In order to maximize the availability of the ESS linac, the impact of a modulator failure should be minimized. The superconducting part of the linac reportedly can still work with one or two cavities not being powered, under the assumption that they are not next to each other. The assumption being used below is that the more unaffected cavities there are between the ones that is without power, the better the possibilities to retune the linac. Interleaving patterns are with one exception constrained to them that can be done on one side of a penetration, i.e. for eight klystrons at a time.