Florescent Lamp Circuits

Florescent Lamp Circuits Points : Florescent Lamp Circuits, practical advice, circuit diagram, ceiling fans, socket outlets, typical overloaded socket outlet, wiring up socket outlets, common mistakes Number of Point per Circuit The number of fluorescent lamps that can be connected to a final sub-circuit is not the same as incandescent lamps of the same wattage. The reason for this is that a choke forms part of the control equipment of a fluorescent lamp, and this considerably reduces the power factor of the circuit. Although a capacitor is nearly always connected to improve factor, the total current taken is still greater than an incandescent lamp of the same wattage. A general formula taking this into account is:

Wattage of fluorescent lamp = Current X voltage/2

For this reason, it is essential that the consumer specifies the wattage of the fluorescent lamps to be installed, not only for the calculation of points per circuit, but for the installation of fittings which are of different lengths for different wattages.

Thus on a 5 amp sub-circuit, with a supply voltage of 230 volts, the maximum number of 80 watt fluorescent lamps that can be connected to one lighting circuit.

= Current rating of sub-circuit X Supply voltage/2 X Wattage of lamps to be connected

= 5 x 230/2 x 80 = 7

A maximum of seven 80 watt fluorescent lamps can be connected to a lighting circuit, fused at 5 amps and wired with 3/.029 cable. A similar calculation can be done with other wattage values, i.e. with a sub circuit fused at 5 amp, supply voltage 230 volts, a maximum of fourteen 40 watt or nine 60 watt fluorescent lamps can be connected etc.

Practical Advice The control gear associated with fluorescent lighting, i.e. inductors, transformers, capacitors etc., if not enclosed in the fitting itself, must be enclosed in an earthed metal box, and the box mounted as near to the lamps as possible. Switches controlling these lamps should have a rating of twice the steady current in the circuit they control. It is usual to install a quick make and slow break switch for a.c. circuits, ordinary quick break switches should not be used.

If the shade and fittings of a fluorescent lamp are made of metal, then the metal must be connected to earth by way of an earth continuity conductor run around the circuit. If the fittings are of insulated construction then this is not necessary. One of the disadvantages of fluorescent or discharge lighting. is the stroboscopic effect of the lamps. This causes objects moving at certain high speeds to appear stationary or move slowly. This could be dangerous especially in factories or other places with rotating or fast moving machines.

In houses where fluorescent lighting has been installed this not really noticeable, nor is it usually dangerous, but in factories it could lead to severe accidents. It can be corrected to a large extent by wiring every alternate lamp on a different phase of a three phase supply. In this way, when a lamp is at zero voltage instantaneously, its neighbor is somewhere, near normal voltage. Circuit Diagram Circuit diagram is the connections for some common standard fluorescent lamp circuits Since there are many makes these diagrams are only meant for guidance, and it is recommended that the manufacture’s wiring diagrams, if available, should be closely followed. Either glow or thermal starters may be fitted. If thermal starters are used, two extra leads (shown dotted) are necessary. These connect to the two springs in the starter socket. Some types of fluorescent lamps have external metal strips and these must be earthed. Ceiling Fans All fans should be suspended on a hook or clamp having double nuts and a double bolt. The size of the clamp rod1 should not be less than tin thick,: The fan must be controlled by a separate switch and must have a speed regulator with an Off position which is capable of reducing the fan speed in steps to at least 40% of full speed. Fans should be hung at a minimum of nine ft. above the floor, and the regulator should be about five ft. above the floor.

Fans can be wired on the lighting circuit with 3/.029 cable and supplied from ceiling roses. Not more than about six fans should be connected to any one final sub-circuit. For .the purpose of estimation of current demand, a fan is assumed to have a wattage rating of 100 watts. A combination of lights and fans can be wired on one circuit but the total current taken must not be more than the fuse rating protecting the circuit. Socket Outlets Many types of socket outlets are available, the most usual being 2 pin 5 amp, 3 pin 5 amp, and 3 pin 15 amp, all either separately switched or with a switch incorporated. Iron clad versions of these are also available for industrial use. The shuttered type of sockets are recommended as these provide extra safety especially where children are concerned.

The installation of 2 pin sockets is not recommended. Even 3 pin sockets are not much use, however, if there are not enough of them installed. Nowadays there are air conditioners, table fans, table lamps, radios, gramophones, electric fires, electric irons, hair dryers, electric razors etc. etc. Very often all these are expected to run from about two socket outlets — one 15 amp and one 5 amp is typical. This result in the inevitable socket adaptors sprouts like mushrooms from an overloaded and usually cracked outlet, a maze of twisted knotted flexible cord and lengths of cord hanging across the room from lamp adaptors.

This is obviously far from safe but the consumer can hardly be blamed if there are only two socket outlets. It is common practice overseas to installs at least three 5 amp socket outlets and two 15 amp socket outlets per room. This practice is recommended for Pakistan and will eventually lead to ring circuits being installed in every house. This is described at the end of this section. Typical Overloaded Socket Outlet The use of socket adaptors is not recommended, especially those designed for 15. A Socket outlets having provision for 5 A plugs. Inevitably the socket outlets are overloaded, both mechanically and electrically, as shown. The only solution is to install more socket outlets per room. No socket outlet should be fixed in a bathroom and electrical apparatus in bathrooms should be of the fixed type.

Wiring Up Socket Outlets Since any sub-circuits having a current rating I exceeding 15 amps may oily feed one point (I.E.E. Regulation 114), obviously not more than three 5 amp socket outlets should be wired on any one sub-circuit. Also, each 15 amp outlet must be wired on an independent and separate circuit using cables not smaller than 7/029.

When connecting up 3 pin sockets to the supply, the red wire (phase conductor) should be connected to the terminal marked “L”, the black wire (neutral conductor) to the terminal marked “N” and the earth wire to the terminal marked “E”.

When conduit is used to socket outlets, the cables used should be either single core V.R.I. or P.V.C. insulated cables. The bare copper earth continuity conductor should in no case be less than 14 S.W.G.

If cables are to be run on battens or concealed in plaster then twin core sheathed cables with concealed earth continuity conductor should be used. Individual sub-circuit fuses should not be mounted on the same panel or board as the socket outlet. This is dangerous in houses where children might remove the fuse and get electrocuted, and it is dangerous in commercial premises where the porcelain mounting may fuses should be enclosed in switch fuse casings or distribution fuse boards, situated at a convenient central point.

Common Mistakes One of the most common mistakes is to install switches or fuses in the neutral instead of the phase conductor of a final sub circuit. Often there appears to be no attempt to find out which of the cables is which when connecting up, with the result that apparatus plugged into a socket outlet can still be alive even with the switch Off. From Fig. it can be seen that if the switch is connected in the neutral conductor, whether it is in the On or Off position, there is still mains voltage present at one of the pins. If the switch is in the Off position, naturally it is assumed that no voltage is present and this could, be extremely dangerous to someone working on supposedly dead apparatus connected to the socket. If, however, the switch is connected in the phase conductor, no voltage is present at the socket pins when in the Off position, so complete safety is achieved.

This is covered in a 2 wire installation permanently connected with earth on one pole single pole switches, circuit breakers and fuses must be fitted in the phase or outer conductor only. Where portable appliances requiring an earth are fed from socket outlets, twin twisted cords should not be used. Only too often appliances with exposed metal work, such as electric irons, refrigerators, electric fires etc. can be seen in houses, supplied by twin twisted cord. In all cases three core circular sheathed flexible cords must be used, as only then can the apparatus be considered safe.