Type HPN and SPT cable have a parallel or duplex construction because the conductors are parallel with a web of insulation that holds the two conductors together. This is sometimes referred to as "zip" because it is easy to tear down during installation. Type HPN heater cable can withstand high heat applications and is used for portable heaters, toasters and irons. Type SPT lamp cable is used primarily for wiring of lamps, clocks, or small appliances.