Restrictions on Multiple Working Length

[Lucy1501]

When browsing Wikipedia and other sources I often find that multiple working is limited by a number of units, e.g. a Class 755 can only work in multiple with three total units.

I’m curious as to what the reason is for this restriction - does signal strength weaken between units? Is it a case of not being tested due to the unlikelihood of longer formations running?

On a somewhat frivolous note, theoretically would it be possible to have every single sprinter, pacer and turbo star in operation couple together and it work just fine?

 

[DanNCL]

On a somewhat frivolous note, theoretically would it be possible to have every single sprinter, pacer and turbo star in operation couple together and it work just fine?

For Pacers and Sprinters there’s a maximum of six cabs that can be in one consist. The issue is power related, someone else can probably explain in much more detail than I can.

Theoretically they could all be mechanically coupled in one consist, but it wouldn’t work.

 

[aleggatta]

On DMUs the limitation is generally down to the control circuits being 24v (engine battery voltage). Because the control voltage is so low it’s very easy to end up with not enough volts to trigger relays/contactors on longer consists.

With modern units it normally comes down to software, electric units have higher control circuit voltage (normally 110v) so generally any limitations are software rather than physical. That being said I’m not sure the local electrical control room would appreciate a 24/36 car electric unit appearing that lacks any sort of power limiter, even just in notch 1!

 

[CDM]

BR Era AC Tightlock EMU's could run up to 16-Car (4x 4-Cars) in ECS, or 12-Car in Service.
Limiting factor is voltage drop on the control wires/brake circuits if the train consist goes over that.
There's also infrastructure limits that affect it (maximum current draw from the OLE and pan bounce when you have too many pantographs in close succession).

Modern multiple units, you run into 'computer says no' scenario's (won't recognise more than 'x' number of units because people chose not to programme and test for consists over a certain length).

 

[Lucy1501]

BR Era AC Tightlock EMU's could run up to 16-Car (4x 4-Cars) in ECS, or 12-Car in Service.

I’m assuming fewer cars in service is due to increased power load due to stuff like air conditioning, passenger cabin lighting, etc, right?

pan bounce when you have too many pantographs in close succession).

Mind explaining what pan bounce is?

 

[newtownmgr]

Maximum 12 vehicles. Continuity of train wire 4 (Emergency Brake) & electrical signal can’t be guaranteed beyond that.

 

[Nick Ashwell]

Mind explaining what pan bounce is?

From an engineering POV rather than purely railways, pantographs move the wire, hence why they will only use, for example, the outer two on a pair of 80x. Too much bounce is dangerous as it can cause dewirement or the pantos losing contact

 

[D365]

Maximum 12 vehicles. Continuity of train wire 4 (Emergency Brake) & electrical signal can’t be guaranteed beyond that.

Depends which multiple working system you are referring to... Sprinters don't strictly have an 'emergency' wire!

 

[edwin_m]

From an engineering POV rather than purely railways, pantographs move the wire, hence why they will only use, for example, the outer two on a pair of 80x. Too much bounce is dangerous as it can cause dewirement or the pantos losing contact

Bounce is more of a problem at higher speeds. "Normal" EMUs have one pantograph near the middle of the unit, and are long enough that pan bounce isn't a problem when two or more are coupled together and running at their maximum speed, whichever way round they are. I think that's why no 3-car AC EMU has ever been allowed faster than 75mph (Edit: yes it has, see below) but 4-car units can run up to 110mph. Faster than that your're into the 80x situation described above.

First generation DMUs had a panel in the cab with rows of 3 lights - 6 rows on all classes I think. Due to some clever wiring through the jumper cables, these could display the status of both engines and the transmission on up to 6 power cars, so I presume that would be the limit for the train formation.

 

[driver9000]

For Pacers and Sprinters there’s a maximum of six cabs that can be in one consist. The issue is power related, someone else can probably explain in much more detail than I can.

Theoretically they could all be mechanically coupled in one consist, but it wouldn’t work.

It was 8 vehicles for 14x and 12 for 15x. A 153 counted as 2 vehicles.

 

[pokemonsuper9]

I think that's why no 3-car AC EMU has ever been allowed faster than 75mph

Am I misunderstanding you or do 331/0s at 100mph (among others) provide exceptions to that rule

 

[Shaw S Hunter]

Am I misunderstanding you or do 331/0s at 100mph (among others) provide exceptions to that rule

Likewise 323s are 90mph units.

 

[D365]

And Class 318/320.

 

[edwin_m]

Am I misunderstanding you or do 331/0s at 100mph (among others) provide exceptions to that rule

Likewise 323s are 90mph units.

And Class 318/320.

I sort of knew someone would point out an exception when I posted that... I didn't expect three though.

 

[InkyScrolls]

I sort of knew someone would point out an exception when I posted that... I didn't expect three though.

Also the 333s when new.

 

[Wyrleybart]

Maximum 12 vehicles. Continuity of train wire 4 (Emergency Brake) & electrical signal can’t be guaranteed beyond that.

This is not totally the case though.
There are a couple of daily diagrams for XC voyagers from and to Central Rivers formed of triples. They are generally any combination of 5car + 5car + 4car equalling 14cars only because it is very messy trying to get 15 x 23m onto a platform at New St.

IIRC the Virgin "crowdbuster" trains via Banbury were diagrammed for triple 5 car 221s in passenger service but don't think AWC run any triples.

== Doublepost prevention - post automatically merged: 6 Apr 2023 ==

Back in the olden days of vaccy DMUs we used to put together a 12 car formation to run the Saturday "Butlins change" train from Penychain near Pwllheli. It was 6x2 car DMUs and we had to check that either end cab had six sets of panel lights to the driver's left hand side. These panels had a bulb for each engine and an "air and axle" light in between so would need to have displayed 12 engines and six transmissions for the power trailer sets. I never found a DMU cab with just four sets of lights, but the chargeman back in 1978 believed there were some. The 2 car DMUs we had were generally classes 101 103 and 108.

 

[newtownmgr]

This is not totally the case though.
There are a couple of daily diagrams for XC voyagers from and to Central Rivers formed of triples. They are generally any combination of 5car + 5car + 4car equalling 14cars only because it is very messy trying to get 15 x 23m onto a platform at New St.

IIRC the Virgin "crowdbuster" trains via Banbury were diagrammed for triple 5 car 221s in passenger service but don't think AWC run any triples.

== Doublepost prevention - post automatically merged: 6 Apr 2023 ==

Back in the olden days of vaccy DMUs we used to put together a 12 car formation to run the Saturday "Butlins change" train from Penychain near Pwllheli. It was 6x2 car DMUs and we had to check that either end cab had six sets of panel lights to the driver's left hand side. These panels had a bulb for each engine and an "air and axle" light in between so would need to have displayed 12 engines and six transmissions for the power trailer sets. I never found a DMU cab with just four sets of lights, but the chargeman back in 1978 believed there were some. The 2 car DMUs we had were generally classes 101 103 and 108.

So why does my companies policy & regs state max 12 vehicles. Might be different regs for Voyagers or dispensation given. I’ve never worked more than 12 be it in service or ECS & be it first gen or 2nd gen units etc

 

[Trainbike46]

So why does my companies policy & regs state max 12 vehicles. Might be different regs for Voyagers or dispensation given. I’ve never worked more than 12 be it in service or ECS & be it first gen or 2nd gen units etc

possibly platform lengths in your area? For electric units, current draw could also play a role?

Depending on whether you count the sleeper service, but that runs up to 16 cars in length.

And I'm pretty sure the 745s and 755s are allowed to run coupled together for rescue purposes (though not in service!), though I'm not 100% sure on that one

 

[newtownmgr]

Coaching stock as always been different. It’s down to cabs & other things.

 

[matchmaker]

Likewise 323s are 90mph units.

380/0 and 385/0 are 100mph.

 

[XAM2175]

The ORR sets these on newer units as part of their interoperability authorisation process. I half suspect it's also based on what was actually asked for and tested by the TOC sponsoring the authorisation - for example, the Class 397 authorisation specifically says that operating several units together isn't permitted because multiple-pantograph operation hasn't yet been tested.

Class 196 has one of the more curious ones; up to four units in multiple but no more than eight vehicles in total - unless it's ECS, where the limit is four units of up to ten vehicles total.

 

[Trainbike46]

380/0 and 385/0 are 100mph.

as are the 755/3s!

 

[Merle Haggard]

Back in the olden days of vaccy DMUs we used to put together a 12 car formation to run the Saturday "Butlins change" train from Penychain near Pwllheli. It was 6x2 car DMUs and we had to check that either end cab had six sets of panel lights to the driver's left hand side. These panels had a bulb for each engine and an "air and axle" light in between so would need to have displayed 12 engines and six transmissions for the power trailer sets. I never found a DMU cab with just four sets of lights, but the chargeman back in 1978 believed there were some. The 2 car DMUs we had were generally classes 101 103 and 108.

On the question of only 4 lights, could these have been the original lightweights (yellow diamond, 79nnn)? I remember reading long ago that the relays on these sets in multiple were all powered from the batteries on the car which had the driver in and this limited the number of engines that could be controlled.

As an aside, and with reference to the 3x221 trains via Chiltern to Euston; interestingly, the coach lettering coped so that the end coach actually displayed 'Coach Q' on the screen. I did take a photo, seems remarkable - letters 'I' and 'O' were presumably omitted as Q is the 17th letter.

 

[driver9000]

The ORR sets these on newer units as part of their interoperability authorisation process. I half suspect it's also based on what was actually asked for and tested by the TOC sponsoring the authorisation - for example, the Class 397 authorisation specifically says that operating several units together isn't permitted because multiple-pantograph operation hasn't yet been tested.

397s running in multiple with various pantograph configurations were certainly tested during 2019. In normal operation 2 sets can be coupled together to make a 10 car train but they have never run in service in pairs.

 

[XAM2175]

397s running in multiple with various pantograph configurations were certainly tested during 2019. In normal operation 2 sets can be coupled together to make a 10 car train but they have never run in service in pairs.

Ah, sorry, I meant to say "hadn't yet been tested" - the authorisation letter is dated 19 July 2019.

 

[Doomotron]

Something that could be relevant...

This is a video of a 23-coach Class 375 formation to rescue a set that lost its third rail shoes. According to the uploader in the comments the rear 3 coaches were the only ones providing any power, but the whole train was connected electronically once the MITRAC system had been tricked into thinking it was just a 12-coach set.

 

[Deepgreen]

Something that could be relevant...

This is a video of a 23-coach Class 375 formation to rescue a set that lost its third rail shoes. According to the uploader in the comments the rear 3 coaches were the only ones providing any power, but the whole train was connected electronically once the MITRAC system had been tricked into thinking it was just a 12-coach set.

While it's not impossible I find it very hard to imagine that a 3 car unit could move 23 cars! The tractive effort would simply not be enough, surely?

 

[Doomotron]

While it's not impossible I find it very hard to imagine that a 3 car unit could move 23 cars! The tractive effort would simply not be enough, surely?

It was, and the train even got up to line speed. Not sure where or how fast (I doubt it got up to the 100mph line speed to the east of Tonbridge for example) but I suspect it got to line speed very slowly!

 

[Deepgreen]

As a slight aside, the SR 4SUBs always ran in a maximum of 8 car rakes, except on Summer Saturdays in the 1950s when 12 car formations were used to Brighton. I believe these were the only passenger workings ever to see 12SUBs. A couple of decades later the Brighton bike ride returns were 12EPB, also never seen in normal service.

 

[REVUpminster]

I might be wrong as it's along time ago, but didn't C2C when running 12 car trains (3 units) require a second man in the rear unit. These train are one person operated with no inter connections. Maybe a reason that10 car trains (2 units are planned for the future.