Medium Voltage Application Guide

ELECTRICAL SUPPLY
4. All current transformers (C.Ts) shall be of the epoxy- resin encapsulated type and shall conform
to the requirements of IEC 60044-1, for the type of duty required.
5. The CT’s shall be installed on the side of the circuit breaker remote from the busbars. The
primary winding shall be of the bar type and of approved cross-section compatible with the circuit
breaker rating.
6. The secondary windings of each set of C.Ts shall be earthed at one point.
7. C.Ts. for protective purposes shall be of the nominated protection Class, rated burden and
saturation factor sufficient to cater for the normal relay settings and load burdens required in the
protection scheme.
8. Current transformers used for metering and indicating instruments shall have accuracy not less
than the nominated; typically Class 0.5 and Class 1.0 respectively. Each transformer shall be
capable of providing the necessary VA to operate the related instruments.
3.12 Labels
1. Each item of equipment shall carry the manufacturer's rating plates, with information and
compliance with the relevant standard.
2. Further labelling shall be provided to indicate the main functions of each service and control
equipment item.
3. All wiring terminal positions and terminations shall be identified by local labels to indicate the
group services, e.g. closing, tripping, etc. This shall be in addition to the cable ferrule method.
3.13 Control Wiring
1. Suitably rated terminal blocks shall be provided for all external cable connections.
2. Terminals for circuits carrying different voltages shall be segregated, labelled and separated with
insulating barriers.
3. Control cabling inside electrical panels shall be with PVC V105 insulated stranded single-core
copper cable. The minimum cross section shall be suitable for the load current and volt-drop for
CT secondary wiring or small power circuits.
4. For other control circuits, the minimum size shall be 1.0 mm sq. Wiring shall be neatly run and
shall be securely fixed in insulated ducting or harnesses with easy access for checking.
5. A suitable control wiring colour schedule shall be provided to differentiate voltages and functions.
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