One of the most common causes of premature motor failure
in single-phase motors is through incorrect wiring. The root
cause of this has been identified as DIY installations and
confusion between the old American colour coding (red;
yellow & black) and the new European colour coding (black;
brown & blue).
The connection in the motor is as per (Fig 1)
Understanding this it is easy to determine the wires.
1.
2.
In 2003 Franklin Electric SA lead four training courses
throughout South Africa in an effort to increase the level of
expertise in the borehole industry. These were received with
great enthusiasm and all in all 2003 was a huge success for
everyone concerned.
As money becomes tighter there is a growing concern for the
DIY market where the end user thinks he can save a little
money by "Doing It Yourself", experience tells us this is not
the case.
3.
The highest reading is obtained through
measuring through the run wire and start wire (1 &
3)(both windings are measured)
The middle reading is the thinner wire (start) and
the common wire (2 & 3)
The low reading is the thicker wire (run) and the
common wire (1 & 2)
NOTE 1: A thinner wires resistance would be higher than a
thicker wire.
NOTE 2: Since the common wire is not a winding, the two
smaller readings should add up to the highest reading (as
long as the measurement is taken on the motor, as the drop
cable would create a slight discrepancy in this addition.)
Franklin Electric's single-phase motor is essentially a "two
phase motor" with a Start and a Run winding. The different
sizes of the copper wire can be seen.The thinner wire is the
start winding, and the thicker wire is the run winding.
NB! This start winding is not designed for continual use and
must be removed from the circuit via the relay supplied in the
Franklin Electric control box
Should there be any uncertainty of the colour coding from
the Lead out cable to the drop cable then there is a simple
procedure to follow in order to get the wires in the correct
place.
Failure to correctly connect the motor to the control box
could result in premature failure of the control box and / or
motor.
In some cases motor protection will not detect the fault fast
enough or even at all. The most common symptoms of
incorrect wiring are blown start capacitors, and in a lot of
cases burnt motors where only the start winding is damaged.
In all cases the failure is relatively fast; therefore care must
be taken to ensure that the wires are correctly connected
before starting the motor.
In order to determine the correct placing of the wires an ohm
(W) meter is required.
There are three possible sequences to measure the three
wires.
Step
1:
Number the wires 1; 2 & 3
Step
2:
Measure & record the winding resistance (W)
between the wires (1 & 2) (1 & 3) (2 & 3)
Note: You should get a low (1 & 2) reading
a middle (2 & 3) reading and a high (1 & 3)
reading.
Step
3:
The wire NOT used to get the highest reading
would be the common. Y (UW)
Figure 1
Step 4: The wires used in the middle reading are the
Start and Common, (common being known) the
remaining wire is the Start. R (Z)
Step 5: The wires used in the lowest reading are the Run
and Common (common being known) the
remaining wire is the Run. B (V)