Memory SNC1D - Drawing Circuit SymbolsVersión en línea Drawing symbols for circuits. por Ms. S Munawar Battery: electrical energy source. Voltmeter: measures voltage. Connected in parallel. Switch: opens and closes the circuit. Fuse: Safety device that has a metal conductor which melts at high, dangerous current levels. Wire: conductor, allows electrons to flow. Lamp/light bulb: specific load, converts electricity to light and heat. Ammeter: measures current, Connected in series. Resistor: general load, converts electricity to heat.