Was chatting to a mate t'other day about an new programme coming on telly about lectrics. "Sound's interesting, " I said, "do you think there will be anything about RCD's in the series?"
I am not a qualified electrician but I think that you should not have RCD's in series. No damage will be done but more than one is just unnecessary similar to two wire fuses in series. This is a simplistic explanation and ignores the the ratings of the RCD's but is a general rule of thumb.