CHPA SERIES
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One of the problems associated with prime power is some equipment can be "floating" above
ground. In this case, if you place one hand on the equipment chassis and the other on earth
ground, you can be jolted, injured, or killed. 440VAC can stimulate an involuntary muscle
response that will either literally throw you across a room or seize and hold you across the voltage
terminals. 600 or more volts can hold you indefinitely. If the potential is sufficient to drive 200
milliamps through your body you will be held indefinitely. Some people consider the 200 to 600
volt range to be worse than potentials of thousands of volts.
General Guidelines
In addition to the above, the following practices have proven effective for personnel who deal
with high voltage equipment.
a.
Hands off. Avoid contact with any potential source of high voltage. Keep hands out
of the equipment when it is operating.
b.
Avoid accidental contact. Make sure that some other part of your body does not come
in contact with the high voltage circuits. It is easy to forget the hazards when you are
concentrating on a frustrating or interesting task. Pens and badges in shirt pockets
could contact the equipment.
c.
Never work on high voltage circuits when you are alone. If anything should happen
to you, your only chance may be prompt action by some other person. Be sure
someone else is present and knows what to do in any emergency (e.g., how to shut
equipment off, first aid, who to call, etc.)
d.
Use one hand when working with high voltage circuits. Many people recommend
that you put one hand in your pocket when you use a probe or other piece of
equipment inside a high voltage section.
e.
Do not float measuring equipment above ground. Make all measurements with
respect to ground. If you float an instrument, do not reach inside the equipment.
Although it is more difficult to get the right setup, it is well worth the effort.
f.
Do not assume that the level of risk is a function of size. Some large high power
voltage equipment looks docile. One reason the equipment is so big is to get the
proper separation between high voltage points. On the other hand, just because the
equipment is small is no assurance of safety. Dense packaging results in more difficult
access and increases the chance that you will accidentally hit the wrong point.
g.
Always discharge high voltage capacitors. High voltage capacitors store a lot of
energy for long periods of time. High voltage capacitors also exhibit a "memory" in
that they can recover after discharge and reach lethal levels. In addition to the
"memory" problem, there have been instances where the built-in safety features have
failed or have been miswired. Each and every time you go to work on a piece of high
voltage equipment, use a discharge device with a long handle to discharge every
high voltage capacitor.
h.
Do not depend on the automatic features of the equipment to save you. You never
know when someone has left a circuit disabled, if there has been a wiring error, or if a
component has failed.