Installation design
Maximum demand with an agreed coincidence factor
- where
- maximum demand current (A)
- connected current of each group (A)
- coincidence factor of that group
Explain this equation
Estimates the maximum demand current of an installation by applying an agreed coincidence factor to each group of loads. Use it when sizing a supply, submain or main switch.
I_group is the connected current of each group of similar loads. f_group is that group's coincidence factor: the fraction of its connected current expected to flow at the time of the overall peak. Σ means add up all the groups. I_demand is the estimated maximum demand.
Not everything runs at full load at once. Scaling each group by its own factor and then adding gives a realistic peak rather than the plain sum of all ratings. Loads that run together continuously take a factor of 1.
20 A at 0.8, 30 A at 0.5 and 10 A at 1 give 16 + 15 + 10 = 41 A, against 60 A connected. Unused groups go in as zero current.
Watch out: factors must come from the actual pattern of use or recognised guidance, not guesswork. Some guides define diversity the other way round, as a number above 1. This model is single-phase, so check phase balance separately.
Not every load necessarily operates at full load at the same time. A documented demand model can apply an agreed coincidence factor to each group and sum the resulting currents.
The factor must reflect the actual use, controls and relevant guidance. It is not permission to apply an arbitrary reduction to a protective device or an individual continuously loaded circuit.
Enter your values to see the result.
Common mistake
Confusing a coincidence factor below 1 with a diversity factor defined as its reciprocal.
Limits
Single-phase grouped-current model. Use justified project coincidence factors, not arbitrary diversity reductions. Phase imbalance and correlated loads need separate consideration. Enter zero current for unused groups.
Sources
The tools calculate the displayed equation. They do not automatically choose cable sizes, approve installations, supply current regulatory tables, certify equipment or replace inspection and testing.