Electrical Power Tools Safety

Electricity typically travels in a carefully directed closed-system. Electrical shock can occur when the body becomes part of this system, or creates a new system path. The actual damage from shock is from current flow (amperes). As little as 50 milliamperes (or 1/20th of an ampere) can cause electrocution. The danger is multiplied by the amount of time (duration) that the shock is applied through the body. A lower voltage of say, a 120 volt household current can cause severe shock or death in as little as 3 or 4 seconds duration. Higher voltages at less duration can cause the same amount of current flow and damage

Shock normally occurs in one of three methods:

Touching both wires of an electrical circuit.

Touching one (hot) wire of an electrical circuit and the ground.

Touching a metallic part that has become energized and the ground.

The last method can be the least-expected type of shock related injury. If the insulation of the electrical parts or wiring inside a tool becomes deteriorated or damaged, electricity can be allowed to flow along the metal parts and body of the tool. This is why "grounding" is so important.

Electrical circuits from utilities have one or more "hot" conductors which have electrical energy, and a neutral or "grounded" conductor. This grounded conductor is the normal path electricity takes back to the utility. If this pathway is interrupted by a person, current can then flow through the person, causing shock. To help prevent this, electrical circuits have an equipment ground, or "grounding" conductor. This is a second, redundant ground path (to be used in cases of equipment defects) which is bonded electrically to the non-current-carrying metal parts of a tool.

By having all metallic parts of tools bonded to a grounding conductor, this conductor- and not the worker can safely carry away any electrical current in the case of a tool's malfunction. When a tool is properly grounded, current through the body is either eliminated, or greatly reduced. This is why OSHA requires either the use of GFCI receptacles, or all tools and extension cords periodically checked for ground continuity.

The GFCI receptacle is especially useful since it will (even without a good ground) sense more amperes flowing out from the power source than back from the tool. Any imbalance greater than 5 millamperes (significantly less than a shock hazard) will cause the receptacle to shut off- usually within 1/40th of a second. If a GFCI receptacle shuts off, the worker can then find the cause of the electrical problem.

Because of the hazards associated with electrical powered tools, care must be taken to examine daily the visible condition of tool and extension cords, especially the cord ends for any damage or defects. Tools should be checked out when returned to the shop before reissuing back out to the workplace.

OSHA has five overall recommendations for electrical tools safety.

Maintain tools in good condition.

Use the correct tool for the job.

Examine each tool for damage before use.

Operate tools according to manufacturer's instructions.

Use adequate personal protective equipment.

This is part one of a two part series on Electrical Power Tool Safety.