Course 3: Basic Electricity October 21 & 23, 2014

1 Objectives

When you have completed this session, you should be able to:

1. Idenfy the electrical measuring instruments used in HVAC/R work and describe their uses. a. Describe how voltage is measured. b. Describe how current is measured. c. Describe how resistance is measured.

2. Idenfy electrical components used in HVAC/R systems and describe their funcons.

3. Idenfy and describe various load devices and explain how they are represented on circuit diagrams.

2 Multimeters

Also known as volt-ohm milliammeters (VOMs).

3 Measuring Voltage

The voltmeter must be connected in parallel with (across) the component or circuit being tested.

4 Clamp-On Ammeter

5 Continuity Testing

• NEVER measure resistance in a live (energized) circuit. The voltage present in a live circuit may permanently damage the meter. Higher quality meters are equipped with a fuse or circuit breaker to protect the meter if this occurs. • Also, a circuit in parallel with the circuit you are tesng can provide a current path that will make it appear as though the circuit you are tesng is good, even when it is not. • The way to avoid this problem is to isolate any single device being tested from the rest of the circuit by physically disconnecng it. 6 Continuity Tester

7 Megohmmeters

Megohmmeter use in the HVAC/R industry:

• Special meters to read very high resistance values, in megohms.

• They apply a high DC voltage to the circuit.

• Test compressor windings with it electrically isolated from all other components.

• A reading over 100 megohms typically indicates a sound circuit, free of contaminaon.

8 Motors

9 Electric Heaters

Electric heaters may appear the same as a resistor on a circuit diagram.

10 Wrap Up - Terms

Ammeter: A test instrument used to measure current ﬂow.

Clamp-on ammeter: An ammeter with operable jaws that are placed around a conductor to sense the magnitude of the current ﬂow.

In-Line Ammeter: A current-reading meter that is connected in series with the circuit under test.

Wrap Up - Terms

Mulmeter: A test instrument capable of reading voltage, current, and resistance. Also known as a volt-ohm-milliammeter (VOM).

Ohmmeter: An electric test instrument designed to measure the resistance, or impedance, of an electrical device or circuit. Also used for the simple purpose of determining if a circuit is connuous (has connuity).

Voltmeter: A test instrument used to measure the potenal diﬀerence, or voltage, between any two points.

Questions