Masterpact™ MP circu it breaker
appendix
recommended inspection
intervals
Masterpactm circuit breakers are designed
to be maintenance-free (see page 37).
However, all equipment with moving parts
requires periodic inspection to ensure
optimum performance and reliability. We
recommend that
the
circuit breakers be
routinely inspected six months after
installation, followed by an annual
inspection. Intervals
can
vary depending on
your particular use and experience.
inspection of terminals
Connections of circuit breaker :
•
terminals may be inspected. If there is
discoloration due to overheating, the joint
should be dissassembled and the surface
cleaned before reinstallation.
It is essential that electrical connections
are made carefully in order to prevent
overheating.
•
Check for terminal tightness.
inspection of main
contacts
The arc chutes are easily removable to
allow access to the main contacts and to
the
wear indicator. It consists of a groove
located within the contacts support
(see p:3). When the breaker is closed, this
groove is entirely covered up by the moving
contacts.
In the end, the wear of the contacts will
make the groove appear.
The contacts will have
to
be changed when
the groove is fully visible.
cleaning
Remove the dust and dirt that may have
accumulated on the circuit breaker surface
and terminals.
mechanical checks
For long periods circuit breakers may not be
required to operate on overload or short
circuit conditions. Therefore it is essential
to operate the breaker periodically.
36
insulation resistance tests
When breakers
are
subjected
to
severe
operating conditions, an insulation
resistance test may be performed as
indicated in NEMA standard publication no
AB2-1984.
An insulation resistance test is used to
determine the quality of the insulation
between phases and phase
to
ground. The
resistance test is made at a DC voltage
higher than the rated voltage, to determine
the actual resistance of the insulation. The
most common method employs a "megger"
type instrument. A 1 000-volt instrument will
provide a more reliable test because it is
capable of detecting tracking on insulated
surfaces. Resistance values below 1
megohm should be investigated.
The insulation test shall be made :
•
between line and load terminals of
individual poles with the circuit breaker
contacts open.
•
between adjacent poles and from poles to
the metallic supporting structure with the
circuit breaker contacts closed. This test
may be made with the circuit breaker in
place after the line and load conductors
have been removed, or with the circuit
breaker bolted to a metallic base which
simulates the in-service mounting.
electrical tests
These tests require equipment for pole
resistance measurement, overcurrent and
instantaneous tripping, in accordance with
NEMA standard publication no AB 2. They
are not within the scope of normal field
operation.
routine and maintenance
guidelines
Important
All tests shall
be
made on circuit
breakers which have
been
de
energized, and disconnected
so
as
to prevent accidental contact with
live parts.
Caution
Since circuit breakers contain
factory-sealed and calibrated
elements,
It
Is essential that the
seal not
be
broken and the circuit
breaker not
be
tampered with.
In the case of malfunction, the
breaker shall
be
replaced at the
Merlin Gerln factory, or by an
authorized representative.
MERLIN GERIN
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