For
anyone
who has
ever had
problems
wiring
relays
or
switch
contacts
then
this
guide
may
help.
Switches
Switches
are
pretty
straight
forward
to wire,
but
problems
may
arise
with
multi-pole
multi-way
switches.
Switch
contacts
are
always
drawn in
the OFF
position.
In the
case of
rotary
switches
the
wiper
arm will
always
be
connected
to the
first
contact
which
will be
the off
position.
The
diagram
below
shows a
2 pole 4
way
switch.
The
first
set of
contacts
or
arc
is
designated
S1a. The
contacts
are
numbered
1
through
4, as
switches
are
always
drawn in
the off
position
then the
contact
connected
to the
wiper
arm will
be the
OFF
position.
In the
diagram
the
contacts
are
labeled
1
through
4 for
clarity
though
with no
labeling
it is
easy to
identify
the
first
contact.
Arc b is
shown
below.
It is
common
practice
in
schematic
drawings
to link
both
switch
arcs
with a
dashed
line
as shown
above.
The
contact
labeled
1 is the
switches
first
position
and
contact
3 is not
used.
With all
multi
pole
switches
the
wiper
arm will
track,
so that
if the
switch
is
turned
from off
two
positions
then
both
wiper
arms on
S1a and
S1b
would
rest on
contact
3.
Relays
and
Contacts
As with
switches,
relays
are
always
drawn in
the off
are
unoperated
position.
Contacts
may be
drawn in
different
ways as
shown
below;
but the
middle
contact
(labeled
2 below)
is the
wiper
arm and
will
move
when the
relay is
energized.
This
contact
is
called
the
changeover
contact,
abbreviated
CO. The
top
contact
(labeled
1) is
the
normally
closed,
NC
contact
(relay
not
energized)
and
contact
3 known
as
normally
open,
NO. When
power is
applied
to the
relay
coil,
the NO
contact
is then
mechanically
and
electrically
contacted
to the
CO
contact.
Relay
Contact
Labeling
As shown
above,
bottom
right
hand
corner
the
relay
has two
changeover
contacts.
The
designation
for a
relay
coil may
be, RL
or just
R. If
there is
more
than one
relay in
a
circuit
then the
usual
method
is to
designate
relays
as RLA,
RLB, or
RA, RB
etc. The
easiest
way to
keep
track of
how many
contacts
belong
to a
particular
relay
coil is
to use a
denominator
with the
amount
of
contacts.
In this
case RLA/2
has two
contacts
and
these
are
appropriately
labeled
RLA1 and
RLA2.
Easy.
Now for
a motor
reversing
circuit
using
non
latching
press
button
switches.
Motor
Reversing
Circuit
This
circuit
uses 4
relays
and 3
push
buttons
for
Stop,
Forward
and
Reverse
control
of a DC
motor.
RLD has
just one
changeover
contact
whereas
RLA, RLB
and RLC
have 2
CO
contacts
each.
Basicly
RLD will
stop the
motor,
RLA
latches
the
motor in
a
forward
direction
and RLB
latches
the
motor in
the
opposite
direction,
whilst
RLC and
its
contacts
provide
the
reversing
for the
motor.
This
circuit
is quite
messy
and it
is
common
practice
to see
the
relay
coil and
its
associated
contacts
separated
some
distance
in the
actual
schematic.
