Specifications

NAIROBI OPERATIONAL HUB
UNOPS Building, UN Lane, Off UN Avenue Tel: [phone]
P.O Box 783,Village Market, 00621 E-mail: [e-mail]
Nairobi, Kenya Website: www.unops.org
UNOPS is ISO 9001 certified
comply with appendix B of IEC 947-2 standard. They shall be immunised
against nuisance tripping as per IEC 255 and IEC 801-2 to 801-5 standards
H. MCCB with ratings upto 250A shall be equipped with thermal magnetic or
electronic trip units which are fully interchangeable types. The breakers
with ratings over 250A shall be equipped with electronic trip units which
shall remain operational for ambient temperatures upto 60°C. Electronic
trip units shall comply with appendix F of IEC 947-2 standard. It shall be
possible to fit lead seals to prevent unauthorized access to the settings of
the electronic and thermal magnetic trip units.
MCCB’s equipped with thermal magnetic trip units shall have adjustable
thermal protection and fixed magnetic protection for current ratings upto
160A. For current ratings greater than 160A the thermal magnetic trip
units shall be adjustable from 5 to 10 times the current rating. In four pole
breakers the neutral pole shall have the tripping threshold equal to that of
the phases unless otherwise stated in the drawings.
K. MCCB’s upto 250A frame size equipped with electronic trip units shall
sense the actual RMS values for:
a) long time protection from 40% to 100% of the trip unit rating,
b) the short time protection shall be adjustable from 2 to 10 times the
thermal setting,
c) the instantaneous protection shall have the threshold fixed between 12
and 19 times nominal current, depending on the rating.
L. MCCB’s over 250A up to 630A frame size shall be equipped with
electronic trip units shall sense the actual RMS values for: : a) long time
protection from 40% to 100% of the trip unit rating, b) the short time
protection shall be adjustable from 2 to 10 times the thermal setting, c)
the instantaneous protection threshold shall be adjustable from 1.5 to 11
times nominal current and d) a thermal memory (in the event of repeated
overloads, the electronic trip units shall optimize protection of cables and
downstream devices by memorizing temperature variations). A load
monitoring function shall be an integral part of the electronic trip units
indicating four load levels (60%, 75%, 90% and 105%) by LED’s (with
flashing LED for 105%). It shall be possible to install with the electronic
trip unit a high threshold earth fault protection, load monitoring and
LED’s in front to indicate the cause of tripping. It shall be possible for the
MCCB to communicate with Building Management System (BMS).
M. The following frame sizes shall be adopted for different breakers: