13.1: Use meters to analyze simple circuits

The trick to effective troubleshooting electrical equipment and circuits is to zero in as quickly as possible on the problem. Using an electric meter will allow you to effectively test the components that are most likely to cause the problem before you unnecessarily dismantle the equipment and replace parts.

Safety

Even though you may normally deal with small voltages and currents, the values are never far away from lethal levels. You can receive a shock or burn from any common electrical circuit. The severity of the electrical shock depends on several factors:

• the amount of current that passes through the body
• the path that the current takes through the body
• type of voltage—AC or DC
• voltage strength
• the length of time that the current flows within the body
• condition of the skin and the body’s chemical makeup
• area of contact

A circuit breaker generally limits normal household light circuits 15 amperes and plug circuits of 20 amperes. This 15 amp device has been designed to trip and open a circuit if the 15-ampere value is exceeded, and it is designed to protect against property damage. It is possible to cause a fatal injury with a current flow of only 50 milliamperes (mA) or five one-hundredths of an ampere. The body is sensitive to relatively small values of current. In comparison, a 100-watt lightbulb draws approximately 0.85 amperes (850 mA) of current when connected to a 120-volt source. Remember, there are 15 amperes available in each standard house circuit.

Electrical shocks, electric burns, and other related injuries occur far too often and, in most cases, go unrecorded. If an accident happens:

• Don’t touch the person and use a conductive tool to free the person that may be electrically energized.
• Shut off the power or pull the plug if it is safe to do so. If you are not able to, get help.
• Remove the person from the contact point using a non-conductive object such as a dry piece of wood or a leather belt.
• Call 911 for help if the person is obviously injured (loss of consciousness, significant trauma, etc.)
• Seek medical attention (first aid) in any case of injury, such as an altered mental state (confusion, slow/slurred speech) or other obvious injuries (laceration, burn, etc.).

When performing maintenance or doing repair work, or when a machine is in an unsafe state, it is vital to eliminate the possibility of the machine being energized unexpectedly. Workers need to guard against contact with electrical voltages and control electrical currents to create a safe work environment.

Make the environment safer by doing the following:

• Protect portable electrical equipment with an approved ground-fault circuit interrupter (GFI) when using the equipment outdoors.
• Ensure all the cords are in good condition, with the caps and plugs well secured on the cables. Ensure the proper U-ground plug is in good working condition.
• Use cords of sufficient gauge for the amount of current used by the tools they are powering. Each tool is labeled with the power that it draws.
• Treat all conductors and bare wires—even apparently de-energized ones—as if they are energized until they are locked out and tagged.
• Do not make any electrical measurements without specific instructions from a qualified person.
• When servicing equipment, be sure it is “locked out,” meaning the electrical service is shut off at a disconnect panel whenever possible, the panel is locked, and the only key is kept by the person working on the equipment.
• When replacing components on mobile equipment, disconnect the battery.