Voltage fluctuations are described by the IEC as cyclical variations of the voltage envelope or a series of random voltage changes of up to 610% of the nominal. In low-voltage networks domestic appliances are significant sources, but each appliance will affect only a limited number of consumers. Fluctuations resulting from industrial loads can affect many consumers, the main effect usually being flicker (see Section 25.2.3). Also step voltage changes due to the connection or disconnection of large loads or capacitor banks can fall into the category of voltage fluctuations (see also Section 25.2.6). Equipment with significant time constants, such as heating elements, is largely unaffected, but some electronic and IT equipment can be seriously affected.