Velleman DVM890CS - Manual (Page 2)

Information sheet
Velleman ® 2/3 Last update: 31/03/2010
2. Overvoltage/installation categories
DVMs are categorized depending on the risk and severity of transient overvoltage that
might occur at the point of test. Transients are short-lived burst of energy induced in
a system, e.g. caused by lightning strike on a power line.
On high-energy circuits this leads to hazardous situations as these circuits might
provide enough current to feed an arc-over resulting in a plasma breakdown or even
explosion.
Higher CAT-identification refers to electrical environments with higher power and
possibly higher energy transients.
A CAT I-rated meter
is suitable for
measurements on
protected electronic
circuits that are not
directly connected to
mains power, e.g.
electronics circuits,
control signals…
A CAT II-rated meter
is suitable for
measurements in
CAT I-environments
and mono-phase
appliances that are
connected to the
mains by means of a
plug and circuits in a
normal domestic
environment,
provided that the
circuit is at least
10m apart from a
CAT III- or 20m
apart from a CAT IV-
environment. E.g.
household
appliances, portable
tools…
A CAT III-rated
meter is suitable for
measurements in
CAT I- and CAT II-
environments, as
well as for
measurements on
(fixed) mono- or
poly-phased
appliances which are
at least 10m apart
from of a CAT IV-
environment, and for
measurements in or
on distribution level
equipment (fuse
boxes, lighting
circuits, electric
ovens).
A CAT IV-rated
meter is suitable for
measuring in CAT I-,
CAT II- and CAT III-
environments as well
as on the primary
supply level.
Note that for all
measurements on
equipment for which
the supply cables
run outdoors (either
overhead or
underground) a CAT
IV meter must be
used.