A guide to electrical materials

Jagvir Goyal

Readers often ask to provide a complete and consolidated guide to electrical fittings and material required for the house. ‘One article is on wires and other on switch selection and it becomes difficult to refer to all,’ says a reader. In an attempt to meet the demand of readers, all information on materials can be presented in one article and on their correct provision in another article. Here is an attempt to provide some basic guidelines that readers can keep in mind when building a house:

The Items: Electric materials required for the house can be listed as under:

1. Conduits & bends

2. AC Conduits

3. Switch boxes

4. Light boxes

5. Fan boxes

6. Junction boxes

7. Wires

8. Switches & Plates

9. MCBs

Each of these materials can be discussed briefly as under:

Conduits and bends: MS conduits, once so much in use, have given way to PVC conduits now. While choosing PVC conduits, always look for heavy duty conduits with a thickness of 2 mm. Look for the ISI-marked conduits. PVC conduits used for electrical wiring are of ¾ inch to 1¼ inch diameter. An easy identification of quality of conduits can be made from the colour markings on them. Heavy duty conduits have green markings and light duty conduits carry red markings. Some medium duty conduits carry blue markings. Bends used with conduits are also made of PVC and are required in large numbers for a house. These are of long type and short type. These are required to extend conduits at right angles. The electrician decides whether at a location, he needs a long bend or short bend.

AC Conduits: Vertical PVC conduits of 50 mm diameter are embedded in the walls these days to run the copper piping connecting indoor and outdoor units of split ACs. These conduits need not necessarily be of heavy duty. The top ends of these conduits emerging at the roof or the walls are provided with end caps to prevent entry of moisture, insects and lizards inside these. The end caps are further sealed with cello tape. Sometimes, the end caps are not available with the conduit suppliers. Their provision should be insisted to keep multiple problems at bay.

Switch boxes: One end of all conduits ends up in switch boxes while the other ends up in electrical fittings. Switch boxes of different sizes are provided in the rooms to receive the conduits and wiring in them. Switch boxes of varying sizes are used as according to the number of switches to be put over it. Switch boxes sizes vary from 3 inch to 12 inch in width and so in depth also. These are square or rectangular in shape and made in 16-gauge sheet metal. Switch boxes should be painted well, both inside and outside with anti-corrosive paint. Use of wooden boxes should be avoided. Switch boxes should have a depth of 2 inch or more.

Light boxes: Light boxes are made of material similar to switch boxes, mostly embedded in sun shades and projections and roof slabs during the pouring of concrete. These accommodate the down-looking concealed lights provided in these slabs and projections. Light boxes are mostly round in shape, about 5 inch deep and provide with holes to allow entry of conduits in them. These are also made in 16 gauge metal sheet and painted with anti-corrosive paint.

Fan hook boxes: Fan hook boxes are also made in 16 gauge metal sheet, painted well with anti-corrosive paint and embedded in the floor slabs during the pouring of concrete. These are hexagonal or octagonal in shape. On their sides, these are provided with holes to allow the conduits to enter them. Generally, these are 4 inch deep and carry a hook inside them to hang the ceiling fan.

Junction boxes: Unlike switch boxes, Junction boxes are made in PVC and are provided in walls to branch out conduits to different switch boxes. These have four outlets at right angles. Interesting part of their manufacturing is that depending upon the size of conduits to be connected through these, these have connecting arms of different diameters, mostly of ¾” and 1” diameter.

Electric wires: First of all, the wire material. Electric wires can be in copper or aluminium. Choose copper wires only. Next, the strands. Wires can have single strand or multiple strands. Choose multiple strands. Next, the ISI mark. Wires can be ISI 694 (Part I) marked or IS 694 (Part II) marked. Choose IS 694 Part I marked wires. Next, the electrolytic grade. Choose copper wires of 99.97% electrolytic grade 99.97%. Next, check wire insulation. It should be three layered. Among the three layers, the first layer is water resistant, second is heat and high temperature resistant and third layer is fire retardant. Heat and fire resistant wires carry a mark HRFR. Check the highest temperature that the insulation can withstand without melting. It should be plus 100 degree Celsius. Next, check the size of wire. Commonly used sizes of wires are 1 sq mm, 1.5 sq mm, 2 sq. mm, 2.5 sq mm and 4 sq mm. Choose 4 to 6 sq mm size for AC points, 1.5 sq mm size for light points and 5 ampere three pin sockets and 2.5 sq mm size for power sockets. Choose 6 sq mm size wires for split AC wiring. Next, check colour of the wire insulation. Choose red, yellow and blue colour insulation for the three phases, black colour for neutral and green for earth wire. Every country has different colour code for electric wires. For example, in the USA, live three phase wires are in black, red and blue and neutral is in gray or white. Only earth wire is in green like India. Next, check length of wire in each coil to be full 90 metres as rates quoted by suppliers are per coil and not per metre length of wire.

Switches and plates: First of all, decide type of switches to be provided —whether conventional or modular. Choose modular switches only. Conventional ordinary switches are rarely used in new constructions. Next, look for the material of the switches. Choose modular switches made of fine quality polycarbonates which are a sort of thermoplastic polymers. Next, look for dust proof, high melting point and flame resistance properties of switches. Such polycarbonates are called FR grade polycarbonates. Next, look for design of switches. Modular switches are produced in different shapes, sizes and designs by different companies. Look for the ones that look pleasing to you and have smooth and straight design. Next, choose colour of the switches. Choose white colour only as white switches and plates never go out of fashion. Next, check their operation. These should be noise proof. Switches shouldn’t make any noise while turning them off or on. And no force should be required to press them on or off. Such switches are called to have ergonomic design. Next, look for the spark shields. Modular switches should have spark shield inside them to conceal high sparking and avoiding any damage or short circuiting due to leakage of current. Next, look for the dust-shield provision. Provision of a dust shield prevents entry of dust inside the switches and helps them retain their new look for years together. Next, look for insulation property. The insulation resistance of modular switches should be more than 2000 Mega Ohms. Such switches are shock proof. Look for life time guarantee of the switches.

Switch plates: Modular switches are provided in a set of two cover plates. The first plate contains the switches and is fixed to the box. This plate has a honeycombed grid plate structure. These plates should be sturdy and strong. Second plate is the front plate that has high gloss. It should be flush type, matching the white colour of modular switches, dust proof, easy to clean, easy to remove and re-fit and of the same brand as that of modular switches.

MCBs: There were times when fuses were provided in the houses. These are now replaced by MCBs. An MCB means Miniature Circuit Breaker. An MCB automatically trips off in case of high voltage or some fault in the electric circuit. Look for original MCBs of reputed manufacturers that provide 3 in 1 protection against earth leakage, short circuit and overload. Look for ISI marked MCBs only. On damage, an MCB should never be repaired but should simply be replaced. ISI marked MCBs of reputed brands don’t get damaged easily and work effectively.

(This column is published fortnightly)