The method
Before using the result
- Constant actual input power during the entered period. Flat energy tariff only; no demand charge, tax or standby allowance.
Worked examples
These original training examples illustrate the method for Journeyman Electrician Core Knowledge Review (JE). Use the matching “Load example” button above to explore a variation; example values are not equipment settings or prescribed criteria.
1. Worked example
Translate watts and operating time into the energy charged by a flat tariff. Distinguish a device power rating from actual period energy.
- Power per device
- 100 W
- Device count
- 10
- Operating time in selected period
- 10 h
- Tariff (currency/kWh)
- 0.15
- Energy = 100 × 10 × 36000 = 36000000 J = 10 kWh.
- Cost = 10 × 0.15.
- Period energy: 36,000,000 J
- Period operating cost: 1.5 currency units
2. Comparison example
Compare a different supplied condition using the same method. For Electrical Exam, the important check is that the input meaning, units and method assumptions still match the problem.
- Power per device
- 100 W
- Device count
- 20
- Operating time in selected period
- 10 h
- Tariff (currency/kWh)
- 0.15
- Energy = 100 × 20 × 36000 = 72000000 J = 20 kWh.
- Cost = 20 × 0.15.
- Period energy: 72,000,000 J
- Period operating cost: 3 currency units
Check your understanding
1. Which relationship is used?
Energy = power × count × operating time; cost = energy in kWh × tariff.
2. Which assumption should you check first?
Constant actual input power during the entered period. Flat energy tariff only; no demand charge, tax or standby allowance.
3. How should you verify a different unit system?
Convert every input to the displayed calculation units first. Equivalent physical inputs must give equivalent results; a unit label alone does not convert a number.
Continue with the matching exam topic
This tool connects to Journeyman Electrician Core Knowledge Review (JE) free practice. Work through a question independently, then use the calculation steps to identify where your method differs. The tool stays free whether or not you choose paid preparation.