Electrical load calculator for single-line diagrams
Give each load on a single-line diagram its rating and SmartSLD adds them up behind every bus and transformer, with transformer loading and bus current. Free, in your browser, no signup.
How it works
- Draw the circuit, or start from the example below.
- Give each load its rated power in kW.
- Totals appear next to every bus and transformer, and the Drawing check panel lists them with kVA, current and loading.
The arithmetic
S = P / cos φ
Loading = ΣS / Sₙ
I = ΣS / (√3 · U)
S is apparent power, P the load's rating, cos φ its power factor (0.9 unless the load says otherwise), U the bus voltage and Sₙ the transformer's rated kVA.
An estimate: every load at its rating at the same time, no diversity factor, no code rules. A load without a rating is counted and flagged, never treated as zero.
The same panel also checks the drawing: wires that look connected but are not, devices with no path to a supply, and voltage levels joined without a transformer.
There is no form to fill in: the editor is the calculator. Change any rating there and every total updates as you type.