Page 30 - Electrical Safety of Low Voltage Systems

Fundamentals of Electrical Safety 13

Each numeral requires different tests be applied to equipment to
obtain the IP rating. The jointed test finger, the rigid sphere, and the
test wire are the standard rating tools.
To guarantee safety, enclosures and barriers are required by inter-
national standards to have at least a degree of protection of IPXXB,
which does not allow access to a person’s finger. The symbol X means
there are no requirements for that specific characteristic numeral. The
IP2X degree of insulation is not equivalent to IPXXB, but better. An
IP2X enclosure, or barrier, in fact, must pass the following two tests:

1. The standard jointed finger (length 80 mm and diameter 12
3
mm), applied with a test force of 10 N to all sides and open-
ings of the enclosure, must not touch any live parts in every
possible position of its two joints.
2. A 12.5-mm-diameter rigid sphere must not entirely pass
through any opening (test force of 30 N).

An IPXXB enclosure, instead, must pass only the above first test
to provide the same degree of safety against electrocution. However,
IPXXB enclosures, although safe for persons, may allow the ingress of
foreign objects of 12.5 mm diameter, or smaller, into the equipment,
and, therefore, might not be suitable in certain locations.
Let us examine the case in Fig. 2.4. The enclosure is “permeable”
to the test sphere, which can penetrate inside, and thus cannot be
classified as IP2X; at the same time, though the enclosure does not
allow contact with live parts, as the jointed finger cannot touch any
live part, ergo its rating is IPXXB.
If enclosures or barriers have readily accessible horizontal top sur-
faces (e.g., height less than 2.5 m), a more stringent insulation is re-
quired. To prevent the additional risk of direct contact due to small

FIGURE 2.4
Enclosure IP1XB.