General Design Guidelines

120-volt receptacles should be located on every open wall such that there is not more than 6 feet of wall space to a given receptacle. Quad outlet boxes are preferred over duplex. Lab bench areas should be equipped with continuous receptacle molding (e.g., Plugmold) strips with receptacles spaced on 6–12-inch centers, or similarly continuous receptacles in raceway.

 

One of the most common electrical shock and fire hazards is the overuse of extension cords and various receptacle multipliers. The designer can preclude this hazard by anticipating a heavy need for receptacles everywhere in the laboratory space. In research laboratories, it is rare to have too many receptacles.

 

8 CCR 2500.7

 

Ceiling-mounted, pendant drop receptacles or floor-mounted receptacles should be provided as needed for laboratories where equipment will be located away from walls.

 

Cords crossing floors create tripping and shock hazards. Cords and caps must be provided with strain relief. For any receptacle mounted on a horizontal work surface, a monument style is preferred over flush mount to minimize the risk of liquid inundation.

 

8 CCR 2500.7

 

Provide receptacles of appropriate voltage and current ratings for known equipment in addition to the general convenience receptacles noted above.

 

To avoid overloading circuits, calculate the sum of all known loads separately from the convenience outlet loads.

 

Individual pieces of research / lab equipment that use 15 amps or greater should have its own dedicated circuit with a knife-disconnect switch located nearby, but not immediately adjacent to, the equipment.

 

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8 CCR 2390.1

NFPA 70

 

Ground Fault Circuit Interrupter (GFCI) protection must be provided for convenience receptacles located within 6 feet of a sink or other wet location. GFCI receptacles should not be used for critical equipment such as refrigeration, sump pumps, or gas detectors. Use dedicated single receptacle outlets for such equipment.

 

Even though the code requirements for GFCIs are not very extensive, these inexpensive devices are among the most effective measures that can be taken to prevent electric shock.

 

NFPA 70

 

Provide GFCI protection for receptacles that feed vessel-heating equipment such as strip heaters for vacuum vessels.

 

A fault from a strip heater to a large metal object such as a vacuum vessel poses a significant risk of shock. In addition, strip heaters are typically two-wire without ground, and the only overcurrent protection that can be provided is GFCI.

 

NFPA 70

 

Adequate clear space must be provided in front and to the sides of each electrical circuit breaker panel and equipment disconnect. Label each circuit breaker panel and similar equipment with requirements to maintain a clear 30-inch-wide x 36–48-inch-deep space (depending on voltage).

 

Chapter 1 of NFPA 70 contains the requirements for maintaining clear working space around electrical equipment. The label is not specifically required by Code, but is a good practice in areas where equipment and supplies are frequently being moved around. An even better practice is to also mark floors with durable lines, preferably diagonally striped.

 

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8 CCR 2340.22

NFPA 70

 

Each circuit breaker panel and similar equipment shall be labeled with a notification of an electrical arc flash hazard as well as available calorie / square centimeter hazard class per NFPA70e.

 

A requirement added to the Code in 2002 mandates a warning label where an arc hazard exists. In open panels and similar equipment, an unprotected worker can be exposed to lethal energy levels if an arc is generated.

 

NFPA 70

 

Circuit-breaker panels should not be located in the laboratory.

 

Panels require a maintained, clear floor space of approximately 9 square feet. Typically, wall and floor space are very valuable in laboratories for research equipment. See number 6, above, for additional information about these spaces.

 

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Each circuit and circuit breaker must be sized to carry no less than 100% of the noncontinuous current load plus 125% of the continuous current load for that circuit.

 

Chapter 2 of the Code outlines the correct methods for sizing circuit conductors and overcurrent devices.

 

NFPA 70

 

Laboratory convenience receptacle circuits should be sized as 20 amp circuits, with no more than 13 duplex devices per circuit.

 

The minimum 15-amp circuit size is usually inadequate for laboratory applications. Convenience outlets are calculated at 180VA per device.

 

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NFPA 70

 

When designing circuit-breaker panels, at least 20–40% additional load capacity and circuit-breaker spaces than required by initial calculations should be provided.

 

The Code suggests engineering room for system growth.

 

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NFPA 70

 

Circuit-breaker panels with built-in lockout devices for each breaker must be specified.

 

All electrical circuits are required to be lockable for maintenance purposes.

 

8 CCR 2320.4

 

Fixed equipment that requires periodic maintenance should be provided with lockable disconnect points (e.g. knife disconnect switch).

 

All electrical equipment is required to be lockable for maintenance purposes. Exception: cord and plug connected equipment.

 

8 CCR 2320.4

 

Electrical equipment and controls within fume hoods should be provided with a disconnect switch within 15 feet and be accessible and clearly marked.

 

This does not apply if the equipment is plug-connected outside of the hood.

 

NFPA 45

 

Electrical receptacles, switches and controls should be located to minimize their exposure to spilled liquids. (e.g. physically above or away from plumbing fittings, cooling water systems, etc.)

 

NFPA 45

 

Do not place strip receptacles (“Plug Mold”) across the front of a chemical fume hood below the work surface. Mounting additional receptacles to the side of the fume hood is preferable.

 

Each branch circuit should carry its own neutral conductor. Do not use multiwire branch circuits that share a grounded (neutral) conductor.

 

The increasing use of electronic equipment introduces harmonic loading onto circuits. In a shared-neutral configuration, these harmonics can result in dangerous conductor overheating.

 

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NFPA 70

 

Each conduit should carry a green insulated equipment grounding conductor.

 

A metal conduit may NOT be considered acceptable as an equipment grounding conductor. It is best to supply a copper wire equipment ground to all receptacles and hard-wired lab equipment. This will provide a lower impedance path, and will ensure grounding integrity. In addition, ground metal-conduits at both ends of wire-paths in excess of 50’ to negate impedance effects on copper ground wires internal to conduits.

 

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Circuits serving sensitive Information Technology or data acquisition equipment should be provided with an isolated grounding conductor in addition to the required equipment grounding conductor. This isolated conductor is to be terminated in an identified isolated receptacle or within the sensitive equipment.

 

It is important to understand that the isolated ground, if desired, must be run in the same raceway with the circuit conductors. Under no circumstances may the earth serve as the sole ground return pathway.

 

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NFPA 70

 

Electrical wiring and equipment meeting the specific requirements of NFPA 70, Chapter 5, for classified locations must be provided if substances used or stored in the laboratory can create a flammable or explosive atmosphere.

 

“Explosion-proof” wiring requires careful engineering and collaboration between experts in fire safety and electrical codes.

 

NFPA 70, 30, 33, 34, 35, 45, 497, 499

 

In locations where high-hazard flammable liquids are stored, pumped and transferred into lab-use containers, install ground-bars along the perimeter of the room where a ground-clamp and bonding clamps can be attached for all components within the flammable liquid handling-equipment. Ground bars must have their own ground-wire attached to the building’s electrical ground rod with no other neutral or ground wire as part of the ground-bar ground wire.

 

Rated clamps and conductors shall be provided to adequately bond containers, hoses, and other dispensing equipment to each other and the grounding system where flammable liquids are to be dispensed.

 

Static electricity must be controlled in dispensing areas.

 

NFPA 77

 

Electrical power shall not be commingled in a cable tray with other utilities (e.g., electrical, gas, water, etc.).

 

Cable trays are used in many labs to organize wiring and other utilities. These can be useful in controlling trip hazards and housekeeping problems, but they are regulated by the Code. Water and gas lines may be run below the cable tray provided that they are not attached to the tray itself. Trays may be stacked to provide space for power in the upper tray and other utilities in the lower tray.

 

NFPA 70

 

Electrical equipment shall be designed and installed such that there is no possibility for a person to make direct contact with any part that may become energized at 50 volts or greater during normal use. Exceptions may be made where the possible exposure current cannot exceed 5 milliamps.

 

The possibility for electrocution is generally agreed to exist by contacting 50 volts or greater. All such exposures should be controlled by confinement within an enclosure such as an interlocked Faraday cage, substantial guarding, isolation, or special interlocks and fail-safe machine control logic that render the installation safe before contact can be made with any conductor.

 

8 CCR 2340.17

 

Electrical drawings should be carefully coordinated with other disciplines to assure that conflicts do not occur.

 

The Code provides very strict rules on clearances, placement of switches, etc. and especially with wiring recessed within a wall, can be very expensive to correct.

 

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