Application Note

Application Note
There’s nothing so annoying as
a breaker that keeps tripping,
usually at the most inopportune
times. More annoying yet is not
being able to figure out why
as the production line stands
silent waiting for you to work
your magic. The pressure’s on!
In this application note, we’ll
discuss how to utilize all the
capabilities of your clamp meter
so you can keep your world up
and running.
We all know that clamp
meters are used to measure
circuit loading. But, with a
bit of ingenuity, you can also
use clamps to tell you which
breaker controls which outlets,
as well as to measure individual
loads (for both load and ground
currents, if any). This can help
you solve load problems quickly
and preserve your reputation as
an ace troubleshooter.
Clamp meters measure
current by determining the
magnetic field around a cur-
rent-carrying conductor. There
is simply no other practical way
to measure current on electri-
cal wiring systems. Breaking
these circuits open to make a
series circuit measurement is
impractical and may even be
a career ending move if you
inadvertently take critical loads
offline. Usually, measurements
are taken at the panel and
include loading and balance
on three-phase feeders. With
the prevalence of harmonic
loads, neutral measurements at
panelboards are also manda-
tory. Current measurements can
also be used to diagnose motor
health.
Beyond these basic mea-
surements that clamps were
specifically designed for,
modern digital clamp meters
have voltage and resistance
measurement capability as
well. That means it’s possible
to make most, if not all, of the
common, everyday measure-
ments using a clamp meter.
If an electrician could take
just one test tool on the job,
it would make sense for him
to choose his clamp meter.
Furthermore, that clamp meter
should be a true-rms model.
The alternative is an average-
sensing model, which costs
less, but will not measure the
Proper use of clamp
meters in commercial
and residential settings
From the Fluke Digital Library @ www.fluke.com/library
current accurately. Whenever
there are electronic loads
(computers, TVs, lighting, motor
drives, etc.) on a circuit, the
average-sensing meter could
be inaccurate. The greater the
electronic load, the greater the
inaccuracy. True-rms clamps
will always be accurate (assum-
ing of course that you’ve kept it
calibrated). So unless you feel
comfortable saying that you’re
not likely to run into those
kind of loads, get a true-rms
clamp. That way you can think
about the job, not the test tool.
In commercial sites especially,
accurate true-rms clamps are
mandatory.