ELECTRICAL SAFETY GENERAL REQUIREMENTS
This section deals with the reliability and effective maintenance of electrical systems that can beachieved in part by careful planning and proper design. The training of personnel in safety related work practices that pertain to their respective job assignments is outlined.
Only qualified persons shall perform electrical repairs. Once a problem is discovered while troubleshooting or maintaining electrical equipment, any further work on this component or system must be suspended until the associated corrective actions are processed through a work control system. It is dangerous for an unqualified worker to attempt electrical repair. Before any electrical maintenance or troubleshooting is performed, sources of electrical energy shall be de-energized, except where it is necessary for troubleshooting, testing, or areas that are infeasible to de-energize. All energy sources shall be brought to a safe state. For example, capacitors shall be discharged and high capacitance elements shall be short-circuited and grounded.
The first consideration for working on any electrical system is to have the circuit positively de-energized. All circuits and equipment must be considered energized until opened, tagged, and/or locked according to an approved procedure and should be proven de-energized by testing with an approved testing device known to be in proper working order. NFPA 70E refers to this as an electrically safe work condition and defines it as “a state in which the conductor or circuit part to be worked on or near has been disconnected from energized parts, locked/tagged in accordance with established standards, tested to ensure the absence of voltage, and grounded if determined necessary.” The electrical hazard controls identified in NFPA 70E are intended to protect a person from arc flash and shock hazards. Due to the explosive effects of some arc events, physical trauma injuries could occur. The personal protective equipment (PPE) requirement identified in NFPA 70E is intended to protect against physical trauma other than exposure to the thermal effects of an arc flash.
Qualified employees performing such tasks as electrical repairs, modifications, and tests on energized electrical systems, parts, and equipment need to comply with the following:
Note: The discussion in #4 above assumes the system voltage is less than the maximum use voltage of the ASTM class of rubber goods used.
The responsibilities and qualifications of personnel for sites that require the use of a safety watch are as follows:
To protect employees from some of the electrical hazards at industrial sites, Federal regulations limit the performance of electrical work to qualified and competent personnel. Specifically, the law requires that only a qualified person or someone working under the direct supervision of a qualified person may perform any repair, installation, or testing of electrical equipment. See
Section 2.8 and the definitions of "Qualified Employee" or "Qualified Person" in Appendix B.
One of the best ways to prevent electrical accidents at industrial sites is to be aware of electrical dangers in the workplace. Once hazards have been identified, they must be pointed out and proper steps taken by a qualified person.
The following, where used, will improve the safety of the workplace:
Management is responsible to provide a workplace that is free from recognized hazards that might cause injury, illness, or death and to comply with the specific safety and health standards issued by Federal, state, and local authorities, particularly OSHA. Managers expect their employees to comply with these regulations for the health and safety of employees. Prevention of injury and illness requires the efforts of all and is a goal well worth achieving.
To ensure safety and protection of employees, managers have the following responsibilities:
Employees are responsible to comply with occupational safety and health regulations and standards that apply to their own actions and conduct, including immediate reporting to management of unsafe and unhealthful conditions.
All modifications to existing and new facilities and projects should be subject to inspection by the Authority Having Jurisdiction (AHJ) or authorized designee to verify compliance with the codes and standards in effect on the date that the work was approved by a final design review. If the installation involves a hazard to life, equipment, or property, current standards and codes should be used to mitigate the hazard.
According to OSHA, all major replacements, modifications, repairs, or rehabilitation performed after March 15, 1972, on electrical systems and equipment installed before March 15,1972, are required to comply with all the requirements of 29 CFR 1910.302 to 1910.308. OSHA considers major replacements, modifications, or rehabilitation to be work similar to that involved when a new building or facility is built, a new addition is built, or an entire floor is renovated.
All electrical equipment, components, and conductors shall be approved for their intended uses.
If any electrical system component is of a kind that any Nationally Recognized Testing Laboratory (NRTL) accepts, certifies, lists, or labels, then only NRTL accepted, certified, listed, or labeled components can be used. A non-listed, non-labeled, noncertified component may be used if it is of a kind that no NRTL covers, and then it shall be tested or inspected by the local authority responsible for enforcing the Code. For example, this would apply to custom-made equipment. The custom-made equipment should be built in accordance with a design approved by the AHJ.
See 29 CFR 1910.399 for definitions relating to OSHA requirements for accepting electrical equipment and wiring methods that are not approved by an NRTL.
Workers who perform electrical or electronic work, where applicable, shall comply with relevant Code of Federal Regulations (CFR) that may identify the following codes and standards.
The standards and performance specifications from the following organizations are recommended and should be observed when applicable:
Where no clear applicable code or standard provides adequate guidance or when questions regarding workmanship, judgment, or conflicting criteria arise, personnel safety protection shall be the primary consideration. Therefore, where there are conflicts between the mandatory requirements of the above codes, standards, and regulations, the requirements that address the particular hazard and provide the greater safety shall govern.
There are two classes of GFCIs, each with a distinct function. A Class A GFCI trips when the current to ground has a value in the range of 4 through 6 milliamperes and is used for personnel protection. A Class A GFCI is suitable for use in branch circuits. A Class B GFCI (commonly used as ground fault protection for equipment) trips when the current to ground exceeds 20 milliamperes. A Class B GFCI is not suitable for employee protection.
Ground-fault circuit protection can be used in any location, circuit, or occupancy to provide additional protection from line-to-ground shock hazards because of the use of electric hand tools. There are four types of GFCIs used in the industry:
The condition of use determines the type of GFCI selected. For example, if an electrician or maintenance person plugs an extension cord into a non-protected GFCI receptacle, the easiest way to provide GFCI protection is to utilize a portable-type GFCI.
See Section 4.14 for ground-fault protection of equipment. GFCIs are devices that sense when currenteven a small amountpasses to ground through any path other than the proper conductor. When this condition exists, the GFCI quickly opens the circuit, stopping all current flow to the circuit and to a person receiving the ground-fault shock.
Figure 1 shows a typical circuit arrangement of a GFCI designed to protect personnel. The incoming two-wire circuit is connected to a two-pole, shunt-trip overload circuit breaker. The load-side conductors pass through a differential coil onto the outgoing circuit. As long as the current in both load wires is within specified tolerances, the circuit functions normally. If one of the conductors comes in contact with a grounded condition or passes through a person's body to ground, an unbalanced current is established. This unbalanced current is picked up by the differential transformer, and a current is established through the sensing circuit to energize the shunt trip of the overload circuit breaker and quickly open the main circuit. A fuse or circuit breaker cannot provide this kind of protection. The fuse or circuit breaker will trip or open the circuit only if a line-to-line or line-to-ground fault occurs that is greater than the circuit protection device rating.
Figure 1: GFCI-protected circuits are one way of providing protection of personnel using electric hand tools on construction sites of other locations.
Differential transformers continuously monitor circuits to ensure that all current that flows out to motor or appliances returns to the source via the circuit conductors. If any current leaks to a fault, the sensing circuit opens the circuit breaker and stops all current flow.
A GFCI will not protect the user from line-to-line or line-to-neutral contact hazards. For example, if an employee using a double-insulated drill with a metal chuck and drill bit protected by a GFCI device drills into an energized conductor and contacts the metal chuck or drill bit, the GFCI device will not trip (unless it is the circuit the GFCI device is connected to) as it will not detect a current imbalance.
The use of GFCIs in branch circuits for other than dwelling units is defined in the NEC 410.4
Ground-fault protection for personnel shall be provided for temporary wiring installations utilized to supply temporary power to equipment used by personnel during construction, remodeling, maintenance, repair, or demolition activities.
For temporary wiring installations: a) All 120-V, single-phase, 15-, 20-, and 30-A receptacle outlets that are or are not a part of the permanent wiring of the building or structure and that are in use by employees shall have GFCI protection for personnel. b) GFCI protection or an assured equipment grounding program (See Section 8.2) for all other receptacles shall be used to protect against electrical shocks and hazards.
Portable GFCIs shall be trip-tested according to the manufacturers instructions.
Figure 2: There are three methods of providing GFCI protection for construction sites.
One of the more promising techniques for improvement of performance of wiring systems with respect to arc-generated fires and intermittent equipment operation is the possibility of using the arc voltage and current signatures to trip circuits by an AFCI. An AFCI is a device intended to provide protection from the effects of arc faults by recognizing characteristics unique to arcing and by functioning to de-energize the circuit when an arc fault is detected (NEC 210.12 and 550.25). AFCIs are evaluated to UL1699, Safety Standard for Arc-Fault Circuit Interrupters, using testing methods that create or simulate arcing conditions to determine the products ability to detect and interrupt arcing faults.
Although NEC 210.12 requires that AFCI protection be provided on branch circuits that supply outlets (receptacle, lighting, etc.) in dwelling unit bedrooms, there is no prohibition against providing AFCI protection on other circuits or location other than the bedrooms. For example, aircraft wire systems utilize AFCIs for newer installation to trip the circuit routed through sensitive areas such as fuel storage areas.
Only qualified workers shall perform work on electrical systems. It is dangerous for unqualified personnel to attempt to do electrical work. There should be an employee training program implemented to qualify workers in the safety-related work practices that pertain to their respective job assignments.
Management should establish formal training and qualifications for qualified workers before they are permitted to perform electrical work. Refresher training is recommended at intervals not to exceed three years to provide an update on new regulations and electrical safety criteria.
The training shall be on-the-job and/or classroom type. The degree of training provided shall be determined by the risk to the employee. This training shall be documented. Qualified employees shall be trained and familiar with, but not be limited to, the following:
Other types of training recommended for electrical workers include the following:
29 CFR 1910.269(a) and 1910.332 also require training for persons other than qualified workers if their job assignments bring them close enough to exposed parts of electrical circuits operating at 50V or more to ground for a hazard to exist.
Safety personnel designated to support electrical safety programs should be knowledgeable and trained at levels commensurate with their duties.
Working space around electrical enclosures or equipment shall be adequate for conducting all anticipated maintenance and operations safely, including sufficient space to ensure safety of personnel working during emergency conditions and workers rescuing injured personnel. Spacing shall provide the dimensional clearance (discussed in the following subsections) for personnel access to equipment likely to require examination, adjustment, servicing, or maintenance while energized. Such equipment include panel boards, switches, circuit breakers, switchgear, controllers, and controls on Heating, Ventilation, and Air Conditioning (HVAC) equipment. These clearances shall be in accordance with NESC and NEC. These working clearances are not required if the equipment is not likely to require examination, adjustment, servicing, or maintenance while energized. However, sufficient access and working space is still required.
NEC 110.26 states that a minimum working space 30 in. wide shall be provided in front of electrical equipment rated at 600 V or less. This provides room to avoid body contact with grounded parts while working with energized components of the equipment. The 30-in.-wide space may be centered in front of the equipment or can be offset. The depth of the working space shall be clear to the floor. Where rear access is required to work on de-energized parts, a minimum of 30 inches shall be provided. There shall be clearance in the work area to allow at least a 90-degree opening of equipment doors or hinged panels on the service equipment. Working spaces may overlap. The depth of the working space shall be 3 ft, 3 1/2 ft, or 4 ft, depending upon existing conditions. The conditions are as follows:
Condition 1: These are exposed live components on one side of a space and ungrounded parts on the other side.
Condition 2: The electrical equipment is mounted or set on one wall, and the wall on the opposite side is grounded. If the qualified worker should accidentally contact the conductive wall while touching live components, a circuit would be completed to ground and a fatal shock might occur.
Condition 3: The electrical equipment is mounted or set on one wall, and additional electrical equipment is mounted or set on the opposite side of the room. There are live components on both sides of the room. The qualified worker might accidentally make contact with live components and be in series with a hot phase and the grounded metal of the electrical equipment, which could produce a fatal shock.
See Figure 3 for the clearance requirements in front of electrical equipment rated 600 V or less.
Figure 3: Minimum Clearances in front of Electrical Equipment (600 V or less)
NEC 110.34 lists minimum clearances required for working spaces in front of high-voltage electrical equipment such as switchboards, control panels, switches, circuit breakers, switchgear, and motor controllers.
There are three conditions to apply:
See Figure 4 for the clearance requirements in front of electrical equipment rated at over 600 V. See NEC for clearance requirements in the rear of electrical equipment.
Figure 4: Minimum Clearances in front of Electrical Equipment (over 600 V)
Switches in service panels, subpanels, or elsewhere shall be marked to show what loads or equipment are supplied.
In according to NEC 110.22, all disconnecting means (disconnect switches or circuit breakers) shall be located for easy access and shall be clearly and permanently marked to show the purposes of the disconnects, unless located and arranged so that the purpose is evident. Labeling should match and be traceable to appropriate drawings. This applies to all existing electrical systems and all new, modernized, expanded, or altered electrical systems. Disconnecting means shall be capable of being locked out where required.
Panelboard circuit directories shall be provided and fully and clearly filled out.
Printed labeling or embossed identification plates affixed to enclosures shall comply with the requirements that disconnects be legibly marked and that the marking shall be of sufficient durability for the environment involved.
As with the disconnecting device, the load should be labeled. For example, the motor, the controller, and the disconnecting device could have the same identification number.
The source supplying power to the disconnecting means and load should be labeled as well. This requirement allows the electrical worker to know the identification of the elements from the source of power through the entire circuit. (See Figure 5.)
Figure 5: Switchgear, panel boards, motor control centers, etc., should identify the loads and elements which they supply.