Electrical Principals Chapter 5 Switches, Fuses, Ground, Receptacles, Basic Circuit Conditions

Switches

Switches A Switch is a device that is used to start, stop, or redirect the flow of electricity in an electrical circuit. A Switch must be rated higher than (or equal to) the voltage and current the Switch is controlling. There are three manual types of Switches used to control the ON/OFF current flow in a circuit and they are two-way, three-way, and four-way switches.

Switches Two-Way Switch is a single-pole, single- throw (SPST). A Two-Way Switch has two positions and they are ON and OFF A Two-Way Switch is used to control a circuit from one location.

Switches Three-Way Switch is a single-pole, double-throw (SPDT) switch. A Three-Way Switch does not have an ON – OFF position. A Three-Way Switch is used to control a circuit from two different locations.

Switches A Four-Way Switch is s double-pole, double-throw (DPDT) switch. A Four-Way Switch changes the electrical connections inside the switch from straight to diagonal. A Four-Way Switch does not have ON – OFF positions. A Four-Way Switch is used with Three- Way switches to control a circuit from three different locatrions.

Switches

Fuses

Fuses A Fuse is an equipment protection device that consists of a thin wire link within a casing. All Fuses have a current rating and this indicates what value of current will generate enough heat to open the Fuse. When the circuit current exceeds the rating of the fuse, the fuse opens (wire link melts) and prevents current from flowing in that part of the circuit.

Fuses Fuses come in a variety shapes, sizes, Fuses are very low resistance devices connected in series with the circuit’s conductors. Fuses for DC current are different from Fuses used in AC circuits. Fuses ARE NOT Interchangeable between AC and DC circuits.

Fuses Fuses also have a voltage rating that indicates the maximum circuit voltage that can be applied across the Fuses by the circuit in which the Fuses resides. This voltage rating, which is important after the fuse has blown, prevents arcing across the blown fuse contacts. Once the fuse has blown, the circuits positive and negative voltages are now connected across the fuse contacts.

Fuses If the voltage is too great, an arc can jump across the gap, causing a sudden surge of current, damaging the connected equipment. Fuses are mounted with Fuses holders and normally are placed at the back of the equipment for easy access. When replacing Fuses ensure the power to the equipment is turned OFF before replacing a blown Fuses.

Ground

Ground Ground is a term used to identify zero potential. All potentials are either positive or negative with respect to ground. Ground, in electricity, is an electrical conductor that is connected to Earth to complete a circuit. In electrical equipment, such as household appliances, the ground conducts electric current that may build up in the appliance because of a "leak" or a short circuit. There are two types of Grounds: Earth and Electrical.

Ground In homes, offices, and buildings or AC circuits, all electrical circuits and appliances are earth grounded. In automobiles, the chassis becomes the ground for all circuits. The ground serves as part of the complete circuit. In electronics, electrical ground serves a different purpose: Ground is defined as the zero reference point against which all voltages are measured.

Receptacles

Basic Circuit Conditions