AnnnA, AnnnB

A lot depends on when a specific layout was installed, as well as local site circumstances.

A typical multi-home layout from the Northern Line - Colliers Wood southbound. S.707A, S.707B, S.707C. Quite simply, the platform area is divided into 3x track circuits, coincidently numbered 707A to C. Once the train clears each track circuit in turn, the three home signals will clear in turn. Generally you would not come to a stand at the B and C signals, unless the train in front had a problem or was itself running up to a red signal ahead.

Sometimes you can get a layout with one or more semi-automatic signals in the sequence, or the whole sequence might be semi. An example of the former would be Kennington s/b CX - BX.51A, FNX.51B, B2. Here the last signal is at braking distance from the facing points just south of Kennington platform, and may thus remain at danger for a variety of reasons. An example of the former is Colindale s/b - AC.12A, AC.12B, AC.12C.

On the Northern Line the highest number of conventional multi-homes was 4 - at South Wimbledon n/b which ran up to A.720D. Other places with many homes that I can think of - Mansion House e/b, King's Cross inner rail, Queen's Park n/b (sort of!), Liverpool Street (Central Line) - now long history, Baker Street sb Jubilee.

How many home signals depends on the traffic requirements at the time of installation. Northern Line tended to have either 2 or 3. Picc Line tends to have 3 in the centre, 2 in the open sections. Bakerloo often has just one home signal. Anything over 3 is generally the exception nowadays, although in the past this was more common.

Back on the Northern Line, there were also two stations with speed-controlled signalling - Oval and Waterloo n/b. Here the sequence ran up to E, the first two signals would clear subject to speed control. A similar arrangement existed at Brent Cross n/b, but here the first signal was A.4160 and the homes were A.416A to C, although they basically worked the same at the other two locations. In all cases, if *any* of the homes were unable to clear, the speed control signal(s) would remain at danger with speed control applicable.

Lastly, from the 1980s onwards use of suffix letters went out of fashion, so on sections like the central part of the District Line, the Uxbridge branch, the entire Bakerloo Line, parts of the Jubilee, and the East London Line, multi homes were each numbered with their own number. So what would have been, for example, A.666A, B & C, would become A.666, A.668 and A.670. I'm not entirely clear why this change was felt necessary.

You also get suffix letters for semi-automatic signals where more than route is controlled by the same lever. So for example, at Edgware the starter from Platform 3 was AE.31B, with a shunt signal beneath numbered AE.31A. Meanwhile, in High Barnet signals the outlet signals were numbered NU.28A to H. Does anywhere nowadays reach H?

It's also worth noting that sites converted to programme machines tended to get semi-automatic signals grouped together with suffix letters, which hitherto had separate numbers. Acton Town in particular springs to mind. I presume this was to simplify arrangements for the benefit of the programme machine circuits.

Hope that's useful.

Extremely

And thanks very much Harsig - omniscient as ever

Both the Simsig explanation and that from Harsig could be true, depending on the site concerned. In the case of Moor Park I'll go with Harsig.

In the past suffix letters were used so that in the event of a signal being added or removed, it didn't interfere too much with the numbering scheme. For example if you had two home signals (say, for arguments sake, A466^A and A466^B, if an additional home signal was needed you could just allocate the C suffix.

In later years when the use of suffix letters died out, in the mid 1980s, sufficient gaps were left in the numbering sequence to allow for any additions late on, so you would get A466 and A468 as the home signals and then A474 (for example) as the starter, allowing for the addition of A472 at a later date.

Additionally, with controlled signals if you needed one to protect, say, a crossover, and one to protect a platform, they would generally be given suffix letters as it would be illogical to not want to clear both at the same time - hence the Kings Cross example. At Kings Cross of course additional signals are needed to meet the headway requirement, so they gained five homes. The last one has two numbers as it is situated between the crossover and the platform, and can be worked by either the lever for the IR Home signals (14) or the shunt signal from the OR to IR (19).