How to Fault Trace on a Small Appliance Using a Multimeter

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Fault tracing an electric circuit using a meter to identify what part has failed and where the problem is.

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Closed Caption:

Hi I'm Mat from eSpares.
In this video I'll be showing you how to
fault trace on a small appliance.
Every simple appliance works by having
a current running through it.
This current begins at the plug live pin on the plug which comes up through the cable, through the switch
through the motor, back up through the switch through
the cable and out through the neutral pin on the plug.
If there's a break on any part of this circuit
your small appliance will not work.
Safety first: Always unplug an appliance before carrying out any work.
This technique can be used on vacuum cleaners,
strimmers, lawnmowers, steam irons even
something as simple as Christmas lights.
So what you need to do grab yourself a multimeter
set it to the resistance setting
and put the probes on the Neutral
and live pins on the plug.
Here we can see we have a reading of 6.2 ohms.
If I turn the switch off on this vacuum cleaner
you can see that the reading changes to Zero
no resistance
This is the same reading
as if the probes were attached to nothing
therefore this machine has no fault.
However if I attach the connectors to the live and neutral on this vacuum cleaner
as you can see there is no resistance reading even if
I turn the machine on or off via the switch
the reading does not change.
Therefore there is a fault in the
circuit of this machine.
So the first thing I need to test
is the fuse within the plug.
If I take that out I can again use the multimeter to test.
One probe on one end and one probe on the other.
And you can see we have a low resistance reading
therefore there is no fault in the fuse.
If I returned the fuse to the plug the next place
we need to check is where the cable meets the switch.
In order to do this I need
to remove the top of the switch cover.
With the switch cover off you can see the we actually have a loose connection to the switch.
Now this is something that we fabricated
in order to best demonstrate fault finding.
In reality it may well be that you don't have a loose cable.
In that case you'd have to check the
switch itself again using the multimeter
to the probes if
you have a lower resistance reading on the switch
there is no problem with the switch and the problem
may well be with the cable where it enters the machine.
If that's the case you would measure from
the switch to the plug to find out if the cable is faulty.
In a lot of motorized small appliances the main problem is with the motor itself.
Here we have a typical vacuum cleaner motor.
Most motors contain carbon brushes.
Now I've started to take the carbon brush out so I'll just take that fully out to demonstrate.
Carbon is an electrical conductor,
the current runs through the carbon brush
through the motor and back out through the switch.
These carbon brushes are in spring loaded holders
so what this will do is extend the carbon brush
making sure that it's constantly in contact with
the metal part of the motor to complete the circuit
What happens is that these carbon brushes wear down
overtime so much so that the carbon
no longer touches the metal part of the motor
therefore not completing the circuit
and you'd have to replace the carbon brushes.
We hope this video has been helpful in
helping you to identify a fault in a small appliance.
Remember spares for most appliances can be found on the espares.co.uk websites
Thanks for watching.