What is the maximum amount of current that can pass through a wrist strap ground cord if it is placed across a 250 Volt source?

Answer

Per ESD Handbook TR 20.20 paragraph 5.3.2.6 Current Limiting “Most wrist straps have a current limiting resistor molded into the ground cord head on the end that connects to the cuff. The resistor most commonly used is a one megohm, 1/4 watt with a working voltage rating of 250 volts. Resistors limit current as defined by Ohm's Law, which states the current is equal to the voltage divided by the resistance. In a practical application, the maximum amount of current through a wrist strap ground cord if it was placed across a 250 Volt source is 250 microamps or 0.25 milliamps. This amount of current is well below the 0.7 milliamps that Underwriters Laboratories uses as the peak current in a LIMITED CURRENT CIRCUIT. See document UL 1950. ”For personnel safety, wrist straps should not be used in situations where there is an exposed electrical circuit of 250 volts or higher.” mA is the abbreviation for milliampere, a unit of current equal to one thousandth (10-3) of an ampere. The abbreviation for microampere is μA, a unit of electric current equal to one millionth (10-6) of an ampere. Instead of m or milli, μ is the Greek letter Mu or micro. So "the maximum amount of current through a wrist strap ground cord if it was placed across a 250 Volt source is 250 microamps or 0.25 milliamps" or 0.00025 amperes while DOD-HDBK-263 states the effect on Humans of zero to 0.001 amperes (1mA) would be at the Perception level.