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13.0.5.1 RESISTOR:

13.0.5.1.1 The resistor elements shall be made of unbreakable, corrosion proof, joint-less stainless steel grids conforming to ASTM standard A240-304. The grids shall be in punched form.

13.0.5.1.2 Resistors shall be able to carry rated current specified in the data sheet for 10 seconds with maximum temperature limited to 790° for stainless steel elements, while limiting the temperature of Aluminium conductor /busbar to 350°.

13.0.5.1.3 If specified in the data sheets, the resistor shall also be sized to carry 10% of the rated current continuously with the maximum operating temperature of resistor elements limited to 415C. Further, the temperature rise of the resistor elements when they carry 10% of the rated current followed by the specified rated current for 10 seconds shall not exceed the temperature limits specified in clause 5.1.2 above. Under the steady state conditions when the NGR carries 10% of the rated current, the surface temperature of the enclosure, excluding the roof but including the separate canopy, shall be limited to maximum 70C.

13.0.5.1.4 Grids shall be mounted on steel rods insulated by special heat-resistant insulating materials, suitable for the above temperatures. Ceramic/ porcelain insulators shall be used to insulate the resistor elements from the enclosure. The insulators and terminal bushings shall have adequate minimum Creepage values (total and protected) for the required voltage grade.

13.0.5.1.4 Resistor banks shall be provided in series and parallel combinations to achieve the overall resistance value. Minimum two banks in parallel shall be provided in the system unless specified otherwise.

13.0.5.2 ENCLOSURE:

13.0.5.2.1 The resistor elements shall be housed in a naturally ventilated Galvanized sheet steel enclosure with minimum IP-31 degree of ingress protection and suitable for outdoor installation.

13.0.5.2.2 The enclosure thickness shall not be less than 3mm. The NGR shall have a suitable arrangement for fixing it on concrete foundations/ grouting in floor.

13.0.5.2.3 The terminals for neutral and earthing connections shall be housed in a separate vermin-proof, weatherproof terminal box with minimum IP-55 degree of ingress protection. The terminal box shall be provided with a separate bolted removable undrilled gland plate of non-magnetic material. This shall be drilled at site to suit the cable entry. A nickel plated brass double compression cable gland of suitable size shall be provided along with the terminal box.

13.0.5.2.4 A separate canopy shall be provided above the enclosure roof with a suitable air gap between them. It shall also cover the terminal compartment. Hooks or handle shall be provided to lift the canopy.

13.0.5.2.5 It shall be possible to periodically clean the resistor elements and enclosure after removing the bolted side covers.

13.0.5.2.6 Facility shall be provided to earth the enclosure at two points. For this purpose, suitably sized studs shall be provided on the sides of the enclosure to accommodate the connection of copper /GI strip.

13.0.5.2.7 The bottom of the enclosure shall be suitably sloped and provided with a drain plug to remove water that may get collected in the enclosures.

13.0.5.3 TERMINALS:

13.0.5.3.1 The two ends of the resistor shall be brought to suitable porcelain bushing type terminals of adequate rating for the neutral and earth connections. The terminals shall be suitable for terminating the specified size of cables / earthing strip and shall be supplied complete with tinned-copper lugs. Bolted type link shall be provided for isolating the resistor at the neutral end.

13.0.5.3.2 Suitable washers shall be provided between the grid element ends and the terminals to maintain good electrical contact.

13.0.5.3.3 The connection between the transformer neutral and the NGR shall be carried out by means of single core cable of size and type as specified in the data sheet.

13.0.5.3.4 The connection between the NGR and the earth pits shall be carried out using Copper /GI Earthing strip as specified in the data sheet.

13.0.5.4 SPACE HEATER:

13.0.5.4.1 A suitable anti-condensation space heater shall be provided inside the NGR enclosure to prevent condensation of moisture. This shall be rated to operate from a 240V, 50Hz single phase supply. The terminals of the space heater shall be brought out to a separate vermin-proof weathervermin-proof terminal box. The terminal box shall have a minimum IP-55 degree of ingress protection and shall be complete with tinned copper lugs and nickel plated brass, double compression cable glands.

13.0.5.4.2 The space heater shall be controlled using a double pole switch, HRC fuse, neutral link and thermostat provided in the terminal box. The switch shall be operatable from the front of enclosure without opening the terminal box cover.

13.0.5.5 CURRENT TRANSFORMER:

13.0.5.5.1 The current transformer, if specified, shall be of cast resin type suitable for the applicable voltage grade and temperature conditions. The secondary connections of the current transformer shall be brought out to suitable terminals provided with a shorting link.

13.0.5.5.2 The CT shall be housed in a separate compartment and avoid locating in resistance box.

13.0.5.5.3 The CT terminals shall be wired in the terminal block with suitable gland plate for terminating the control cable.

13.0.5.6 COOLING:

13.0.5.6.1 The Neutral Grounding resistor shall be air cooled. Forced cooling shall not be used. If required louvers can be provided in the enclosure provided they are completely guarded on the inside with a fine wire mesh.

13.0.5.7 NAMEPLATE MARKING:

13.0.5.7.1 The equipment shall be provided with a stainless steel nameplate located prominently indicating particulars such as make, tag number of the equipment, rating and other relevant details.