Understanding the 3 way switch

The 3 way switch is a simple device once you’ve understood how they are wired up and how they work. You will need this knowledge for most BoPi installations as they are present on almost all electrical pannel to control the pump and have the advantage of allowing you to override any sort of automation when you’re cleaning the filters or want to do a backwash of the sand filter.

A 3 way switch has as its name indicates, 3 positions. Usually “on”, “off”, “auto” or “I”, “0”, “II”. It also has 3 connectors on the back side.

In the “Off” or “0” position, none of the connectors are connected together. In either the “On”/”I” or “Auto”/”II” positions, one of side connectors is connected to the middle one, allowing current to flow through the switch.

The important thing to note about the round 3 way switch that we usually find on pool electrical panels is that the outside connections are reversed to the writing on the front. If “on”/”I” is the top position, its the bottom connector that will be connected to the middle one. The opposite also being true.

In the case that concerns us, the 3 way switch is usually used to control the pool pump. The middle connector is the output to the pump power contact and top and bottom connector are the inputs, either from a Lead wire for the “On/”I” position or a Lead Wire via BoPi for the automatic position (originally usually from a timer when you don’t have BoPi).