11
Two-Breaker cable interlock.
Details are given to calculate the correct cable length. More
information on three-breaker and other combinations of cable
interlocks is available on request.
Vertically Mounted:
Referring to Fig. 48, cassette pitch ‘A’ is from the bottom face
of one cassette to the bottom face of the other. Dimension ‘A’
can be no less than 60 cm. Ensure that the minimum cable
radius is not less than 125mm. Minimum cable length is A +
100 cm. Longer cables can be used, however, they must be
free from obstruction and no longer than 3m.
Horizontally Mounted
Referring to Fig. 49, measure distance ‘A’ from the right hand
face of one cassette to the right hand face of the other. Ensure
that the minimum cable radius is not less than 125mm. Cable
length is A + 67 cm. Longer cables can be used, however,
they must be free from obstruction and no longer than 3m.
Routine inspection – Fixed or withdrawable ACB (types A,
D & H)
Recommended annually or following interruption of a short
circuit.
Arcing contact system
• Withdrawable breakers should be drawn out to the
maintenance position.
• Remove arc chutes (Fig. 50).
Fig. 50
• Inspect the arc splitter plates and sides of the mouldings for
signs of wear or damage. Replace as necessary.
Note:
Arc chutes on ‘M-PACT’ circuit breakers have a unique
design feature. They are reversible to extend useful life.
Reversal of the arc chutes during each routine inspection is
recommended.
• With the breaker in the ON position, check the gaps between
fixed and moving arcing contacts.
• If greater than 2.5mm, and there is no evidence of contact
damage, loosen the fixed contact screw and adjust the gap to
2.5mm. Retighten the screw (12Nm torque).
• If excessive contact wear or damage is evident, both fixed and
moving arcing contacts should be renewed and the gap set to
2.5mm.
• If the gap is less than 1mm, reset to achieve a gap between
2.5 and 1mm by adjusting the fixed contact as above. Should it
not be possible to achieve at least a 1mm gap, the contact
system should be renewed.
• Even if gaps are within operating tolerance (1mm - 2.5mm)
always check contact screws for tightness to 12Nm torque.
Circuit Breaker operation
•
Check ON and OFF action of the breaker manually and by
remote means if appropriate.
•
Check tripping action by means of the undervoltage, if fitted.
•
Check that all indicators function correctly.
•
Check number of operations, if counter is fitted, to the
breakers specification.
Cassette checks
•
Ensure the base of the cassette is clear of debris or foreign
objects.
•
Prop open the top and bottom shutters (procedure as
described previously) and inspect the cassettes fixed contacts
for excessive wear or damage.
•
Check the operation of the carriage switch, if fitted, whilst
racking the ACB into and out of CONNECTED position.
M-PRO protection
•
Test operation of the circuit breaker against selected
protection settings (refer to section 2) using an M-PRO Test
Box (optional accessory).
•
Continuity check the mechanical trip alarm, if fitted, whilst test
box tripping the M-PRO.
•
Check contact wear menu (for M-PRO 20/30/40), if initiated.
•
Continuity check REF inter-trip, if fitted.
Isolating contacts (for withdrawable ACB’s)
Remove the circuit breaker from cassette housing and place on
a suitable working surface. Inspect the rear clusters contacts for
signs of overheating and wear. Remove the cluster contacts
using the special cluster pliers (part number LLA11YY207).
Clean the isolating contacts and terminals with a soft clean cloth
to remove any old grease or dirt and apply a thin film of BP white
paraffin grease (grade 8802).
Top ACB
Bottom ACB
‘A’ cm
10 cm (min.) cable clearance
ACB 1
ACB 2
‘A’ cm
14 cm (min.) cable clearance
Fig. 48
Fig. 49
