Cable Splicing Materials and Tools

Question 1

What are the principal factors in selecting a conductor?

Answer 1

Materials, Flexibility, Shape, Size (current-carrying capacity).

Question 2

What are the two most common conductor materials?

Answer 2

Copper and aluminum.

Question 3

Why is aluminum used despite lower conductivity than copper?

Answer 3

It is lighter in weight and may reduce initial cost, but requires a larger size.

Question 4

What problem occurs when aluminum is exposed to moisture or other metals?

Answer 4

Galvanic action and “cold flow,” making it hard to splice and terminate.

Question 5

What are the standard flexibility classes of conductor stranding?

Answer 5

Solid, Class B (standard), Class C (semiflexible), Class D (flexible), Class G (extra flexible), Class H (very flexible).

Question 6

Name five common shapes of stranded conductors.

Answer 6

Concentric Round, Compact Round, Compact Sector, Annular, Segmental.

Question 7

What is a concentric round conductor?

Answer 7

Wires of the same diameter wrapped around a center wire in layers.

Question 8

What are the advantages of compact round conductors?

Answer 8

Smaller diameter, better weight and space usage, but less flexible.

Question 9

What is the purpose of a compact sector conductor?

Answer 9

To achieve a smaller cable diameter and reduce reactance and voltage drop.

Question 10

What does an annular conductor help reduce?

Answer 10

Skin effect in large cables.

Question 11

What is the segmental conductor used for?

Answer 11

Reduce skin effect with multiple electrically separated segments.

Question 12

What does AWG stand for and what does it measure?

Answer 12

American Wire Gauge; measures conductor size.

Question 13

What happens when you decrease AWG gauge number?

Answer 13

Conductor diameter and current-carrying capacity increase.

Question 14

What is the rule when increasing by 3 AWG sizes?

Answer 14

Doubles area and weight, halves D-C resistance.

Question 15

What is the rule when increasing by 6 AWG sizes?

Answer 15

Quadruples diameter.

Question 16

What is the rule when increasing by 10 AWG sizes?

Answer 16

Multiplies area/weight by 10, divides resistance by 10.

Question 17

What is the function of strand shielding in power cables?

Answer 17

To eliminate voltage stress in voids between conductor and insulation.

Question 18

What materials are commonly used for strand shielding?

Answer 18

Conductive tapes, paints, rubber, graphite compounds.

Question 19

Why must strand shield adhere to insulation?

Answer 19

To prevent ionization in air pockets.

Question 20

What are the three main categories of insulating materials?

Answer 20

Thermosetting, Thermoplastic, Laminated.

Question 21

What is thermosetting insulation?

Answer 21

Requires vulcanization, does not soften when reheated.

Question 22

What is thermoplastic insulation?

Answer 22

Can be reheated and reshaped; softens repeatedly.

Question 23

List 5 evaluation criteria for insulation.

Answer 23

Heat aging, insulation resistance, power factor, dielectric constant, resistance to moisture.

Question 24

What are advantages of impregnated paper insulation?

Answer 24

High dielectric strength, low power factor, thinner insulation.

Question 25

What are disadvantages of impregnated paper insulation?

Answer 25

Water deterioration; needs a difficult-to-handle lead cover.

Question 26

What is varnished cambric insulation made of?

Answer 26

Woven cotton cloth with insulating varnish.

Question 27

What’s a disadvantage of varnished cambric?

Answer 27

High power factor, needs lead sheath.

Question 28

What’s notable about rubber insulations?

Answer 28

Flexible, but degrades in oil, ozone, and sunlight.

Question 29

Temperature range of rubber insulation?

Answer 29

60°C to 130°C.

Question 30

What is butyl insulation known for?

Answer 30

Heat, ozone, and moisture resistance.

Question 31

Strength of silicone insulation?

Answer 31

Fire resistant, flexible to -54°C, but expensive.

Question 32

What is EP insulation?

Answer 32

Ethylene-propylene rubber; excellent heat and weather resistance.

Question 33

What is PVC insulation mainly used for?

Answer 33

Low-voltage power and control cables.

Question 34

Key traits of PVC insulation?

Answer 34

Resistant to chemicals; poor at high temps.

Question 35

What is polyethylene insulation known for?

Answer 35

Moisture resistance, low dielectric loss, good strength.

Question 36

Difference between polyethylene and cross-linked polyethylene?

Answer 36

Cross-linked has better mechanical and heat properties.

Question 37

Name three organizations that set cable standards.

Answer 37

IPCEA, NEMA, UL.

Question 38

What are the insulation thickness levels?

Answer 38

100% (fast clearing), 133% (slow clearing).

Question 39

Function of insulation shielding?

Answer 39

Confine dielectric field and control voltage stress.

Question 40

Purpose of non-metallic tape shielding?

Answer 40

Contact insulation and metallic components for shielding.

Question 41

What is metallic shielding used for?

Answer 41

Reduces shock hazard and provides electrostatic shielding.

Question 42

Function of bedding tapes?

Answer 42

Provide mechanical strength under the sheath.

Question 43

Filler tape use?

Answer 43

Fill interstices between conductors for a uniform shape.

Question 44

Purpose of cable jackets?

Answer 44

Protection from mechanical, electrical, and moisture damage.

Question 45

Four jacket types?

Answer 45

Fibrous, Rubber/Rubber-like, Thermoplastic, Metallic.

Question 46

What does jute serve as?

Answer 46

Binder, cushion, and corrosion protection.

Question 47

Why are glass fiber jackets used?

Answer 47

High-temp and weather resistance.

Question 48

What is asbestos used for?

Answer 48

Heat resistance in wet/underground cable sheaths.

Question 49

What is natural rubber’s weakness?

Answer 49

Affected by ozone, sunlight, and oil.

Question 50

What synthetic rubbers are used?

Answer 50

Neoprene and Buna-N.

Question 51

What thermoplastics are used for jackets?

Answer 51

PVC and Polyethylene.

Question 52

What is nylon’s role?

Answer 52

Strong mechanical outer jacket, oil-resistant.

Question 53

Four types of metallic sheath?

Answer 53

Lead, Aluminum, Steel, Copper.

Question 54

What is lead sheath known for?

Answer 54

Most effective against weather, oxidation, moisture.

Question 55

Why is aluminum less ideal?

Answer 55

Needs corrosion protection and has higher A-C losses.

Question 56

Types of steel armor?

Answer 56

Flat-tape, interlocked-tape, wire, basket-weave.

Question 57

What is a concentric neutral cable?

Answer 57

Neutral wires wrapped around insulation.

Question 58

Why use concentric neutrals?

Answer 58

Safer and cheaper for underground systems.

Question 59

What is a jacket over concentric neutral for?

Answer 59

Chemical protection and physical durability.

Question 60

Four keys to a reliable cable joint?

Answer 60

Sound design, quality materials, good workmanship, thorough testing.

Question 61

What should a joint avoid?

Answer 61

Voids, stress concentrations, poor insulation contact.

Question 62

Define longitudinal stress.

Answer 62

Voltage stress along the length of the insulation.

Question 63

Recommended max longitudinal stress?

Answer 63

2 volts/mil; up to 6 volts/mil at insulation taper.

Question 64

What does radial stress cause?

Answer 64

Stress buildup at connector causing breakdown.

Question 65

What must semi-conducting tape do?

Answer 65

Continue shielding and manage stress across connectors.

Question 66

Why avoid air voids in splices?

Answer 66

They can ionize and cause corona, breakdown.

Question 67

Three ways to eliminate voids?

Answer 67

Use proper materials, good workmanship, minimize air gaps.

Question 68

What are key features of good insulating tape?

Answer 68

High stretch, ozone resistance, moisture sealing.

Question 69

Shelf life of non-vulcanizing tape?

Answer 69

Five years.

Question 70

What is typical resistance for semi-conducting tape?

Answer 70

1,000 to 3,000 ohms/square.

Question 71

What causes tracking failure?

Answer 71

Surface contamination, improper cleaning, exposed insulation.