Hunter Technical Support Document
Is there a minimum distance the pump start relay must be from an irrigation controller?
While most of the time the distance between the controller and pump start relay doesn't create any problems, every once in a while the wires on the 24V coil can allow electromagnetic noise to travel back to the controller. This noise is made when the contacts on the pump start relay make and break the connection.
It's recommended to use a minimum distance of 15ft (4.5m) separation between the controller and the relay, to help dampen any electromagnetic noise.
In addition to this recommendation, Hunter also recommends all controllers be mounted 15ft (4.5m) away from pumps and high voltage devices.