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If a mat and the wrist strap are connected together, do they need to be connected to earth (ground) potential? - Doug, Australia

No, but the equipment being worked on should be both unplugged and electrically connected to the ESD mat. As long as all conductive parts, (body's skin, ESD mat, equipment chassis, parts being handled, etc.), are at the same potential, there will be no opportunity for an ESD event (discharge). Earth ground happens to be a very convenient reference voltage to connect to. If you ensure that all conductive parts are tied to earth ground, then you meet the same requirement that they are at the same potential. It is when you have a difference in the potential (voltage or net charge) between two conductors that, (either touch together or come in near proximity), will lead to a discharge (ESD event).

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