Figure 17. Weatherproof box (driptight) for outdoor wiring.
Figure 18. Weatherproof boxes (watertight) for wet locations.
Figure 17. Weatherproof box (driptight) for outdoor wiring.
Figure 18. Weatherproof boxes (watertight) for wet locations.
Electrically, there is no difference between wiring inside or outside a building. However, the materials and installation procedures are considerably different. Outdoor wiring must be able to withstand exposure to water, weather and corrosive environments. This is certainly the case for wiring septic system dosing tanks. While there are several types of systems for outdoor and underground wiring, based on what materials are used, each has specific applications.
Outdoor equipment used in residential wiring must be weatherproof. The two most common types of weatherproof equipment are driptight and watertight. Driptight equipment seals against water falling vertically. Driptight boxes are usually used for control or circuit breaker panels. Watertight boxes seal against water coming from any direction. Individual junction boxes, switch boxes and receptacle boxes will usually be of the watertight type.
Driptight boxes are usually made of painted sheet metal and have shrouds or shields that deflect rain falling from above. An example of a driptight unit is shown in Figure 17. These boxes are not waterproof and should not be used where water can spray or splash on the unit.
Watertight boxes are designed to withstand temporary immersion or spray streams from any direction. They are commonly made of cast aluminum, zinc-dipped iron, bronze or heavy plastic and have threaded entries for watertight fittings and gasketed covers.
Be aware that the National Electric Code requirements state that all ground level outlets must be ground-fault circuit interrupter (GFCI) protected. Figure 18 shows a watertight switch box and receptacle.
Two different 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. Both approaches are illustrated in Figure 19.
Figure 19. Power and control system for onsite wastewater system.
Figure 20. Example electrical cable types.
Running wire 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 acceptable for installation where it is directly in contact with soil. Rigid PVC conduit made from polyvinyl chloride can be used above ground. High-density polyethylene conduit is suitable for underground installation. Do not use thinwall conduit (EMT) for underground or outdoor installation.
An underground feeder (UF) cable (Figure 20) can be buried without conduit protection. Physical protection for underground cable is highly recommended to reduce the risk of spading through the cable at a later time. A redwood board buried just above the cable is highly recommended to provide physical protection. Do not use nonmetallic (NM) cable (Figure 20) 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, as shown in Figure 19, appropriate connectors and bushings are needed for transitions from one system to the other. Minimum burial requirements apply to wire in conduit and cables. Table 6 lists the National Electric Code requirements for each type of installation.
Figure 21. Two-switch control system for dosing tank.
Figure 22. Three-switch control system for dosing tank.
Table 6. Required burial depths for branch circuits (after 2005 National Electric Code, Section 300.5).
| Cable | Rigid Metal Conduit | Non-Metallic Conduit | |
| Directly in soil | 24 in. | 6 in. | 18 in. |
| Under residential drive | 18 in. | 18 in. | 18 in. |
| Under 4 in concrete slab no vehicle traffic | 18 in. | 4 in. | 4 in. |
Control switches sense the water level in the dosing tank and signal the pump or alarm system. A failure of the control switches can cause sewage to back up into the home or come out the top of the dosing tank. Follow some simple guidelines to avoid control problems.
First, select the appropriate switches. Mercury float switches encased in plastic or neoprene are recommended. In Figure 21, one switch is used to start and stop the pump. In Figure 22, one switch is used to start and a different switch is used to stop the pump. In both cases, a separate switch is used to activate the alarm system if the liquid level rises too high in the tank. Some switches handle power to the pump directly, while others require a relay.
Second, if possible, make no electrical connections inside the dosing tank. This includes plug-ins, screw-type, twisted wire, boxes, relays or any other type of connection that requires movement to connect or operate. If connections or splices must be made, they should be located in a watertight, corrosion resistant junction box with watertight, corrosion-resistant fittings and a gasketed cover.
An alarm system is used to alert the homeowner to a pump malfunction by means of an audible and/or visual signal. Therefore, the alarm system must be powered in such a way that if the pump circuit fails the alarm will still operate. Provide a means to turn off the alarm without losing power to the pump.
The cables that connect to the pump control switch, alarm switch and pump all originate from the pump and alarm control center. The center should either be inside a weatherproof box or on a post near the entrance port to the dosing tank. Locating the control and alarm center inside a nearby building (such as a basement or garage) is also acceptable, however access for service and inspection may be less convenient. Never place the control system inside the dosing tank or access passageway. The moisture in the dosing tank will cause the system to corrode and fail.
Locate the control center in a weatherproof enclosure mounted to a treated wood or steel post near the entrance to the dosing tank. A typical outdoor pump and alarm control centers are shown in Figure 23. It is important to use wire, connectors and weatherproof enclosures appropriate for outdoor use.
Figure 23. Outdoor control center with built-in pump control.
A pump motor relay with built-in motor overcurrent protection is shown in Figure 23. The pump motor start and stop switches control the relay coil current. Conduit is shown for physical protection of the conductors and cables entering and leaving the box.
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, as shown in Figure 23. 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 high quality electrical putty to prevent the movement of moisture and corrosive gases into the control box. Power cables used in these installations, such as Type 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 1 horsepower or greater (circuit breaker or switch) must be clearly marked and in sight of the pump location or lockable. This prevents inadvertent reactivation of the circuit during servicing of the unit. Under certain circumstances, for large pumps or long distances to the power source, 240 volt equipment may be desirable.
Figure 24. Pressure tests with clogging(a) and leaks(b) in the mound system.
Power to the pump and alarm system control center, when located outside a building, will most frequently be supplied by an underground branch circuit from a nearby service entrance or sub-panel. Follow electrical code specifications for materials and burial depths as described earlier. Avoid routing buried wiring through existing or anticipated gardens or landscaping areas to minimize the chances of damage due to spading.
Power to the control center should be from a single individual branch circuit with no other loads. The circuit breaker or fuse supplying this circuit should be clearly marked at the service entrance location.
Monitoring and maintenance for the pressure distribution system is required after operation.
If clogging becomes severe, clean laterals with a brush on a plumbing snake. If cleaning is not effective, lateral pipes may need to be replaced. By placing laterals in 4-inch shielding pipe, they can be cut at the manifold, slid out at the turn up and a new pipe can be slid in and glued into place.