Electrical QC Notes – Electrical QC Question Paper

Main keywords for this article are Electrical QC Notes, Electrical QC Question Paper, MOTORS AND GENERATOR QC QUESTIONS, SUBSTATION QC QUESTIONS, CABLES QUESTIONS.

Electrical QC Notes – Electrical QC Question Paper

Electrical QC Notes, Electrical QC Question Paper

  • What do you mean by NEC & IEC?

Ans: NEC-National Electrical Code (NFPA 70)
IEC International Electro technical Commission

  • What is the specification for NEC & IEC low voltage cables?

Ans:  NEC Low voltage cable shall be rated 600 volt and shall have a minimum temp rating 90°C dry/ 75°C wet. IEC low voltage cable shall be rated 600/1000 volt and shall have a minimal rating of 80 °C.

  • How to measured insulation resistance test for cables?

A: .Measure insulation resistance test to phase to phase and phase to ground for 1 minute duration

  • What is the minimum acceptance value for measuring insulation resistance test?

A: Rated voltage+ 1kv in mega ohms.

  • What are the 3 classified locations in electrical area classification? Define?

a) .Class 1 zone O location – is an area in which ignitable concentration of flammable gases or vapor are present continuously or for long period of time. 
b) Class 1 Zone 1 location – is an area in which ignitable .concentration of flammable gases or vapor are likely to exist under normal operating condition or may exist ) frequency because of repair or maintenance operation or because of leakage. 
c) Class 1 zone 2 location – is an area in which ignitable concentration of flammable gases or vapor are not likely to occur in normal operation and if they occur they will exist only for a short period.

  • What method used in ground connection to ground grid?

By thermite welding (cad weld) or brazing

  • What is the minimum $ize of grounding cable used for connection of equipment to ground rod or ground grid?

A: 25mm {# 4 AWG)

  • Q: What is the minimum size of grounding cable if buried and used for grid and / or interconnection of ground rod?

A: 70mm2 (2/0 awg)

  • What is the minimum length and diameter for copper jacketed steel rod?

2.4 meter long and 16mm in diameter

  • What is system grounding?

A: Three phase electrical system shall be grounded @ the neutral point of the wye-connected winding of the transformer or generator of connected directly to ground grid or electrode.

  • What is the difference between neutral and ground?

A: Ground – is non current carrying conductor
Neutral – is current carrying conductor only when the load is unbalance.

  • What is the max acceptable value for individual earth rod measurement?

A: 25 ohm

  • What is the minimum equipment grounding connection to the equipment frame (motor, generator & transformer) operating @ 1000 volt or greater?

A: Two (2) connection to a supplementary electrode


  • For total enclosed fan coil motor with temperature rise based on 1.0 service factor and class B insulation, what is the permitted winding temp rise above a 50°C?

A : 70 °C

  • How will you test the motor?

Check the winding resistance of motor lead and measure insulation resistance of winding terminal lead to the ground.

  • Q: For motor, transformer and generator operating @ a nominal voltage of 480v, what is the minimum connection to a supplementary grounding electrode?

Ans: One-1

  • What is the allowable steady state voltage drop for low voltage system motor branch circuit?

A: Maximum of 3%, providing the maximum total voltage drop for the main, feeder, and branch circuit does not exceed 5%.

  • How will you do if the rotation of the motor was reversed?

A: Interchange the connection of L1 and L3 to the motor terminal block.


  • In electrical room, what is the required minimum maintained illuminance level @ vertical face of switch gear @ 1700 mm?

A : 300 LuX

  • What is the unobstructed horizontal space to be provided in installation of switchgear inside the substation?

A: 2 meter in front and 1 meter in back & sides

  • what is the maximum rating of panel board used in industrial facilities?

A: Rated 400 amps or less

  • Bus duct or cable bus shall be used with power transformer if the forced cooled site rating of the transformer is what?

A: Transformer rating is greater than 1200 amps.


  • Define substation?

A: Substation is any assemblage of electrical equipment which includes a power transformer rated 751 kva and larger or switchgear rated 1KV and higher.

  • What is the minimum clear space above the tray inside substation?

A:  All cable trays shall a minimum of 300 mm.

  • What is the minimum headroom inside substation passage way?

A: Minimum of 2.3 meter


  • What is the working space in front of each battery rack or enclosure?

At least 1 meter

  • What is the minimum horizontal separation of battery cell to equipment with arcing contacts?

A : 1.5 meter

  • What is the minimum clearance to be maintaining above each cell to allow proper air circulation & to permit filling, testing and replacement of cells from ,he access aisles?

A: 150mm

  • What is the minimum air space between battery cells?

A: Shall be 10mm


  • What is the mounting height of plant lighting fixtures positioned over stairways, platforms, elevated walkways and landing?

2.03 m from the bottom of fixture to the floor directly beneath.

  • What is the minimum duration of emergency lighting in the event of normal power failure?

One and half (1. ½) hour

  • In battery rooms what type of lighting fixtures shall be used?

Shall be enclosed and gasketed vapor tight corrosion resistant?


  • How will you test medium voltage cable (5 KV through 35 KV)

A. New installation of cable and splices shall be 5KV megger tested and then D. C high potential tested after installation and prior top placing in service.
IEC cable rating          Inject voltage                     Duration
6/10KV                                  36KV                                   15Min
12/20 KV                               64KV                                    15Min

  • Q:  What is the minimum depth of direct buried cable from grade level to top surface of cable for 600V & below, over 600V to 35KV and over 35KV? ·

A: System voltage 600V&below  –  610 mm
Over 600V to 35 KV – 920 mm ·
Over 35KV – 1070 mm

  • What is the minimum creepage distance of medium & high voltage termination operating @ 2.4 KV and above installed outdoor and indoor to the ground?

A: a) 40 mm per. KV line to line nominal system voltage (outdoor)
b) 25 mm per kv line to line nominal voltage system (indoor)

  • What is the color-coding for individual power phases, neutral and ground?

A: Line1-Red
Line 2 – Yellow
Line 3 -Blue

Neutral – White or Gray
Ground – Green or green w/yellow stripes

  • What is the minimum size of conductor for the following voltage rating?

A: 600V & below control                     2.5mm2
600V & below (power)                          4mm2
5KV                                                                10mm2
15,KV                                                             35mm2
35KV                                                              50mm2
69KV                                                              120mm2

  • What is the minimum crossing or parallel clearance between direct buried cable?

A: 300mm

  • What is the minimum separation (above or below ground) between a power cable operating @ 100 V or above, up to 34.5 KV and a parallel or crossing power or control cable operating at Less than 1000 volt?

A:  Shall be 300 mm, except when the medium voltage cable is armoured or metal clad

Main keywords for this article are Electrical QC Notes, Electrical QC Question Paper, MOTORS AND GENERATOR QC QUESTIONS, SUBSTATION QC QUESTIONS, CABLES QUESTIONS.

List of Test Requirements for Electrical Equipment

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