Handbook of Electrical Installation Practice - BeKnowledge

460 Handbook of Electrical Installation Practice
Fig. 17.3 Typical range of contactors covering three-phase AC3 ratings 4–400kW.
PRODUCT STANDARDS FOR CONTACTORS
Previously, contactors were marketed as meeting IEC 158, BS 5424, or even BS 775.
The current product standard is IEC 947 published in the UK as BS EN 60947.
These standards all laid down general design and performance requirements for the
products and included various design or ‘type’ tests to verify the ability of a device
to perform the duty for which it is sold. The test currents and typical service switching
currents for industrial motor control applications are summarised in Table 17.1.
An individual sample contactor must be able to complete a test sequence in order
to confirm its rating. For a contactor intended to be used in an AC3 application, the
test sequence would consist of:
• 50 operations making ten times the rated current, 25 operations to be performed
with the coil energised at 85% of rated voltage followed by 25 operations with
the coil energised at 110% rated voltage; followed by:
• 50 operations making and breaking eight times the rated current at 105% of rated
voltage; followed by:
• 6000 operations making and breaking two times the rated current, followed by a
dielectric test.
Any failure of the test item during this test sequence would mean that the complete
test sequence must be repeated on a new test sample.
The test currents, voltages, power factors and time intervals between test operations,
together with the test sequence requirements for other utilisation categories,
are specified in IEC 947 or BS EN 60947 which should be consulted for full details
of test requirements.