A plurality of daisy-chained switching circuit cards are each coupled to a different active circuit card. Feed-through circuit cards are each coupled to spare circuit cards having substantially identical circuitry to the active circuit cards. The feed-through circuit cards are also daisy-chained with the switches on the switching circuit cards. The switching circuit cards can replace the feed-through circuit cards and the active circuit cards replace the spare circuit cards in order to vary the size of the spare groups (a group of spare circuit cards and active circuit cards) and also the quantity of the spare groups.