33 real Cable & Busbar Sizing questions from the Electrical Design bank, as asked in Indian campus drives and tech interviews. Every question has a verified answer and an AI-tutor explanation on placd — free to start.
1. What is IS 1255?
Junior
A.Indian code of practice for installation and maintenance of power cables up to 33 kV, covering laying depth, bending radius and jointing
B.IS 1554 covers PVC-insulated power cables up to 1.1 kV; IS 7098 covers XLPE cables, Part 1 up to 1.1 kV and Part 2 for 3.3–33 kV
C.cable sized so the drop from source to load at full current stays within about 3% for lighting and 5% for power circuits
D.multipliers for ambient temperature, ground thermal resistivity, depth of laying and grouping whose product reduces the tabulated current rating
2. Which term means: "Indian code of practice for installation and maintenance of power cables up to 33 kV, covering laying depth, bending radius and jointing"?
5. Which term means: "cross-linked polyethylene allows 90 °C continuous conductor temperature and 250 °C short-circuit limit versus 70 °C and 160 °C for PVC"?
A.XLPE vs PVC insulation — about 12 times overall diameter for multicore XLPE power cables and 15–20 times for single-core HV cables during installation
B.XLPE vs PVC insulation — cross-linked polyethylene allows 90 °C continuous conductor temperature and 250 °C short-circuit limit versus 70 °C and 160 °C for PVC
C.XLPE vs PVC insulation — Indian code of practice for installation and maintenance of power cables up to 33 kV, covering laying depth, bending radius and jointing
D.XLPE vs PVC insulation — rated Icw such as 50 kA for 1 s verified by type test, with peak withstand Ipk about 2.1–2.2 times Icw for high fault levels
8. Which term means: "IS 1554 covers PVC-insulated power cables up to 1.1 kV; IS 7098 covers XLPE cables, Part 1 up to 1.1 kV and Part 2 for 3.3–33 kV"?
A.IS 1554 and IS 7098 — copper bars carry roughly 1.2–1.6 A/mm² and aluminium 0.8–1.0 A/mm² in ventilated enclosures before temperature-rise verification
B.IS 1554 and IS 7098 — cross-linked polyethylene allows 90 °C continuous conductor temperature and 250 °C short-circuit limit versus 70 °C and 160 °C for PVC
C.IS 1554 and IS 7098 — cable sized so the drop from source to load at full current stays within about 3% for lighting and 5% for power circuits
D.IS 1554 and IS 7098 — IS 1554 covers PVC-insulated power cables up to 1.1 kV; IS 7098 covers XLPE cables, Part 1 up to 1.1 kV and Part 2 for 3.3–33 kV
11. Which term means: "multipliers for ambient temperature, ground thermal resistivity, depth of laying and grouping whose product reduces the tabulated current rating"?
A.Derating factors — about 12 times overall diameter for multicore XLPE power cables and 15–20 times for single-core HV cables during installation
B.Derating factors — multipliers for ambient temperature, ground thermal resistivity, depth of laying and grouping whose product reduces the tabulated current rating
C.Derating factors — tray width chosen so cables occupy no more than about 40–50% of the tray with one-diameter spacing between power cables to preserve ratings
D.Derating factors — copper bars carry roughly 1.2–1.6 A/mm² and aluminium 0.8–1.0 A/mm² in ventilated enclosures before temperature-rise verification
A.Short-circuit withstand of cable — multipliers for ambient temperature, ground thermal resistivity, depth of laying and grouping whose product reduces the tabulated current rating
B.Short-circuit withstand of cable — IS 1554 covers PVC-insulated power cables up to 1.1 kV; IS 7098 covers XLPE cables, Part 1 up to 1.1 kV and Part 2 for 3.3–33 kV
C.Short-circuit withstand of cable — about 12 times overall diameter for multicore XLPE power cables and 15–20 times for single-core HV cables during installation
D.Short-circuit withstand of cable — minimum conductor area equals I·√t divided by k, with k about 143 for copper and 94 for aluminium XLPE (90 °C to 250 °C)
A.Voltage drop criterion — minimum conductor area equals I·√t divided by k, with k about 143 for copper and 94 for aluminium XLPE (90 °C to 250 °C)
B.Voltage drop criterion — tabulated list of every cable with tag, from/to, size, cores, length, route and gland type used for procurement and site pulling
C.Voltage drop criterion — cable sized so the drop from source to load at full current stays within about 3% for lighting and 5% for power circuits
D.Voltage drop criterion — tray width chosen so cables occupy no more than about 40–50% of the tray with one-diameter spacing between power cables to preserve ratings
20. Which term means: "tabulated list of every cable with tag, from/to, size, cores, length, route and gland type used for procurement and site pulling"?
A.Cable schedule — tray width chosen so cables occupy no more than about 40–50% of the tray with one-diameter spacing between power cables to preserve ratings
B.Cable schedule — tabulated list of every cable with tag, from/to, size, cores, length, route and gland type used for procurement and site pulling
C.Cable schedule — cross-linked polyethylene allows 90 °C continuous conductor temperature and 250 °C short-circuit limit versus 70 °C and 160 °C for PVC
D.Cable schedule — IS 1554 covers PVC-insulated power cables up to 1.1 kV; IS 7098 covers XLPE cables, Part 1 up to 1.1 kV and Part 2 for 3.3–33 kV
23. Which term means: "tray width chosen so cables occupy no more than about 40–50% of the tray with one-diameter spacing between power cables to preserve ratings"?
A.Cable tray sizing — cable sized so the drop from source to load at full current stays within about 3% for lighting and 5% for power circuits
B.Cable tray sizing — tray width chosen so cables occupy no more than about 40–50% of the tray with one-diameter spacing between power cables to preserve ratings
C.Cable tray sizing — copper bars carry roughly 1.2–1.6 A/mm² and aluminium 0.8–1.0 A/mm² in ventilated enclosures before temperature-rise verification
D.Cable tray sizing — minimum conductor area equals I·√t divided by k, with k about 143 for copper and 94 for aluminium XLPE (90 °C to 250 °C)
A.Minimum bending radius — about 12 times overall diameter for multicore XLPE power cables and 15–20 times for single-core HV cables during installation
B.Minimum bending radius — minimum conductor area equals I·√t divided by k, with k about 143 for copper and 94 for aluminium XLPE (90 °C to 250 °C)
C.Minimum bending radius — tray width chosen so cables occupy no more than about 40–50% of the tray with one-diameter spacing between power cables to preserve ratings
D.Minimum bending radius — cable sized so the drop from source to load at full current stays within about 3% for lighting and 5% for power circuits
A.Busbar short-time withstand — rated Icw such as 50 kA for 1 s verified by type test, with peak withstand Ipk about 2.1–2.2 times Icw for high fault levels
B.Busbar short-time withstand — IS 1554 covers PVC-insulated power cables up to 1.1 kV; IS 7098 covers XLPE cables, Part 1 up to 1.1 kV and Part 2 for 3.3–33 kV
C.Busbar short-time withstand — Indian code of practice for installation and maintenance of power cables up to 33 kV, covering laying depth, bending radius and jointing
D.Busbar short-time withstand — tabulated list of every cable with tag, from/to, size, cores, length, route and gland type used for procurement and site pulling
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