Why is the long common electrode always grounded in the 61F's Floatless Level Controller connection?

There are three reasons for this ground.

1. Preventing Improper Operation Due to Inductive Noise

Since there is just a weak current (about 1 mA at 8 VAC) between the 61F Controller and the electrodes, it is easy for inductive noise to cause improper operation when there is no ground.

2. Protecting the 61F Controller from Surge Voltage

The common electrode must be grounded properly to protect the 61F Controller's internal circuits from surges caused by lightning or other equipment.

3. Preventing Electric Shock

The ground is needed to prevent electric shock in case of electric leakage.