Manual of basic techniques for a health laboratory - libdoc.who.int

16 Manual of basic techniques for a health laboratoryFig. 2.3 An electricity meterONOFFThe electricity meter (Fig. 2.3)An electricity meter measures and records the amount ofelectricity used. It indicates:— the voltage, measured in volts (220V, 110V, etc.);— the strength of the current, measured in amperes (A);— the frequency of the alternating current, e.g. 50 hertz(Hz) (cycles per second).Some types of meter have switches or buttons:— a flip-switch that can be flipped one way to cut off theelectricity supply to the whole building (the mainsfuse) and the other way to restore it;— a button marked “OFF” that can be pushed to cut offthe electricity supply;— a button marked “ON” that can be pushed to restorethe electricity supply.The flip-switch or “OFF” button also acts as a circuitbreaker,automatically cutting off the current when the circuitis overloaded. When this happens, first find and correctthe fault that caused the cut-off, then press the “ON” buttonor flip the switch to restore the current.Setting up new electrical equipmentVoltageCheck that the voltage marked on the instrument is the same as that of your electricitysupply. The instrument has a label on it stating the voltage with which itmust be used. The voltage of your electricity supply is marked on your electricitymeter.Dual-voltage equipmentDual-voltage instruments can be used with two different voltage supplies.There is a device on the instrument that enables you to select the appropriatevoltage, i.e. the voltage marked on your electricity meter. Depending on the instrument,this device may be:— a lever or switch that can be moved to the 110V position or the 220V position(Fig. 2.4(a));— an unwired plug that can be transferred from the 110V position to the 220Vposition (Fig. 2.4(b));— a screw that can be turned to the 110V position or the 220V position (Fig.2.4(c)).(c)(a)(b)Fig. 2.4 Dual-voltage instruments