Home Instrumentation Questions Top 50 Questioner Instrumentation Inspection and Quality Control CBT 2021 – Part-05

Top 50 Questioner Instrumentation Inspection and Quality Control CBT 2021 – Part-05

 أفضل 50 مستجوبًا لفحص الأجهزة ومراقبة الجودة CBT 2021 – الجزء -05

Top 50 Questioner Instrumentation Inspection and Quality Control CBT 2021 – Part-05

Q. What is the maximum %age of crosssectiona conduit can be filled containing three(3) or more wires?

40% as per NEC Ch. 9 Table 1.

Q. What is PVC in cable insulation an abbreviation for?

Poly Vinyl Chloride

Q. What is the purpose of drain/shield in instrumentation wires?

To reduce electrostatic noise and unwanted voltage.

Q. Per Aramco Standards, what is minimum separation between low voltage power

cables and instrumentation cables in cable trays.Minimum “300 mm.”

Q. Per NEC, what is the maxm. Distance between supports for 2inch rigid steel conduit.

Horizontal : 4.9 mtrs. (16 Feet)

Vertical : 6 mtrs.

[As Per NEC Article –Table 344:30 (B) (2)]

Q. Per Saudi Aramco standard, what is the minimum size of grounding grid conductor[cable]?

70 mm2

Q. Per NEC, what would be the size of equipment grounding copper conductor for

equipment protected by overcurrent device rated 600 amperes?

NEC‐ article : 250 Table‐122. 1 AWG copper(35‐50mm2) or 2/0 AWG copper –clad (70mm2)

Q. Per NEC, what would be the size of grounding electrode copper conductor for

alternating current system having largest service conductor sized 350 kcmil?

1600 AMP. Copper conductor 4/0 AWG 120mm2

Q. How the grounding conductor would be connected to underground grounding grid?

a) By thermite welding or brazing .

b) By approved grounding compression connectors.

Q. What do the following letters denote on electrical equipment and explain the markings?

Exd –Explosion Proof Glands or Flame Proof

11B – Combustible dust Acetaldehyde, Ethylene

T5 ‐ 100°C Temp.






T6 ‐ 85°C

Q. On electrical equipment being used in hazardous area you may see the letter UL or C.S.A, what do these abbreviations stand for?

UL – Under Writer Laboratories

C.S.A –Canadian Standard Association

Q. A 3 phase system has phase to phase 480V AC , what is the phase to earth/neutral voltage? Show calculation.

480/√3 =277V Line current = √3 phase voltage (√3 = 1.732)

Q. Per NEC , what are the instances where seals fittings are needed?

When a conduct run is crossing hazardous boundaries below ground requires boundary seal,

side, electrical equipment, junction box & conduit. Any breaking, sparking & heat producing

device must be required fittings.

Q. How to minimize the effect of breathing in conduit installation?

Low point drain and breather shall be provided.

Q. Name type of cables suitable for class 1, division 1 and division 2 locations?

Class1, division 1 ,and division2 locations suitable cable is XLPE , Polyethylene , EPR , Armored

cable .

Q. How many degrees bend permitted in a conduit run?

360° between pull box to pull box.

Q. Per NEC, what is the minimum number of conduit threads should be engaged at hazardous locations?

Five (5) Full Threads should be engaged.

Q. What is the color code of grounding neutral and phase conductor?

Grounding ‐ Green

Neutral – White

Phase – Black

Q. What is minimum temperature rating for low voltage?

90° C Dry & 75°C Wet

Q. Name the type of tests required for testing following cables:

• Medium voltage power cables – Megger test & DC High Potential test

• Catholic protection – Holiday test

• Low voltage cables – Megger test & continuity test.

Q. Name some of the tests required for testing following equipment:

1. Oil type transformers – Winding test and Ratio test

2. Electrical Motors – Winding test, Resistance test, Megger test

3. Batteries – specific gravity, voltage, current

4. Circuit Breakers – Megger & Ductor test, primary current Trajection test

Q. What is the NEMA rating for electrical enclosures installed in the following environments:

1. Indoor – NEMA – article – 250

2. Outdoor – 3R , 3CR4

3. Corrosive environment – 4X

Q. Per NEC , what is the minimum working clearance in front of low voltage electrical equipment?

Minimum 3 Feet (900mm)

Q. Per S. Aramco standard , what is the ambient temperature rating for electrical equipment?


Q. How many divisions and groups class Ι atmospheric hazards are divided into? And what are the locations covered by each division?

Class Ι ‐ zone 0 – flammable gasses or vapor are present in air

classΙ ‐ zone Ι ‐flammable gasses or vapor are likely to exist under normal operation condition

Q. Define following for enclosures containing arching electrical device and installed in hazardous area?

1. Type – NEMA type 4x

2. Safety factor – Exia

3. Flame tight – Exid

Q. What type of equipment is this statement describing? 

The energy released from thistype of equipment is insufficient to cause ignition.

Class Ι zone Ι location

Q. What are the most important things to check on lighting fixture installed in a hazardous location? And where these need to be shown?

To be check and confirm fixture are explosion proof it should shown in fitting name flute itself.

Q. Per Aramco standard, what are the acceptable types of underground conduits?

Threaded rigid steel hot dip galvanized and pre coated.

Q. What is IEEE standard work clearance around high voltage transformers? 

Minimum – 10 feet – 3mtrs. as per NEC table – 110.31

Q. Per Aramco standards, what is the maximum resistance value per mined for a grounding system at industrial area?


Q. How many threads of rigid steel conduit must be engaged in a hazardous area?

5 threads. As per NEC – 501.4 (A) (1)

Q. How do you determine the correct size equipment ground conductor for a 1600 amp. Overcurrent device?

As per NEC – article . Table – 250 – 122 ‐ Ground Conductor for – 4/0 AWG – 120 mm2

Q. What size junction is required if you have a 4” conduit straight in and straight out? What size for angle pulls?

As per NEC – 314.28

For straight in and straight out: less than 8 times ‐ 8×4=32”inch

For angle pulls : less than 6 times ‐ 6×4=24”inch

Q. What is the maximum percent of cross section a conduit can be filled containing 3 or more conductors?

40% as per NEC chapter – 9 table – 1

Q. What are the requirements for conductor insulation at light fixture terminations?

Insulation minimum thickness 0.25mm that have insulated suitable temperature not less than


Q. What is the maximum number of overcurrent devices allowed in a panel board?

As per NEC – 408.15 42 number.

Q. What is a “T” number as it relates to equipment in a Hazardous Area?

Temperature class. As per NEC table – 500.8(B)

Q. Can you use light fixtures as a raceway?


Q. Where are conduit supports required for rigid steel?

Horizontal : 3 mtrs vertical : 6 mtrs . As per NEC – 344.30

Q. Where are seal fitting required?

Instrument side and enclosure side in hazardous area.

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