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SAFETY MODEL STAGE 3—CONTrOLLING HAZArDS: SAFE WOrK ENVIrONMENT

Equipment needs to be grounded under any of these circumstances:

The equipment is within 8 feet vertically and 5 feet horizontally of the floor or walking surface.

The equipment is within 8 feet vertically and 5 feet horizontally of grounded metal objects you could touch.

The equipment is located in a wet or damp area and is not isolated.

The equipment is connected to a power supply by cord and plug and is not double-insulated.

Use GFCIs

The use of GFCIs has lowered the number of electrocutions dramati- cally. A GFCI is a fast-acting switch that detects any difference in current between two circuit conductors. If either conductor comes in contact—either directly or through part of your body—with a ground (a situation known as a ground fault), the GFCI opens the circuit in a fraction of a second. If a current as small as 4 to 6 mA does not pass through both wires properly, but instead leaks to the ground, the GFCI is tripped. The current is shut off.

There is a more sensitive kind of GFCI called an isolation GFCI. If a circuit has an isolation GFCI, the ground fault current passes through an electronic sensing circuit in the GFCI. The electronic sensing circuit has enough resistance to limit current to as little as 2 mA, which is too low to cause a dangerous shock.

GFCIs are usually in the form of a duplex receptacle. They are also available in portable and plug-in designs and as circuit breakers that protect an entire branch circuit. GFCIs can operate on both two- and three-wire ground systems. For a GFCI to work properly, the neutral conductor (white wire) must (1) be continuous, (2) have low resistance, and (3) have sufficient current-carrying capacity.

Portable GFCI.

GFCIs have their limitations.

GFCIs help protect you from electrical shock by continuously moni- toring the circuit. However, a GFCI does not protect a person from line-to-line hazards such as touching two “hot” wires (240 volts) at the same time or touching a “hot” and neutral wire at the same time. Also be aware that instantaneous currents can be high when a GFCI is tripped. A shock may still be felt. Your reaction to the shock could cause injury, perhaps from falling.

Test GFCIs regularly by pressing the “test” button. If the circuit does not turn off, the GFCI is faulty and must be replaced.

Page 50

Section 7

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