Key Engineering Takeaways
- An SLD documents breaker ratings, cable cross-sections, fault current withstand levels, and metering enclosures.
- Load schedules establish Maximum Demand (kVA) using standard diversity factors recognized by DEWA.
- Three-phase loads must be balanced within a 10% tolerance across Red, Yellow, and Blue phases.
- Accurate calculations prevent over-specifying costly cables while guaranteeing adequate power margins.
The Purpose of an Electrical Single Line Diagram (SLD)
An electrical Single Line Diagram (SLD) is the foundational architectural blueprint of a power distribution network. Using standardized IEC and British Standard (BS) electrical symbols, the SLD shows how electrical energy flows from DEWA’s intake supply point down to branch miniature circuit breakers (MCBs).
Core Elements Required on Every Compliant DEWA SLD
- Incomer Specifications: Main circuit breaker type (MCCB / ACB), fault level withstand capacity (kA), and CT metering ratio.
- Distribution Feeders: Cable cross-sectional area (e.g., 4C x 70mm² XLPE/SWA/LSZH), length, and containment method.
- Protective Devices: Residual Current Devices (RCDs) with 30mA trip ratings for socket outlets and 100mA/300mA time-delayed trip ratings for lighting and mechanical equipment.
- Earthing & Bonding System: Main earth terminal (MET) sizing, earth electrode pit locations, and bonding conductor cross-sections.
Load Calculation Formulae & Diversity Factors
Engineers calculate total connected electrical load and apply diversity factors reflecting that not all equipment runs simultaneously:
- Connected Load (CL): The sum of the rated power (kW) of all connected appliances, lighting, and mechanical plant.
- Maximum Demand (MD): Computed by multiplying connected loads by their approved diversity factors:
- Lighting circuits: 0.90 to 1.00 diversity.
- General 13A socket circuits: 0.50 to 0.70 diversity.
- Air conditioning compressors: 1.00 diversity.
- Commercial kitchen equipment: 0.70 to 0.80 diversity.
Submitting an unbalanced or over-estimated load schedule results in immediate rejection by DEWA, while under-estimating causes frequent nuisance tripping and dangerous cable overheating. Abbadi Tech guarantees balanced, mathematically proven calculations stamped by certified UAE electrical engineers.
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