• Our booking engine at tickets.railforums.co.uk (powered by TrainSplit) helps support the running of the forum with every ticket purchase! Find out more and ask any questions/give us feedback in this thread!

Class 306 AC Conversion

Status
Not open for further replies.

76020

Member
Joined
1 Nov 2012
Messages
154
I know it was a long time ago and before my time I might add but does anybody know how the Shenfield Metro service was maintained when the Class 306 EMU's were converted from 1500V DC to 6.25/25KV AC. The changeover from DC to AC was over a weekend in November 1960, I think 5-6th, so were the Class 306 run as 6 car trains instead of the regular 9 car trains beforehand so that a number could be converted to AC ready for after the changeover, I guess that is the only way they could do it, or was other EMU's used on the new AC Shenfield Metro service instead.
Another question I have is does anybody know how long the conversion took as there was a lot of work required to be done with two out of the three cars having to be modified.
The other DC units running from Liverpool Street were of course the Class 307 which were all sent to Eastleigh for conversion to AC in 1960 and the then new Class 302's took their place on the Liverpool Street-Southend Victoria and Liverpool Street-Chelmsford services until their return in 1962.
The former Great Eastern Main has had three different voltages used in it's lifetime as an electric railway, 1500V DC and 6.25/25KV AC, although Shenfield-Chelmsford was converted from 1500V DC to 25KV AC from the outset, can anyboby think of another railway that has used three different power systems, anywhere in France for example.
 
Last edited:
Sponsor Post - registered members do not see these adverts; click here to register, or click here to log in
R

RailUK Forums

507020

Established Member
Joined
23 May 2021
Messages
1,859
Location
Southport
I’ve become interested in this recently. The 306s were identical to the 506s used on the Woodhead electrification to Hadfield and Glossop, being part of the same batch of LNER electrification carried out by the Eastern Region after the war and only being numbered differently under TOPS.

The conversion must have involved some sort of transformer being fitted to the units and the wires being re-energised at the new voltage, but I wish I knew about it in more detail. The 506s were scrapped when the line to Hadfield and Glossop was converted to AC rather than receiving the same conversion.

As for lines that have used 3 systems, the Manchester South Junction & Altrincham Railway was electrified in 1931 using the same 1500V DC overhead system as Shenfield and Woodhead, converted to standard 25kV 50Hz AC in 1971 by BR and then converted again to 750V DC overhead when it became part of the Metrolink. I can think of other lines that have used 3 power systems with one of them being Diesel.
 

Magdalia

Established Member
Joined
1 Jan 2022
Messages
3,011
Location
The Fens
I have never looked into this until now but a bit of research has come up with most of the answers. Sources are Railway Observer October 1960 and March 1961, plus volume 7 of Peter Kay's LTS history.

Shenfield-Chelmsford was closed to electric traction at the start of the winter timetable on 12 September 1960, with various diesel hauled services calling at Shenfield and an additional DMU shuttle service between Shenfield and Chelmsford. This timetable is what's shown in the winter 1960 ER public timetable. At least part of the DMU shuttle service was covered with DMUs borrowed from Marylebone: on 17 September 51863/59726/59746/51864 was being used. These were also used on the Southminster branch.

The class 306 units were modified at Stratford. This involved moving the pantograph, and changing LNER diamonds for Stone Faively, plus fitting of transformers and rectifiers. 30 units were fully modified in advance and the ac equipment tested on the Colchester-Clacton branch. These had a temporary "bypass" that allowed them to work on dc until the big changeover. The remaining 62 units had preparatory structural alterations for moving the pantograph but remained dc until after the big changeover.

That big changeover was on the weekend of 5 and 6 November 1960, though it was originally intended to be in August 1960. Shenfield-Chelmsford was energised at 25kv and all of Liverpool Street-Southend was 6.25kv.

From 7 November 1960 the Shenfield and Southend Victoria services were covered by the 30 converted class 306s plus a large number of class 302s built for the LTS electrification. By March 1961 more than 50 of the remaining class 306s had been modified for ac and returned to traffic, after testing between Shenfield and Chelmsford. The DMUs on loan from Marylebone returned in March 1961 but it is not clear what they were used for after 7 November 1960.

The class 307 dc to ac conversion was a bit of a nightmare, with the units not returning to traffic until 1962. Peter Kay's account suggests that they were converted at Stratford, what is the source for conversions being done at Eastleigh?

The LTS units did a lot of work on the routes to and from Liverpool Street before taking up permanent duties to and from Fenchurch Street, including covering for classes 305 and 308, but that's another story. In this respect it was just as well that the LTS electrification ran late, with a virtually full electric service not starting until June 1962.
 

Ken H

On Moderation
Joined
11 Nov 2018
Messages
6,288
Location
N Yorks
I have never looked into this until now but a bit of research has come up with most of the answers. Sources are Railway Observer October 1960 and March 1961, plus volume 7 of Peter Kay's LTS history.

Shenfield-Chelmsford was closed to electric traction at the start of the winter timetable on 12 September 1960, with various diesel hauled services calling at Shenfield and an additional DMU shuttle service between Shenfield and Chelmsford. This timetable is what's shown in the winter 1960 ER public timetable. At least part of the DMU shuttle service was covered with DMUs borrowed from Marylebone: on 17 September 51863/59726/59746/51864 was being used. These were also used on the Southminster branch.

The class 306 units were modified at Stratford. This involved moving the pantograph, and changing LNER diamonds for Stone Faively, plus fitting of transformers and rectifiers. 30 units were fully modified in advance and the ac equipment tested on the Colchester-Clacton branch. These had a temporary "bypass" that allowed them to work on dc until the big changeover. The remaining 62 units had preparatory structural alterations for moving the pantograph but remained dc until after the big changeover.

That big changeover was on the weekend of 5 and 6 November 1960, though it was originally intended to be in August 1960. Shenfield-Chelmsford was energised at 25kv and all of Liverpool Street-Southend was 6.25kv.

From 7 November 1960 the Shenfield and Southend Victoria services were covered by the 30 converted class 306s plus a large number of class 302s built for the LTS electrification. By March 1961 more than 50 of the remaining class 306s had been modified for ac and returned to traffic, after testing between Shenfield and Chelmsford. The DMUs on loan from Marylebone returned in March 1961 but it is not clear what they were used for after 7 November 1960.

The class 307 dc to ac conversion was a bit of a nightmare, with the units not returning to traffic until 1962. Peter Kay's account suggests that they were converted at Stratford, what is the source for conversions being done at Eastleigh?

The LTS units did a lot of work on the routes to and from Liverpool Street before taking up permanent duties to and from Fenchurch Street, including covering for classes 305 and 308, but that's another story. In this respect it was just as well that the LTS electrification ran late, with a virtually full electric service not starting until June 1962.
Did thy just have a transformer and rectifier supplying DC to the existing DC kit (Bit like a 313) or was there a more fundamental conversion?
 

Taunton

Established Member
Joined
1 Aug 2013
Messages
10,069
I believe the LTS electrification was always planned to be after the GE conversion, with thir trains built earlier to help the DC conversion. The temporary use accounts for the fact that the trains for this last Eastern Region electrification, the LTS, looked older than those built for the GE AC lines, as the standard BR spec changed in the meantime.

The physical voltage changeover was made more straightforward by the insulators and wiring for 1500v DC proving satisfactory for 6.25kV as well. The 6.25kV went all the way to Southend Victoria, the whole of the DC system, there was no changeover to 25kV apart from Shenfield-Chelmsford. Likewise on the Lea Valley scheme the 6.25/25kV changeover was beyong Broxbourne. This meant that the second class-only sets, both for Shenfield and for Chingford/Enfield, spent almost all their initial lives on the lower voltage, things being progressively changed again to full 25kV in the 1970s-80s. Converting the Shenfield to Chelmsford section to 25kV took several months, and a dmu substitute was run for the few local electric services which were running there.

There's a lot of detail of the 6.25kV arrangements, including a full map of their extent, and detail for how the conversion from DC was done as well, in the official Railway Inspectorate accident report into the explosions that happened initially on both the GE lines and in Glasgow. It's here : https://www.railwaysarchive.co.uk/documents/MoT_EMUFailures1962.pdf

Somebody on here wrote a while ago that because the wiring etc had been done initially for high DC currents, when the recent rewiring was progressively done of the life-expired 1940s wiring, which involved many weekends, the scrap value of the substantial recovered cabling paid for the work!

** - Edited to add the report link
 
Last edited:

Snow1964

Established Member
Joined
7 Oct 2019
Messages
6,166
Location
West Wiltshire
There is quite a bit of history on this link (and I hadn’t realised 6 units were built before WW2 and were originally blue and cream)

The original dc pantographs we’re above one cab, so if a unit got turned could potentially have two pantographs few meters apart


The changeover used units built for LT&S (class 302) on a temporary basis
 

507020

Established Member
Joined
23 May 2021
Messages
1,859
Location
Southport
Do you know why this was necessary, please?
There was no space for a transformer and rectifier on the motor car, but there was on the trailer car, so the pantograph was moved to create a centre pantograph trailer. I believe this involved swapping the low and high roof sections between the cars.
 

etr221

Member
Joined
10 Mar 2018
Messages
1,051
The Shenfield (306 as they became) sets were 'handed' and could only be coupled (to work in multiple) the same way round - and they were always kept that way round - for this reason they were banned from one side of the Hythe triangle, to avoid getting turned.

Do you know why this was necessary, please?
As built the sets were DMB-T-DT - with all the (dc) traction equipment on the DMB.
Conversion to ac involved moving the brake compartment - with pantograph above to the intermediate trailer, which was also fitted with transformer and rectifier to supply dc (AIUI continuously at 1500v) to the Motor coach (rebuilt to have more passenger space in place of the brake compartment), which retained the control gear.

During the very early 1960s, some the LM region (304) units were also on the GE.
 

507020

Established Member
Joined
23 May 2021
Messages
1,859
Location
Southport
The Shenfield (306 as they became) sets were 'handed' and could only be coupled (to work in multiple) the same way round - and they were always kept that way round - for this reason they were banned from one side of the Hythe triangle, to avoid getting turned.
This is very interesting. Did this mean a motor car must be coupled to a driving trailer whether in a 6 or a 9 car formation? Were the motors supposed to be at the Shenfield or the Liverpool Street end? By contrast, the Southport and Ormskirk (502) sets, whether full 3 car sets or 2 car sets with a blunt end were supposed to be coupled with the motor cars at the outer ends, but they could be turned on the triangle at Meols Cop and photographic evidence shows sometimes they ran with a motor in the middle, but always a cab at both ends for obvious reasons.
As built the sets were DMB-T-DT - with all the (dc) traction equipment on the DMB.
Conversion to ac involved moving the brake compartment - with pantograph above to the intermediate trailer, which was also fitted with transformer and rectifier to supply dc (AIUI continuously at 1500v) to the Motor coach (rebuilt to have more passenger space in place of the brake compartment), which retained the control gear.
Moving the guards van seems much more complicated than just moving the pantograph, unless the structure of it supported the weight of the pantograph which would seem to be a clever design choice enabling such a rearrangement which wouldn’t be possible with modern units, hence pantograph wells on 444s and 450s. Did any precautions need to be taken with regards to the new 1500V DC cable between coaches?
 

Taunton

Established Member
Joined
1 Aug 2013
Messages
10,069
As built the sets were DMB-T-DT - with all the (dc) traction equipment on the DMB.
The Class 306, as built, were essentially an overhead variant of the 1938 Wirral class 503 units, again designed and built by the same two manufacturers, BRCW and Met-Cam, in combination, with air doors (which were novel), and all the DC power equipment in one end car. The air doors had actually been developed for London Transport for the O/P subsurface line stocks, also by these two companies.
 

Bald Rick

Veteran Member
Joined
28 Sep 2010
Messages
29,176
Somebody on here wrote a while ago that because the wiring etc had been done initially for high DC currents, when the recent rewiring was progressively done of the life-expired 1940s wiring, which involved many weekends, the scrap value of the substantial recovered cabling paid for the work!

That’s not true. What is true is that the weight of stuff that came out was three times that of what went in. But the scrap value certainly didn’t pay for the job (Although it did reduce the total bill).
 

306024

Established Member
Joined
23 Jan 2013
Messages
3,946
Location
East Anglia
This is very interesting. Did this mean a motor car must be coupled to a driving trailer whether in a 6 or a 9 car formation? Were the motors supposed to be at the Shenfield or the Liverpool Street end? By contrast, the Southport and Ormskirk (502) sets, whether full 3 car sets or 2 car sets with a blunt end were supposed to be coupled with the motor cars at the outer ends, but they could be turned on the triangle at Meols Cop and photographic evidence shows sometimes they ran with a motor in the middle, but always a cab at both ends for obvious reasons.

This 306 thread is making me all nostalgic :)

The motor coach was always at the Shenfield end. That’s the one without the jumper cables on the front, which were only carried on the driving trailer. Incidentally when I used them in the 70s the motor coach and half the driving trailer were non-smoking, the pantograph and the other half of the driving trailer were for smokers.
 

paul1609

Established Member
Joined
28 Jan 2006
Messages
7,235
Location
Wittersham Kent
That’s not true. What is true is that the weight of stuff that came out was three times that of what went in. But the scrap value certainly didn’t pay for the job (Although it did reduce the total bill).
That's not necessarily due to the change from dc to ac either. From experience rewiring ships the improvement in cable manufacture and insulation plus computer design means you can often find bigger weight savings than 1/3 even staying on the same electrical system.
 

Bald Rick

Veteran Member
Joined
28 Sep 2010
Messages
29,176
That's not necessarily due to the change from dc to ac either. From experience rewiring ships the improvement in cable manufacture and insulation plus computer design means you can often find bigger weight savings than 1/3 even staying on the same electrical system.

quite so.
 

Taunton

Established Member
Joined
1 Aug 2013
Messages
10,069
The Shenfield (306 as they became) sets were 'handed' and could only be coupled (to work in multiple) the same way round - and they were always kept that way round - for this reason they were banned from one side of the Hythe triangle, to avoid getting turned.
Was it possible to get turned round by going round both sides of the Stratford "balloon", the two routes from there up towards Temple Mills? I don't know how far the wires extended up there at the time, before or after the Lea Valley electrification.
 

Magdalia

Established Member
Joined
1 Jan 2022
Messages
3,011
Location
The Fens
Was it possible to get turned round by going round both sides of the Stratford "balloon", the two routes from there up towards Temple Mills? I don't know how far the wires extended up there at the time, before or after the Lea Valley electrification.
No. The lines at Channelsea, High Meads and Temple Mills were electrified in the late 1980s.

Did thy just have a transformer and rectifier supplying DC to the existing DC kit (Bit like a 313) or was there a more fundamental conversion?
My source gives the impression that, yes, a transformer and rectifier supplied DC to the existing DC kit.
 
Last edited:

76020

Member
Joined
1 Nov 2012
Messages
154
I have never looked into this until now but a bit of research has come up with most of the answers. Sources are Railway Observer October 1960 and March 1961, plus volume 7 of Peter Kay's LTS history.

Shenfield-Chelmsford was closed to electric traction at the start of the winter timetable on 12 September 1960, with various diesel hauled services calling at Shenfield and an additional DMU shuttle service between Shenfield and Chelmsford. This timetable is what's shown in the winter 1960 ER public timetable. At least part of the DMU shuttle service was covered with DMUs borrowed from Marylebone: on 17 September 51863/59726/59746/51864 was being used. These were also used on the Southminster branch.

The class 306 units were modified at Stratford. This involved moving the pantograph, and changing LNER diamonds for Stone Faively, plus fitting of transformers and rectifiers. 30 units were fully modified in advance and the ac equipment tested on the Colchester-Clacton branch. These had a temporary "bypass" that allowed them to work on dc until the big changeover. The remaining 62 units had preparatory structural alterations for moving the pantograph but remained dc until after the big changeover.

That big changeover was on the weekend of 5 and 6 November 1960, though it was originally intended to be in August 1960. Shenfield-Chelmsford was energised at 25kv and all of Liverpool Street-Southend was 6.25kv.

From 7 November 1960 the Shenfield and Southend Victoria services were covered by the 30 converted class 306s plus a large number of class 302s built for the LTS electrification. By March 1961 more than 50 of the remaining class 306s had been modified for ac and returned to traffic, after testing between Shenfield and Chelmsford. The DMUs on loan from Marylebone returned in March 1961 but it is not clear what they were used for after 7 November 1960.

The class 307 dc to ac conversion was a bit of a nightmare, with the units not returning to traffic until 1962. Peter Kay's account suggests that they were converted at Stratford, what is the source for conversions being done at Eastleigh?

The LTS units did a lot of work on the routes to and from Liverpool Street before taking up permanent duties to and from Fenchurch Street, including covering for classes 305 and 308, but that's another story. In this respect it was just as well that the LTS electrification ran late, with a virtually full electric service not starting until June 1962.
Thank you for your responce and the information above, this was one heck of a changeover to say the least.
I have found memories of riding the Class 306 from Liverpool Street to Stratford, there used to be a neutral section just east of Bethnal Green and if you was in the middle car travelling through it, a loud bang from the works of the unit made most people jump!

I’ve become interested in this recently. The 306s were identical to the 506s used on the Woodhead electrification to Hadfield and Glossop, being part of the same batch of LNER electrification carried out by the Eastern Region after the war and only being numbered differently under TOPS.

The conversion must have involved some sort of transformer being fitted to the units and the wires being re-energised at the new voltage, but I wish I knew about it in more detail. The 506s were scrapped when the line to Hadfield and Glossop was converted to AC rather than receiving the same conversion.

As for lines that have used 3 systems, the Manchester South Junction & Altrincham Railway was electrified in 1931 using the same 1500V DC overhead system as Shenfield and Woodhead, converted to standard 25kV 50Hz AC in 1971 by BR and then converted again to 750V DC overhead when it became part of the Metrolink. I can think of other lines that have used 3 power systems with one of them being Diesel.
Thank you for your responce, I can think of quiet a few that have used two different power systems but there are not many with three to say the least.

I have never looked into this until now but a bit of research has come up with most of the answers. Sources are Railway Observer October 1960 and March 1961, plus volume 7 of Peter Kay's LTS history.

Shenfield-Chelmsford was closed to electric traction at the start of the winter timetable on 12 September 1960, with various diesel hauled services calling at Shenfield and an additional DMU shuttle service between Shenfield and Chelmsford. This timetable is what's shown in the winter 1960 ER public timetable. At least part of the DMU shuttle service was covered with DMUs borrowed from Marylebone: on 17 September 51863/59726/59746/51864 was being used. These were also used on the Southminster branch.

The class 306 units were modified at Stratford. This involved moving the pantograph, and changing LNER diamonds for Stone Faively, plus fitting of transformers and rectifiers. 30 units were fully modified in advance and the ac equipment tested on the Colchester-Clacton branch. These had a temporary "bypass" that allowed them to work on dc until the big changeover. The remaining 62 units had preparatory structural alterations for moving the pantograph but remained dc until after the big changeover.

That big changeover was on the weekend of 5 and 6 November 1960, though it was originally intended to be in August 1960. Shenfield-Chelmsford was energised at 25kv and all of Liverpool Street-Southend was 6.25kv.

From 7 November 1960 the Shenfield and Southend Victoria services were covered by the 30 converted class 306s plus a large number of class 302s built for the LTS electrification. By March 1961 more than 50 of the remaining class 306s had been modified for ac and returned to traffic, after testing between Shenfield and Chelmsford. The DMUs on loan from Marylebone returned in March 1961 but it is not clear what they were used for after 7 November 1960.

The class 307 dc to ac conversion was a bit of a nightmare, with the units not returning to traffic until 1962. Peter Kay's account suggests that they were converted at Stratford, what is the source for conversions being done at Eastleigh?

The LTS units did a lot of work on the routes to and from Liverpool Street before taking up permanent duties to and from Fenchurch Street, including covering for classes 305 and 308, but that's another story. In this respect it was just as well that the LTS electrification ran late, with a virtually full electric service not starting until June 1962.
According to Wikipedia the Class 307's were converted to AC at Eastleigh but this may not be the case as I have been informed that Wikipedia is not 100% accurate but anyway here is the link
Quote "However, in the late 1950s / early 1960s, these lines were converted to the 6.25 kV/25 kV alternating current (AC) overhead system, which was adopted as standard and coincided with the introduction of new Class 302 (AM2) units. Therefore, from 1960 to 1962, the entire AM7 fleet was extensively rebuilt at Eastleigh Works to allow units to operate from the new voltage system"
 
Last edited:

507020

Established Member
Joined
23 May 2021
Messages
1,859
Location
Southport
Thank you for your responce, I can think of quiet a few that have used two different power systems but there are not many with three to say the least.
There are a lot which have used 2 different systems, but I believe all of these were converted from experimental or obsolete systems to standard ones.
 
Last edited by a moderator:

Magdalia

Established Member
Joined
1 Jan 2022
Messages
3,011
Location
The Fens
According to Wikipedia the Class 307's were converted to AC at Eastleigh, please see this link
Quote "However, in the late 1950s / early 1960s, these lines were converted to the 6.25 kV/25 kV alternating current (AC) overhead system, which was adopted as standard and coincided with the introduction of new Class 302 (AM2) units. Therefore, from 1960 to 1962, the entire AM7 fleet was extensively rebuilt at Eastleigh Works to allow units to operate from the new voltage system"
I'm suspicious of "according to Wikipedia" where no source is given. In this Wikipedia entry I can't see what the source is for the rebuilding being done at Eastleigh.
 

yorkie

Forum Staff
Staff Member
Administrator
Joined
6 Jun 2005
Messages
67,764
Location
Yorkshire
I'm suspicious of "according to Wikipedia" where no source is given. In this Wikipedia entry I can't see what the source is for the rebuilding being done at Eastleigh.
I agree; the original source should be linked to, and quoted (in quote tags, by using the quote button).

When someone says "according to Wikipedia", this demonstrates a lack of understanding about how Wikipedia works. I find kids are better than adults at this, as they are taught about this at school these days. But enough of that on this thread!

If there is no source provided in a Wikipedia article, the best thing to do is ignore the Wikipedia article and identify a suitable alternative source, therefore @76020 can you amend your post accordingly please? Many thanks :)
 

Taunton

Established Member
Joined
1 Aug 2013
Messages
10,069
I can think of quiet a few that have used two different power systems but there are not many with three to say the least.
North London Line has gone from 4th rail electrification to 3rd rail, some time in the 1970s, then to 25kV more recently.
 

Peter Mugridge

Veteran Member
Joined
8 Apr 2010
Messages
14,817
Location
Epsom
I'm suspicious of "according to Wikipedia" where no source is given. In this Wikipedia entry I can't see what the source is for the rebuilding being done at Eastleigh.
Could this be a confusion with the later refurbishment of the 302s which was carried out at Eastleigh in the mid 1980s?

Here's 302 308 being dragged west through Clapham Junction in 1983, off the West London Line connection and via East Putney.
 

Attachments

  • Peter Archive 589.jpg
    Peter Archive 589.jpg
    124.2 KB · Views: 36
  • Peter Archive 590.jpg
    Peter Archive 590.jpg
    690.9 KB · Views: 36

Helvellyn

Established Member
Joined
28 Aug 2009
Messages
2,012
Is the conversion of the 306 and 307 units the reason they were so classified? By build date you'd think they would have been 302/303, but if not converted to AC until the start of the 1960s they seem to slot into the AC classification by conversion date rather than build date.
 

Peter Mugridge

Veteran Member
Joined
8 Apr 2010
Messages
14,817
Location
Epsom
Is the conversion of the 306 and 307 units the reason they were so classified? By build date you'd think they would have been 302/303, but if not converted to AC until the start of the 1960s they seem to slot into the AC classification by conversion date rather than build date.
No, they were originally classified AM6 and AM7; when the TOPS numbering came in they simply retained the last digit on all the overhead powered electric units.
 

507020

Established Member
Joined
23 May 2021
Messages
1,859
Location
Southport
No, they were originally classified AM6 and AM7; when the TOPS numbering came in they simply retained the last digit on all the overhead powered electric units.
They wouldn’t have been AM6 as DC units would they? 306 is of course the TOPS numbering but 3xx replaced AM as the designation for AC multiple units. Others e.g. 502s or 506s have the designation for DC outside the SR and must have been called something else originally. Would 306s and 506s not have been part of the same class?
 

Helvellyn

Established Member
Joined
28 Aug 2009
Messages
2,012
They wouldn’t have been AM6 as DC units would they? 306 is of course the TOPS numbering but 3xx replaced AM as the designation for AC multiple units. Others e.g. 502s or 506s have the designation for DC outside the SR and must have been called something else originally. Would 306s and 506s not have been part of the same class?
You've put that a better way than I did, even as AM6 and AM7 that places them after newer units. Which makes me think the conversions were authorised between the AM5 (305) and AM8 (308) orders.
 

Taunton

Established Member
Joined
1 Aug 2013
Messages
10,069
I think we often read too much into classification and numbering logic from past times - it was probably done by various junior clerks on the day; some would reuse numbers assigned to aborted projects, some would not, etc. You can see this in things like TOPS loco renumbering, mostly done in a tight sequence from 001 upwards, but the 03 was done with the last 3 digits as before instead, leading to big numbering gaps. It didn't matter, there were lots of numbers to play with, just a different person did it a different way.
 
Last edited:

delt1c

Established Member
Joined
4 Apr 2008
Messages
2,125
I always thought the reason they took the class 306 was that they AC conversions from what was to 506. Same reason that 504 was a DC unit and 304 the AC equivalent but 4 car
 

507020

Established Member
Joined
23 May 2021
Messages
1,859
Location
Southport
I always thought the reason they took the class 306 was that they AC conversions from what was to 506.
They were, but the Hadfield/Glossop units were not designated Class 506 until the introduction of TOPS either, several years after the conversion. TOPS did use an entirely logical numbering system at first with similar units or different unit types operating in the same area e.g. 306/506 were the LNER units and 104/304/504 running most of the other Manchester services.
 
Status
Not open for further replies.

Top