During recent workshops one recurring area of questions deals with proper wiring for onsite wastewater treatment systems. This issue is coming to the fore because more sites require alternative systems with pumps, or use treatment units that need electrical connections.
In addition, numerous states now require effluent screens, and these need alarms to prevent backups into the house in case they clog.
First and foremost, electrical installations must comply with all applicable laws and ordinances, including the latest codes, rules and regulations of the public authority having jurisdiction. Proper wiring materials and installation procedures are critical to the safety of the installer, sewage system users, and anyone who will work on the system in the future.
The key regulations generally incorporate the National Electrical Code, and only licensed or authorized professionals should do the electrical work. Having said that, one thing we often hear from installers is: “I had an electrician come out and do the wiring and connections, but they did not understand what they were working with, so it was a poor installation.”
Whether you are not qualified to do your own electrical installations or hire electricians to do the work, here are some critical items to consider.
Outdoor vs. indoor
Materials and installation procedures for outside wiring are considerably different from those for indoor wiring. Outdoor wiring must withstand exposure to water, weather and corrosive environments. This is certainly true for wiring septic system pump tanks. So if your electrician starts using indoor wiring boxes and other indoor components, you can highlight that this is not the place for them.
The pump must be properly wired. This means making sure that:
• The fittings are watertight.
• The conduit is properly sealed so that gases cannot advance through the control panel.
• The wire from the electrical box to the pump is properly sized.
The inside of the tank is a very corrosive environment, so the splices or wiring must be protected if connections will be made there. Sealing of the conduit is also critical. In many states, there must be a vent or separation of the conduit from the control panel.
The best situation is to avoid making electrical connections inside the tank — including plug-ins, screw-type connections, twisted wire, boxes, relays, or any other connection that requires movement to connect or operate. If you must make connections or splices inside the tank, locate them in a watertight, corrosion-resistant junction box with watertight, corrosion-resistant fittings and a cover sealed by a gasket.
Keep out the weather
Outdoor equipment used in wiring must be weatherproof. The two most common types are driptight and watertight. Driptight equipment seals against water falling vertically. The boxes are usually made of painted sheet metal and have shields that deflect rain falling from above. These boxes are not waterproof and should not be used where water can spray or splash on the unit. 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 watertight. They are commonly made of cast aluminum, zinc-dipped iron, bronze or heavy plastic. They will have threaded entries for watertight fittings and covers sealed by gaskets.
Power to the pump and alarm system control box, when located outside a building, will most often be supplied by an underground branch circuit from a nearby service panel. To prevent wiring damage in the future, avoid routing buried wiring through areas where the homeowner may plant a garden or landscaping features. Power to the control center should be on a separate circuit and must be clearly labeled on the control panel to make sure the homeowner does not inadvertently shut off the power.
Two methods, or a combination of the two, are commonly used in outdoor wiring. One method is to place the electrical wires inside a conduit. The other is to use cable. In either case, you must protect the conductor from physical damage, water and corrosion.
Rigid conduit made from aluminum or steel provides protection. Aluminum is not recommended where it is directly in contact with soil. Rigid PVC pipe can be used above ground. High-density polyethylene conduit can be used underground. Do not use thin-wall conduit (EMT) for underground or any outdoor installations.
An underground feeder cable can be buried without conduit protection, but physical protection is recommended to reduce the risk of someone spading through the cable at a later date. This is particularly important around the septic tank. A treated board buried just above the cable will afford protection. Do not use nonmetallic cable for underground installations. It will not withstand the moisture conditions in the soil.
Proper capacity
Make sure the wire has the proper capacity for the electrical demands of the pump. You can do this by comparing the length of wire necessary from the pump to the power box and the horsepower required for the pump. Using these two values, you can select the proper wire size. Run a separate wire for the alarm, and put it on a separate circuit.
You can combine the conduit and cable methods. Conduit can be used around cable for physical protection and is particularly useful to protect cables where they enter and exit the soil. If you use conduit and cable together, you need appropriate connections and bushings for the transitions from one system to the other.
The power cable or wiring should run in conduit into the tank. Seal the area around the conduit entering the tank to keep surface water from entering the tank. If the conduit provides a continuous connection between the control center box and the tank, plug the conduit entrances with electrical putty to keep moisture and corrosive gases from entering the control box.
We hope these guidelines highlight some things to look for as you install wiring or oversee an electrician in installing onsite treatment systems.
