This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol6", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
Although it is usual throughout the building trade to confine the hours of working to those of daylight, it frequently happens that, for one reason or another, a building has to be proceeded with at the highest possible rate of speed. In such cases some form of artificial light becomes necessary in order to carry on the work during the hours of darkness, and it thus comes about that the apparatus for supplying this light becomes part of the plant of every large contractor. There are several more or less well-known appliances of a portable nature in use for this purpose, a few of which are described hereunder. In dealing with electric lighting in this connection it must be understood that it is only referred to in order to set forth the economical methods of using it for temporary-lighting, and in no way approaches the question of permanent electric lighting, which has been dealt with in a previous volume.
One of the best known and, until recent years, most generally used lamps for general contractors' work is the naphtha or paraffin "Flare Lamp" (Fig. 257). It is a simple and cheap appliance, and, apart from the fact that the light given is somewhat unsteady and not brilliant enough to illuminate large areas, sufficiently serviceable and safe in use. If properly cleaned at frequent intervals it will burn for many hours without any attention. The lamp consists of a large reservoir to contain the illuminant, which reservoir is placed above the burner, to which it is connected by a brass tube, the oil therefore running by gravity without the aid of any wick, and the supply being regulated by a tap or cock placed at the point where the brass tube joins the reservoir. The burner itself, which is annular in shape, is so constructed that the oil is heated considerably before it reaches the flame, so much so that it is actually vaporised, and therefore issues from the orifices in the form of vapour and under slight pressure. For this reason the flame is large and flat and the combustion of the vaporised oil nearly perfect - the outrush of the vapour from the small holes in the annular burner causing a corresponding inrush of air to the flame, on the principle of the injector. The oil supply once regulated by the tap, the lamp will continue to burn until the supply is exhausted. To start the lamp it is necessary to turn on a small flow of oil from the reservoir, and then hold the burner in the flame of a fire (often a handful of burning shavings is all that is needed) for a few minutes until it becomes sufficiently heated to cause the vaporising action before referred to. After this the functioning of the lamp becomes automatic. These lamps can be had either with a tripod support as shown, or with a ring attached to the reservoir, by which they can be suspended from a hook or nail in any convenient position.
A great advance on the Flare Lamp is the Wells Light (B, Fig. 257), a means of obtaining efficient illumination which has come into general use among contractors more or less recently. In principle it does not differ greatly from the older type, the flame being obtained from vaporised paraffin in the same way. The essential difference consists in the reservoir being placed below the burner and the addition of an air pump, by means of which the oil is put under pressure and forced up and through the burner. The result of this arrangement, coupled with a form of burner modified to suit the altered conditions, is a large body of intensely brilliant flame of considerable length, burning with a great degree of steadiness. The oil reservoir is made large enough to contain a supply of oil for 10 or 12 hours, and is very strongly built of steel plate to safely withstand the air pressure from the pump. After starting, the only attention needed by this appliance is an occasional pumping in of more air under pressure as the oil diminishes in the reservoir.
When the conditions under which a large building is to be erected warrant the necessary expenditure, undoubtedly the best means of obtaining light is by electricity. In London and other large cities a supply of current for this purpose can generally be obtained from some Electric Lighting Company's mains running through the streets adjacent to the site. While the same care should be exercised with regard to the actual jointing of the wires and cables used in this case as with cable used in permanent lighting, it is not necessary to install the same elaborate arrangements for carrying the conductors to the points where the light is required. Provided a well-insulated cable be used, it can be clamped to the beams of staging or scaffolding by means of cleats (Fig. 258) placed about 10 feet apart and secured to the timber by means of the central screw. When incandescent or glow lamps are used they can be suspended direct from the free
Temporary Lighting of Works during Construction 145 ends of the cables themselves, or branches therefrom, or they can be attached to a length of twin flexible wire so that they can be moved, within a limited area, to the most convenient position. An open wire guard should in all cases be fitted over the lamp, to protect it from any chance blow or fall.
For illuminating large areas, such as yards or the fronts of buildings, the arc lamps come into play. These can also be fitted up quite cheaply for temporary work: a scaffold pole with a cross bar at the top arranged in the form of a gallows answering very well as a means of suspension. As, however, the lamp has to be lowered from time to time to put in fresh carbons, the wiring has to be arranged to suit this. The cables leading to the lamp should be carried half way up the pole (Fig. 259) and firmly secured there, the remaining length from this point to the lamp terminals being left free. A pulley should be provided at the end of the gallows arm, and through this a small wire cord passed and made fast to the ring provided at the top of the lamp, so that it can be conveniently pulled up into position, the other end of the cord being made secure round a cleat at the foot of the pole. In no case should an arc lamp be suspended by the cables conveying the current, as the constant bending over the pulley-wheel is certain to damage them in course of time. There are several forms of arc lamp on the market, the enclosed arc type being perhaps most in favour for the present purpose, owing to the fact that the carbons are not consumed so fast as in the open type, and therefore do not require renewal so frequently, thus minimising the attention necessary. The question of the voltage or pressure of the supply company from which the current is taken has to be taken into account in this case as well as in that of power hoists, etc., and should be considered on its merits before making temporary electric lighting material a part of a contractor's permanent plant. That is to say, the cables and incandescent lamps suitable for a voltage of 100 would be quite useless for 220 or 240 volts.
With regard to arc lamps, as these can only be run at a uniform pressure of 50 volts whatever their power (or in the case of the enclosed arc, 100 volts), the question simply resolves itself into the putting of two or more in " series."
The whole difficulty is solved at once, however, if the contractor undertakes to provide his own source of electric supply. For this purpose a portable engine with a dynamo mounted upon a bracket on the boiler is the most convenient (Fig. 260). This arrangement has been proved by experience to work very satisfactorily, and the whole plant in connection with it can then be confidently counted on as a permanently useful part of the contractor's gear. A simple switchboard containing a main switch and fuse, a voltmeter, an amometer, and a suitable number of distributing switches, each having its own fuse, completes this most useful portion of the up-to-date builder's plant.