Never actually found this answered anywhere (inc. search) but is it not unreasonable to use one half rope for moving together and abseiling? If they're rated to hold a leader fall, after all? I'm sure I remember reading somewhere this is a big no-no, though it could have been talking about twin ropes; I've forgotten exactly.
2. Half ropes are tested with a 55-kg mass on one strand. It must resist 5 successive falls and the impact force during arrest of the first fall must be less than 8-kN (800daN). Why 55 kg ? Because ropes which hold 5 falls with 55-kg in practice hold 2 falls with 80-kg, which has been allowed as sufficient security for a half rope which is not used to hold repeated falls on one strand.
> is it not unreasonable to use one half rope for moving together and abseiling?
Abseiling on half ropes, using two strands, is perfectly normal and always has been. There is also no reason why you can't to abseil on a single strand but you would have twice the amount of rope stretch and half the amount of friction which may or may not be an issue.
Half ropes are regularly used when moving together. However, 'moving together' potentially describes a wide range of scenarios. Whilst in many, perhaps even most cases, a half rope may be suitable, it will depend on the exact situation (terrain, rock type, environmental conditions, ability of the party etc.) if that is the case.