Sometimes you find yourself working on a job where the original installer decided to save money by simply using the same colour wire all around. Its ‘black’ wire to the master, the stations and the common rather than the multi-core version pictured above.
What happens though if your dog rips up all the rear solenoids and you are simply left with 4 black wires poking out of the ground? How do you work out which one is common and which ones are power?
Option A is trial and error and with just 4 wires the permutations aren’t too bad to have a chance of getting it right. But a smarter option is this:
a) Get a mate to help.
b) Run a new strand of wire directly from the contoller common terminal to the rear where the broken wires are. It might mean you need 30 m of wire.
c) Connect the new common wire to the common probe on your multimeter which you have turned on to <200V.
d) Have your friend stand at the control box and turn on each station in turn. Connect the positive probe from your multimeter to the other wires in turn. When you get 25 V or thereabouts then you know it is a power wire.
e) The one wire that produces no response is then the common.