Electrical – Is ‘grounding a desktop PC via 1MΩ resistor’ unsafe when working inside the case

earthesdgroundingmainssafety

Activity: maintenance (installing/replacing hardware parts, like motherboard, CPU, DIMMs, graphics cards) inside an ATX case. Goal: ESD protection and user safety.


Original question: Is 'grounding a desktop PC via the power cable' safe when working inside the case? Answer: in theory, maybe. In practice: NO!

Edited question: Is 'grounding a desktop PC via low impedance (less than 1Ω) path' safe when working inside the case? (Considering the PSU is completely disconnected from live and neutral.) Answer: if a dissipative antistatic mat should be grounded via 1MΩ resistor, then a good conductive surface like the unpainted inside of an ATX case should too.

New question: Is 'grounding a desktop PC via 1MΩ resistor' unsafe when working inside the case? (Considering the PSU is completely disconnected from live and neutral.) Answer: probably not as PE (Protective Earth) is only needed when an appliance is plugged into a wall outlet.


People often advice 2 things to prevent ESD damage:

  1. Antistatic wrist strap, connected to the case of your desktop PC.
  2. The PSU should be turned off, but still plugged into the wall outlet.

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I do understand a low impedance path is desirable in case of a residual-current. But when a PC is powered on, you should not be working inside the case anyway.

If the power cable is disconnected, then is a low impedance path to mains earth safe when you are building a PC or doing maintenance (installing/replacing hardware parts) inside the case? Can the case become a shock hazard in a worst case scenario?

After all, you're probably going to touch the unpainted conductive inner surface of the case at least a few times, while (un)screwing things. Should there be another resistor?

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Best Answer

NO! You really don't want to work inside the case with the power cable plugged in period. You are relying on a switch for safety, which is simply not enough isolation even if it is open.

PC should be unplugged and grounded through a standard anti-stat cable with alligator clip end.

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Wrist-strap should go direct to ground, not through PC case.