It's a ring on the stage area controlled by a sound Guardian, that circuit and 4 more rings are also controlled by E-stops and intruder alarm.
The original installation was done with 2 contactors per circuit, switching each end of the ring. I don't recall how, but I discovered one contactor had failed meaning the ring was only being fed from one end. I replaced with a contactor big enough to switch the whole of the 32A supply then a PIR described it as a ring feeding a ring. Eventually by making some minor changes it became a parallel fed contactor feeding a ring.
I'll have to try to decipher my scribbled notes to remember much more than that.