Desco Europe ESD - Questions And Answers

If you are working around 230V and have an ESD discharge to the 230v can you get injured? I'm pondering that the discharge path resistance might be sufficiently low to effectively connect you directly to the 230V. Just pondering. - Anonymous, USA

First, the safety of the individual always comes before ESD protection. All means should be made to limit any exposure of line voltage or high voltage to an operator. If you are employing ESD protection, then most likely you are wearing a standard wrist strap that has a 1 megohm resistor to ground. Even if you made direct contact with 230 volts, the resistor would limit the current to 230 uA or 0.23 mA which is considered a safe level by UL and the MIL-STD-454. For protection to the user, the series resistance (all resistances in line to ground) should be greater than 1 megohm to sufficiently limit the current to the operator. If the point of contact is an ESD event (discharge) to a metal conductor, then it is fair to say that that contact resistance is zero, but you still have to add all the other resistances to get the equivalent resistance of the grounding circuit. This may include: skin resistance from finger (discharge) to wrist strap, contact resistance of skin to wrist band, wrist band resistance to buckle, buckle to snap resistance, 1 megohm resistance in series with coil cord, coil cord resistance, common point ground contact resistance, and finally ground cord to ground resistance. The sum of all these resistances [equivalent resistance] may be something like 1.2 megohms to less than 9 megohms. If you contact 230 volts with this equivalent resistance, then the current is limited below even 0.23 mA.

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