AC Electrical Connections System Grounding

AC ELECTRICAL CONNECTIONS — SYSTEM GROUNDING

AC WIRING

GeneratorVoltage Connections

The generator output voltage and maximum current rating are specified on the generator set nameplate. Line-to-neutral voltage is always the lower voltage shown and the line-to- line voltage is the higher rating.

The generators are available at the voltages shown in the wiring diagram of the genset. The genset is connected at the factory to produce a specified voltage per customer order.

Before shipping, the factory tests the generator set at the specified voltage.

Load Connections (Connecting the Load)

All loads are connected to the generator by bolting the stranded load wires to the appropriate terminals on the generator output circuit breaker. The terminals are marked for identification to indicate the line and neutral connections.

Load Balancing

When connecting loads to the generator set, balance the loads so the current flow from each line terminal is about the same. This is especially important if both single phase and three phase loads are connected. Unbalanced loading of a genset causes unbalanced phase voltages.

Any combination of 1Ø and 3Ø loading can be used as long as each line current is about the same, within 10% of the median value and no line current exceeds the nameplate rating of the generator. Check the current flow from each line after connections by observing the control panel ammeter.

Correct grounding in standby systems that are solidly grounded is a function of the

NOTE transfer switch equipment used (solid neutral or switched neutral).

Grounding

The following is a brief description of system and equipment grounding of permanently installed AC generators within a facility wiring system. It is important to follow the requirements of the local and county electrical codes.

System Grounding

System grounding is the intentional grounding of the neutral point of a wye-connected generator, the corner of a delta- connected generator, or the neutral point of one phase winding of a delta-connected generator, depending on the system voltage required in the application. It is common to ground the neutral point of a wye-connected generator and bring out the neutral (grounded circuit conductor) in a 3Ø four-wire system.

Acorner-grounded delta system has a grounded circuit conductor that is not a neutral and a "wild leg" that must be identified by orange color coding and connected to the middle pole of the 3Ø equipment.

System Grounding Methods

Solid Grounding

This method is typically used and required by the National Electrical Code (NEC) on all low voltage systems (600 volts and below) with a grounded circuit conductor (most often a neutral).

The system is grounded with a direct connection by a conductor (the grounding electrode conductor) with no intentional impedance to earth (grounding electrode).

Ungrounded

Ungrounded systems are special applications where no intention of connection is made between the AC generator system and earth. These systems are occasionally used on 3Ø three-wire systems (no grounded circuit conductor) operating at 600 volts or below, where continuity of power with one ground fault is required or desirable, and qualified service electricians are on site. An example would be a critical process industry.

PAGE 76 — INDUSTRIAL GENERATOR SETS — APPLICATION & INSTALLATION MANUAL — REV. #4 (09/07/07)