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PROTECTIVE DEVICES

PROTECTIVE DEVICES. Safety Protective devices - devices designed to automatically limit or shut off the flow of electricity in the event of a ground-fault, over-load or a short circuit in the wiring system . PROTECTIVE DEVICES. Fuses

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PROTECTIVE DEVICES

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  1. PROTECTIVE DEVICES • Safety • Protective devices - devices designed to automatically limit or shut off the flow of electricity in the event of a ground-fault, over-load or a short circuit in the wiring system

  2. PROTECTIVE DEVICES • Fuses • An "over-current" device that is placed in a circuit to protect the circuit from excessive spikes in current • They automatically open or break the current path when the amount of current becomes excessive • Can be fixed by replacing with a new fuse • Use the size and type of fuse that is recommended by the manufacture • Never use anything other than a fuse to complete a circuit (wire, foil, solder) • Replace with the correct current rating or smaller • Replace with the correct voltage rating or higher

  3. PROTECTIVE DEVICES • Circuit breakers • An "over-current" device that is placed in a circuit to protect the circuit from excessive spikes in current • They automatically open or break the current path when the amount of current becomes excessive • They can be fixed by resetting the circuit breaker

  4. PROTECTIVE DEVICES • Ground-fault-circuit-interrupters (GFCI) • The GFCI is designed to shut off electrical power with in as little as 1/40th of a second • It works by comparing the amount of current going to the equipment against the current returning from the equipment • If the difference exceeds 6mA the GFCI stops current quickly enough to prevent electrocution • The GFCI is often found in wet locations such as bathrooms or kitchens • The GFCI can be fixed by resetting the GFCI

  5. PROTECTIVE DEVICES • Surge protectors/suppressors • Also called surge arrestors • Limits surge voltages (spikes) to prevent damage to equipment power supplies • Used at power service-entrances to protect against lightning strikes • Also as an adapter that plugs into the wall to interface with equipment • Protects sensitive computerized equipment

  6. WIRE SIZING • Wire Sizing • Two methods or standards for wire sizing • Based on the diameter or size of the wire • AWG • American wire gauge • Range is from #40, the smallest, to #4/0 (four aught), the largest

  7. WIRE SIZING • kcmil • Thousands of circular mils • One inch = 1000 mils • Circular mils of a wire equal the diameter of a single strand multiplied by the number of strands • Starts at 250 kcmil and increases to 2000 kcmil • Larger size wire is measured in this way • Picks up where AWG stops

  8. WIRE SIZING • Grounding • Definition - system of conductors that provide a current path from electrical circuits or equipment to earth • Purpose - to protect the operator and patient from electrical shock

  9. WIRE SIZING • Terms • Grounding conductor • Green wire or green with one or more yellow stripes • Not used as the normal current carrying wire • Fault condition current carrying wire only • Must be of sufficient size to carry enough current to trip a protective device • Characteristics • Grounded conductor must be a solid wire (uninterrupted) from the transformer to the disconnecting means • Grounding conductor and grounded conductor may be tied together at disconnecting ends (common) or run individually

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