⚙️ Section 1 — Project Settings

Field	What to Enter	Where to Get It	Typical Value
Project Name	Name of the building or area you are calculating the load for	Project brief, drawing title block, or your own reference	e.g. "Office Block — Level 3"
Supply Voltage	The voltage of the main electrical supply to the building	Utility supply letter, incoming switchboard single line diagram. Middle East/UK/Europe = 400V	400V (most countries)
System Type	Whether the supply is 3-phase or single phase. Almost all commercial buildings use 3-phase	Utility supply letter or incoming switchboard drawing	3-Phase for all commercial
Overall Power Factor	Ratio of real power (kW) to apparent power (kVA). Affects kVA and current calculations	Utility requirement (usually 0.90 minimum) or CIBSE Guide K. Use 0.85 if unknown	0.85 – 0.92 typical
Spare Capacity %	Additional capacity for future expansion. IEC 60364 requires minimum 20% spare on all new installations	Client brief or project specification. Hospitals and data centres: 25–30%	20% standard, 25% critical

💡 Section 2 — Lighting Load

Field	What to Enter	Where to Get It	Typical Value
W per fitting	Use when you know exact number of fittings and wattage of each. Best for detailed design stage	Lighting layout drawing (count fittings) and luminaire datasheet (get wattage)	LED downlight: 18–24W
W per m²	Use at early design stage when only floor area is known. A power density figure is used instead of counting fittings	Floor area from architectural drawing. Power density from CIBSE Guide A or SLL Lighting Guide	Office LED: 10–15 W/m²
Demand Factor	Proportion of lighting assumed on simultaneously. Always 1.0 for lighting — all lights could be on at the same time	IEC 60364-3 or CIBSE Guide K. Emergency lighting: 1.0. General lighting: 1.0	1.0 for all lighting

🔌 Section 3 — Small Power / Outlets

Field	What to Enter	Where to Get It	Typical Value
Power per outlet	The rated wattage of each outlet or piece of connected equipment	Equipment datasheet, client equipment schedule, or standard assumption per outlet type	Office outlet: 150–200W
Quantity	Total number of outlets or equipment items of this type in the area	Power layout drawing or outlet schedule — count from electrical drawing	Count from drawing
Demand Factor	Proportion of outlets assumed in use simultaneously. Not all outlets will be used at the same time — this accounts for diversity	CIBSE Guide K Table 4.1, BS 7671 Appendix 4. Office general outlets: 0.4–0.5. Dedicated equipment: 0.7–0.9	Office outlets: 0.4–0.5

❄️ Section 4 — HVAC Equipment Load

Field	What to Enter	Where to Get It	Typical Value
Power (kW shaft)	The mechanical shaft power of the motor — NOT cooling capacity. Enter motor kW, not tonnage or kW of cooling	HVAC equipment datasheet — look for "Motor kW" or "Input Power kW". Mechanical engineer equipment schedule or vendor technical submittal	AHU motor: 5.5–55kW
Motor Efficiency	Efficiency of the electric motor. Tool calculates: Electrical kW = Shaft kW ÷ Motor Efficiency	Motor datasheet or IEC 60034-30 efficiency class tables. IE3 motors required in most countries. If unknown use 0.88	IE3: 0.88–0.93
Demand Factor	Proportion of HVAC running simultaneously at full load. Chillers rarely run at 100% — this accounts for part-load operation	CIBSE Guide K or project M&E specification. Chillers: 0.8–0.9. AHUs: 0.75–0.85. FCUs: 0.7	Chiller: 0.85 \| AHU: 0.8

❄️ Important: For chillers enter the compressor motor kW (electrical input), not cooling capacity. Example: a 500kW cooling chiller typically has a 150–200kW compressor input. Check the chiller datasheet for "Compressor Input kW".

⚙️ Section 5 — Mechanical Equipment (Motors & Pumps)

Field	What to Enter	Where to Get It	Typical Value
Power (kW/HP)	Shaft power rating of the motor or pump — the mechanical output power. Can be entered in kW, W or HP	Motor nameplate data, pump datasheet, mechanical equipment schedule or pump curve. Look for "Shaft Power kW" or "Motor Rating kW"	CHW pump: 5.5–22kW
Motor Efficiency	Efficiency of the electric motor. Formula: Electrical kW = Shaft kW ÷ Motor Efficiency	Motor nameplate, manufacturer datasheet or IEC 60034-30 standard efficiency tables. IE3 motors mandatory in most countries from 2023	IE3 motor: 0.88–0.95
Demand Factor	Proportion of motors running simultaneously at full load. Do NOT add standby pumps — they do not contribute to load	CIBSE Guide K Table 4.2. CHW pumps: 0.8. Fire pumps: 1.0 (must always be 100%). Standby: 0 — do not add	Duty pump: 0.8 \| Fire: 1.0

⚙️ Standby equipment: Do NOT add standby pumps or standby fans to the load calculation. Only add duty equipment. Standby equipment does not contribute to electrical load as it only runs when the duty unit fails.

📊 Understanding the Results

Result	What it Means	How it is Used
Connected Load (kW)	Total rated power of ALL equipment assuming everything runs at 100% simultaneously — worst case maximum	Sizing individual circuit protective devices (MCBs) and cable sizes at equipment level
Design Load (kW)	Connected load multiplied by demand factors — the realistic expected maximum load at peak conditions	Sizing main LV switchboard, incoming supply cables and transformer
Total kVA	Design load with spare capacity added, divided by power factor. This is what the transformer and utility supply must provide	Transformer sizing (must be ≥ total kVA), utility capacity request, generator sizing
Current per Phase (A)	Current flowing in each phase. Formula: I = kVA × 1000 ÷ (√3 × V) for 3-phase	Sizing main incoming cable, main incomer switch and busbar rating
MCB/MCCB Rating	Recommended standard IEC breaker size = Current × 1.25 rounded up to next standard size	Starting point for main incomer protection. Verify with fault level and discrimination study

📋 Recommended Step-by-Step Workflow

Step 1 — Set Project Details

Enter project name, supply voltage (400V for Middle East/UK), select 3-phase, set power factor (0.85 default) and spare capacity (20% minimum per IEC).

Step 2 — Add Lighting Load

Use W/m² at early design stage or W per fitting at detailed design. Get floor areas from architectural plans. Use LED power densities from CIBSE Guide A.

Step 3 — Add Small Power

Count outlets from electrical drawing. Use client equipment schedule for specific loads. Apply demand factor 0.4–0.5 for general office outlets per CIBSE Guide K.

Step 4 — Add HVAC Loads

Get motor kW from mechanical engineer's equipment schedule or HVAC datasheets. Enter shaft kW and motor efficiency. Do NOT add standby equipment.

Step 5 — Add Mechanical & General

Add pumps, lifts, compressors from mechanical schedule. Add UPS, EV chargers under General. Fire pumps always use demand factor 1.0.

Step 6 — Review Results

Check Full Schedule tab for complete load list. Use kVA for transformer sizing. Use current (Amps) for main cable and incomer sizing. Check PF recommendation.

⚡ Electrical Load Calculator