In most cases, one side of a capacitor is grounded. However, it is not true that this is the case in all designs. The only guaranteed safe way to discharge a capacitor is through a suitable resistor across its terminals.
Grounding either pin of a capacitor to frame ground does not necessarily cause a discharge. In fact, it may apply power to some circuit that does not expect it, potentially damaging it.
Standard safety practices should be followed during installation, inspection, and maintenance of capacitors. Additionally, there are procedures that are unique to capacitor banks that must be followed to protect field operators and equipment in accordance with the NESC – National Electrical Safety Code.
Capacitor banks generally require very little maintenance because they are static type of equipment, but don’t be fooled by this statement. Capacitors are well known for their dangerous reaction when something goes wrong. Standard safety practices should be followed during installation, inspection, and maintenance of capacitors.
So for capacitors, if a capacitor is polarized (has a + and - node), then all you need is to make sure that the voltage at the + node is greater than or equal to the voltage at the - node. You do NOT have to connect the - node to ground. YOu still need a decent discharge path on that.
The substation and distribution capacitor banks should be inspected and electrical measurements be made periodically. The frequency of the inspection should be determined by local conditions such as environmental factors and type of controller used to switch the capacitors on and off. 7. Visual Inspections