INTRODUCTION:

The industries in India covering all the sectors took great strides after independence. The Government also introduced five year plans to give boost to the industries. In recent past also with the concept of “Make in India” saw rise of many startups. Accordingly, the electrical power requirement grew manifold. Use of high consumption loads, motive power loads etc made the safety of operating personnel of prime importance. Various BIS and National Electricity Code were drafted by the concern government departments in respect of wiring installation in Industrial buildings. In this article, an attempt is made to high light some of the provisions of Indian standards and National electricity Code.

STEPS FOR DESIGNING A WIRING SYSTEM IN INDUSTRIAL BUIDLINGS:

• Assessment of general characteristics of the installation:

1. Purpose of the installation, its use etc.

This shall amongst other elements, primarily include:

1. Maximum demand.
2. Diversity

• Type of supply, (3 phase, 4 wires or 1 phase, 2 wires)

1. Earthing arrangement for the supply system.
2. Prospective short circuit current at the origin of the supply.
3. Adequate capacity standby supply for safety services, its assessment, nature etc.

• Every installation should be divided in to circuits so as to avoid danger and minimize inconvenience in the event of the fault and facilitate safe operation, inspection, testing and maintenance of installation.

1. External influences on the installation.

An assessment of external influence on the electrical installation should be taken in to consideration. The external influences can be of environment, humidity, mechanical stress, height, lightning, wind, condition of evacuation during emergency, contact of persons with earth potential etc.

1. Compatibility:

Every equipment should be carefully chosen in respect of its behavior in the event of transient over voltages, starting current drawn by it, harmonic current etc. so that it does not affect harmfully on the other electrical equipment, services .

1. Maintainability:

An assessment shall be made of the frequency and quality of maintenance that the installation can reasonably be expected to receive during its intended life. This assessment shall, wherever practicable, include consultation with the person or body who will be responsible for the operation and maintenance of the installation. It should facilitate:

1. Any periodic inspection, testing, maintenance and repairs likely to be necessary during the intended life can be readily and safely carried out;
2. the protective measures for safety remain effective during the intended life;
3. and the reliability of equipment is appropriate to the intended life.

1. Supplies for safety services:

The need for safety services and their nature is generally regulated by statutory authority. Depending on that decision in this respect should be taken.Generally following supplies for safety services are considered

1. Storage batteries.
2. Generator set.
3. Express feeder from a different source from the supply company.

• Protection for safety:

The requirements for protection for safety of persons, livestock and property involve protection against electric shock, thermal effects, overcurrent, overvoltage and undervoltage and a measure of isolation and switching of electric circuits. The protective measures may be applicable to the entire installation or a part or an item of equipment.

1. Protection against direct/indirect contact:

Persons or livestock should be protected from such type of contact by provision of automatic disconnection of the supply on the occurrence of a fault likely to cause a current to flow through a body in contact with exposed conductive parts, where the value of that current is equal to or greater than the shock current. RCCB or earth fault relays should be provided at suitable locations.

1. Protection against thermal effects:

During normal operation of the electrical equipment, there shall be no risk of persons or livestock suffering burns. The operating personnel may be given proper PPEs to protect against the danger from burns.

1. Protection against over current and earth faults:

Where metalwork of electrical equipment, other than current-carrying conductors, may become charged with electricity in such a manner as to cause danger if the insulation of a conductor should become defective or if a fault should occur in any equipment:

The metalwork shall be earthed in such a manner as will cause discharge of electrical energy without danger, or other equally effective precautions shall be taken to prevent danger. Every circuit shall be arranged so as to prevent the persistence of dangerous earth leakage currents. Where metalwork is earthed, the circuits concerned shall be protected against the persistence of dangerous earth fault currents by:

1. a) the overcurrent protective devices required
2. b) a residual current operated device or equally effective device.

• Cable, conductors and wiring materials:

 All the cable, conductors and wiring material used should conform to the relevant Indian standards. Generally, armored cables are used in Industries. The flexible wires are laid in metal conduits. The distribution panels used should be dust proof and in some cases water proof. Preferably they should have protection of IP65 for reliability and longer life service.

1. The cross-sectional area of every cable conductor shall be such that its currentcarrying capacity is not less than the maximum sustained current which will normally flow through it.
2. Busbars, busbar connections and bare conductors forming part of the equipment of switchboards shall comply as regards currentcarrying capacity and limits of temperature.
3. Cables connected in parallel shall be of the same type, cross-sectional area, length and disposition and be arranged so as to carry substantially equal current.
4. In determining the current-carrying capacity of bare conductors, account shall be taken of the arrangement made for their expansion and contraction, their joints, and the physical limitations of the metal of which they are made.
5. The size of every bare conductor or cable conductor shall be such that the voltage drop within the installation does not exceed a value appropriate to the safe functioning of the associated equipment in normal service.
6. For polyphase circuits in which imbalance may occur in normal service, through significant inequality of loading or of power factors in the various phases, or through the presence of significant harmonic currents in the various phases, the neutral conductor shall have a cross-sectional area adequate for the maximum current likely to flow through it.

• Erection of installation:

1. Qualified persons and with good workmanship should be employed.
2. The characteristics of any electrical material should not be impaired during erection.
3. Proper color codes should be used. The earth terminal and the neutral conductor should identify and tagged at their terminations.
4. The conductors should be joined to the electrical equipment with a safe and reliable joint /termination.
5. Earthing should be done in accordance with IS 3043. Every metal enclosure should have two distinct earthing connections as provided in clause 41 (xii) of CEA safety regulations.
6. One meter clear space should be left in front of every switch board.
7. Wiring diagrams should be prepared and displayed.
8. Warning boards should be provided at appropriate places.

• Testing:

Following tests should be performed before commissioning:

1. Insulation Resistance test.
2. Earthing pit resistance test.
3. RCCB tripping test.
4. Polarity test.
5. Earth loop impedance test.
6. Continuity of earthing conductors.

• Light fittings:

In industrial premises lighting fittings shall be supported by suitable ‘pipe/conduits, brackets fabricated from structural steel, steel chains or similar materials depending upon the type and weight of the fittings.

References: IS 732, NEC-2011