Electrical Power Tools

You will be using portable electric power tools
on the job. Electricity is usually in the form of temporary
power, covered by Article 590 of the NEC.
NEC 590.6(A) requires that “All 125–volt,
single-phase, 15-, 20-, and 30-ampere receptacle
outlets that are not a part of the permanent wiring
of the building or structure and that are in use by
personnel shall have ground-fault circuit interrupter
protection for personnel.”
Because this requirement is often ignored or
defeated on job sites, you should carry and use as
part of your tool collection a portable GFCI of the
types shown in Figure 1-3—an inexpensive investment
that will protect you against possible electrocution.
Remember, “The future is not in the hands of
fate, but in ourselves.”
Digital Multimeters
Some statistics show that more injuries occur
from using electrical meters than from electric shock.
For safety, electricians should use quality
digital multimeters that are category rated. The
International Electrotechnical Commission (IEC)
Standard 1010 for Low Voltage Test, Measurement,
and Control Equipment rates the ability of a meter
to withstand voltage transients (surges or spikes).
This standard is very similar to UL Standard 3111.
When lightning strikes a high line, or when utilities
are performing switching operations, or when
a capacitor is discharging, a circuit can “see” voltage
transients that greatly exceed the withstand
rating of the digital multimeter. The meter could
explode, causing an arc flash (a fireball) that in all
probability will result in personal injury. A properly
selected category-rated digital multimeter is able to
withstand the spike without creating an arc blast.
The leads of the meter are also able to handle high
transient voltages.
Digital multimeters also are category rated based

on the location of the equipment to be tested, because
the closer the equipment is to the power source, the
greater the danger from transient voltages.
Cat IV multimeters are used where the available
fault current is high, such as a service entrance,
a service main panel, service drops, and the house
meter.
Cat III multimeters are used for permanently
installed loads such as in switchgear, distribution
panels, motors, bus bars, feeders, short branch circuits,
and appliance outlets where branch-circuit
conductors are large and the distance is short.
Cat II multimeters are used on residential branch
circuits for testing loads that are plugged into
receptacles.
Cat I multimeters are used where the current
levels are very low, such as electronic equipment.
Note that the lower the category rating, the lower is the meter’s ability to withstand voltage transients. If
you will be using the multimeter in all of the above
situations, select the higher category rating.
Category-rated digital multimeters also contain
fuses that protect against faults that happen when the
meter is accidentally used to check voltage while it
is inadvertently set in the current reading position.
To learn more about meters, visit the Web site
of Fluke Corporation, http://www.fluke.com, for
a wealth of technical information about the use of
meters and other electrical and electronic measuring
instruments.