Electrical Systems Design Guidelines

Flashcards covering electrical system design guidelines, DEWA substation regulations, LV distribution, power factor correction, earthing, lighting design, telecom, and life safety systems.

What is the required spare capacity for the utility lead-in underground cables?

The capacity must include an additional $10\%$ spare capacity on top of the estimated maximum building demand for normal expansion.

According to DEWA guidelines, what is the maximum number of transformers that a single $11\,\text{kV}$ Ring Main Unit (RMU) can feed?

A single RMU can feed a maximum of $2$ transformers.

Under the $N-1$ offline criterion for an $11\,\text{kV}$ ring supply, what is the required operational capability if one feeder fails?

The remaining feeder must be capable of meeting the entire demand for a maximum duration of $6\,\text{hours}$.

What is the maximum sustained load (summer rating) of an $11\,\text{kV}$ feeder using $3/\text{C } 300\,\text{mm}^2$ Copper XLPE cable?

$175\,\text{A}$ / $3\,\text{MW}$.

What power factor must a client maintain at the point of connection with DEWA's MV Network?

Between $0.95$ (lagging) and unity.

What are the minimum clear height requirements for a single-room substation at ground floor and a transformer room at basement level?

A minimum of $3.7\,\text{m}$ for a single-room substation at ground floor, and a minimum of $3.0\,\text{m}$ for a transformer room at the basement level.

What finished floor level (FFL) elevation difference must be maintained for a substation room relative to the outside adjacent ground level towards the door side?

$0.15\,\text{m}$ to $0.30\,\text{m}$ higher than the outside adjacent ground level.

What are the required floor areas and minimum room widths for single-room substations housing $1 \times 1000/1500\,\text{kVA}$ and $2 \times 1000/1500\,\text{kVA}$ transformers?

$33\,\text{m}^2$ with a minimum width of $4.57\,\text{m}$ for $1 \times 1000/1500\,\text{kVA}$, and $55\,\text{m}^2$ with a minimum width of $6.1\,\text{m}$ for $2 \times 1000/1500\,\text{kVA}$.

In a split-room ground-floor substation, what are the spatial requirements for the RMU room housing one set of RMU controlling $2$ transformers?

An area of $9.0\,\text{m}^2$ with a minimum width of $3.0\,\text{m}$ towards the door side.

What working clearances must be maintained around floor-standing panels in LV electrical rooms according to DEWA?

$750\,\text{mm}$ behind floor-standing panels, and $1500\,\text{mm}$ between floor-standing panels or between a panel front and the wall.

What are the required dimensions for the main telecom room and typical floor telecom room in buildings with $100$ to $300$ tenants or an area exceeding $7000\,\text{m}^2$?

Main telecom room: $3\,\text{m} \times 3\,\text{m} \times 3\,\text{m}$; Floor telecom room: $1.5\,\text{m} \times 1.5\,\text{m} \times 3\,\text{m}$.

What are the minimum area and dimension requirements for a Fire Command Center (FCC) room?

A minimum floor area of $19\,\text{m}^2$ with a minimum single dimension of $3\,\text{m}$.

What are the maximum permissible motor ratings for 1-phase and 3-phase motors without requiring specific DEWA approval for bulk supply?

Up to $3.7\,\text{kW}$ ($5\,\text{HP}$) for 1-phase motors, and up to $110\,\text{kW}$ ($150\,\text{HP}$) for 3-phase motors.

What ambient temperature variation range must motor starter thermal overload relays compensate for automatically?

Between $2.8\,^\circ\text{C}$ and $48\,^\circ\text{C}$.

At what DEWA service feeder ratings is centralized power factor correction via capacitor banks mandatory for commercial and residential installations?

Feeders of $200\,\text{A}$ and above for commercial premises, and feeders of $400\,\text{A}$ and above for residential premises.

What is the maximum number of floors that a single busbar riser can supply in Dubai versus Abu Dhabi?

A maximum of $12$ floors in Dubai, and a maximum of $10$ floors in Abu Dhabi.

What are the minimum conductor cross-sectional areas permitted for lighting circuits and utility socket circuits?

$2.5\,\text{mm}^2$ for lighting circuits and $4\,\text{mm}^2$ for utility sockets.

What is the required mounting height range for tap-off units installed in a busbar riser from the finished floor level?

Between $500\,\text{mm}$ and $1800\,\text{mm}$ from the finished floor level.

At what circuit breaker rating threshold at the point of supply must metering via Current Transformers (CTs) be provided?

$160\,\text{A}$ and above (direct-connected meters are used up to $125\,\text{A}$).

What are the specification requirements for a consumer's main earth electrode regarding rod diameter, installation depth, spacing, and resistance?

A $20\,\text{mm}$ diameter copper core bonded earth rod installed to a minimum depth of $3\,\text{m}$, spaced at least $6\,\text{m}$ apart if multiple rods are installed, with total earth electrode resistance not exceeding $1\,\Omega$.

In a Faraday Cage Lightning Protection System, what are the mesh sizes and down conductor spacings specified for Class I and Class IV LPS?

Class I: mesh size of $5\,\text{m} \times 5\,\text{m}$ with down conductor spacing of $10\,\text{m}$; Class IV: mesh size of $20\,\text{m} \times 20\,\text{m}$ with down conductor spacing of $20\,\text{m}$.

How are Class II and Class III luminaires classified based on their protection against electric shock?

Class II features double insulation, while Class III luminaires are supplied at Safety Extra Low Voltage (SELV).

What are the recommended Ingress Protection (IP) ratings for outdoor installations, mechanical plant rooms, and bathrooms?

$\text{IP}65$ for outdoor installations, $\text{IP}65$ for mechanical plant rooms, and $\text{IP}44$ for bathrooms.

How are correlated colour temperatures (CCT) categorized into Warm, Intermediate, and Cool appearances?

Warm: below $3300\,\text{K}$ (reddish); Intermediate: $3300\text{--}5300\,\text{K}$ (white); Cool: above $5300\,\text{K}$ (bluish).

According to CIBSE guidelines, what are the recommended illuminance levels (lux) for reception desks, kitchens with meal cooking, and general corridors?

Reception desk: $300\,\text{lux}$; Kitchen with meal cooking: $500\,\text{lux}$; Corridors: $100\,\text{lux}$.

What is the maximum allowable travel distance to reach the nearest manual call point (break glass) along escape routes in parking areas?

The travel distance must not exceed $45\,\text{m}$.

What is the minimum retention period required for CCTV recordings under SIRA regulations for multi-floor buildings?

Recordings must be retained for at least $31\,\text{days}$ for all cameras.

What are the maximum horizontal cable distance and combined patch/line cord length limits for Cat-6 structured cabling?

Maximum horizontal cabling distance is $90\,\text{m}$ between outlet and patch panel, and the sum length of all patch and line cords for one outlet must not exceed $10\,\text{m}$.

Under SIRA regulations, at what building size does providing 24/7 security guards become mandatory for multi-floor residential buildings?

Mandatory for buildings with $50$ residential units and above (optional for buildings with less than $50$ units).