I heard that this particular combination is banned because coupling to a 142 causes some fault with the fire alarms on the 170. That might equally be utter nonsense that somebody made up, though, or I might have misremembered it.
This is more what I was looking for
Thanks - a very comprehensive answer. Yes, you're right, it is fed from the rearmost vehicle. I'm not sure what happens if that battery's dead - is it fed from elsewhere in the formation, or is it just cross-fed via the remote supply on that unit? To do otherwise would seem to compromise the integrity of train wire 4.
I do remember on a depot isolating the start battery on the end vehicle on two units coupled together years ago with a trainee to try to prove that the train could still be moved because the feed for TW4 would simply be found from elsewhere in the train. I don't think there is necessarily away for us as drivers to know which start battery is being used if the rearmost is unavailable. It also begs the question as to what would happen if the engine on the rear vehicle is shut down and the battery volts dropped, is there a cut-off low voltage? 22.5v low volts protection applies to the auxiliary batteries but I'm not sure about start batteries.
That's not a regular working as per the OP, but here's a similar one from Feb. 1985 at Ashtead - 33034+EPB+CIG to Dorking.
It has to be fed from the rear of the train, though, surely? That's what ensures the integrity of train wire 4 - the supply from other vehicles in the formation is deliberately cut off when coupled to another vehicle to ensure that it has to come from the rearmost vehicle and that if the train becomes divided then that supply will be lost. My understanding is that the supply is one that can be fed via the remote supply, so if the battery on the rearmost vehicle is dead or isolated then it'll take it from the adjacent vehicle's battery via the jumper cables, but that if both vehicles on the rearmost unit are dead then you're in trouble (as there's no remote supply facility through the BSI coupler, of course).
That's exactly the situation that I found myself in with both vehicles on the rear two-car unit completely dead. I don't know if there's low voltage protection (I'm sure there must be?) or whether it was just so far gone that it couldn't even operate the relays in the circuit, but the end result was the same!
'A Merry Crompton Christmas'!
I'm making an assumption here that train wire 4 is a loop around the train capable of being energised by any one of the start batteries on the train - we were told that TW4 was the electrical equivalent of the brake pipe on an air-braked train but I rather think that's too simple a comparison
That's cool!
very interesting as a Pembrokeshire local
One of the reasons steam locos were used to haul 303s was transfers between Hyndland Depot and the Cathcart Circle. The City Union link was, and still is, unwired. The problem was that in the early days there were no air braked diesels available, so some elderly ex-Caledonian locos were retained for these duties as they still had their Westinghouse brake.
Ta, both. An interesting discussion! I'm certainly in no position to prove anyone wrong, but it would be good if someone has a definitive answer.
...and this...
I'm sure that any train crew can confirm/deny but I always thought 12 cabs was the maximum, reducing to eight cabs for formations including Pacers. I'm not sure why there is a difference. Northern definitely used to have a 4 x 142 set off Newton Heath in the afternoon.
Was the class 33 ever sandwiched between the 4TC and the leading VEP? Must have been surreal siting at the front of the VEP with the 33 thrashing away at 85 mph just outside the window.
