Understanding Time Switches
Although it's sometimes confused with a timer switch—a device that simply turns off a device such as a light fixture or vent fan after a prescribed amount of running time—a time switch serves a different function. Time switches essentially keep track of the time of day and turn power on and off at whatever times are desired by the user.
Time switches are often used for outdoor lighting, swimming pool pumps, outdoor pond pumps, water heater recirculating pumps, and other devices that need to be turned on and off at particular times of day.
How Time Switches Work
Traditionally, time switches have been analog devices with a rotating mechanism that makes a complete revolution every 24 hours. Within the mechanism two or more "on-off" switches open and close the current flow based on however the user sets the mechanism. Although this kind of time switch is becoming less common for standard 120-volt circuits, it is still often used for 30-amp or 40-amp circuits, such as those that serve swimming pools or hot tub heating units.
Today, however, there are digital electronic forms of time switch that operate by means of a built-in battery and clock that keep track of time. These switches are programmable and can turn the current flow on and off multiple times during the day. They can even be programmed to allow for different on-off cycles for different days of the week. These switches have become for time switches on standard 120-volt household circuits.
Anatomy of a Mechanical Time Switch
Mechanical (analog) time switches usually are contained in a small box or cabinet that may have a lockable cover. Inside the door cover, there is usually an instruction label that explains how to set the ON-OFF cycle, as well as listing the ratings of the device. For example, it might say "40 amps, 125 volts, 690 VA pilot duty, 1 HP." These figures will choose a time switch that matches your need.
This kind of time switch time is set by lifting up on the timer dial and turning it to the proper time, then making the necessary adjustments to pegs or levers that control the on-off cycles. When power is applied to the time switch, the motorized dial will keep time, just like a clock or watch.
This kind of time switch is wired into a circuit much like a small appliance circuit, with an incoming electrical (LINE) cable connected to screw terminals on the switch, and the outgoing power cable connected to LOAD terminals.
Anatomy of a Digital Time Switch
Newer digital time switches are quite similar to modern dimmer switches in the way they are wired. They generally fit into standard wall switch boxes, and most have wire leads that connect directly to circuit wires with wire connectors. A faceplate with a LED screen and touch buttons allow you to set the time of day, then program in the ON-OFF cycles you need. Wiring this kind of switch is no more difficult than wiring a standard wall switch.
Tools and Supplies You Will Need
- Time switch
- Combination tool or wire strippers
- Wire connectors (wire nuts)
- Pigtail wires (as needed)
Note: This project shows how to make the basic wire connections for a time switch once the circuit cables and switch box have been installed. Running cables or adding a circuit may require the help of a licensed electrician before the switch can be connected.
How to Wire a Mechanical Time Switch
Before making wire connections, make sure the circuit carrying power to the time switch cabinet is turned off.
Connect the Ground Wire
When wiring a mechanical time switch, begin by connecting the ground wires. This is done by attaching one end of grounding pigtail wire to the green ground screw on the time switch, then joining the other end of the pigtail to the incoming and outgoing circuit ground wires, using a wire connector (wire nut).
Tuck the ground wires along the inside of the switch box, away from the terminal connections. Bend the wires in such a way that they can't touch any connection points and short out.
Connect the Neutral Wires
The next step in wiring the time switch is to connect the neutral wires. Cut an 8-inch length of white insulated wire as a pigtail, then strip 1/2-inch of insulation from each end. Insert one bare end of the pigtail into the neutral screw terminal on the switch and tighten the screw. This terminal may be marked NEUTRAL, or it may be indicated as a neutral by a silver-colored screw.
Join the other end of the pigtail to the incoming and outgoing white circuit wires and connect them together with a wire connector (wire nut).
Tuck the excess wire into the top of the switch box.
- Note: Some time switches may have separate screw neutral screw terminals for the incoming and outgoing neutral wires. If so, simply connect each circuit neutral wire to one of the available neutral screw terminals.
Complete the LINE Connection
The hot wire connections for a mechanical timer switch include both a LINE and LOAD connection. The LINE connection is where the incoming hot wire from the power source is connected, while the LOAD connection carries power onward from the switch to the appliance or device.
Strip 1/2-inch of insulation from the black wire on the incoming cable (delivering power from the source), and insert the end of this wire into the screw terminal marked LINE. Tighten the screw snugly, then bend the excess wire into the bottom of the box.
Complete the LOAD Connection
Strip 1/2 inch of insulation from the black wire in the outgoing cable (the one carrying power onward to the appliance or device), then insert the end of this wire into the screw terminal marked LOAD and tighten down the screw. Tuck the excess wire into the bottom of the box.
Install the Flash Shield
For safety purposes, time switches come with a wire terminal flash shield that shields you from a flash that could occur when a hot wire comes in contact with a neutral or ground wire. For safe operation, this shield must be in place. It simply slides over a plastic tab that holds it in place. You'll notice that the shield has reference markings to show the proper wiring connections.
Set the Time
Set the switch to the correct time of day, then set the ON-OFF cycle as desired. Follow the manufacturer's directions when making time settings.
How to Wire a Digital Time Switch
Connecting a digital, programmable time switch is done in much the same way as with a modern single-pole dimmer switch. Some digital time switches will have screw terminals to which the circuit wires are connected, while other switches have wire leads that are connected to the circuit wires with wire connectors. Most typically, there are three wire leads: a green ground lead, a black LINE lead, and a blue LOAD lead. Digital time switches generally have no neutral wire connections.
Before making wire connections, make sure the circuit carrying power to the switch box is turned off.
Connect Ground Wires
Connect the green grounding wire on the switch to the circuit grounding wires, using a wire connector. (If the switch has a grounding screw instead of a lead, use a grounding pigtail to connect it to the circuit grounding wires.)
Connect LINE Wires
Connect the black wire lead (the LINE) on the switch to the hot wire from the power source, using a wire connector. (If the switch uses screw terminals rather than wire leads, connect the feed circuit wire to this screw.)
Connect LOAD Wires
Connect the blue wire lead on the switch (the LOAD) to the circuit hot wire leading to the appliance or device.
Carefully tuck the wires into the box, push the switch into the wall box, then attach the mounting straps to the box. Attach the cover plate, then program the switch according to manufacturer's directions.