IN modern house-lighting off a public supply, the current usually is alternating current at a pressure of about 240 volts. This pressure is sufficiently high to give anyone who touches a bare live conductor, or any metal part connected directly with it, a severe and even fatal shock. The reader is therefore warned to open the main switch before doing any- thing to any of the electric fittings of the at each end of it. 13Ut the conductor house. Merely opening the wall switch to from B to T is still in connection with the a lamp, for example, does not make it main and becoming alive many times a safe to take the lampholder to pieces.
It should be added that in private-electric lighting installations – plants using ELECTRIC LIGHT
ELECTRIC LIGHT direct current – the lamp switches are always in the positive conductors, i.e.. those connecting the positive terminals of the dynamo with the lamps, etc. Opening a lamp switch would in this case give protection, as the return conductor (T to B) could have no dangerous pressure in it,
THE WIRING OF EXTENSIONS ANY amateur electricians make extensions from the house circuits into garages, outhouses, etc., so a few remarks on the subject of extensions will be in place.
Assuming that the worker has not the knowledge and skill needed for carrying the conductors through protective metal tubes, or fixing wooden casing, his choice -will probably be between cabtyre-sheathed and lead-sheathed conductors. Either of these may safely be exposed to the weather, and be held in position by staples, which in the case of lead-sheathed wires must be of tinned brass and not of copper.
Lead-sheathed wires must have the sheathing earthed by a wire leading to a water pipe or a plate buried in the ground, as otherwise any leakage from the conductors into the sheathing might give a shock to anyone touching the last.
For alternating current both conductors should be inside one sheathing, if it is of metal; but for continuous current each conductor should be in a separate sheath.
Making branches by soldering wires on to the through conductors is permissible only if the soldering is done very thoroughly with a non-corrosive flux and carefully taped over. The parts which will be soldered together should be scraped bright before solder is applied.
A box contains a porcelain block enclosing brass parts and screws which enable either conductor to be connected with a branch wire running to the lamp or switch. An independent wire, A, connects lamp and switch.
Under the second system, known as looping-in , the through conductors are continuous. Wherever a switch or lamp is to be brought into circuit, a loop in a conductor is carried to it and the wire is bared, twisted into a point, and clamped into the fitting. Then it passes on to the next lamp or switch. Hern also an independent wire is needed between lamp and switch.
NEW INSTALLATIONS to a new house that is to be wired for A electric lighting the specification should specify: – – (a) The enclosure of conductors in screwed conduits or tubes. These protect the conductors excellently against mechanical damage and damp, and any adjacent woodwork against the risks of fire through short-circuiting or arcing; and give any escaping current an easy passage to earth; (6) Two-point switching for staircase and passage lights, so that lamps may be switched on ahead of and switched off behind the user. Such switching may also be convenient in bedrooms where it is desirable to be able to control a lamp both at the door and from the bed; (c) Isolating switches for each circuit between main-switch and fuses; or, alternatively, quickly removable safety holders for the fuses; (d) That the contractor supply the householder with a drawing showing the positions of all conduits, whether visible or concealed, and indicating what points are supplied from each circuit; and any other particulars that may be useful in case of replacements or additions at a future time.
Even if there is no immediate intention of using electricity for heating or cooking, or for running small household machinery, it may prove economical to have the necessary tubing, and junction, and draw- through boxes fitted while this can be done easily and cheaply. The conductors can be drawn into the tubes when needed, and as current for power – which covers heating-purposes – is supplied at a much lower rate than fighting current, there may eventually be a considerable saving.