How voltage and current can get you ................................................
Your body is like a big resistor. Usually, your body’s resistance is high enough
to prevent damage when you’re exposed to low voltages. However, certain
conditions can lower your body’s resistance, lowering the amount of voltage
needed to cause you serious damage, such as giving you a nasty burn. Those
conditions might include handling electronics with sweaty palms or trying to
change your 12 volt (V) car battery on a rainy day — either can turn a slight
tingle into a fatal event.Both AC(alternating current, such as the power from your wall outlet) and
DC(direct current, such as from a battery) voltage can damage you in differ-
ent ways:AC voltage:This type of voltage regularly reverses direction. This can
cause your heart to shift its regular beating pattern in a condition known
as ventricular fibrillation.If this happens, your heart muscles go out of
whack in a way that causes blood to stop pumping. In this situation,
even if you cut the current, your heart might not be able to find its
proper rhythm, and you could die.DC voltage:This type of voltage is on constantly and causes your mus-
cles to contract and seize up quickly (including your heart muscle). If
you grab an electrical device in conditions that cause your body to con-
duct DC voltage, your hands could become frozen (unable to let go of the
device), and your heart could stop. If someone cuts the current quickly,
though, your heart might begin to beat again (and you’ll be able to
attend that Rotary luncheon next week).Short of killing you, electric shock can cause burns as the current dissipates
across your body’s natural resistance (that is, your skin).How much is too much? ......................................................................
Most resistance in your body is in your skin. If your skin is wet or damp, that
resistance is lowered. If you handle an electrical device with damp hands,
even voltages under 20V or so (not enough to even light a low-wattage lamp)
might be sufficient to do you serious damage. The 120V coming out of your
electrical outlet has a lot of punch: more than enough to kill you.Four AA batteries in series — which is what we use in the projects in this
book — generate only about 6V. We did that on purpose to keep you rela-
tively safe.18 Part I: Project Prep