Datasheet-1

When wires from different parts of a circuit connect
accidentally then we have a “short circuit”. A short
circuit is a wiring path that bypasses the circuit resist-
ance, creating a no-resistance path across the bat-
teries. It is the “easiest” path through the circuit, it is
not always the “shortest”. A short circuit will activate
the fuse in your battery holder and/or quickly drain
your batteries. Be careful not to make short circuits
when building your circuits. Always check your wiring
before turning on a circuit. See page 10 for examples
of short circuits.
Project 9
Fuse
Build the circuit, set the meter (M5) to the 1A setting, and turn on the slide switch
(S1). The lamp (L4) lights.
What do you think would happen if you push the press switch (S2) for a moment?
Try it.
What do you think would happen if you pushed the press switch for a while? Try it.
You should see the current increase, then drop down after a few seconds.
1A
Name some devices in your home that have a fuse.
Pushing the press switch bypasses the lamp, making the
meter the only resistance in the circuit. The meter has very
low resistance on its 1A setting, so there is nothing in the
circuit to limit the current. When you push the press switch,
the high current (>1A) activates a safety fuse in the battery
holder (B3) after a few seconds, which lowers the current
enough to protect the batteries and
other components from being
overloaded. The fuse shuts off
shortly after the circuit problem it
had detected is corrected. The
fuse is the small yellow component
inside the battery holder.
This wire melts to
break the circuit.
Fuses are designed to shut down a circuit when the current
is abnormally high (indicating something is wrong, such as
a component failure, bad design, or a person using it im-
properly). This shutdown prevents further damage to the cir-
cuit, and can prevent explosions or fires. Fuses are
important for safety and most electrical products have one,
especially if they use electricity supplied by your local elec-
tric company.
Some fuses need to be replaced after they “blow”, but oth-
ers can be reset by flipping a switch, and some (like the one
in your battery holder) can reset automatically. Every home
has an electrical box of resettable fuses, it may look like this:
Some fuses have spe-
cial wires designed to
break when an unex-
pectedly high current
flows through them.
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