3. The carbon monoxide gas present in the exhaust of the engine is extremely poisonous. Under no circumstances should this gas be allowed to collect in a closed room; therefore, means have to be provided to discharge the engine exhaust to the outdoors. Exhaust can be vented by extending the exhaust pipe through the wall or roof of the building. Support the exhaust pipe and make certain that there is no obstruction and avoid right-angle bends, ifpossible. Also, whenever possible, arrange the exhaust system so that the piping slopes away from the engine. In this way, condensation will not drain back into the cylinders. If the exhaust pipe should have to be installed so that loops or traps are necessary, a drain cock should be placed at the lowest point of the system. All joints have to be perfectly tight; and where the exhaust pipe passes through the wall, you have to prevent the discharged gas from returning along the outside of the pipe back into the building. Exhaust piping inside the building has to be covered with insulation capable of withstanding a temperature of 1500°F.
After the generating units have been set in place and bolted down, Builders then can proceed to erect the building, using the necessary information provided by the CEs.
After setting up a portable generator, your crew must do some preliminary work before placing the generator in operation. First, they should make an overall visual inspection of the generator. Have them look for broken or loose electrical connections, bolts, and cap screws; and see that the ground terminal wire (No. 6 AWG minimum ) is properly connected to the ground rod/grounding system. Check the technical manual furnished with the generator for wiring diagrams, voltage outputs, feeder connections, and prestart preparation. If you find any faults, you should correct them immediately.
When you install a power plant that has a dual- voltage alternator unit, make certain that the stator coil leads are properly connected to produce the voltage required by the equipment.
Proper grounding is also a necessity for personnel safety and for prevention of unstable, fluctuating generator output.
INTERNAL LEADS. - The voltage changeover board permits reconnection of the generator phase windings to give all specified output voltages. One end of each coil of each phase winding runs from the generator through an instrumentation and a static exciter current transformer to the reconnection panel. This routing assures current sensing in each phase regardless of voltage connection at the reconnection board assembly. The changeover board assembly is equipped with a voltage change board to facilitate conversion to 120/208 or 240/416 generator output voltage. Positioning of the voltage change board connects two coils of each phase in series or in parallel. In parallel, the output is 120/208; in series, the output is 240/416 volts ac. The terminals on the changeover board assembly for connection to the generator loads are numbered according to the particular coil end of each phase of the generator to ensure proper connections.
Remember that you are responsible for the proper operation of the generating unit; therefore, proceed with caution on any reconnection job. Study the wiring diagrams of the plant and follow the manufacturer's instructions to the letter. Before you start the plant up and close the circuit breaker, double-check all connections.
GROUNDING. - It is imperative that you solidly ground all electrical generators operating at 600 volts or less. The ground can be, in order of preference, an underground metallic water piping system, a driven metal rod, or a buried metal plate. A ground rod has to have a minimum diameter of 5/8 inch if solid and 3/4 inch if pipe, and it has to be driven to a minimum of 8 feet. A ground plate has to be a minimum of 2 square feet and be buried at a minimum depth of 2 l/2 feet. For the ground lead, use No. 6 AWG copper wire and bolt or clamp it to the rod, plate, or piping system. Connect the other end of the ground lead to the generator set ground stud.
The National Electrical Code® states that a single electrode consisting of a rod, pipe, or plate that does not have a resistance to ground of 25 ohms or less will be augmented by additional electrodes. Where multiple rod, pipe, or plate electrodes are installed to meet the requirements, they are required to be not less than 6 feet apart.
It is recommended that you perform an earth resistance test before you connect the generator to ground. This test will determine the number of ground rods required to meet the requirements, or it may be necessary to construct a ground grid.Continue Reading