Facility Safety Management

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Wiring and Outlet Protection

BY STEVE MONTGOMERY

To maximize safety in your facility, a regular program of maintenance for electrical systems should be established.

The NFPA 70E Standard for “Electrical Safety in the Workplace” establishes specific guidelines for electrically safe work conditions, how to safely work on or near live parts, and safety-related installation and maintenance requirements. Furthermore, NFPA 70B describes “Recommended Practice for Electrical Equipment Maintenance.”

Both documents should be part of a good maintenance library and should be used as daily guides.

Wiring devices and portable wiring generally experience more wear and tear than most other electrical equipment components. Impact, heat, abrasion and numerous plug insertions can damage or wear receptacles. Worn outlets can create both shock and fire hazards.

For example, electrical wiring connectors deteriorate with usage. A loose wire junction can develop higher resistance to current flow due to arcing, pitting, oxidation, corrosion, and contamination. When high currents flow through a high resistance junction, it creates heat. Heat decomposes most types of plastic used for insulation. Degraded insulation can result in fires.

Thus regular maintenance should be performed on wire connections. Circuit wire connections at load centers should be checked for adequate tightness on a regular basis. Junctions under wire nuts should be checked for good mechanical connections, and wire nuts tightened.

Bad Wire Junctions Create Fire Hazards

On receptacle outlets, screw connections should be used instead of the quick rear-insertion connections on the back. Screw connections stay tight longer. Avoid use of the ‘push in’ type wire connectors on the back of 120V duplex receptacles. The small bayonet connectors can become weakened and loose just by pushing a wired receptacle outlet back into an electrical box. Weak connector contacts often lead to increased connection resistance due to reduced contact surface area, arcing, oxidation, and pitting.

Again, the excess heat from high current flowing through these higher resistance connections can lead to fires.

Receptacle outlet screw connections should be tightened regularly, even once per year or more frequently. For facilities in the U.S., UL requires that duplex receptacle outlet wire-connection screws shall survive 1.8 Newton-meters of force without stripping or breaking. For Canadian facilities, CSA 42-99 requires that duplex receptacle outlet screws shall handle 1.6 Newton-meters of tighten down force.

To provide good tightness without damaging the screw (and thus creating a bigger hazard); use a torque screwdriver to ensure screws are consistently tightened within the design range of electrical outlets. To ensure compliance and reduce liability, have the torque screwdriver calibrated and keep a certificate of compliance. Also keep records of service for screw connection tightness on your electrical receptacles.

Outlet receptacle sockets should also have good grip force on electrical device plugs. Loose connectors create three hazards: 1)loss of power to critical devices, 2) shockhazard, and 3) fire hazards.

Loose sockets mean that plugs can either fall out or be easily pulled out accidentally. Facilities for medical patient care should meet the requirement of standards NFPA 99 and/or CSA Z32 for Health Care Facilities.

These standards require regular maintenance of electrical outlets and represent good practices for all residential, commercial and industrial facilities.

For example, NFPA 99 recommends regularly doing the following:

• Checking the “electrical continuity of all required equipment, grounding conductors, and their connections;” and

• Testing “fixed receptacles, equipment connected by cord and plug, and fixed electrical equipment when first installed, where there is evidence of damage, after any repairs, and at intervals not exceeding six months.”

Both NFPA 99 and CSA Z32 standards set limits on plug retention force. Although both of these standards are for critical applications, these safety concepts apply to all electrical receptacles. Good maintenance practice should include regular receptacle retention checks to maximize fire and shock protection for facilities. Tight plug sockets hold plugs in place once fully inserted. Partially inserted plug blades expose live voltages to fingers and create a line-to-neutral shock hazard. The best ways to prevent injury from Line-Neutral shocks is to keep electricity OFF at receptacle sockets until needed, ensure adequate receptacle retention force, and keep plugs fully inserted in receptacles.

Shock Fault Circuit Interrupters (SFCI) in outlets and Tamper Resistant outlets help prevent shocks at unoccupied receptacles. For residential construction in the U.S.A. starting in 2008, receptacles will require Tamper Resistant mechanisms, which keep a spring loaded cover over both sockets on a 120V single phase socket so that children cannot easily insert metal objects into the sockets.

Shock Fault Circuit Interrupters accomplish the same electrical isolation by using a normally-open electro-mechanical relay switch in series with the electrical wiring.

The SFCI closes the switch when a tagged plug is fully inserted in the receptacle. Thus open receptacles are electrically dead; only receptacles with plugs inserted receive electricity.

FSM

Steve Montgomery, P.E., a member of the International Association of Electrical Inspectors (IAEI), National Fire Protection Association (NFPA), International Fire Marshals Association (IFMA), and Institute of Electrical & Electronics Engineers (IEEE), leads the operations team at OFI, Inc (www.safeplug.com).

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