Hi, I'm Vance and welcome to Repair and Replace. Multimeters are an essential tool for testing
electrical circuits and components. Whether its checking a battery, extension
cord, or troubleshooting an appliance, multimeters can help determine exactly what has failed. If you've never used a digital multimeter
or if you're looking to refresh your knowledge, then this episode will get you started. First we'll review how electricity works. Then we'll learn how to test for continuity. Finally we'll do some safe voltage tests and
talk about the limits of testing current. Lets begin. To understand what a multimeter can measure,
lets quickly review some fundamentals. Electricity is the movement of electrons from
one atom to another. The flow of electrons through a wire is somewhat
similar to the flow of water inside of a pipe. Voltage or potential difference is the
pressure from the power source that pushes the electrons
through the wires. Current or amperage is the flow of electrons
within a circuit.
Resistance measured in ohms is the amount
that a material will resist the flow of electrons. Conductors have low resistance allowing electrons
to move easily through them. Insulators have an extremely high resistance
to the flow of electrons. For example copper wire is insulated by a
plastic sheath. If we connect these wires together to a power
source we get a complete electrical circuit. Batteries provide direct current or DC power
as the current always flows in a single direction. This is represented by a dashed line on the
multimeter Your home runs off 120 volts alternating current
or AC power. The direction that the current flows is changing
60 times a second or at 60 hertz. This is represented by the sine wave.
In either case the electrons always need a
continuous path to return to the source. This is continuity, or a closed circuit. If we disrupt this path with rubber, plastic,
or by air in the case of a broken wire, the electrons will not flow,
as there is no continuity. This is an open circuit. In many cases the lack of continuity
in a single component will prevent an appliance from
working properly. To setup the multimeter, plug the meter leads
into the terminals. Usually they are color coded red for positive
and black for neutral or common. Some meters will have 2 positive terminals. One terminal is for voltage and resistance,
and the other is for measuring amperage. Always inspect the multimeter before use.
Never use a multimeter that
has a damaged case or test leads with nicked
or damaged insulation. To be safe, always hold the multimeter from
the insulated handles. Even 120 volts in your home can be deadly
so use caution before testing any live voltage. If you're unsure at any point,
then it's best to contact a professional. Your model might look a little different but
all multimeters have the same common controls. Volts AC, Volts DC, resistance in Ohms,
and resistance with tone, which will beep when
there's continuity.
As well you can test for capacitance, amps
AC and amps DC. Some multimeters are auto-ranging and will
automatically adjust the units displayed. In other models you'll have to set the multimeter
to the most accurate range. For example if we test continuity
at the 20K setting, and we get a reading of 2.6,
then the resistance is 2600 ohms. To test a component for continuity,
first set the multimeter to the Ohms, or resistance
with tone setting. Safely disconnect the power, and remove the
wires or connectors. Now remove the component or isolate it. Next touch each probe to each component terminal. If there is no continuity then the multimeter
will display OL or Open Loop. This means the component will need to be replaced. If there is continuity you'll get a reading
above 0 ohms but the resistance will vary between load or non-load components.
Non-load components such as switches,
thermostats or fuses, provide an unrestricted path for
the electricity to pass through. These will typically have a resistance reading
between 0 and 1 ohms. Load components include
heating elements, solenoids, motors, or any component that
consumes power. They will need a specific resistance value
to function correctly. For example oven bake elements commonly have
a resistance of 20 – 40 ohms. Whereas hot surface ignitors
can range from 30 to 200 ohms. This is different for each component and will
vary between models. If you want to learn more about the various
components in appliances, then watch the video linked below. As well continuity tests
can be useful when troubleshooting other electrical items
in your home. This includes extension cords, light switches,
and receptacles. The volts DC setting can be used to test batteries
and other small electronics.
For example a fully charged AA battery
will be close to 1.5 volts, whereas a weak battery will be much lower at
1.2 volts and should be replaced. By setting the multimeter to volts AC you
can test to see if a receptacle has power and is wired correctly. The small plug is the hot wire that is providing
the power. The larger plug is the neutral wire which
returns to the power source. The rounded plug is the ground wire. If at any point a hot wire touches
the metal casing, the ground wire provides a safe
return path back to the source. When testing live voltage it's essential
to use caution. Always start with the neutral wire first before
connecting to the hot. If you connect to the hot side first, the
other multimeter probe now becomes energized which increases the risk of a shock.
Testing from neutral to hot will show approximately
110 to 120 volts. Testing from ground to hot will also show
around 120. This will verify if the ground wire has a
complete path back to the breaker panel. When testing from neutral to ground there
should be no significant reading. If there is a 120 volt reading then the receptacle
might not be wired correctly or there could be
a short in the circuit. A standard multimeter can be useful for testing
the current in small DC circuits, but in most cases it's not safe and it's
impractical to test the current in your appliances or in
the live wires in your home.
Clamp meters can detect the magnetic fields
around a single wire which allows amperage to be measured without cutting any wires. These meters are more expensive and require
some expertise to use effectively. Its best to leave these tests to the professionals. For more troubleshooting on
water heaters, furnaces and appliances, then subscribe to our channel. And if you need help, you can call
or visit an AMRE location to talk with our knowledgeable staff. Thanks for watching..
