By Sara Heger
Power to the pump and alarm system, when located outside a building, will most frequently be supplied by an underground branch circuit from a nearby service entrance or subpanel.
Follow electrical code specifications for materials and burial depths. Avoid routing buried wiring through existing or anticipated gardens or landscaping areas to minimize the chances of damage due to spading. Power to the septic system should be from a single branch circuit with no other loads. The circuit breaker or fuse supplying this circuit should be clearly marked at the service entrance location.
Two methods, or a combination of the two, are common in outdoor wiring. One method is to place electrical wires inside a conduit. The other is to use cable. In either case, protection from physical damage, water and corrosion must be provided. Running wires through sealed conduit provides physical, water and corrosion protection. Several kinds of conduit are acceptable for outdoor use. Rigid metal conduit made from aluminum or steel provides equivalent wire protection. However, aluminum conduit is not recommended for installation where it is directly in contact with soil. Rigid PVC conduit can be used above ground. High-density polyethylene conduit is suitable for underground installation. Do not use thin wall conduit (EMT) for underground or outdoor installations.
An underground feeder cable can be buried without conduit protection, but physical protection for underground cable is highly recommended to reduce the risk of spading through the cable later. This is particularly true around the septic tank. Do not use nonmetallic cable for underground installations. While it is an excellent material for interior wiring, it will not withstand the moisture conditions in the soil.
Combining the conduit and cable wiring methods is also an option. Conduit can be used around cable for physical protection. Conduit is particularly useful to protect cables where they enter and exit the soil. If conduit and cable are used in combination, appropriate connectors and bushings are needed for transitions from one system to the other. Minimum burial requirements apply to wire in conduit and cables. The size of the wire is determined from the electrical need (the motor size) and the length of wire. The table gives wire specifications for various lengths and motor ratings.
Make sure the wire has the proper capacity for the electrical demands of the pump. This is done by comparing the length of wire necessary from the pump to the power box and the horsepower required for the pump. Having these two values allows for proper selection of the wire sizes. A second wire should be run for the alarm and should be on a second circuit.
The power cable to the pump and float switch cables running from the control center into the tank should be run in conduit (metal or PVC) where physical protection is needed. The area around the conduit entering the tank should be sealed to prevent surface water from entering the tank through the conduit. If the conduit provides a continuous connection between the control center box and the tank, the conduit entrance to the box should be plugged with electrical putty to prevent the movement of moisture and corrosive gases into the control box. Provide an outlet for the wires through the side of the cleaning access. Consider installing a section of 6-inch plastic pipe with a cap alongside the cleaning access to contain the pumping station wires.
Power cables used in these installations, such as Types SE, SJ or SOW, must be suitable for moist and corrosive environments. The power cable to the pump must have a grounding conductor (usually a green insulated wire) to ground the pump motor frame. Metallic conduit should not be used for equipment grounding to or within the tank. Since the pump is considered a motor load, it must have appropriate disconnecting means. The disconnect for units of one horsepower or greater (circuit breaker or switch) must be clearly marked and either in sight of the pump location or lockable. This prevents inadvertent reactivation of the circuit during servicing of the unit. Below 1 hp, receptacles and plugs listed for motor loads (hp listed) may be used.
Wires for float switches should be color-coded for easy identification. Do not cut off extra wire since it allows service providers to pull components out of the tank to service them. Roll the extra wire up and tether it inside of the riser.
When wiring is conveyed over long distances, wire size must be appropriately increased to compensate for the resulting power loss. All the electric lines must be contained within code approved conduits and junction boxes. Because of the corrosive nature of wastewater, gases and moisture all conduits should be sealed. The openings in electrical conduit should be sealed to prevent moisture and gases from entering the enclosure. Duct seal is the best choice for this since it will effectively seal the openings while remaining flexible.