Electrical energy
Electrical energy is the amount transferred over time, measured in joules (J) or, on electricity bills, kilowatt-hours (kWh). A load drawing a steady 1 kW for two hours uses 2 kWh. Power describes the rate of transfer; energy describes the accumulated amount. A battery capacity quoted in kWh is therefore different from its power rating in kW.
How the ideas connect
Compare a battery's kWh capacity with a load's kW power to separate amount from rate. Maximum demand asks how much an installation may draw at once; it does not describe the energy used across a day. These are different questions about the same loads.
Where Electrical energy fits in the learning path
The Electrical Science section covers these units:
- Circuit Fundamentals
Curriculum mapping: C&G 2365 Units 202/302.
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- Ohm's LawElectrical Science
- Battery Energy Storage SystemsThe Regs and Practice Papers
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- Electrical Science — quiz previewFree · Electrical Science
- 18th Edition Exam — quiz previewPlus · The Regs and Practice Papers
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The realistic peak current an installation will draw, worked out from the connected load with diversity applied. It is the figure the supply arrangements are sized against — tails, main switch, distribution equipment — and the first number a designer needs before any circuit-level decisions make sense.
Maximum demand
Read the Maximum demand entryCompare related terms
Open a meaning to compare its role with Electrical energy, or follow its full entry.
Maximum demand
The realistic peak current an installation will draw, worked out from the connected load with diversity applied. It is the figure the supply arrangements are sized against — tails, main switch, distribution equipment — and the first number a designer needs before any circuit-level decisions make sense.
Read the Maximum demand entryElectrical power
Electrical power is the rate at which electrical energy is transferred, measured in watts (W) or kilowatts (kW). A 1 kW load transfers energy twice as fast as a 500 W load. In a DC circuit, power equals voltage multiplied by current. For AC loads, real power also depends on power factor, so multiplying voltage and current alone does not always give watts.
Read the Electrical power entryDC — Direct Current
Direct current flows in one direction, although its size can vary. A battery supplies DC, while an inverter can convert DC from a battery into AC for suitable loads. DC does not mean low voltage or harmless: direction of flow and voltage level are separate ideas. Insulation resistance instruments use a DC test voltage, but that is not the normal supply voltage of the circuit.
Read the DC entryA definition is a start. Using it in a real question is where it sticks.