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cool or warm white
• G4 back or sidepin:
8 SMD $15.00
10 SMD $20.00
15 SMD $25.00
• Festoon 37mm or 42mm
6 SMD $15.00
MR11- 6 SMD $15.00
MR16-15 SMD $25.00
• BAY15D Tower
18 SMD $35.00
For full details see our website
11 Babbage Rd, E-Roseville NSW 2069
Tel: 02 9417 8455
Fax 02 9417 8423
by Kurt Küpper*
* Kurt Küpper is director of Aquavolt
Electric Boat Parts. Tel: 02 9417 8455
So what else would you like to know? You are welcome to send in questions about
boat electrics or suggestions for topics that you would like explained.
Think of two switches, one controlling
a cabin light, the other a horn.
Clearly you want to be able to switch
on a cabin light and then go about your
activities, and only come back to the
switch once you want to turn the light off.
However, you only want the horn to be
activated for as long as you are holding
your finger on that switch.
The light switch is called a latching
switch, because it latches in whatever
position it has been left. The horn switch
is a momentary switch, because it is only
momentarily on while being activated,
and automatically switches off when you
let go of it.
Most switches only complete a circuit
when they are activated. If you think that is
stating the obvious, what about the switch
that is fitted to a circuit for a fridge light?
When the switch is not being pressed down
by the fridge door because that has been
opened, the circuit is on. When the door
is closed and the switch is pressed down,
the circuit is interrupted so that the light
is turned off.
Switches are described by their
condition in the unactivated state, or
‘normal’ state. The switch for the horn is
thus a ‘normally open’ (NO) switch, and
the switch for the fridge light is a ‘normally
closed’ (NC) switch.
In some instances it is required that
more than one circuit is switched by one
activation, e.g. it may be necessary to
switch both the positive and the negative
wires on and off. Essentially this means
that there are two adjacent switches that
are controlled by one lever.
Although less common, there are
instances when more than two circuits
must be switched by one activation. We
define how many sets of contacts are
switched as the number of poles, e.g a
one pole switch or a three pole switch.
Two pole switches are commonly called
‘double pole’ switches.
That’s not where the options end
though, as we get switches that can be
operated in two directions, e.g. a switch
that controls an anchor windlass. This we
call a ‘double throw’ switch, as opposed
to the single throw switch that we used
for the horn. The winch switch will have
an ‘off’ position between the ‘up’ and
‘down’ positions, so it is called a ‘centre
off, double throw’ switch.
There are some double throw switches
that do not have a centre off position, i.e.
they either switch the one way or the other.
These are called ‘change over’ or ‘on-on’
switches. An example of these are the
switches used when you wish to control
one light from two different positions,
e.g. with one switch at the cabin door and
another next to the bunk.
In written descriptions of switches it
is usual to indicate an ‘off’ position with
a ‘0 ’ (zero) and an ‘on’ position with a ‘1’.
Brackets are used to indicate momentary
positions. Single or double pole are
abbreviated SP and DP, Single or Double
Throw ST and DT.
Thus a single pole off-on switch would
be SPST 0-1, a double pole winch switch
would be DPDT (1)-0 -(1).
A switch with a stalk or lever is generally
called a toggle switch. The very common
switches with a chrome plated brass toggle
are an example. When the toggle has
two flat surfaces it is sometimes called a
Also commonly used are rocker
switches. These have a rectangular or
round actuator that pivots across their
centre lines like a see-saw.
Momentary switches often have a
button that gets pushed in to make the
switch a ‘push switch’. Less frequently
used are latching push switches, which
you push once to activate them, and push
again to release them. These are often
called ‘push-push’ switches or ‘alternate
Rotary switches are controlled by
rotating the actuator. These are particularly
used when more than two switch positions
Lastly we should mention the pull
switches that were extensively used on
boats in the past. They are activated by
pulling out the activating knob away from
the panel that the switch is mounted on.
Sometimes these are double pole, with the
one pole being activated in a first stage,
and both poles being activated when
the knob is pulled out fully to a second
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