in accordance with the British Standard Specification No. 31 (revised September, 1910) for Steel Conduits for Electrical Wiring or in brass or copper conduits. All conduits must comply with the following conditions (Rule 132, § 248) :—

(«) They must be electrically and mechanically continuous throughout. Plain slip sockets do not comply with this rule, some form of screwed or grip joint being necessary, giving ample and permanent electrical conductivity and mechanical rigidity throughout. For medium pressures heavy-gauge screwed conduits must be used.

(b) At the outlets of switches, boxes, and fittings, the ends of the conduits

must either terminate in metal outlet boxes, or they must socket into blocks, preferably of incombustible material. The conductors must in all cases be mechanically protected throughout their entire length.

(c) They must have all open ends bushed to prevent abrasion.

(d) They must be earthed (Rules 34 and 35, § 269). In dry places isolated

single lengths of tubing need not be earthed if adequately enamelled, or otherwise insulated, externally.

(e) In damp places they must be watertight.

(/) They must be efficiently drained if liable to internal condensation, the conduits preferably being sloped to drainage positions.

(g) Sharp bends or elbows are prohibited except at outlets. Inspection elbows are permissible.

CHAPTER 11.

Systems of Installing Wiring— (continued).

Open Insulated Wiring.

253. General Description of Cleated System.—In the cleated system the lead and return wires are spaced off the walls by distance pieces, with grooves for keeping the wires apart, and a cap to hold them in position. Alternatively each conductor may be carried by a series of porcelain reels. Wooden cleats were used in early days, but they have been superseded by porcelain; these are made in various sizes according to the wire they have to carry, with either two or three grooves, and with either one or two screw holes going through both components. They are fixed to wooden plugs in the walls, and the bases should be resting on two or more raised projections, so that they are not in contact with the wall except at these feet. If a good quality of cable is used the cleated system is thoroughly reliable and very cheap; but, however neatly it is installed, it is sure to look ragged after a time. Long straight runs, fixed taut to start with, may remain so; but, whenever there is any slack, as at bends, etc., the tautness will assuredly be lost. Other disadvantages of the system are the harbouring of dust and the liability to damage when the walls are repainted. Dust is also attracted electrostatically, and deposited in a trail on the wall behind the negative wire. Cleated wires should be held apart at crossings by sheet, block, or tubular spacing pieces (cl. 50, § 254).

254. Specification continued — Cleated System. — The following clauses dealing with cleated wiring are additional to the general specification given in § 240 :—

46. Wires to be risible.—All cleat wiring shall be run as far as possible on the beams, where it is visible.

47. ClcaU.—All cleats are to be of porcelain of approved design and must consist of two parts, a bottom piece and a cap. A special pattern of cleat should be used if necessary where conductors pass round corners, so that there may be no risk of the conductors touching the walls owing to sag or stretching. Cleats are to be fixed at distances not greater than 3 feet apart and at regular intervals. There mu9t be no apparent ' sag' on the conductors.

48. (1) Finny of Chats.—In ordinary cases, cleats will be attached to wall plugs arranged as provided for in clause 14 (§ 240).

(2) Where practicable, the same method will be adopted in the case of stone walls, but when, owing to irregular coursing or other reasons, it is impracticable to fix the cleats in a regular and workmanlike manner, a wood batten is to be provided and fixed with not less than one wall plug per four-foot run. The batten to be of teak or other approved hard wood f inch thick and 1 inch wider than the cleat used, to be beaded or chamfered on the edges, wrought all over and varnished or painted two coats before fixing, as may be ordered by the Engineer.

(3) Brass screws must be used to secure cleats to wall plugs or battens.

(4) Where reasons exist which prevent the use of wall plugs or battens, cleats must be attached to the wall or ceiling in a manner approved by the Engineer.

49. Distance apart of wires.—For pressures between 60V and 250V cleats are to be of such dimensions that, in the case of branch leads, conductors shall not be less than 1 inch apart centre to centre; in the case of sub-mains, not less than 1^ inches apart centre to centre; in the case of mains, not less than 2f inches apart centre to centre. For pressures exceeding 250V, wires to be not less than 1 inch from any surface, and 4 inches apart centre to centre; in all cases wires to be tightly stretched and securely held:

Provided that this clause shall not apply to twin conductors used with the approval of the Engineer.

50. Crossing of conductors.—Where cleated conductors cross each other, they may be either looped over to maintain the prescribed distance or they may be fixed to an insulating bridging piece which will rigidly maintain a separation of at least an inch between the poles. If the point of crossing be within 10 feet of the ground or floor-level, an insulating bridging piece must be used:

Provided that this clause shall not apply to twin conductors used with the approval of the Engineer.

51. Protection.—No cleat wiring is to be left unprotected within 4 feet of a floor. When brought through a floor it must be enclosed in conduit.

255. I.E.E. Rule as to Cleated Wiring.—Rule 67 of the I.E.E.

wiring rules applies to open wiring with unarmoured conductors and runs as follows :—

67. Conductors without Mechanical Protection.—Conductors, insulated as in Class A (Rule 45, § 181), excepting flexibles (Rule 70, § 257), and lead-covered conductors (Rule 68, § 260), may be used where suitable without mechanical pro. tection (i.e. without conduit, casing, armouring, etc.) when in view and not exposed to injury, under the following conditions :—

(a) Spacing.—They must be supported in such a manner as to secure the
permanent spacing of the conductors from walls, ceilings, and all struc-
tural metal work and metal piping.
(6) When carrying more than 6A conductors must also be spaced from
each other.

(c) Protection through Walls, etc.—Where passing through walls, in or through
partitions, under floors or behind panelling, they must be protected
by wood casing or tubes (Rules 63 and 64, §§ 252, 243).

As regards (b), it will be seen that clause 49 of the specification in the preceding paragraph does not permit of unspaced cleated wires, whatever the current may be.

256. Open Wiring with Twin Flexible Wire.—Instead of using separate wires with spacing cleats, twin flexible wires may be carried on small button insulators, which prevent them making contact with the walls. If these insulators are in one piece the wires are untwisted and pressed over them, but two-part button insulators are preferable. In any case the use of the system should be confined to temporary work, or to permanent work at very low pressures, e.g. 50 or 25V. The system is unsuitable for running circuits on woodwork, or anywhere where a short-circuit between the wires might cause a fire. Flexible wires are liable to deteriorate rapidly owing to flies using them as resting-places, and it is no uncommon thing for a pendant fitting to fall owing to a short-circuit, due to deterioration from this cause. For certain classes of fittings flexible wires are necessarily used, but for the general wiring of circuits they are not recommended.

257. I.E.E. Rules as to Flexible Wiring.—Rules Nos. 70 and 71 of the I.E.E. wiring rules deal with open wiring with flexible conductors. The following is the text :—

70. Where permitted.—Flexibles (Rules 32, 102, and 103, §§ 231, 207) may be used—

(a) Pendants.—For pendant and portable appliances.

(6) Sub-circuits.—For low-pressure sub-circuits from fuse boxes (except in premises coming within the provisions of the Factory and Workshop Acts and the Coal Mines Regulations Act, in warehouses, or in places of public resort) provided that they comply with the following requirements :—

(i) Locution.—They must not be carried in positions exposed to injury

or out of sight, except in conduits, complying with (ii) below.

(ii) Division Walls.—Where passing directly through division walls they

must be protected by incombustible waterproof conduits.

(iii) Floors.—They must not pass through floors nor be carried unprotected

within 4 feet of the floor level.

(iv) Supports.—They must be firmly supported, and, unless protected by

conduits, they must be attached to insulators. The supports must be spaced not more than 3 feet apart.

(v) Joints.—They must be without joints, except in junction boxes.

71. Connections.—Connections between flexibles and hard wires must be effected only by means of screw terminals in junction boxes, porcelain or other connecting boxes, or ceiling roses, and not by soldering; and where flexibles from fittings unavoidably pass into ceilings they must be enclosed in conduits terminating in metal junction boxes.

Metal-sheathed Systems.

258. Henley, Kaleeco, and Helsby Systems; Corrosion of Lead.—

The Henley patent concentric and twin lead-covered systems of wiring have been considerably used of late, and have points in their favour, especially the latter. The system introduced by Messrs Callender under the trade name of ' Kaleeco ' is in many ways similar, and the remarks on the one may be taken to apply to the other. The use of lead-covered wire is not in itself novel in house wiring; but this system claims to get rid of the defects which were found to arise previously. Chief among these was the deterioration of the thin lead sheath from the chemical action of salts in the walls, aided by electrolysis. Chemical corrosion of lead is particularly troublesome where organic acids (acetic and tannic acids, etc.) are present. Perfect continuity throughout the lead sheathing, and good connection with earth, are essential if electrolysis is to be avoided, and special devices are used to ensure this; and by running the wires on the surface the lead covering is not subjected to chemical action. There is always a danger of the lead covering becoming slightly ' alive ' through leakage, and the leakage current, however slight, causes slow but persistent electrolytic corrosion at the points where it enters or leaves the lead sheath. The result is that the lead is pitted and perhaps pierced, and the insulation breaks down. On heavy lead-sheathed cables purely chemical corrosion is of little importance, but leakage or local currents may cause serious electrolytic damage. By bonding all the sheaths together and earthing them we ensure that the leakage current enters and leaves the sheath by a metallic, instead of an electrolytic, path. The sheathing on these patent wires is substantial,1 and it is claimed to be suitable for burying in walls; but, if this is done, it is certainly advisable to fill in the chase with plaster of Paris, or with neat Portland cement mixed with pure water, rather than with lime mortar or ordinary lime plaster. The wires are more usually carried on the surface, clipped or saddled to the walls, but they can easily be run out of sight to a large extent; they are also readily bent round corners and cornices, and the wiring can be made very inconspicuous.

The Helsby system consists of lead-covered wires braided externally. The protection afforded by the braiding against corrosion has been found effective, and the system is making headway in the East. 1 Messrs Henley state that the covering on their wires is a lead alloy.

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