Fans and Exhaust Fans

Fans and Exhaust Fans Points : fans and exhaust fans, exhaust fans, testing of installation, insulation resistance test, testing of earth continuity path, earthed electrode resistance test Fans and Exhaust Fans Fans The fans shall be suspended from hooks or shackles by means of suspension rods. Rubber insulators (shackle) shall be provided between the hooks and suspension rods. There shall be no joints in the suspension rod. The canopies on top of the suspension rod shall hide the suspension. The lead-in-wire from the ceiling rose shall be of 1.5 mm2 size and shall be protected from abrasion. The fan blades shall be kept at least 2.75 metres above the floor unless specified otherwise. Exhaust Fans The exhaust fan point shall be wired as near the place of installation as possible and shall be provided with 15-A switch. The exhaust fan shall have air displacement capacity suitable to provide the required number of air changes. If necessary, more than one exhaust fans shall be provided. The recommended air changes for various services arc given in Appendix G. The exhaust fan shall be erected so that the dirty gas shall exhaust, into the atmosphere. The exhaust fans shall be located such that the complete area is properly ventilated.

The mounting ring shall be fixed by means of rag bolts grouted in the wall. A circular hole, suitable to the size of the exhaust fan, shall b provided at the proper place in the wall. The hole and other items shall be neatly plastered to the original finish of the room. If desired, a suitable cylindrical box of 1.5 mm (16 SWG) thick mild steel may be routed in the circular hole. The box shall be painted with matching colour over a coat of red oxide primer. The exhaust fan shall be connected to the outlet with wire of 2.5 mm2 size. Testing of Installation The following tests, in sequence shall be carried out in completion and the defects revealed shall be made good:

1. Polarity Test: Polarity test of non-linked single pole switch
(i) In a two wire low voltage installation, a test shall be made to verify that all non-linked, single pole switches have been fitted in the same conductor throughout and that such conductor has been connected to an outer or phase conductor or to the non-earthed conductor of the supply.

(ii) In a three or four wires installation, a test shall be made to verify that non-linked, single pole switch is fitted in a conductor connected to one of the outer or phase conductor of the supply. 2. Insulation Resistance Test (1) The insulation resistance shall be measured by applying between earth and the whole system of conductor or any section thereof with all fuses in place and all switches closed.

Except in earthed concentric wiring, all lamps in position or both poles of installation otherwise electrically connected together, a D.C. voltage of not less than twice the. working voltage, provided that it does not exceed 500 volts for medium voltage circuit. Where the supply is derived from three wires (A.C. or D.C.) or poly-phase system the neutral pole of which is connected to earth direct or through added resistance, the working voltage shall be deemed to be that which is maintained between the outer or phase conductor and the neutral.

(ii) The insulation resistance in mega-ohms of an installation measured as in (i) shall be not less than 50 divided by the number of points on the circuit, provided that the whole installation need not be required to have insulation resistance greater than one mega-ohm.

(iii) Control rheostat, heating and power appliances and electric signs may, if desired, be disconnected from the circuit during the test, but in that even the insulation resistance between the case of framework and all live parts of each rheostat, appliances and sign shall be not less than half of a M ohm

(iv) The insulation resistance shall also be measured between all conductors connected to, one pole or phase conductor of the supply and all the conductors connected to the middle wire or to the neutral or to the other pole of phase conductor of supply. Such a test shall be made after removing all metallic connections between the two poles of the installation and in these circumstances; the insulation resistance between conductors of the installation shall be not less than specified in (ii).

(v) On completion of an electric installation (or an extension to an installation) a certificate shall be furnished by the contractor, countersigned by the certified supervisor under whose direct supervision be installation was earned out. This certificate shall be in a prescribed form as required by local electric supply authority and also on form given in Appendix-E. 3. Testing of Earth Continuity Path: The earth continuity conductor including metal conduits and metallic envelopes of cables in all cases shall be tested for electric continuity and electrical resistance of the same along with the earthing lead. It includes any added resistance or earth leakage circuit- breaker measured from the connection with the earth electrode to any points in the earth continuity conductor iii the completed installation shall not exceed one ohm. 4. Earthed Electrode Resistance Test The following procedure shall be adopted when it is decided to measure the resistance of an earth electrode.

(i) Alternating current of a steady value shall be passed between the earth electrode X, which shall be separated from the earthing system for carrying out the test, and an auxiliary earth electrode, Y placed at such distance from X that the resistance areas of the two electrodes do not overlap.

(ii) A second auxiliary earth electrode, Z, made of 13 mm mild steel and driven up to one meter into the ground shall then be inserted half-way between X and Y and the voltage drop between X and Y measured. The resistance of the earth electrode is then the voltage between X and Z divided by the current flowing between X and Y, provided there is no overlap of the resistance area. (iii) To check, the value of the resistance, two further readings shall be taken with the second auxiliary, electrode Z, moved 5 metres further from and 5 metres neared to X respectively. If the three results are substantially in agreement the mean of readings shall be taken as the resistance of the earth electrode X If there is no such agreement, the tests shall be repeated with the distance between X and Y increased.

(iv) The test shall be made with a hand driven earth tester, comprising a direct reading ohm-meter, if there is wandering of the pointer of the instrument, the speed of the generator should be increased or decreased as required.

(v) On completion of the electric installation, or of an extension to the installation, a certificate shall be furnished by the contractor countersigned by the certified supervisor under whose direct supervision installation was carried out in prescribed from

Appendix-4. In addition to this,. test certificate prescribed by the local electricity authorities shall also be given. Electrification The following general points are to be considered.
1. (i) System of Writing (ii) Method of ‘wiring
2. Particulars of load. (i) Total load (ii) Total current (iii) Designing current.
3. No. of Sub-circuits, based on the above.
4. Distribution points in circuit.
5. Lay out: (i) Line diagram (ii) Flow diagram (iii) Photographic view diagram.
6. Size of cable. (i) From Central Distribution Board (CDB) (ii) In Sub-Circuit.
7. Main Switch.
8. Distribution box
9. Size and Length of conduits.
10. Size and Length of cable required from DB to load points based on voltage drop Calculation.
11. Cost of materials including CST, ST, SC and transport.
12. Labor for wiring.
13, Total charges if any.
14. Over head charges, contingencies etc.
15. Special fittings if any.