ESD suppressors are semiconductors that protect electronic components and systems from electrostatic discharge (ESD), the sudden and uncontrolled transfer of an electrical charge between conductors. They are installed near the protected line and connected in parallel with the signal line. Most products consist of diode arrays. ESD suppressors protect static-dissipative equipment from overvoltage transients by clamping voltages to levels which circuits can withstand. They shunt the majority of the ESD current away from the data line to a reference, usually the power rail and chassis ground. During production, transient voltage suppression (TVS) increases chip yields according to standards such as charged device model (CDM) and machine model (MM). During end-use, ESD suppressors protect electronic products such as cell phones, personal digital assistants (PDA), and computers according to test methodologies such as IEC 61000-4-2 from the International Electrotechnical Commission (IEC).