7 and 1x 171/8.
The conductor will be in the rear unit as per the regulations for this station. They will use the conductor's panels in any one of the vehicles of that unit, including either of the cabs, to open all the doors subject to their safety checks. Crowborough station platforms are six coaches long and therefore there is no need to be in the rearmost platformed vehicle to open only the doors from there to the active cab. The Door Deselect button will not be pushed. Door Deselect would happen at this station in an 8+ coach 171 formation only.
If we then dispatch and arrive at Eridge, the platform on the mainline side is 5 coaches long. The conductor must release the doors on any formation of six coaches and above by using Door Deselect and release. This means they must be in the rearmost platformed vehicle and use the Door Deselect button before releasing the doors (subject to safety checks which we are omitting for clarity). Doors other than the conductor's local door are always released per
vehicle on a 171 and not per door. This means that if the only conductor's panel in the 5th coach is at the London end of the train, but there is still a door at the country end which is in that vehicle, then upon operation of the Door Deselect button and releasing the doors, that door should also open.
The confusion lies in the distinction between doors and vehicles. Except for the conductor's local door operation (used for the safety checks at the start and end of dispatch), it is irrelevant where in the vehicle they release the doors, so long as it is the correct vehicle.
However, if it is a quiet station (such as, say, Ashurst), the whole door opening and dispatch procedure is sometimes very brief. By the time the doors are released and then closed, anyone in a coach not platformed may walk/run down the train and only arrive at the first door on the platform just as the train is about to leave. Due to the position of the conductor's panels, this may mean that only the local door at the other end of the vehicle is open (and indeed just closing), so it looks like the doors did not release at one end. This would not be the case.
