Ground Fault Protection of Construction Tools

In a construction site environment, flexible cords cord connectors, receptacles, and cord and plug connections are all subject to hazards that can damage the insulation of the equipment. Therefore, the electrical protection and protective devices installed must be tested to ensure the safety of personnel.

OSHA 29 CFR 1926 (b)(ii)(iii) defines two specific means of preventing ground fault electrical shocks on construction sites: An assured equipment grounding conductor program and the provision of ground fault circuit interrupters (GFCI). Under these preventive measures, there would appear to be a requirement for more meaningful testing than that defined in the OSHA standard.

Grounding Conductor Program

The OSHA standard requires a scheduled and recorded assured equipment grounding program covering all cord sets and receptacles that are not part of the building or structure, as well as all equipment connected by cord and plug which can be used by employees. The program must incorporate visual daily inspections of electrical equipment to identify any external defects such as insulation damage and aging--an indication of internal damage.

One or more designated competent persons should establish and implement the program. A written description of the program, along with specific procedures, must be available on site for employees to reference as needed.

Although diligent and conscientious daily visual inspection help identify faulty cords, connectors and portable appliances, electrical testing must be performed to ensure that the grounding of the equipment is fully effective.

The OSHA regulation defines two tests that must be performed:

1. All equipment grounding conductors are to be tested for continuity and are to be electrically continuous.
2. Every receptacle and attachment cap or plug must be tested for the correct attachment of the equipment grounding conductor, which in turn must be connected to its proper terminal.

The standard states that if resistance of the equipment grounding conductor is significantly greater than 1 ohm, tools with even small leakages become hazardous. Also, if the grounding conductor has a low resistance, no shock should be perceived when leakage current of tools is below 1 amp. However, no mention is made regarding what the pass level for the resistance of the grounding conductor should be.

For a meaningful test, an indication that the resistance of the conductor is within an acceptable safe figure would appear to be essential. Therefore, using a lamp and battery or a bell and battery, as mentioned in the standard as suitable methods for testing the grounding conductor, would be inadequate because these devices only discern that there is electrical continuity in the conductors; they do not indicate the level of resistance.

An ideal instrument for the two tests is one that provides a clear reading as to whether the resistance of the grounding conductor is within prescribed safe limits. In other words, a type of "go/no go" tester that delivers a clear pass or fail indication. The need for such an instrument is further strengthened on two accounts. First, tests must be performed frequently: before initial use, after repairs and before being placed back into service, before use after an incident that could have been suspected to have caused damage, and at intervals not exceeding three months. Second, the standard requires that each test of every particular item of equipment must be documented. The ability to state that the equipment resistance levels continued to be within a specific pass level gives greater assurance to the test results and if a "fail" is recorded on the test instrument the item concerned can, with full justification, be pulled from service.

Provision of Ground Fault Circuit Interrupters

In addition, the OSHA Standard for Ground Fault Protection on Construction Sites requires the provision of approved GFCI for all 120 volt, single phase, 15- and 20-amp receptacle (i.e. portable) outlets that are not part of the permanent wiring of the building and structure, and are in use by employees.

A GFCI senses small imbalances in a circuit caused by current leakage to ground. For grounded equipment on a construction site, OSHA requires that the GFCI must operate when the leakage current exceeds 5mA + 1mA within a time of 0.25 milliseconds to ensure that any possibility of electrocution is eliminated.

The standard does not, however, define any testing of the operation of the GFCI to confirm that it performs to these requirements. To ensure that a GFCI is mechanically fully effective, the test button on the device should be operated every three months.

The leakage current and time operation of a GFCI should be tested at least once a year. Testing a GFCI to the noted requirements will confirm that the device is providing continuous fully effective ground fault protection of the relevant equipment on construction sites.