First and most important, I am not recommending that you use your
body as an electrical tester. However, there are some subjective
indicators you can glean from your experience. Sensations from static
electricity come from a high voltage spark between you and ground.
What you feel the heat, pressure from superheated expanding air, and
hear a pop. It produces a very small explosion near the surface of
the skin.
Small static charges differ from household electricity shocks in
that they produce the spark and don’t stimulate muscles to twitch. If
your household electricity current were strong enough to spark, pop
etc, you would be receiving the “shock of your lifetime” probably
strong enough to kill. Household current passes through the body
stimulating the nerves that control muscles causing muscles to
contract, vibrate, and twitch, hence the “jolt.”
Static charge is a much higher voltage but is built up on the
surface of your skin. When you get close to a grounded object it
produces the very small lightning bolt that does not actually pass
through your body. It can be more comfortably discharged by holding a
metal object in your hand, using it to touch something that is
grounded. The micro-explosive spark then initiates from the metal
object rather than the surface of the skin. (OK when you are sure
you are dealing with static, not a good idea to use to determine
whether it is static you are dealing with.)
So, the indications aRe: Static electricity will give a single
pop-zap, discharging the charge from your body, and be done. Static
will use any path to ground, even if it is not associated with the
motor. A shock from a faulty electrical connection would be a
tingling or jolt that occurs over a period of time while you are
touching the machine. If you touch the machine again, you may get
another shock.
If you are getting the jolt type shock, then you need to investigate
further. A three prong plug and receptacle is an indication of a good
path to ground but does not guarantee it. Hardware stores sell a
relatively inexpensive tester for testing the wiring of your
receptacle. If the receptacle is wired correctly, you need to check
to ensure that your main breaker box has what is called a grounding
electrode. It is a metal rod driven into the ground outside near your
electric meter. It will have a wire clamped to it that comes from
your breaker box.
If all of that is in order you need to ensure that the three prong
cord has the green wire properly attached to the metal casing of your
motor. Depending on the type, old motors can sometimes still give
small electrical shocks even when everything is properly grounded.
Many motors have carbon brushes (pads that conduct electricity to the
spinning part of the motor. The brushes can cast off dust that
provides a low grade path from the energized (hot) wire to the
casing.
If all of your grounding is proper, you can have a ground fault
interrupter receptacle installed that will prevent shocks from the
casing by tripping whenever the electricity takes a shortcut to
ground (like through the casing or through you). When it trips, it
shuts off the electricity supply to the motor. A frequently tripping
GFI would be an indication that your needs servicing. Worn motor
brushes can ruin the motor. A good motor repair shop will replace
brushes, turn armature, and clean out the dust from the brushes.
Howard Woods
Eagle, Idaho.
