DEWA electrical engineer exam practice

Q: As per the DEWA Regulations for Electrical Installations 2017, what is the nominal LV supply voltage and tolerance?

230/400 V ±10%, 50 Hz. DEWA supplies 230/400 V ±10%, 50 Hz, 3-phase 4-wire, in line with IEC 60038. 220/380 V is the older Gulf supply value and 60 Hz is not used anywhere in the UAE.

Q: What is the maximum main earth electrode resistance allowed by DEWA for each incoming supply / MDB?

1 Ω. DEWA requires the main earth electrode resistance not to exceed 1 Ω for each incoming DEWA supply / MDB. This is much stricter than the theoretical TT limit from RA × IΔn ≤ 50 V, so it is a very common exam question.

Q: What is DEWA's minimum conductor size for utility socket outlet circuits?

4 mm². DEWA specifies 4 mm² minimum for utility socket outlets. This is larger than typical UK radial practice, and it also helps keep within the 4% voltage drop limit in hot ambient conditions.

Q: The DEWA Regulations for Electrical Installations 2017 edition supersedes which earlier edition?

1997 edition. The 2017 edition replaced the 1997 edition and pulled in the amendments and guidelines DEWA had posted on its website over the years.

Q: As defined in the DEWA regulations, extra-low voltage normally does not exceed:

50 V a.c. or 120 V ripple-free d.c.. ELV is normally not exceeding 50 V a.c. or 120 V ripple-free d.c., between conductors or to earth. Watch the trap option that swaps the a.c. and d.c. values.

Engineers who design, supervise or sign off electrical installations on the DEWA network in Dubai are expected to know the DEWA Regulations for Electrical Installations (2017 Edition) and the BS 7671 principles behind them.

DEWA-style questions keep coming back to the same themes: the 230/400 V supply and where the neutral is earthed, the 4% voltage drop limit, the 1 Ω main earth electrode and 0.5 Ω earth continuity limits, RCD protection, cable sizing in high ambient temperatures, and testing before energization. This page lists the values to know and gives sample questions, then lets you sit a timed paper.

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What the questions cover

Cables & voltage drop, Calculations, Earthing & bonding, Fire, life safety & ELV, Protection & RCDs, Regulations & procedures, Renewables & EV, Safety & isolation, Special locations, Supply & earthing, Switchgear & PFC, Testing & inspection.

Main references: DEWA Regulations for Electrical Installations, 2017 Edition.

Key values to know

Supply 230/400 V ±10%, 50 Hz, 3-phase 4-wire (cl. 1.2)
Neutral earthed at DEWA substation only; not earthed elsewhere in the installation (cl. 1.2)
Protective conductor generally the armour of the DEWA service cable (cl. 1.2)
Max voltage drop 4% of nominal from point of supply (cl. 4.2.3)
Min conductor for utility socket outlets 4 mm² (cl. 4.2.2)
Main earth electrode ≤ 1 Ω per incoming supply / MDB (cl. 5.2.4)
Any point of ECC to main earth electrode ≤ 0.5 Ω (cl. 5.2.4)
Main electrode as close to MDB as possible; electrodes ≥ 6 m apart (cl. 5.2.3)
30 mA RCD for circuits supplying mobile equipment up to 32 A
ELV ≤ 50 V a.c. / 120 V ripple-free d.c.; LV ≤ 1000 V a.c. between conductors, 600 V to earth
TN final circuits ≤ 32 A: 0.4 s; TT: 0.2 s (Table 41.1)
Distribution circuits: TN 5 s, TT 1 s
TT: RA × IΔn ≤ 50 V
RCD: ≤ 300 ms at 1 × IΔn, ≤ 40 ms at 5 × IΔn
Insulation: 500 V d.c. ≥ 1 MΩ; SELV/PELV 250 V d.c. ≥ 0.5 MΩ
Max Zs = 230 × 0.95 / Ia (B: 5 In, C: 10 In, D: 20 In)
CPC (Table 54.7): ≤16 → same; 16-35 → 16; >35 → half
Main bonding ≥ 6 mm² Cu; supplementary 4 mm² (2.5 mm² protected)
Buried earthing conductor, no corrosion protection: 25 mm² Cu
Adiabatic S = √(I²t) / k

Sample questions with answers

1. As per the DEWA Regulations for Electrical Installations 2017, what is the nominal LV supply voltage and tolerance?

220/380 V ±6%, 50 Hz
230/400 V ±10%, 50 Hz
240/415 V ±6%, 50 Hz
230/400 V ±5%, 60 Hz

Show the answer

Answer: B - 230/400 V ±10%, 50 Hz

DEWA supplies 230/400 V ±10%, 50 Hz, 3-phase 4-wire, in line with IEC 60038. 220/380 V is the older Gulf supply value and 60 Hz is not used anywhere in the UAE.

Reference: DEWA Regs 2017, cl. 1.2 Electric supply

2. What is the maximum main earth electrode resistance allowed by DEWA for each incoming supply / MDB?

0.5 Ω
1 Ω
5 Ω
10 Ω

Show the answer

Answer: B - 1 Ω

DEWA requires the main earth electrode resistance not to exceed 1 Ω for each incoming DEWA supply / MDB. This is much stricter than the theoretical TT limit from RA × IΔn ≤ 50 V, so it is a very common exam question.

Reference: DEWA Regs 2017, cl. 5.2.4

3. What is DEWA's minimum conductor size for utility socket outlet circuits?

1.5 mm²
2.5 mm²
4 mm²
6 mm²

Show the answer

Answer: C - 4 mm²

DEWA specifies 4 mm² minimum for utility socket outlets. This is larger than typical UK radial practice, and it also helps keep within the 4% voltage drop limit in hot ambient conditions.

Reference: DEWA Regs 2017, cl. 4.2.2

4. The DEWA Regulations for Electrical Installations 2017 edition supersedes which earlier edition?

1979 edition
1997 edition
2008 edition
2012 edition

Show the answer

Answer: B - 1997 edition

The 2017 edition replaced the 1997 edition and pulled in the amendments and guidelines DEWA had posted on its website over the years.

Reference: DEWA Regs 2017, introduction

5. As defined in the DEWA regulations, extra-low voltage normally does not exceed:

25 V a.c.
50 V a.c. or 120 V ripple-free d.c.
110 V a.c.
120 V a.c. or 50 V d.c.

Show the answer

Answer: B - 50 V a.c. or 120 V ripple-free d.c.

ELV is normally not exceeding 50 V a.c. or 120 V ripple-free d.c., between conductors or to earth. Watch the trap option that swaps the a.c. and d.c. values.

Reference: DEWA Regs 2017, definitions

6. For a TT system, what is the maximum disconnection time for a final circuit rated not exceeding 32 A at 230 V?

0.1 s
0.2 s
0.4 s
5 s

Show the answer

Answer: B - 0.2 s

Table 41.1 of BS 7671 gives 0.2 s for TT final circuits ≤32 A at 230 V (0.4 s for TN). This short time is usually met by an RCD rather than an overcurrent device.

Reference: BS 7671 Table 41.1

7. Which steps form part of a safe isolation procedure?

Lock off the isolator and fit a caution tag
Prove the voltage indicator on a proving unit before and after testing
Test between all conductor combinations, including line to earth
Rely on the switch position indicator to confirm it is dead

Show the answer

Answer: A, B, C - Lock off the isolator and fit a caution tag; Prove the voltage indicator on a proving unit before and after testing; Test between all conductor combinations, including line to earth

Isolate, lock off and tag, prove the tester, test all combinations, then prove the tester again. The switch position alone never proves a circuit is dead; contacts can weld or the wrong circuit may be isolated.

Reference: GS38; BS 7671 537

8. What minimum illuminance does BS EN 1838 require for open area (anti-panic) emergency lighting?

0.2 lux
0.5 lux
1 lux
5 lux

Show the answer

Answer: B - 0.5 lux

Open area (anti-panic) lighting needs 0.5 lux minimum across the core area, excluding a 0.5 m border.

Reference: BS EN 1838

Practise the full paper

The Electrical Licensing Exam Lab has timed papers with an answer sheet, calculation drills with fresh numbers every time, tap-the-diagram and virtual instrument questions, 3D labs, a daily challenge and automatic pass or fail results with a full review.

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These questions are written from the published regulations and standards and are not copied from any real exam. Authorities and boards do not publish their question banks, and pass marks and formats can change, so confirm the current details with the body concerned.