Part 5: Electrical Systems
While most all of the tools introduced in previous sections of this book can be used to perform many electrical maintenance tasks, other tools, some especially specific to the electrical trades, will be introduced in this section.
Electrical Meters and Testers
- Direct Current (DC)- DC is an electric current that is uni-directional, so the flow of charge is always in the same direction.
- Alternating Current (AC)- Alternating current changes its direction of flow at a specific frequency known as its’ Hertz (Hz) rating. In the United States, AC current changes 60 times per second or a rate of 60 Hz. In Europe the rating for AC current is 50 Hz
- Continuity- A complete pathway for current to flow.
- Polarity- Refers to the north and south poles of magnetic fields. Direction of flow of the current in DC circuits. Referred to as positive and negative.
- Make sure the meter you are using has a rating equal to or exceeding the highest value of electrical quantity you are measuring.
- Always wear safety glasses when using test and measurement instruments.
- Wear rubber gloves when testing or measuring “live” electrical circuits or equipment.
- Keep your clothing,hands, and feet as dry as possible when taking measurements.
- Never work on energized circuits unless absolutely necessary.
- Don’t work alone, especially on “‘live” circuits.
- If you must take measurements on energized circuits, make sure you have been properly trained to work with “live” circuits.
- Recalibration is necessary from time to time to bring a meter back to its intended level of accuracy.
- Handle all meters with care; they are fragile, sensitive instruments.
- Keep the meters clean and dry.
- Don’t store analog meters next to strong magnets; magnets can cause the meters to become inaccurate.
- Don’t expose meters to large temperature changes.
- Make sure you know the type of circuit you are testing (AC or DC)
- Never let the value being measured exceed the range of the meter.
- Multimeters and ohmmeters will need to have their batteries changed from time to time.
- Many meters have fuses to protect them from exposure to excessive voltage or current values.
- Re-calibrate measuring instruments once a year.