1. EET 323 – Electrical System Design Lecture 4: Wiring Devices
Radian Belu, PhD

2. Lecture Objectives
Upon completion of this lecture the students will be able to: 1. Understand the operation and application of standard toggle switches, including 3-way and 4-way switches 2. Understand the various rating of switches, receptacles, and disconnect switches 3. Understand characteristics of single and duplex receptacles 4. Understand the grounding requirements for receptacles 5. Understand the operation of ground fault receptacle 6. Specify the proper NEMA configuration of receptacles 7. Specify and apply isolated ground receptacle 8. Understand the ratings and types of various disconnect switches 9. Specify and apply disconnect switches 10. Apply, calculate, and select devices studied in this lecture

3. Chapter Outline
Various types of wiring devices used in electrical power distribution
Switches, receptacles, and disconnects
These devices are used to control the flow of electrical current and power and to allow for desired operation of other devices and equipment
Types and ratings of wiring devices
The use of disconnect switches to control and isolate electric equipment.

4. Toggle Switches
The switches used in most residential and commercial applications, for controlling the light fixtures, and occasionally to control small motor loads are toggle switches
Most of these switches have two positions, and many of them are marked with the ON and OFF positions.

6. Contact Arrangements
The contact arrangements of the toggle switches refers to the internal switch arrangement that is accomplished by the switch.
Notice that many toggle switches are self-contained with no externally visible switch contacts, with the exception of disconnect switches.
The switch arrangement is specified by the number of poles (the number of inputs to the switch) and by the number of throws (the number of outputs affected by the switch operation).
SPST (single-pole single-throw, Figure 402(A)) – the most common switch arrangement for toggle switches, with a single conductor entering and leaving the switch. The switch has two states: ON or OFF. SPST switches are commonly used to control the switching operation of light fixtures from a single location.

8. Contact Arrangements (cnt.)
DPST (double-pole single-throw, Figure 402(B)) – two separate inputs are switched to two separate outputs (2 separate outputs can be switched OFF and OFF from two separate inputs. This type of switch is commonly used to switch two ungrounded (hot) conductors in a circuit. It is also permissible to switch both the ungrounded and grounded (neutral) circuit conductors as long as both are switched simultaneously.
SPDT (single-pole double-throw, Figure 402(C)), also known as a three-way switch – the input may be switched to one of two distinct outputs. One possible application of the SPDT switch is to switch of the ungrounded conductor supplying two separate loads in and alternating fashion (only one load energized at any given time).

9. Contact Arrangements (cnt.)
DPDT (double-pole double-throw, Figure 402(D)) – two distinct inputs are connected to two distinct outputs; the arrangements is similar to having two distinct SPDT switches controlled by a single operation level. The DPDT switch could be used to switch two ungrounded conductors supplying separate loads in an alternating fashion with one of the load energized at any given time. It is also possible to switch the ungrounded and grounded conductors simultaneously with a DPDT switch.

10. Toggle Switch Applications
The most common SPST switch application (Figure 4-3(A))) to connect a load to a source, between an ungrounded and grounded conductors. The load is energized or de-energized by operating the switch.
The DPST switch can be used to energized or de-energized a load connected between tow ungrounded conductors or between the ungrounded and grounded conductor of a system (Figure 4-3(B)). It is permissible to switch a load connected between the ungrounded and grounded conductor of a system provided both the ungrounded and grounded conductors are switched simultaneously.

11. Toggle Switch Applications
The most common use of the SPDT switch is as a three-way switch (see Figure 4-4, showing an application requiring 2 three-way switches connected in series to control the switching operation of a lighting outlet). The common terminal on a 3-way switch will be darker in appearance than other two terminals (so-called travelers).
In this way, the lighting outlet can be controlled from two separate locations, such as from each end of a hallway or from two entrances of a building.

13. Toggle Switch Applications
A modification of the DPDT switch is commonly used in conjunction with tow 3-way switches to control a lighting outlet from 3 or more locations (so-called four-way switch). The internal switching arrangement of the 4-way is the same as that of DPDT switch, but with two internal connections connecting 2 pairs of output terminals together (Figure 4-5(A)). The 4-way switch has two terminal connections on the source side and other two on the load side.
Inspection of Figure 4-5(A) reveals that with the switch in one position, terminal a is connected to c, and terminal b is connected to d; while the switch in the other position, terminal a is connected to d, and terminal b is connected to c, with only one traveler energized at a give time. The lighting outlet can be controlled from three separate locations.

15. Switch Ratings
In addition to the voltage and current ratings, toggle switches are rated for either AC operation only or AC/DC.
Section (A) and (B) of the NEC specifies the required capabilities of the switches of AC and for AC/DC operation.

17. Receptacles
The connection of the load to the source can be done through a variety of receptacle configurations. The connections to the receptacle are typically made by screw terminal connections on the sides of the receptacle
The ungrounded terminals are, in generally bronze in color, and the grounded terminals are silver in color.
The equipment-grounding conductor terminal is green in color and is located near the top or bottom of the receptacle.

34. Wiring Receptacles
Duplex receptacles may be split-wired for a division of load between two circuits supplying the receptacles (Figure 4-16).
The receptacles are supplied by two circuits from a two-pole breaker, which ensures that both hot conductors are de-energized in the event of a short circuit on either of the tow circuits supplying the receptacles
The strap connecting the two hot terminals of each receptacle must be remove to allow for the connection of two circuits to each receptacle, otherwise the strap short-circuits the two ungrounded conductors of the system.
The voltage potential between the two hot terminals of split-wired receptacles is 240 V for a single-phase, 3-wire system
The hot conductors are typically pigtailed

36. Wiring Receptacles
The connection of the grounded (neutral) conductor to split-wired receptacle must be pigtailed to each of the receptacle. If one of the receptacle must be removed, the pigtail would be removed from the terminal receptacle only, with continuity of the grounded conductor maintained to other receptacles in the group.
If the continuity of the grounded conductor is broken, the potential voltage of the grounded conductor terminal (neutral) will float between 0V and 240 V, with the actual voltage determined by the load impedance

39. Disconnects – Construction and Ratings
Disconnect switches (Figure 4-18) are heavy-duty devices used to disconnect a load from the electric supply; The ratings of disconnect switches are much higher than those of toggle switches
The most common application of a disconnect switch is in motor circuits where a physical means of disconnecting and de-energizing the motor is desired
Disconnect switches are usually enclosed in a metal housing, with an operating handle located on the right-had side of the enclosure

40. The switch contacts are usually of a knife-type construction, with both movable and stationary contact assembly, with a wiping action taking place between contacts, during the switch operation, which keeps the contact clean for a good electric operation

41. Disconnects – Construction and Ratings
The switch contact operation mechanism allows for a quick-make, quick-break operation to minimize arcing
Disconnect switches are available as either fused or un-fused
The fused-type switch has a fuse-holder in addition to main switch contacts, allowing the switch to accommodate the appropriate rated fuse for over-current and short circuit protection of the downstream equipment. A current0limiting fuse may be installed only, acting to limit the let-through fault current in the case of a short circuit.
Disconnect switches are typically rated at either 240 V for general duty or 600 V for heavy-duty applications. The voltage rating of the switch must equal or exceed the line-to-line system voltage

43. Disconnects – Construction and Ratings
The ampere ratings of disconnect switches are 30 A, 60 A, 100 A, 200 A, 400 A, 600 A, 1600 A, 2000 A, 4000 A and 6000 A. The rating of the fuse installed in a disconnect must be equal to or less than the rating of the switch. The physical dimensions of the fuse make it unfit into the fuse-holder of a disconnect switch having lower than that of the fuse.
In addition to their ampere ratings, the disconnect switches typically have a power rating as well. The power rating of the disconnect switch must exceed the power rating of any motor connected to the load side of the switch

47. Applications
The most common application of the 3PDPT and 4PDT switches is the switching of ungrounded and grounded conductors of 3-phase system (Figure 4-21(A)). This type of switching arrangement may be used in conjunction with an emergency generator to switch from the normal utility power supply to the emergency generator supply. The switching is often done automatically by the transfer control logic systems
The 3DPT switch, only the three ungrounded conductors are switched. The 4PDT switch (Figure 4-21(B)) allows the grounded (neutral) to be switched as well as the ungrounded conductors. The 4PDT switch is often used in transfer switches applied to systems having ground fault protection

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THE END of the Lecture
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