100% of the first 3000W + a smaller percentage of the remainder.
Assume two distribution boards: DB1 MD = 12 kW, DB2 MD = 10 kW Diversity factor = 1.2 Main MD = (12 + 10) / 1.2 = (similar to above)
: Lighting-load demand factors range from 25% to 100% depending on occupancy type
Maximum Demand (MD) calculation is the backbone of electrical installation design. It determines the size of switchboards, main cables, transformers, and utility service fees. While the theory is straightforward (avoiding the summation of nameplate ratings), the practical execution is where most engineers either save millions or create hazardous bottlenecks. After testing three major software suites and manual methods against real-world buildings, here is my detailed review.
While specific standards provide detailed tables, a common professional "rule of thumb" for residential assessments involves three steps:
Listing all individual circuits and their full connected loads.
Used primarily in industrial environments, engineers map out the exact interlocking logic and duty cycles of machinery. If Machine B cannot start until Machine A turns off, their loads are not added together.
A level 2 residential EV charger can draw 7.4kW to 22kW continuously for hours. If unmanaged, this instantly doubles a home's maximum demand. Engineers now use smart energy management systems (EMS) that dynamically throttle EV charging currents based on real-time household demand to keep the total load below the main breaker limit.
"I'm not gambling," Elias corrected. "I am applying and statistical analysis. I am calculating the probability of coincidence."
Based on a calculated maximum demand of , the engineer will select a standard main service circuit breaker of 50A or 63A and size the incoming supply cables to safely carry at least that capacity over the required distance without excessive voltage drop. Modern Challenges: EV Charging and Solar PV
: A common thumb rule is to take 100% of the largest circuit's rating and 40% of all remaining circuits.
