The group of Second Class carriages were coded 'B'.
They were placed in service from 1858 to 1886, with a sole Second Class carriage built in 1893. From 1886 onwards, First Class carriages coded _A__ were downgraded to Second.
The introduction of bogie carriages to country service cascaded stock allowing older vehicles to be scrapped or converted to works cars.
When the railways took over some private companies some of the stock from those companies was consolidated into the fleet. This accounts for some carriages in built in 1855 when the government railways commenced running in 1858.
In the mid to late 1890s, older stock was marked with a 'H' to indicate 'Holiday' traffic; stock stored for use until busy holiday times of the year. The cars were eventually coded _BH_. In the 1910 recoding these cars were recoded to _YH_.
The B/BH group was numbered 1 - 479.
In the 1910 recoding the 'B' class was recoded to _Y__. To remove gaps in the numbers caused by conversions and scrappings, the carriages were renumbered as they were recoded.
The Y/YH group were in the 1 - 385 group.