1. Wooden moulding should never be concealed, and should not be used in damp places or in buildings subject to acid fumes, such as ice houses, breweries, or stables, etc.
2. Wooden moulding selected for use should be formed of good straight stock and free from knots, knot holes and other imperfections. The saving effected in the lower cost of second hand moulding does not compensate for the additional cost increase in its working.
3. When wooden moulding is used in connection with solid pipe or flexible tube conduit, an iron box or conduitlet must be installed where the system of wiring changes, as shown in [fig. 875]. The pipe conduit is secured to the box by means of lock nuts, with porcelain bushings or flexible tubes protecting the wires. In all cases the loom should run up to the moulding.
Fig. 875.—Method of tapping outlets for feeder circuits when wiring with wooden moulding.
Arc Light Wiring.—All wiring for high voltage arc lighting circuits should be done with rubber covered wire. The wires should be arranged to enter and leave the building through an approved double contact service switch which should close the main circuit and disconnect the wires in the building when turned "off" and be so constructed that they will be automatic in their action, not stopping between points when started and to prevent arcing between points under any circumstances, and should indicate plainly whether the current is "on" or "off." Never use snap switches for arc lighting circuits. All arc light wiring of this class should be in plain sight and never enclosed, except when required, and should be supported on porcelain or glass insulators which separate the wires at least one inch from the surface wired over. The wires should be kept rigidly at least eight inches apart, except, of course, within the lamp, hanger board or cut out box or switch. On side walls, the wiring should be protected from mechanical injury by a substantial boxing, retaining an air space of one inch around the conductors, closed at the top (the wires passing through bushed holes) and extending not less than seven feet from the floor. When crossing floor timbers in cellars or in rooms, where they are liable to be injured, wires should be attached by their insulating supports to the under side of a wooden strip not less than one-half an inch in thickness.
Arc Lamps on Low Pressure Service.—For this service there should be a cut out for each lamp or series of lamps. The branch conductors for such lamps should have a carrying capacity about 50 per cent. in excess of the normal current required by the lamp or lamps to provide for the extra current required when the lamps are started or should a carbon become stuck without over fusing the wires. If any resistance coils be necessary for adjustment or regulation, they should be enclosed in non-combustible material and be treated as sources of heat; it is preferable that such resistance coils be placed within the metal framework of the lamp itself. Incandescent lamps should never be used for resistance devices. These lamps should be provided with globes and spark arresters, as in the case of arc lamps on high voltage series circuits, except when the closed arc lamps are used.
4. Wooden moulding should never be run in elevator shafts, or shafts of any kind, and should never be run on the inner side of the outside walls of the buildings, as these locations are usually subject to dampness.
5. In laying out feeders it is usually cheaper to use iron conduit in a shaft, than to run moulding through the floor timbers.
6. When tapping outlets for feeder circuits, an iron outlet box with cover should be used, as shown in [fig. 886]. The one splice box is held up to the outlet box already installed by means of two long screws, and the loom is run right up to the moulding so as to leave no exposed wire.
Fig. 876.—Circular fixture block for outlet from moulding work on ceiling.
7. Wherever fixture outlets are installed, a circular fixture block as shown in [fig. 876] should be used, to give a good support for the fixture and to make a neat backing for the fixture canopy. The wires should be brought through the fixture without cutting and disfiguring the canopy.
Concealed Knob and Tube Wiring.—This method of wiring should be discouraged as far as possible, as it is subject to mechanical injury, is liable to interference from rats, mice, etc. As the wires run according to this method are liable to sag against beams, laths, etc., or are likely to be covered by shavings or other inflammable building material, a fire could easily result if the wires become overheated or short circuited.