Electrical Safety Is Your Responsibility
Standard wall outlets in the U.S. provide a nominal 120 volts AC and are rated to deliver currents between 15 and 20 amps. Under certain conditions, it is possible to receive a lethal shock from much lower voltages than these. Inside a computer, and especially the monitor, voltages as high as 30,000 volts can exist—even after the power is turned off.
It is vital to follow basic electrical-safety guidelines when servicing a computer. There is no substitute for good old common sense. However, here are a few tips:
- When in doubt about the correct way to safely service a part of a computer, don't do it. Have an experienced professional do the necessary work.
- Always use grounded outlets and power cords.
- Switch the power off and disconnect all equipment from its power source before removing any covers.
- Always replace blown fuses with fuses of the correct rating and type.
- Do not work alone—you might need help in an emergency.
- Remove all jewelry and any wristwatch. These are conductors and can cause short circuits.
- Have trained personnel service computer power supplies and monitors; these devices use and store potentially lethal voltages (often for days or longer).
- Work with one hand. Using two hands can cause a direct circuit, via your heart, from one object to another.
In the U.S., common AC wiring uses the following color coding:
|Live or hot||Black|
|Ground||Green or bare copper|
Color codes for AC wires and DC wires can be different. For example, the ground wires on the P8 and P9 connector for an AT-style motherboard are black.