WIRING DIAGRAMS FOR A TYPICAL STANDBY GENERATOR
For simplicity, the diagrams presented are one-line diagrams. Actual wiring consists of two ungrounded conductors and one grounded “neutral” conductor. Equipment grounding of all of the components is accomplished through the metal raceways that interconnect the components.
The neutral bus in a panelboard that serves selected loads must not be connected to the metal panelboard enclosure. Connecting the neutral conductor, the grounding electrode conductor, and the equipment grounding conductors together is permitted only in the main service panelboard.
If you were to bond the neutral conductor and the metal enclosures of the equipment (panelboard, transfer switch, and generator) together beyond the main service panelboard, you would create a parallel path. A parallel path means that some of the normal return current and fault current will flow on the grounded neutral conductor and some will flow on the metal raceways and other enclosures. This is not a good situation!
Manufacturers of generators in most cases do not connect the generator neutral conductor lead to the metal frame of the generator. Instead, they connect it to an isolated terminal. Then it is up to you to determine how to connect the generator in compliance with the NEC and/or local electrical codes.
Most inspectors will permit the internal neutral bond in a portable generator to remain in place. In fact, when you purchase a portable generator, you should insist the neutral-to-case bond is in place.
Without the bond, an overcurrent device cannot function on a ground fault because a return path does not
exist. For permanently installed generators, inspectors will generally not permit a bond between the
generator neutral and the metal frame of the generator because of the explicit requirements in the NEC.
A sign must be placed at the service-entrance main panelboard indicating where the standby
generator is located and what type of standby power it is.
The total time for complete transfer to standby power is approximately 45–60 seconds. To further give the homeowner assurance that the standby generator will operate when called upon, some systems provide automatic “exercising” of the system periodically, such as once every 7 or 14 days for a run time of 7 to 15 minutes.
WARNING: When an automatic type of standby power system is in place and set in the automatic
mode, the engine may crank and start at any time without warning. This would occur when the utility
power supply is lost.
To prevent possible injury, be alert, aware, and very careful when working on the standby generator equipment or on the transfer switch. Always turn the generator disconnect to the “Off” position, then lock out and tag out the switch, warning others not to turn the switch back “On.” In the main panelboard, locate the circuit breaker that s upplies the transfer equipment, turn it “Off,” then lock out and tag out the circuit breaker feeding the transfer switch.