GROUNDING OF ELECTRICAL EQUIPMENT SYSTEM FOR SAFETY

Grounded electrical systems are required to be connected to earth in such a way as to limit any voltages imposed by lightning, line surges, or unintentional contact with higher voltage lines. Electrical systems are also grounded to stabilize the voltage to earth during normal operation.

If, for example, the neutral of a 120/240 V, wye-connected secondary of a transformer were not grounded, instead of being 120 V to ground, the voltage could reach several hundred volts to ground. A wye-connected electrical system becomes very unstable if it is not properly grounded.

OSHA 1910.304(f)(7)(iii) Grounding of equipment. All non-current-carrying metal parts of portable equipment and fixed equipment including their associated fences, housings, enclosures, and supporting structures shall be grounded.

However, equipment that is guarded by location and isolated from ground need not be grounded. Additionally, polemounted distribution apparatus at a height exceeding 8 feet above ground or grade level need not be grounded.

In 29 CFR 1910.303, “General Requirements,” OSHA states under “(b) Examination, installation, and use of equipment (1) Examination” that “Electrical equipment shall be free from recognized hazards that are likely to cause death or serious physical harm to employees.”

This section continues with “other factors which contribute to the practical safeguarding of employees using or likely to come in contact with the equipment.” One of these “other factors” is proper grounding.

If the non-current-carrying metal parts of electric equipment are not properly grounded and these parts become energized, then any employee “using or likely to come in contact with the equipment” is at risk of an electrical shock that may or may not be fatal. This is a risk that must not be taken.

Proper grounding can effectively eliminate this shock hazard by providing a permanent and continuous low impedance path