CHAPTER 2 EQUIPMENT PROTECTION

Question 1

• designed to detect and RAPIDLY INTERRUPT low-level equipment ground faults.

• operates on the same principle as GFCI (ground fault circuit interrupter) protection by monitoring the current drawn through the conductors of an electrical circuit and quickly shutting off power when the current is not equal.

Answer 1

GROUND FAULT PROTECTION

Question 2

• A particular type of SENSING TRANSFORNER. It encircles the conductors in the switchboard or panel board and produces a low-current output signal if all current flowing to the load does not return to the source through the phase or neutral conductors.

• The low-current output is sensed by a ground fault _________ with adjustable sensitivity and time delay settings. When a signal above the sensitivity setting persists beyond the time delay setting, the relay operates to open the switch or circuit breaker.

Answer 2

CURRENT TRANSFORMER

Question 3

• A SUDDEN INCREASE IN ELECTRICAL CURRENT OR VOLTAGE or voltage that is very short in duration.

• The said increase may be caused by a lightning strike or by a sudden power spike caused by a problem in the utility transmission and generating system.

• May damage sensitive equipment such as computers, televisions, machines, etc.

Answer 3

POWER SURGE

Question 4

• A measure of the level of surge that an SPD can withstand.

• Manufacturers specify the surge ratings of their SPDs.

Answer 4

SURGE RATING

Question 5

• An electrical device that prevents power surges from reaching electric and electronic equipment or another device.

• They work by instantly limiting the transient voltage from a power surge to a safe level for the equipment they protect by diverting the large surge current safely to the ground.

• It also diverts the surge by allowing the current to flow past rather than through the protected equipment.

Answer 5

SURGE PROTECTION DEVICE

Question 6

A semiconductor device used mainly on AC power applications with surge ratings ranging from a few hundred to many thousands of amps.

Answer 6

METAL OXIDE VARISTOR ( TYPES OF SURGE PROTECTION DEVICES )

Answer 7

TYPES OF SURGE PROTECTION DEVICES

Question 8

A primary surge protection component with a surge rating of several thousand amps comprises a sealed tube containing a particular gas that breaks down at a given voltage rise time.

Answer 8

GAS DISCHARGE TUBES (TYPES OF SURGE PROTECTION DEVICES)

Question 9

A secondary surge protection component used for ACCURATE CLAMPING of surge voltages. It has a quicker response time than the GDTs and provides a more accurate clamping voltage than MOVs.

Answer 9

ZENER DIODE (TYPES OF SURGE PROTECTION DEVICES)

Question 10

A circuit comprising different types of surge protection components, taking advantage of each component’s strengths. A hybrid may combine the high surge capability of a GDT with the accurate voltage clamping of a surge diode

Answer 10

HYBRID CIRCUIT

Question 11

• It refers to the peak instantaneous current, measured in amperes (A), drawn by an electrical appliance or piece of equipment (e.g., power supplies, AC motors, lamps, and lighting ballasts) is first turned on.

• An ___________ can also be reduced by an ____________ limiter, which protects circuits that encounter high inrush loads up to 30 times the rated current for the one-half cycle at 60 Hz and eliminate nuisance tripping. However, many techniques are used to limit _______________.

Answer 11

INRUSH CURRENT, INPUT SURGE CURRENT

Question 12

are the most used inrush current limiter for power supplies and motors.

Answer 12

NEGATIVE TEMPERATURE COEFFICIENT (NTC) THERMISTORS

Question 13

• a thermally sensitive resistor with a resistance that changes significantly and predictably due to temperature changes.

• When equipment is first turned on, the NTC thermistor is cooled, and its resistance is high, limiting current flow.

• Resistance decreases rapidly as the

thermistor self-heats, allowing near-full current to flow (at 61 Ω).

Answer 13

THERMISTOR

Question 14

• A disadvantage is that when the NTC thermistor is switched off, it initially _______ heat, so it offers little _________ and cannot limit the inrush current until heat is dissipated.

• The cooldown time varies according to the device, its mounting method, and ambient temperature.

Answer 14

retains, resistance

Question 15

• Lightning discharges have been measured from ________ A to more than __________ A, with rise times to peak current of less than 10 microseconds (10 millionths of a second).

As a result, lightning causes more damage, injuries, and deaths each year than tornadoes, hurricanes, or floods. • Lightning discharges have been measured from 2000 A to more than 200 000 A, with rise times to peak current of less than 10 microseconds (10 millionths of a second). As a result, lightning causes more damage, injuries, and deaths each year than tornadoes, hurricanes, or floods.

Answer 15

LIGHTNING PROTECTION, 200, 200 000

Question 16

• He first suggested protecting buildings and other structures from the effects of direct lightning strikes by the use of protective conductors.

• His theory stated that lightning protection must provide a direct path for the lightning bolt to follow to the ground, and it must prevent destruction, injury, or death as the current travels that path.

Answer 16

benjamin franklin

Question 17

• sometimes called air terminals, are placed at the top of the protected structure. These lightning rods have equally spaced a maximum of __ ft, apart from the structure’s high points.

• A network of _________ copper or aluminum tape (thick, flat cable) bonds the rods to grounding electrodes driven into the earth. _____ roof vents in the proximity of the lightning rods are also connected to the conductive tape

• The system of vertical rods, tape, and ground electrodes is designed to present a low _______ (resistance) path to the lightning current that diverts current away from the building’s structural parts.

• A surge protection device can minimize the damaging effects of a lightning strike. Additionally, power passing through electrical circuits can generate relatively high magnetic fields that damage electronic equipment.

Shielding the wiring can minimize damage.

Answer 17

VERTICAL LIGHTNING RODS, 20, conductive, metal, impedance

Question 18

• A _________ location is when fire or explosion hazards may exist because of flammable gases or vapors, flammable liquids, combustible dust, or quickly ignited fibers under regular operation or abnormal operating conditions.

Answer 18

hazardous