There are three reasons for this grounding.
- 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. - 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. - Preventing Electric Shock
The ground is needed to prevent electric shock in case of electric leakage.
