NSTM Chapter 300, Electric Plant - General Flashcards Preview

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Flashcards in NSTM Chapter 300, Electric Plant - General Deck (143):
1

For repair activity work conducted shipboard not IAW NSTM Chapter 300, a ___ between shipyards/repair activities and Ship's Force

Memorandum of agreement must be documented

2

For naval applications, voltages greater than or equal to ___ are considered high voltage

1000 volts

3

The resistance of a human body is about ___

500 ohms

4

When the skin is damp the resistance of a human body is about ___

300 ohms

5

A situation where electrical current passes through air gaps between ungrounded conductors or between conductors and grounded components

Arc flash

6

Another product of an arc flash is the incident energy, which is ___

Radiant energy

7

Radiant energy is expressed in ___

Calories per centimeter squared (cal/cm^2)

8

Threshold for a second degree burn

1.2 cal/cm^2

9

Threshold for a third degree burn

10.7 cal/cm^2

10

Two major hazards with an arc flash

Arc temperature
Incident energy

11

Occurs when the severity of an arc or short circuit current causes destructive heating and explosive vaporization of both the surrounding air and the metal in the current path

Arc blast

12

The unobstructed distance from exposed energized circuits within which unprotected skin could receive a second degree burn if an arc flash were to occur

FPB

13

FPB

Flash Protection Boundaries

14

The FPB distance aboard a ship for 450-volt circuits is ___

4 feet

15

The FPB distance aboard a ship for 4160-volt circuits is ___

11 feet

16

The FPB distance aboard a ship for 13.8K volt circuits is ___

13 feet

17

An FPB of 4 feet is applicable to circuits with rated voltages between ___

30-1000 volts

18

An FPB of 11 feet is applicable to circuits with rated voltages between ___

1000 to 5000 volts

19

An FPB of 13 feet is applicable for voltages ___

Greater than 5000

20

The FPB does not need to extend past ___

Permanent solid structure

21

Intentionally connects the non-current carrying conductive parts of electrical equipment, such as the enclosure, frame, or chassis, to ground through a low-resistance path

Equipment grounding

22

The purpose of equipment grounding

If energized electrical conductor contacts the enclosure due to fault or damage, it shunts the current away from possible human contact

23

Grounding of metal enclosing cases, bases, frames, and structural parts of electrical equipment shall be IAW ___

MIL-STD-1310 and MIL-E-2036

24

On metallic hull ships, grounds can be provided by the fact that the metal enclosing cases or frames are ___

In contact with one another and the metal structure of the ship

25

A ground must be provided for equipment mounted on a hinged door if the voltage exceeds ___

30 volts

26

Resistance to ground should be less than ___

0.1 ohm

27

___ systems provide a limited amount of current when one phase is faulted to ground, and thus allows critical equipment to continue operation until steps can be taken to remove the fault

Ungrounded

28

___ system designed so that a phase conductor fault to ground will produce high current and quickly trip the circuit breaker or blow the fuse

Grounded neutral

29

Electric utility service for wiring ashore uses ___ system

Grounded neutral

30

___ system is isolated from the ungrounded power system at the upstream supply transformer

Grounded neutral receptacle

31

Some ships use ___ for improved personnel safety over that which standard circuit breakers provide

Ground fault current interrupt equipment

32

Both conductors of a shipboard receptacle have a ___

Potential between the conductors and the ground

33

Ashore receptacles has one ___

Neutral conductor which is connected to ground at the source

34

The resistances of an ungrounded system when ___, form the insulation resistance of the system

Combined in parallel

35

Insulation resistance of the system is measured using ___

500-volt DC megger or installed ship's active ground detector

36

Contain capacitors connected from the conductors to the ground

Electromagnetic Interference Filters

37

Used to reduce interference to shipboard electrical and electronic equipment

Electromagnetic interference filters

38

Ungrounded high voltage power systems have a high failure rate due to ___

Transient overvoltage surges

39

The surges in an ungrounded high voltage power system is the result from ___

Oscillations that occur because of the system's inherent inductance and capacitance

40

Ships with electrical systems rated ___ are designed with high resistance grounding subsystems

1000 volts and above

41

High resistance grounding subsystems are normally contained within an enclosure with ___

A three-phase transformer connected in a wye/delta configuration with an open delta secondary. A resistor is connected across the open delta secondary

42

Absorbs and clamps voltage spikes on the main AC bus

Transient voltage surge suppression systems

43

Arc Fault Detection systems are installed on ___ where they ___

Switchboards and load centers
Continuously monitor the interior of these enclosures for arcing faults

44

Arc fault detection systems can sense ___

Pressure, gassing particles, and light

45

AFD systems consist of ___

Pressure sensors, thermal ionization detectors, photo sensors, and control units that monitor the sensors

46

In an AFD system the thermal ionization detector is associated with ___

The continuous thermal monitor system

47

In an AFD system the control circuitry requires ___ to indicate the presence of an arc and trip the switchboard isolation

Both a photo sensor and its corresponding pressure sensor

48

Do not join extension cords longer than ___ together

25 ft

49

Never join more than ___ extension cords together

2

50

Extension cords up to ___ are permissible

100 ft

51

___ use silicon-controlled rectifiers vice mechanical contacts to provide dual power supplies to individual loads

Static automatic bus transfer switches

52

Electrical systems require a minimum of ___ isolation points in each conductor isolation path

One

53

All electrical work should be approached with a focus on ___

What could go wrong

54

CO permission is not required when performing ___

IVV or safe-to-work voltage checks

55

The safety observer for work on energized circuits must ___

Be trained in first aid, know what breaker isolates the system and be ready to operate it immediately, and not engage in any distracting behavior

56

For work on energized circuits greater than ___ a safety line shall be attached to the worker

300 volts

57

IVV

Initial Voltage Checks

58

When shorting a capacitor to drain the charge it should be done ___

Three times about ten second apart

59

When energized wiring and non energized wiring are located in close proximity to each other

Capacitive coupling

60

Detecting stray voltage using Simpson 260 the reading should be ___

Less than fill scale deflection on the 2.5V scale

61

Detecting stray voltage using DVM set to low impedance mode or Fluke stray voltage eliminator installed the reading should be ___

Less than 3 volts

62

Capacitive storage is verified as indicated by ___

Minimum of 5 seconds with steadily decreasing voltage indication

63

To dissipate capacitor stored energy the ground must have a reading of ___

Less than 0.1 ohm

64

Do not approach or take a conductive object without an approved insulating handle closer than ___ to potentially energized exposed equipment without proper PPE

2 ft

65

Establish an electrical safety and arc flash area while checking that ___ equipment is deenergized

Greater than 1000 volts

66

Proximity voltage tester must be ___ from equipment being tested

8 inches or closer

67

STW

Safe-to-work

68

If all circuits are ___ STW checks are not required

30 volts or less

69

Safety devices installed in power and lighting circuits and in control circuits to protect the equipment and circuits from damage due to excessive current

Fuses

70

Silver plated fuses develop a ___ over time that does not affect performance

black oxide coating

71

SIlver plated fuses are designated by ___

The letter S following the current rating of the fuse

72

If the replacement fuse blows, then ___

A fault probably exists

73

___ before replacing a fuse

Deenergize the circuit

74

Do not use ___ to grab a fuse that remains in the fuse barrel when the fuseholder is removed

A bare hand

75

For circuits ___ or less, fuses may be removed or replaced without deenergizing the load

10 amps

76

Some indicator types of panel mounted fuse receptacles contain riveted connections that carry current. These connections are required to be ___

Soldered to achieve a low-resistance connection

77

A draw-out type circuit breaker uses a ___ to remove

Racking mechanism

78

The imaginary plane formed by the opening of an electrical enclosure

Electrical safety plane

79

If electrical components are mounted on the door, then the plane includes ___

The arc formed by the doors edge as it swings open

80

No precautions are required for visual inspections of equipment or circuits rated ___ or less

30 volts

81

For visual inspections, erect a barrier at least ___ from the electrical plane of the equipment

2 ft

82

Minimum PPE to wipe water off of equipment

Rubber gloves

83

Have an attached cord, are hand-held or frequently handles while operated, and are plugged into an electric power receptacle

Portable electrical tools and devices

84

A unit that is not hard-wired, can be moved, but normally is stationary while operating

Mobile electrical equipment

85

Equipment brought onboard by the owner for personal use

Personal electrical equipment

86

Use rubber gloves when using metal-cased tools that are not marked as ___

Double insulated

87

When performing work that could tear the rubber gloves ___

Wear leather gloves over them

88

If damage or defects are found in portable cord and plug-connected hand-held equipment and cords, then ___

Remove from service, and turn it into tool issue or the electrical safety officer

89

Isolated receptacle units are isolated from ___ by ___

The main power distribution system
Transformers

90

Isolated power receptacles circuits are limited in length to reduce the ___ to an acceptable level

Line-to-ground capacitance

91

Isolated power receptacles limit ground leakage to less than ___

10 mA

92

Refers to the existence of two separate insulating systems within a tool or device

Double insulated

93

The term "double insulated" stamped on a device is a ___ designation

Underwriters Laboratories (UL)

94

Computer power strips of the marine type must have ___

A metal case, double-pole switch/circuit breaker, and dual thermal fuses. Must provide both common and normal mode protection and be listed by a nationally recognized testing laboratory

95

Marine power strips have the commercial item description of ___

A-A-50622

96

If the power cord must be more than 25 ft long, the equipment must be ___

Permanently mounted and hard-wired

97

Commercially available mobile electrical equipment must not be used aboard ship unless ___

They have been approved for shipboard use

98

Three-conductor flexible cables should be ___

Type SO or ST, black, white, and green

99

The length of power cords for high-current equipment should be ___

Only as long as required

100

Testing of electrical equipment other than visual inspections should be done in a workshop equipped with ___

An electrically safe work bench and insulating rubber deck covering

101

Grounding conductors shall be ___ and have minimum cross-sectional area of ___

Stranded
9000 circular mils (AWG #10)

102

The conduction of electricity across the surface of a dielectric

Creepage

103

The shortest distance between two conductors or between a conductor and ground, measured along the surface of the insulating material

Creepage distance

104

By increasing the creepage distance, the creepage current is ___

Reduced

105

In order to use air as insulation, a solid insulating material must be used for ___

Support to maintain the required air-spacing distance between uninsulated conductors

106

Insulation systems are classified by temperature because ___

Temperature has the predominate effect of insulation life

107

Insulation life will decrease by one half for every ___ above the specification limit

10 - 15 degrees C (50 to 59 degrees F)

108

Class B or F insulation systems: maximum temperature rise

120 degrees C minus (nameplate max ambient)

109

Class H insulation systems: maximum temperature rise

145 degrees C minus (nameplate max ambient)

110

Class N insulation systems: maximum temperature rise

170 degrees C minus (nameplate max ambient)

111

For top-curved surfaces having a radius greater than 3 inches and for top-flat surfaces, surface creepage distance shall be increased ___ where these surfaces have irregularities which permit the accumulation of dust and moisture

33%

112

Three methods of taking temperatures in wiring

Thermometer
Resistance
Infrared

113

The ability to withstand potential difference and is usually expressed in terms of voltage at which the insulation fails due to electrostatic stress

Dielectric strength

114

Maximum dielectric strength values can be measured only by ___

Testing to destruction

115

Two reasons for using an ungrounded power system aboard a ship

Improve reliability of power
Prevent galvanic corrosion

116

Insulation resistance should be verified in reference to the ___ in which the winding is embedded, between ___, and between ___

Metallic structure
Individual windings on the same component
Isolated brush rigging polarities

117

When testing rotor windings, the test voltage should be applied between the copper conductors and a metallic part of the rotor rather than the ___ in order to ___

Stator
Eliminate the insulating effect of oil in the bearings

118

For portable tools, appliances, and cable assemblies, measure the insulation resistance of each line terminal to the ___ and to the ___

Equipment frame
Metal shell of the equipment plug

119

The ratio of the 10 minute insulation resistance value to the 1 minute insulation resistance value

Polarization Index

120

The polarization index test is useful for ___

Appraising the cleanliness and dryness of a winding

121

Insulation resistance of a winding will normally ___ with the duration of the test voltage

Increase

122

The measured insulation resistance of a dry winding in good condition will reach a fairly steady value in ___

10 to 15 minutes

123

The measured insulation resistance of a wet or dirty winding will reach a fairly steady value in ___

1 or 2 minutes

124

For most equipment, the minimum acceptable value of polarization index is ___

2.0

125

Following a DC high-potential test, hold the ground for at least ___

Four times the accumulated test period or 1 hour, whichever is longer

126

Perform a ___ before a high-potential test

500 volt megger

127

No more than ___ AC high-potential tests should be made during the repair process

One

128

An electronic device designed specifically to stress the whole winding's insulation system by applying a series of pulses between turns of a coil, between coils, between phases of two windings or two legs of a winding, and from the windings to ground to detect short circuits

Surge tester

129

Two methods of sealing an explosion-proof enclosure

Completely filling the voids with liquid
Hermetic sealing

130

Being incapable of releasing sufficient electrical energy under normal or abnormal conditions to cause ignition of a specific hazardous atmospheric mixture

Intrinsically safe equipment and circuits

131

The ___ of paint from electrical equipment should be avoided

Removal

132

Repainting of electrical equipment should be done only when ___

Necessary to prevent incipient corrosion due to lack of paint

133

Paint should never be applied to any ___ in electrical equipment

Insulating surfaces

134

Water piping near electrical equipment should be ___

One continuous length

135

Rule of thumb for using electric lamps to keep equipment dry is to provide ___ for each ton of machine weight

100 watts

136

The temperature in the secured equipment should be kept about ___ above the ambient air temperature

2.8 to 5.6 degrees C (5 to 10 degrees F)

137

Desiccant should be composed of ___

Silica gel or clay

138

___ desiccant is required with machines that use carbon brushes

Clay

139

Silica gel desiccant will cause carbon brushes to ___

Deteriorate rapidly

140

Bags of desiccant are never to be placed inside a ___

Motor enclosure

141

Transparent plastic sheet to wrap secured equipment should be at least ___ thick

4 mils

142

When the relative humidity reaches ___, the desiccant should be replaced

40%

143

Core testing is mandatory for all motors requiring ___ when repairs are accomplished

Rewind