to be completed with working EKT. Communication between signal boxes for block working is by a block bell system with a series of bell codes, with additional phone lines for more in depth conversation to take place. The signal boxes use two types of frame, both manufactured at the GWR signal works in . The older frames are the 1892 developed Stud frame, which replaced the original twist frames. It operates in a similar manner to tappet locking except that the blades are curved. The remained signal boxes use 5-bar tappet locking frames dating from the 1930s. Power supply within the boxes is standard 110-volt AC, 50 Hz, derived via transformer from the standard UK/EU 230-volts AC individual supplies. Inside the box, most voltages are DC, with standards derived from those in operations during British Railways ownership of the line. Isolated level crossings are fed direct from mains supply, but use a locally derived railway standard 24-volts DC. "Switching Out" Crowcombe Heathfield Crowcombe Heathfield Signal Box can be "switched out". When done, this reduces the amount of block sections on the railway to 4. Switching out is a procedure conducted by the signallers at Bishops Lydeard, Crowcombe Heathfield and Williton. Once complete, bell codes are transmitted between Bishops Lydeard and Williton using separate block bell instruments in their respective signalboxes for the long section, and thus a different, long section token is used for the full line between Bishops Lydeard and Williton. No signalman is required at Crowcombe Heathfield when the box is switched out. When switched out, the points are set and locked for the main platform (Down Platform) and all signals for said platform are cleared in both directions, transforming Crowcombe Heathfield into a single platform station. The route and signals cannot be changed until the box is switched back in. Rolling stock Photographs of the line when operated by the Bristol and Exeter Railway show that their 4-4-0ST locomotives were the regular motive power. Later years saw types such as GWR 4500, 4575, and 5101 'prairie' 2-6-2Ts, 2251 'Collett goods' 0-6-0s, 5700 'pannier tank' 0-6-0PTs and 4300 'mogul' 2-6-0s. In British Railways' time, these were replaced by Western Region NBL Type 2, Hymek Type 3 diesel-hydraulic locomotives, Swindon and Gloucester cross-country diesel multiple units (DMUs). Today, the line is operated by a variety of preserved steam and diesel locomotives and DMUs. Most of these are typical of