I was extending the ring circuit in my daughters flat recently, the system has the old metal conduit with red and black wires inside. When checking out the system, I noticed that I was getting 250v between the red wire and the metal conduit. I went back to the consumer unit, and with the isolator off, I still get 250v from the incoming red, before the switch, and the earth. Is this a fault, or is it normal in older systems.