Chapter 2 Safety 29 by coming in contact with both current-carrying conductors or with the hot conductor and the ground. When this happens the worker receives an electrical shock and may be electrocuted. Power tools made of metal are insulated against acciden- tal grounding. This reduces the danger, but does not eliminate it. Make sure that the tool you are using is grounded. The electrical system should also be checked for proper ground. Any break in the grounding wire makes the grounding system inoperative. When the ground conductor is bro- ken or missing, the worker may become the easi- est path for electrical current to take during a tool malfunction, causing electric shock or electrocu- tion. The integrity of a grounding wire of a power cord can be checked with an ohmmeter or a con- tinuity tester. Circuit breakers and fuses provide some pro- tection against shock. They are designed to open the circuit if a short should occur. A much more efficient protective device, shown in Figure 2-13, is a ground fault circuit interrupter (GFCI). It detects tiny amounts of current and opens the cir- cuit before shock can occur. A GFCI device can be attached to a power cord supplying electric- ity to a power tool. It is an especially important safety measure whenever moisture is present on the jobsite. 2.10 Compressed Air Some of the tools carpenters use are powered by compressed air. These are called pneumatic tools. The pressure used to power these tools is usually 80–100 pounds per square inch (psi). That is enough pressure to cause particles to puncture human skin and do serious damage if directed at the eyes or ears. Goodheart-Willcox Publisher Leviton Figure 2-13. A GFCI provides protection against electrical shock. A—The power pole outlets often include a GFCI. B—If the outlet is not GFCI-protected, a portable power distribution center can be installed to provide a number of GFCI outlets. A B Copyright Goodheart-Willcox Co., Inc.