From protection relay coordination to solar PV sizing, AJapps covers protection, cable & conductor sizing, earthing, power quality, backup power, instrumentation, renewables and facilities engineering — built on cited IEC, IEEE, NEC and NFPA references, hand-verified, free to use, no signup required.
Most online electrical calculators handle one job — a single voltage-drop formula, a single motor FLC lookup — in isolation, with no citation for where the numbers come from. AJapps takes the opposite approach: every module is built around a named clause or table in a recognized standard (IEC, IEEE, NEC, NFPA, BS, or a manufacturer/industry loading guide where no single standard applies), every result that depends on a rule-of-thumb correction factor says so explicitly instead of presenting it with false precision, and every calculator ships with an “About this tool” panel plus hover tooltips on every input so you can see exactly what a field means and which clause drives it before you commit numbers to a design.
Protection & relay engineers doing IDMT grading and CT/VT sizing; design and consulting engineers running cable, earthing, lighting, conduit/tray and load studies; EPC and site engineers sizing transformers, generators, UPS and motor protection; solar, BESS and EV infrastructure designers; and electrical engineering students who want to see the standard clause behind every formula, not just an answer.
Full per-standard citations, edition notes and worked-example verification figures are documented on each calculator's own “About this tool” panel.
81 live calculators across 10 categories — protection, cabling, earthing, transformers, power quality, motors, backup power, instrumentation, renewables and facilities. Each category page lists every calculator with a full “About this tool” panel.
IDMT relay coordination and grading, differential and earth-fault protection, arc flash, breaker/fuse sizing, and generator paralleling/fault contribution.
Cable and conductor sizing, fill and pulling calculations, and overhead/distribution line voltage regulation and losses.
Earthing grid design, lightning protection and rolling sphere method, touch voltage, and static/ESD hazard checks.
Transformer, CT, VT and busbar sizing/rating, plus insulation resistance and polarization index condition tests.
Power factor correction, harmonics, demand studies, voltage/load balance, unit conversion and tariff estimation.
Motor branch-circuit sizing, motor protection, and VFD energy savings.
Battery sizing, UPS sizing, emergency power sequencing, genset fuel, and energy storage (BESS).
4-20mA loop budgets, intrinsic safety, thermocouple/RTD conversion, and fire & gas loop power.
Solar PV string/inverter sizing and EV charge point sizing — with room to grow as more renewables tools ship.
HVAC electrical sizing, lighting design, elevators, data-center PUE, life-cycle cost, and heat management.
Every formula traces to a named standard clause or table — IEC, IEEE, NEC, NFPA or BS — documented on the calculator itself, not buried in a help file.
Where a figure is an engineering rule-of-thumb rather than a literal standard value (e.g. a derating rate), the tool says so instead of overstating accuracy.
Runs in the browser. Results, checks and pass/fail limits update instantly as you adjust inputs.
Every calculator on AJapps will stay free for single-relay, single-circuit results. Subscribers will unlock multi-device TCC overlays, exportable coordination reports, saved projects and more.