Hi,
After inspecting the wiring from a previous installation I've noticed that the person who installed the wiring originally has used an 8 core cable to supply two detectors, and connect the global tamper in series which to me seems acceptable, but they have also spured the 12V supplies from one detector to anther.
Would this be acceptable if I left it as it is?, as each zone will still be independent from one another?, just to be honest I've never really come across many cases like this and if it was me I would use a 6 core cable for each detector!