As an electrical and electronics design engineer, here is my perspective.
First of all, I don't believe the main concern is anything to do with static electricity.
As part of Type Approval testing, it is common to "zap" Equipment Under Test with static discharges up to 8kV (direct contact) and up 15kV (air discharge). These voltages are applied to the outside of the EUT case or enclosure (not to the inputs/outputs). Equipment should survive this "zap" test unscathed. N.B. These tests are often performed on a wooden table.
https://www.silabs.com/documents/public/application-notes/AN895.pdf
What I believe you're experiencing is leakage currents from the AC mains, flowing through a Class-Y safety capacitor. These capacitors are part of the EMI/RFI filtering circuits found in most ATX PSUs.
It is normal to find a Class-Y capacitor connected between the AC Line input (115/230V AC) and Chassis, plus a second Class-Y capacitor between Neutral and Chassis. When the metal chassis (ATX case) is not correctly earthed, the two Class-Y capacitors form a "capacitive divider".
https://www.allaboutcircuits.com/technical-articles/safety-capacitor-class-x-and-class-y-capacitors/
If you measure the voltage on the ATX PSU metalwork with respect to ground (safety earth) using a multimeter, you'll see approximately half mains voltage, i.e. 57.5V AC for a 115V supply, or 115V AC for a 230V supply. With 230V AC mains, you might get a neon screwdriver to light up if you touch the blade to chassis.
https://resources.altium.com/p/how-use-class-x-and-class-y-safety-capacitors
Due to the fact these Class-Y capacitors have a fairly low capacitance, e.g. 0.01uF, they maintain a relatively high impedance at 60Hz/50Hz mains frequencies, but a much lower impedance in the Megahertz range where they are most effective at reducing RFI. In the diagram above, the two Class-Y capacitors are running in a "common mode noise reduction" circuit, with the centre point supposedly earthed for correct operation.
As a result of the high impedance Class-Y capacitive divider, all you feel when touching computer metalwork on an unearthed chassis with dry fingers is a slight buzzing sensation. If you rub the back of your finger over the chassis, this buzzing sensation increases.
The half mains voltage on the chassis may, or may not be above the SELV limit, depending on where you live. In countries where the AC mains is 220V to 240V, half mains voltage is above the SELV safety limit.
https://www.electricalsafetyfirst.o...is-the-difference-between-selv-pelv-and-felv/
You are unlikely to sustain a life threatening shock from such a high impedance source, but it's a warning that something far more serious could occur. If a fault occurs inside an ATX PSU and the AC mains or HT rectified DC supply touches the chassis, it could become life threatening.
When the chassis is correctly earthed, fault currents flow safely down to ground and a fuse or circuit breaker will probably trip. When the chassis is not correctly earthed, fault currents may flow through your body and kill you. It takes little more than 20 to 30mA flowing through your heart muscle to stop it beating.
Conclusion, ATX PSUs are designed to be used with a safety earth. They are not "double isolated" designs which can work without an earth. You must earth your ATX PSU if you want to stay safe.
If your building manager/owner claims your AC outlets are earthed but you suspect otherwise, get a qualified electrician to check. Don't take the word of untrained person (idiot), ask a professional.
Where I live, government regulations mandate that all domestic and office mains outlets must be earthed. It is very, very unusual indeed to find a mains socket without an earth, but wires can become disconnected and errors made during installation.
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