ment are carried out, the devices must be deenergized and all capacitors discharged safely. Furthermore, this deenergized and/or discharged condition must be verified before proceeding. Note that the Occupational Safety and Health Administration (OSHA) Control of Hazardous Energy Standard (29 CFR § 1910.147, Lock out/Tag out) applies.

All new electrical equipment should be inspected on receipt for a certification mark. If the device bears a certification mark from UL (Underwriters Laboratories Inc.), CSA (Canadian Standards Association), ETL (originally a mark of ETL Testing Laboratories, now a mark of Intertek Testing Services), or CE (Conformance European–Communaut Europenne or Conformit Europenne), detailed testing and inspection are not required. If the device does not bear one of these certification marks, the device should be inspected by an electrician before it is put into service.

Each person participating in any experiment involving the use of electrical equipment must be aware of all applicable equipment safety issues and be briefed on any potential problems. Trained laboratory personnel can significantly reduce hazards and dangerous behavior by following some basic principles and techniques: checking and rechecking outlet receptacles (section 7.C.1.1), making certain that wiring complies with national standards and recommendations (section 7.C.1.2), reviewing general precautions (section 7.C.1.3) and personal safety techniques (section 7.C.1.4), and ensuring familiarity with emergency procedures (section 7.G).

7.C.1.1 Outlet Receptacles

All 110-V outlet receptacles in laboratories should be of the standard design that accepts a three-prong plug and provides a ground connection. Replace two-prong receptacles as soon as feasible, and add a separate ground wire so that each receptacle is wired as shown in Figure 7.1.1 The ground wire is preferably (but not required by code) on top to prevent anything falling onto a plug with exposed prongs, and will contact the ground before contacting the hot or the neutral line.

It is also possible to fit a receptacle with a ground-fault circuit interrupter (GFCI), which disconnects the current if a ground fault is detected. GFCI devices are required by local electrical codes for outdoor receptacles and for selected laboratory receptacles located less than 6 ft (1.83 m) from sinks if maintenance of a good ground connection is essential for safe operation. These devices differ in operation and purpose from fuses and circuit breakers, which are designed primarily to protect equipment and prevent electrical fires due to short circuits or other abnormally high current draw situations. Certain types of GFCIs cause equipment shutdowns at unexpected and inappropriate times; hence, their selection and use need careful planning. Be aware that GFCIs are not fail-safe devices. They significantly reduce the possibility of fatal shock but do not entirely eliminate it.


FIGURE 7.1 Representative design for a three-wire grounded outlet. The design shown is for 15-A, 125-V service. The Specific design will vary with amperage and voltage.

Locate receptacles that provide electric power for operations in laboratory chemical hoods outside the hood. This location prevents the production of electrical sparks inside the chemical hood when a device is plugged in or disconnected, and it also allows trained laboratory personnel to disconnect electrical devices from outside the hood in case of an accident. Cords should not be routed in such a way that they can accidentally be pulled out of their receptacles or tripped over.

Simple inexpensive plastic retaining strips and ties can be used to route cords safely. For laboratory chemical hoods with airfoils, route the electrical cords under the bottom airfoil so that the sash can be closed completely. Most airfoils are easily removed and replaced with a screwdriver.

7.C.1.2 Wiring

Fit laboratory equipment plugged into a 110-V (or higher) receptacle with a standard three-conductor line cord that provides an independent ground connection to the chassis of the apparatus (see Figure 7.2). Ground all electrical equipment unless it is double-insulated. This type of equipment has a two-conductor line cord that meets national codes and standards. The use of two-pronged cheaters to connect equipment with three-prong grounded plugs to old-fashioned two-wire outlets is hazardous and should be prohibited.

Limit the use of extension cords to temporary (<1 day) setups, if they are permitted at all. Use a standard three-conductor extension cord of sufficient rating for the connected equipment with an independent ground connection. In addition, good practice uses only extension cords equipped with a GFCI. Install electrical


1The outlet is always “female”; the plug is always “male.”

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