Each end of the railway is a separate booster district, fed by its own DB150 booster. This provides up to 10A track power; with an N gauge loco taking perhaps 0.25A, it is definitely overkill. The accessory decoders are fed by the DCS100 booster output, ensuring they always have power.
Each booster district is split into separate power zones. The principle I've used here is to separate the main lines from the station & yard areas: derailments are much more likely in those, and they need to be separated. The main lines, on the other hand, are unlikely to suffer because the train movements are more simple: consequently these don't need to be broken up as much.
The South Downs Railway has four reverse loop zones. One reverse loop - with three parallel storage tracks - is located under Portsmouth station. The other, with a single track, is in front of Petersfield station. These tracks each need their own autoreverser. Each reverse loop area - under Clanfield and by Petersfield - has its own PM42 channel for short circuit protection: I have used two because they are in separate booster districts.
Here is a list of the zones used on the railway:
| Booster | Board | Channel | Zone | Track Area |
Block Dets |
Detectors |
|---|---|---|---|---|---|---|
| DB150 1 | PM42 31 | 1 | A | Portsmouth Approach & platforms | 12 | 52 53 54 55 57 58 59 60 65 66 67 68 |
| DB150 1 | PM42 31 | 2 | B | Portsmouth Yard, Engine Shed & Eastleigh | 9 | 50 51 56 61 62 63 64 69 70 |
| DB150 1 | PM42 31 | 3 | C | Green line at Portsmouth end | 12 | 25 26 27 28 36 38 71 73 74 99 100 109 |
| DB150 1 | PM42 31 | 4 | D | Portsmouth Loop 3 reverse loop | 2 | 33 102 |
| DB150 1 | PM42 32 | 1 | E | Portsmouth Loop 1 reverse loop | 2 | 35 104 |
| DB150 1 | PM42 32 | 2 | F | Portsmouth Loop 2 reverse loop | 2 | 34 103 |
| DB150 1 | PM42 32 | 3 | G | Orange line at Portsmouth end | 14 | 23 24 29 30 31 32 37 39 72 75 76 101 105 110 |
| DB150 1 | PM42 32 | 4 | H | Reverse loops isolator | 0 | |
| DB150 2 | PM42 33 | 1 | J | Reverse loop isolator | 0 | |
| DB150 2 | PM42 33 | 2 | K | Clanfield | 8 | 17 18 19 20 21 81 82 83 |
| DB150 2 | PM42 33 | 3 | L | Green line | 16 | 12 14 15 22 42 43 44 45 49 77 80 94 95 96 106 107 |
| DB150 2 | PM42 33 | 4 | M | Orange line | 12 | 13 16 40 41 46 47 48 79 97 98 108 111 |
| DB150 2 | PM42 34 | 1 | N | Petersfield Loop | 2 | 11 88 |
| DB150 2 | PM42 34 | 2 | P | Fiddle yard green | 12 | 2 3 4 5 84 85 86 87 117 118 119 120 |
| DB150 2 | PM42 34 | 3 | R | Fiddle yard orange | 12 | 6 7 8 9 90 91 92 93 113 114 115 116 |
| DB150 2 | PM42 34 | 4 | S | Fiddle yard sidings | 4 | 1 10 89 112 |