How many cars are typically powered in a multiple unit?

[railfan458sw]

For example with the class 317 or 700 does the 1st car pull the whole train and all the other carriages have no power to pull? Or another example - the class 801, how do they move? Do they only have one car pulling ie the end car?

 

[DanNCL]

For example with the class 317 or 700 does the 1st car pull the whole train and all the other carriages have no power to pull? Or another example - the class 801, how do they move? Do they only have one car pulling ie the end car?

That varies from unit to unit. Most Electric units have both motor (powered) and trailer (unpowered) carriages, diesel units generally have all carriages powered.

A 317 (this also applies to 319s, 321s, 322s, 325s and 455s) is formed Trailer - Motor - Trailer - Trailer.

A 9 car 800/801/802 is formed Trailer - Motor - Motor - Trailer - Motor - Trailer - Motor - Motor - Trailer. A 5 car 800/801/802/803 is formed Trailer - Motor - Motor - Motor - Trailer.

An 8 car 700 is formed Motor - Trailer - Motor - Trailer - Trailer - Motor - Trailer - Motor. A 12 car 700 is formed Motor - Trailer - Motor - Motor - Trailer - Trailer - Trailer - Trailer - Motor - Motor - Trailer - Motor.

 

[Ken H]

For example with the class 317 or 700 does the 1st car pull the whole train and all the other carriages have no power to pull? Or another example - the class 801, how do they move? Do they only have one car pulling ie the end car?

The kit in the drivers cab is called the 'master controller'. When a driver changes the position of the controller, it sends messages down train wires to the traction equipment on the train. They then all act in the same way to make the train go.

That varies from unit to unit. Most Electric units have both motor (powered) and trailer (unpowered) carriages, diesel units generally have all carriages powered.

A 317 (this also applies to 319s, 321s, 322s, 325s and 455s) is formed Trailer - Motor - Trailer - Trailer.

A 9 car 800/801/802 is formed Trailer - Motor - Motor - Trailer - Motor - Trailer - Motor - Motor - Trailer. A 5 car 800/801/802/803 is formed Trailer - Motor - Motor - Motor - Trailer.

An 8 car 700 is formed Motor - Trailer - Motor - Trailer - Trailer - Motor - Trailer - Motor. A 12 car 700 is formed Motor - Trailer - Motor - Motor - Trailer - Trailer - Trailer - Trailer - Motor - Motor - Trailer - Motor.

You have chosen an old example for an EMU. With better power electronics and AC motors, most newer emus have far more axles motored. More motors means better adhesion so quicker acceleration and more regeneration.

 

[skyhigh]

You have chosen an old example for an EMU. With better power electronics and AC motors, most newer emus have far more axles motored. More motors means better adhesion so quicker acceleration and more regeneration.

Those were the classes the OP asked about though.

 

[edwin_m]

The kit in the drivers cab is called the 'master controller'. When a driver changes the position of the controller, it sends messages down train wires to the traction equipment on the train. They then all act in the same way to make the train go.

And indeed if compatible multiple units are coupled together, the driver controls the motors in the coupled unit too. So, unlike locomotive hauled trains, longer trains of multiple units have the same power to weight ratio and generally can meet the same point to point timings.

 

[norbitonflyer]

For example with the class 317 or 700 does the 1st car pull the whole train and all the other carriages have no power to pull? Or another example - the class 801, how do they move? Do they only have one car pulling ie the end car?

In most modern units, including the examples you give, the lead car does no pulling at all. Most electric units built since 1960 have an unpowered vehicle at the front (and back). The standard arrangement for most BR-era ac units, and DC units from the Class 42x range onwards, was to have a single power car in the middle of a 3- or 4-car unit. This helps traction as the unpowered wheels help "clean" the track before the powered wheels reach it. It was noticeable that in icy conditions the old Bournemouth electrics, instead of the normal formation 8TC + 4REP (T-T-T-T + T-T-T-T + M-T-T-M) with the REP at the London end, would be formed with the REP in the middle of the formation. This worked because in the winter only one TC unit continued to Weymouth behind a 33: a 33 would have struggled with eight on and a full heating load.

Older units (Class 41x) and the PEP family (313/4/5, 507/8) did have the powered cars at the ends

 

[Domh245]

In most modern units, including the examples you give, the lead car does no pulling at all. Most electric units built since 1960 have an unpowered vehicle at the front (and back). The standard arrangement for most BR-era ac units, and DC units from the Class 42x range onwards, was to have a single power car in the middle of a 3- or 4-car unit. This helps traction as the unpowered wheels help "clean" the track before the powered wheels reach it. It was noticeable that in icy conditions the old Bournemouth electrics, instead of the normal formation 8TC + 4REP (T-T-T-T + T-T-T-T + M-T-T-M) with the REP at the London end, would be formed with the REP in the middle of the formation. This worked because in the winter only one TC unit continued to Weymouth behind a 33: a 33 would have struggled with eight on and a full heating load.

Older units (Class 41x) and the PEP family (313/4/5, 507/8) did have the powered cars at the ends

This held true until about the 1990s - Networkers and pretty much all subsequent stock (Electrostars, Desiros classic & city, civity, juniper, etc) have had driving motors, the only exceptions that come to mind are the 80x, the 395s, and some of the Aventra family which will 'cross-feed' traction power between cars, blurring the lines of traditional motor-cars

 

[XAM2175]

Most electric units built since 1960 have an unpowered vehicle at the front (and back). The standard arrangement for most BR-era ac units, and DC units from the Class 42x range onwards, was to have a single power car in the middle of a 3- or 4-car unit.

That was BR's convention, yes, but most manufacturers have since gone back on it. Siemens convention on all UK Desiros is to use driving motors and intermediate trailers, and only to start inserting intermediate motors when above five-car lengths (with an exception being the 717s having one intermediate motor). Most, if not all, Electrostars also use driving motors, as do Hitachi's 385s, and CAF's 331s and 397s.

Alstom went off on their own direction with the Junipers and only fitted motors to the inside-end bogies of each driving motor (458/0 UIC classification: 2'Bo'+2'2'+Bo'2'+Bo'2').

 

[Fincra5]

Depends. 700s are 50-50 Motor Coaches / Trailer Coaches...

A 377(4 car) is 3 Motor Coaches, 1 Trailer...

Older EMUs are 1 Motor Coach, 3 Trailers but then a 313 is 2 Motor, 1 Trailer...

No set rule it seems!

 

[43096]

Alstom went off on their own direction with the Junipers and only fitted motors to the inside-end bogies of each driving motor (458/0 UIC classification: 2'Bo'+2'2'+Bo'2'+Bo'2').

Bombardier went in the same direction with the majority of the Electrostars.

 

[100andthirty]

In most modern units, including the examples you give, the lead car does no pulling at all. Most electric units built since 1960 have an unpowered vehicle at the front (and back). The standard arrangement for most BR-era ac units, and DC units from the Class 42x range onwards, was to have a single power car in the middle of a 3- or 4-car unit. This helps traction as the unpowered wheels help "clean" the track before the powered wheels reach it. It was noticeable that in icy conditions the old Bournemouth electrics, instead of the normal formation 8TC + 4REP (T-T-T-T + T-T-T-T + M-T-T-M) with the REP at the London end, would be formed with the REP in the middle of the formation. This worked because in the winter only one TC unit continued to Weymouth behind a 33: a 33 would have struggled with eight on and a full heating load.

Older units (Class 41x) and the PEP family (313/4/5, 507/8) did have the powered cars at the ends

This is not exactly true. All the trains supplied by Siemens (350, 380, 444, 450, 700, 707, 717) have their end cars powered. Electrostar trains have the end cars powered too. For the Aventra series some have power cars at each end, and at least one version has a trailer car at one end and a motor car at the other.

It was the later mk1 carriage based EMUs, CIG/VEP and the later mk3 carriage based designs that had trailer end vehicles. The discussion about adhesion really only works for these designs. The merits of having just two bogies providing the tractive effort for a 4-car set, are much less relevant in today's world where higher performance is required and sanders help with adhesion.

 

[Taunton]

There have been a range of approaches over time, enough to say that there is probably no golden advantage of any one over the other.

Call me a reactionary, but I've never particularly liked lightweight non-powered cars at the front, with heavier powered ones pushing from behind. There seem to have been a number of high speed accidents where an unpowered front car striking an obstruction - car, or cattle - has led a significant derailment (Lockington, Polmont, Great Heck) where one just has to wonder what might have happened if the formation was the other way round.

Classic diesel multiple units were commonly formed half-and-half with power cars and trailers, the former typically had two underfloor engines, driving the inner wheels of the two bogies. It seemed like an idea to build them all powered, with just one engine each, instead, and Cravens built a large batch of these. They were a considerable failure, and didn't last long, one of the issues was with two of everything the power cars had been nicely balanced for weight etc at each end. With just one it was unbalanced, resonance set in, and there were a range of other problems.

 

[mcnw35282]

In a class 507/508, the end cars are powered, the centre car is not.

 

[edwin_m]

Call me a reactionary, but I've never particularly liked lightweight non-powered cars at the front, with heavier powered ones pushing from behind. There seem to have been a number of high speed accidents where an unpowered front car striking an obstruction - car, or cattle - has led a significant derailment (Lockington, Polmont, Great Heck) where one just has to wonder what might have happened if the formation was the other way round.

I'd say there was a big difference between a push-pull with a loco on the rear and a multiple unit in this respect. The train that derailed at Polmont had a Class 47 on the rear (112 tonnes) and the leading vehicle was a mk2, can't immediately find a reference for its weight but probably less than 35 tonnes. So a sudden deceleration at the front would set up some significant compressive forces, creating a risk of jack-knifing.

Nor can I find per-car weights for a 317, but Wikipedia has individual axle loads for a 319 and figure for the car with transformer and motors is only 60% more than that of the heaviest non-motorised car. The discrepancy may be slightly more for a 317 as that has less equipment (eg no shoegear) on the non-motor cars, but still nowhere near as much as with the push-pull.

Classic diesel multiple units were commonly formed half-and-half with power cars and trailers, the former typically had two underfloor engines, driving the inner wheels of the two bogies. It seemed like an idea to build them all powered, with just one engine each, instead, and Cravens built a large batch of these. They were a considerable failure, and didn't last long, one of the issues was with two of everything the power cars had been nicely balanced for weight etc at each end. With just one it was unbalanced, resonance set in, and there were a range of other problems.

However all the Sprinter and subsequent classes have one engine per car, driving both axles of one bogie.

 

[100andthirty]

I'd say there was a big difference between a push-pull with a loco on the rear and a multiple unit in this respect. The train that derailed at Polmont had a Class 47 on the rear (112 tonnes) and the leading vehicle was a mk2, can't immediately find a reference for its weight but probably less than 35 tonnes. So a sudden deceleration at the front would set up some significant compressive forces, creating a risk of jack-knifing.

Nor can I find per-car weights for a 317, but Wikipedia has individual axle loads for a 319 and figure for the car with transformer and motors is only 60% more than that of the heaviest non-motorised car. The discrepancy may be slightly more for a 317 as that has less equipment (eg no shoegear) on the non-motor cars, but still nowhere near as much as with the push-pull.

However all the Sprinter and subsequent classes have one engine per car, driving both axles of one bogie.

It's best to think of a loco at the back of a push-pull set as the equivalent of a number of carriages, just in a shorter length. If the leading vehicle hits an obstruction, the combined kinetic energy of all the vehicles should swat away most obstructions. What has to be watched for is something that causes the wheels to be unloaded especially on a curve or in proximity to points.

At Polmont, the train was on a right hand curve. When it hit the cow, it appears that the leading left hand wheel managed to run over part of its carcass causing it to derail. Once derailed the wheels wanted to go straight on and after nearly 100m, the left hand wheel fell down the side of the ballast shoulder causing the vehicle to overturn (heavily summarised). It wasn't the collision, but the derailment that led to the damage and casualties.

Similarly, at Great Heck, something dislodged from the road vehicle caused the leading bogie to derail into the 6-foot. This continued for some time until the train met the turnouts when it was suddenly deflected left which caused the jack-knifing. Again, not the collision, but the derailment.

Finally at Stonehaven the landslip effectively formed a ramp which derailed the HST vehicle which was much heavier than the Polmont or Great Heck driving trailers.

I'm stressing these points as in other circumstances, trains have hit obstructions and not been derailed.

This means that it's not just the mass that matters, but the nature of the collision (eg head on or oblique) and the quality of the steel bars called lifeguards which are positioned in front of leading wheels to sweep obstructions off the track.

I' gone into some detail, as the factors in collisions are many and complex.

 

[edwin_m]

It's best to think of a loco at the back of a push-pull set as the equivalent of a number of carriages, just in a shorter length. If the leading vehicle hits an obstruction, the combined kinetic energy of all the vehicles should swat away most obstructions. What has to be watched for is something that causes the wheels to be unloaded especially on a curve or in proximity to points.

At Polmont, the train was on a right hand curve. When it hit the cow, it appears that the leading left hand wheel managed to run over part of its carcass causing it to derail. Once derailed the wheels wanted to go straight on and after nearly 100m, the left hand wheel fell down the side of the ballast shoulder causing the vehicle to overturn (heavily summarised). It wasn't the collision, but the derailment that led to the damage and casualties.

Similarly, at Great Heck, something dislodged from the road vehicle caused the leading bogie to derail into the 6-foot. This continued for some time until the train met the turnouts when it was suddenly deflected left which caused the jack-knifing. Again, not the collision, but the derailment.

Finally at Stonehaven the landslip effectively formed a ramp which derailed the HST vehicle which was much heavier than the Polmont or Great Heck driving trailers.

I'm stressing these points as in other circumstances, trains have hit obstructions and not been derailed.

This means that it's not just the mass that matters, but the nature of the collision (eg head on or oblique) and the quality of the steel bars called lifeguards which are positioned in front of leading wheels to sweep obstructions off the track.

I' gone into some detail, as the factors in collisions are many and complex.

Indeed. Can't disagree with any of that. A few things to add...

Concentrated weight of a locomotive at the rear is probably more dangerous in an accident than the equivalent weight of coaches, because they are separated by couplings. Even with traditional rigid bodyshells these will dissipate some of the energy from the ones further back. Stock built since the mid-1990s has "crumple zones" in the end of each car which will increase this mitigation. However, the type of head-on collision they are intended to mitigate is now very rare due to TPWS and other safety measures introduced about the same time. I don't believe crumple zones have significantly reduced the consequences of any UK accident, although they might have done so at Carmont, had it been a more modern unit that included them. On the other hand, a more modern unit would have had passengers in the leading vehicle.

At Polmont the front of the leading vehicle fetched up hard against a tree. This made it much more severe than if it had just run on and decelerated more gradually.

I had it from the head of the former BR Research that the dynamic modelling after Ufton Nervet (I think) couldn't replicate what happened until they took account of the cables that were added to prevent the bogie detaching. I think this meant that the DVT hitting the landrover lifted the body, and this in turn is what lifted the bogie off the rails. Those cables were added after Potters Bar, where some of the damage was due to bogie separation. At Great Heck the turnouts slewed the derailed passenger train into near head-on collision with the oncoming freight, and without the unfortunate coincidences of the crossover and the oncoming train it would probably have slide to a stop with much less damage.

 

[Snow1964]

The Southern region 4REPs had two motor cars at outer ends, with two (ex hauled stock) trailers between them.

However all other Southern units from 1963-75 had one motor car with 4 powered axles, so quarter of wheels were motored

The 1950s units had 2 powered bogies, but they were at outer ends (under cabs and adjacent guards van), the inner end was a unpowered bogie, so again was quarter of wheels motored

The 1930s 5 and 6 car mainline sets had 8 powered axles in 2 motor cars with 3 or 4 trailers between them.

Some of the newer generation have motored vehicles, but not all 4 axles are motored, so have to be careful as description as a motor can be partial motored

 

[contrex]

At Polmont, the train was on a right hand curve. When it hit the cow, it appears that the leading left hand wheel managed to run over part of its carcass causing it to derail.

I believe the shoulder blade of an ox was used in tests to verify the possibility after Polmont happened. I believe George Stephenson replied "Aye, for the coo", when asked at a parliamentary committee if it would be a bad thing if a train struck a cow on the line.

 

[43096]

Similarly, at Great Heck, something dislodged from the road vehicle caused the leading bogie to derail into the 6-foot. This continued for some time until the train met the turnouts when it was suddenly deflected left which caused the jack-knifing. Again, not the collision, but the derailment.

Ufton Nervet was similar.

I had it from the head of the former BR Research that the dynamic modelling after Great Heck couldn't replicate what happened until they took account of the cables that were added to prevent the bogie detaching. I think this meant that the DVT hitting the landrover lifted the body, and this in turn is what lifted the bogie off the rails. Those cables were added after Potters Bar, where some of the damage was due to bogie separation. At Great Heck the turnouts slewed the derailed passenger train into near head-on collision with the oncoming freight, and without the unfortunate coincidences of the crossover and the oncoming train it would probably have slide to a stop with much less damage.

Unless there was a clairvoyant involved, that's not the case. Great Heck was 2001, Potters Bar was 2002.

 

[edwin_m]

Unless there was a clairvoyant involved, that's not the case. Great Heck was 2001, Potters Bar was 2002.

Apologies, I may have been thinking of Ufton Nervet not Great Heck. I will edit my post.

 

[43096]

Apologies, I may have been thinking of Ufton Nervet not Great Heck. I will edit my post.

Ufton Nervet was 2004! Or could it have been Hatfield, which also involved Mark 4 stock?

 

[norbitonflyer]

It's best to think of a loco at the back of a push-pull set as the equivalent of a number of carriages, just in a shorter length. If the leading vehicle hits an obstruction, the combined kinetic energy of all the vehicles should swat away most obstructions. What has to be watched for is something that causes the wheels to be unloaded especially on a curve or in proximity to points.

At Polmont, the train was on a right hand curve. When it hit the cow, it appears that the leading left hand wheel managed to run over part of its carcass causing it to derail. Once derailed the wheels wanted to go straight on and after nearly 100m, the left hand wheel fell down the side of the ballast shoulder causing the vehicle to overturn (heavily summarised). It wasn't the collision, but the derailment that led to the damage and casualties.

Similarly, at Great Heck, something dislodged from the road vehicle caused the leading bogie to derail into the 6-foot. This continued for some time until the train met the turnouts when it was suddenly deflected left which caused the jack-knifing. Again, not the collision, but the derailment.

Finally at Stonehaven the landslip effectively formed a ramp which derailed the HST vehicle which was much heavier than the Polmont or Great Heck driving trailers.

I'm stressing these points as in other circumstances, trains have hit obstructions and not been derailed.

This means that it's not just the mass that matters, but the nature of the collision (eg head on or oblique) and the quality of the steel bars called lifeguards which are positioned in front of leading wheels to sweep obstructions off the track.

I' gone into some detail, as the factors in collisions are many and complex.

Lockington was a collision between a 1st generation DMU with a driving trailer leading, and a van. The evidence suggested the van's engine block was substantial enough to derail the leading bogie

 

[brad465]

Going by where the traction motor sounds are, 465s have both the front and back cars powered, while 466s only have one (presumably having both powered would be too much for its weight), which can ordinarily be identified as the car without the toilet in.

 

[edwin_m]

Ufton Nervet was 2004! Or could it have been Hatfield, which also involved Mark 4 stock?

So after Potters Bar, so my theory may not be correct but at least the timeline stands up this time.

 

[TommyJ]

Is there any standard way of telling from the outside of a particular coach whether it’s motored or a trailer? Does it show in the data panel at all?

 

[driver9000]

Is there any standard way of telling from the outside of a particular coach whether it’s motored or a trailer? Does it show in the data panel at all?

The data panel shows the type of vehicle so M indicates a Motor (powered) vehicle eg DMS, DMF, MS etc...

 

[ComUtoR]

Going by where the traction motor sounds are, 465s have both the front and back cars powered, while 466s only have one (presumably having both powered would be too much for its weight), which can ordinarily be identified as the car without the toilet in.

A 465 Metcam is basically 2* 466s. So a motor at both ends

 

[TommyJ]

The data panel shows the type of vehicle so M indicates a Motor (powered) vehicle eg DMS, DMF, MS etc...

Great thank you I will look out for that.

 

[Poppysdad]

This is not exactly true. All the trains supplied by Siemens (350, 380, 444, 450, 700, 707, 717) have their end cars powered. Electrostar trains have the end cars powered too. For the Aventra series some have power cars at each end, and at least one version has a trailer car at one end and a motor car at the other.

It was the later mk1 carriage based EMUs, CIG/VEP and the later mk3 carriage based designs that had trailer end vehicles. The discussion about adhesion really only works for these designs. The merits of having just two bogies providing the tractive effort for a 4-car set, are much less relevant in today's world where higher performance is required and sanders help with adhesion.

In addition one of the biggest changes with the post privatization era EMU's was that on some designs of trains the "Motor" cars only use a single powered bogie. If I remember correctly the Juniper and Electrostar Platforms from Alstom and Bombardier (Alstom) both used a single powered bogie on a motor cars whereas the Desiro Platform from Siemens used two powered bogies on a motor car.

 

[norbitonflyer]

Is there any standard way of telling from the outside of a particular coach whether it’s motored or a trailer? Does it show in the data panel at all?

Used to be by the numbers - DMU motor coaches in the 50xxx-53xxx range (plus single cars in the 55xxx range) Although the noise was the easiest way of telling. Driving trailers originally 56xxx, later 54xxx. Trailers 59xxx
EMU motors in a range starting at 61000, (except catering vehicles 69xxx) trailers and driving trailers in the 7xxxx series.

But now the numbers are all over the place