Application Note

3 Fluke Corporation Basic power quality methodology and common culprits
Shared neutrals on branch
circuits
Causes load interaction and over-
loaded neutrals.
Laser printers and copiers sharing
branch circuits with sensitive
loads
Guaranteed periodic voltage sags and
switching transients.
Miswired receptacles
(N-G swapped)
Hard to believe, but they are out
there in quantity. Guaranteed to put
return currents on the ground con-
ductor and create a noisy ground.
Data cables connected to
different ground references
at each end
Ouch! Shows up as voltage between
equipment case and the data cable
connector.
Hi-frequency noise
The most effective high frequency
grounding technique is the installa-
tion of a Signal Reference Grid (SRG).
And in a class by
themselves
Isolated ground rods (below)
They’re a safety hazard because the
earth is a high impedance path and
will prevent enough current from
flowing to trip the breaker. They also
cause ground loops; after all, every
electron still has to go back where it
came from. One of the g
reat mysteries
of PQ is how some manufacturers can
insist that their equipment warranty
is void unless an isolated ground rod
is installed.
Illegal N-G bonds
Guaranteed to put retur
n currents on
ground. Not only is it a PQ problem,
it’s a plumbing problem. Circulating
g
round currents cause c
orrosion of
water pipes.
Over
voltage Summary Description
Categor
y
C
AT IV* Three-phase at utility connection,
any outdoors conductors (under 1000 V)
CAT III Three-phase distribution (under 1000 V), including
single-phase c
ommercial lighting and distribution panels
CAT II Single-phase receptacle connected loads
CAT I Electronic
*CAT IV product specifications are not yet defined in the standard.
International Safety Standards for Test Tools
IEC 61010 establishes interna-
tional safety requirements for low
voltage (1000V or less) electrical
equipment for measurement, con-
trol and laboratory use. The low
voltage power distribution system
is divided into four categories,
based on the proximity to the
power source. Within each cate-
gory are voltage listings—1000V,
600V, 300V, etc.
The key concept to understand
is that you should use a meter
rated to the highest category, as
well as the highest voltage, that
you might be working in. For PQ
troubleshooters, that means a
meter rated to CAT III 600 V or
CAT III 1000 V (the specifications
for CAT IV have not yet been
defined by IEC). We recommend
that you do not use CAT II rated
meters, scopes or test leads and
probes on CAT III circuits. The
CAT ratings should be marked
near the voltage inputs of the
instrument. Meters designed to
IEC 348, the previous standard,
will typically not meet the more
stringent safety specs of IEC
6
1010 CAT III 600/1000 V.
IEC 61010 requires increased
protection against the hazards of
transient overvoltages. Transients
can cause an arc-over inside an
inadequately protected meter.
When that arc-over occurs in a
high energy environment, such
as a three-phase feeder circuit,
the result can be a dangerous arc
blast. The potential exists for
serious harm to personnel as well
as damage to the meter.
Independent Testing and
Certification
Manufacturers can self-certify
that they meet IEC 61010 specs,
but there are obvious pitfalls for
the end-user in self-certification.
Certification by an independent
testing lab provides assurance
that the meter meets IEC require-
ments
. Look for a symbol and
listing number of an independent
testing lab such as UL, CSA, TÜV,
VDE, etc. UL 3111, for example, is
based on IEC 61010.
Fluke Corporation
PO Box 9090, Everett, WA USA 98206
Fluke Europe B.V.
PO Box 1186, 5602 BD
Eindhoven, The Netherlands
For more information call:
In the U.S.A. [phone] or
Fax [phone]
In Europe/M-East/Africa (31 40) 2 675 200 or
F
ax (3
1 40) 2 6
7
5 222
In Canada (8
00) 36-
F
LU
K
E or
Fax [phone]
From other countries [phone] or
F
ax [phone]
116
Web access: http://www.fluke.com
©2004 Fluke Corporation. All rights reserved.
Printed in U
.S
.A. 10/2004 2403240 A-US-N Rev A
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