How do you coordinate the grounding and bonding of multiple generators in parallel or in island mode?

1 Grounding and bonding methods

When grounding and bonding generators, the type of load, generator configuration, and local codes and standards should be taken into account. Common methods include solid grounding, where the neutral of the generator is connected to the ground electrode for a low-impedance fault current, resistance grounding, which limits the fault current and arc flash hazard but allows voltage rise on the equipment, reactance grounding, which also limits the fault current but creates a capacitive effect that may cause overvoltages and harmonics, and ungrounded, which eliminates ground fault current but can cause transient overvoltages and difficulty in locating faults. To select the proper method for your generators, consult the manufacturer's recommendations as well as relevant codes and standards.

2 Connecting the generators to a common ground bus

When you operate multiple generators in parallel or in island mode, you must connect them to a common ground bus to ensure the same reference point for voltage and frequency, and even distribution of fault currents. To do so, identify the neutral and ground terminals of each generator (usually marked as N or X0 and G or PE, respectively). Then, connect the neutral terminals of all generators to a common neutral bus with copper conductors of suitable size and insulation based on the generator rating and expected fault current. Similarly, link the ground terminals of all generators to a common ground bus with copper conductors that meet the same criteria. Finally, attach the common ground bus to a ground electrode system consisting of one or more ground rods, plates, or pipes buried in soil or embedded in concrete with a resistance as low as possible (preferably less than 5 ohms).