Circuit Diagrams and Schematics Lesson Plan PSTS: C6-6

Anticipated Problems What symbols are used in wiring diagrams and schematics, and how are they drawn? What rules should be followed in diagramming various circuits? How can a person diagram electrical circuits using keyless lampholders, pull-chain lampholders, duplex receptacles, and single-pole switches?

Anticipated Problems How can a person diagram circuits using lampholders with three-way and four-way switches? How can a person diagram circuits using a combination single-pole switch and receptacle with a lampholder and applications where receptacles are split for switching?

Terms combination single-pole switch and receptacle control terminal duplex receptacles four-way switches (DPDT) keyless lampholders pull-chain lampholders switch loop connection three-way switches (SPDT) traveler terminals

Draw a Wiring Circuit To successfully draw a wiring circuit on paper, you need to use various symbols that represent the equipment and techniques that will need to be followed in wiring. Other resources may use different symbols. The exact symbol is not as important as how to construct diagrams that will allow the wiring to be accomplished correctly.

Draw a Wiring Circuit In cable, four colors or kinds of wire exist for use. The symbols used for conductors and their respective colors are black wire, white wire, red wire, and bare ground wire.

Cable

Various Devices Various devices are used as lampholders, switches, and receptacles. Duplex receptacle Keyless lampholder (light) Pull-chain lampholder Single-pole switch Three-way switch Four-way switch Combination single-pole switch and receptacle

Basic Electric Symbols

Basic Electric Symbols

Various Devices Additional symbols are used to identify terminals and indicate if wires are spliced or just crossing over. These are brass-colored terminal, silver-colored terminal, green-colored terminal, wires spliced, and wires crossing but not connected.

Diagramming Rules To successfully diagram circuits, a few rules will be helpful. Various techniques exist for diagramming a circuit, and they will not all be covered in this lesson.

Diagramming Rules Generally, black and red conductors carry “hot” power or current from the source (SEP) to the devices within the circuit. The white conductor always is used to carry the current back to the source. This conductor often is referred to as the neutral conductor.

Diagramming Rules Some applications would require a white conductor to actually carry “hot” current, which is a switch loop connection. When completing the diagram, it may be helpful to first draw the white, neutral conductor from the source to its final destination within the circuit.

Diagramming Rules Pull-chain lampholders and duplex receptacles are normally wired so they have “hot” or unswitched power at all times.

Pull-Chain Lampholders Pull-chain lampholders are devices with a built-in switch turned off and on at the lampholder with a string or chain.

Duplex Receptacles Duplex receptacles are double plug-in outlets, which may be installed in a variety of box types. If a person desires half of a duplex receptacle to be controlled by a switch, the entire receptacle would not be wired hot.

Keyless Lampholders Keyless lampholders are devices controlled by a separate switch or switches in the line. Switching is always done in the ungrounded or “hot” conductor.

Switch Loop Connection On occasion, it may be more convenient to bring the source into the lampholder first and then go to the switch, which is a switch loop. A switch loop connection is a two-wire cable union with the white wire as the hot line to the switch.

Three Way Switches Three-way switches (SPDT) are devices used in pairs to control lights or receptacles from two locations. Three-way switches have three screws or terminals. The control terminal is the darkest terminal; it can be called the common terminal.

Traveler Terminals Traveler terminals are the two terminals that receive current when the control terminal is activated via a toggle switch. When the toggle switch is in one position, the common terminal carries current to one traveler terminal. When the toggle switch is in the other position, the common terminal carries current to the other traveler terminal.

Three Way Switches When diagramming and wiring three-way switches, the hot current always enters the control terminal of one of the switches and always exits out of the control terminal of the other switch. The traveler terminals from one of the switches must connect to the traveler terminals of the other switch with no interference.

Four-Way Switches Four-way switches (DPDT) are devices used in conjunction with a pair of three-way switches to control the same light(s) from three or more locations. The four terminals on a four-way switch are all considered traveler terminals. Three-way switches are always wired on ends where switching is needed, and the four-way switches are wired between the two three-way switches.

Four-Way Switches Two traveler terminals from the four-way switch connect to the two traveler terminals from one of the three-way switches. The other two traveler terminals from the four-way switch connect to the two traveler terminals of the other three-way switch. When more than one four-way switch is used, the traveler terminals connect from one switch to the next.

A Combination Single-Pole Switch & Receptacle A combination single-pole switch and receptacle is a device used when a switch and receptacle are desired in the same box. In most cases, the receptacle is always wired “hot,” and the switch is used to control a light or a series of lights. In special cases, the switch may be wired to control the receptacle.

Diagramming Electrical Circuits Various wiring applications can be completed using keyless lampholders, pull-chain lampholders, duplex receptacles, and single-pole switches. Several examples of circuits and diagrams are to follow.

Diagramming Electrical Circuits

Diagramming Electrical Circuits

Diagramming Electrical Circuits

Diagramming Electrical Circuits

Diagramming Electrical Circuits

Diagramming Electrical Circuits

Diagramming Circuits Using Lampholders Many homes have a need to control a light or lights from more than one location. In a stairway where a homeowner would want to turn on a light at the bottom of the stairs and shut it off at the top of the stairs or vice versa.

Diagramming Circuits Using Lampholders

Diagramming Circuits Using Lampholders

Diagramming Circuits Using Lampholders

Diagramming Circuits Using Lampholders

Diagramming Circuits Using Lampholders

Diagramming Combination Circuits In special situations, a person may need to have the switch and receptacle located in the same box. In other situations, a duplex receptacle could be used for plugging in a table lamp that could be turned “on” and “off” using a wall switch. The other half of the receptacle could be used for a clock or other electrical device that would require power at all times.

Diagramming Combination Circuits

Diagramming Combination Circuits

Diagramming Combination Circuits

Review How are pull-chain lampholders and duplex receptacles are normally wired? What type of devices have a built-in switch turned off and on at the lampholder with a string or chain? What is a traveler terminal? When is it used?