Open wiring vs. exposed wiring

February 29th, 2008, Published in Articles: Vector

by Brian Bilton

I often see accredited persons in their test reports condemn an installation because of open wiring, confusing open wiring with exposed wiring.

Fig.1 is a case in point. This is a typical example of exposed wiring, and whether it complies or not is debatable. It is certainly not good workmanship when compared with yesteryear standards, but pretty near common practice compared with today’s standards.
Compare the same standard applied in Fig. 2, and decide which you would rather have in your installation. It is the same light fitting but the wires are terminated a different way. Fig. 1 was quicker and therefore costs less. Fig. 2 took longer, and needed extra material and therefore costs more. The first guy got the job; the second guy lost the job because he was a “rip off”.
The house was sold and the third sparky failed the job in Fig. 1 because it had open wiring. So who is right? If you refer to my last article in the Nov/Dec 2007 issue of Vector: “Is the roof space a joint box?” you will see my personal feeling. The “old school” (those who are more than 50) have all agreed with me. The new guys say I would never last in business, and that’s probably why I am not in business any more.
If we go to the current version of the Code (SANS 10142-1:2006) we read-
6.4.5 Open wiring
Note:
Open wiring consists of single-core insulated conductors that operate at not more than 250 V to earth; however, this is not a recommended installation method for new installations.
6.4.5.1 Open wiring shall not be installed
a) under thatched or wood-shingle roofs,
b) in parts of a roof space where the working height is less than 750 mm,
c) in roof spaces that are intended to be used (or are used) for storage, unless the wiring is suitably protected against mechanically damage,
d) within 1 m of a trap door unless the wiring is suitably protected against mechanical damage, or
e) where it will be in contact with flammable material.
6.4.5.2 Each conductor of an open wiring system shall be visible where it is installed on, over, or next to beams that can be used for walking on, or
it shall be suitably protected against mechanical damage.
6.4.5.3 Conductors shall
a) be fixed at intervals not exceeding 1,5 m to building elements such as
walls, rafters or purlins,
b) if there is no ceiling, be at least 3 m above floor level,
c) Deleted by amendment No. 5.
d) Deleted by amendment No. 5.
e) Deleted by amendment No. 5.
f) be supported within 600 mm of the point where they enter conduit or other building elements, and
g) be fixed in such a way that the fixing method does not impair the conductor insulation.
6.4.5.4 Where conductors enter a conduit, the conductors shall not be strained. Metal conduit shall project enough to allow a bush and an earth
clip to be fitted.
6.4.5.5 Where the current-carrying capacity of conductors is impaired by thermal insulating material, the appropriate correction factors shall be applied.
If you are older than 50 you will recognise that the latest version of the code has a significant number of amendments and you will understand why things are not what the used to be! J
Standard regulations for the wiring of premises
Open wiring means the systems of installing uncased insulated conductors as described in Regulation 402:
Open wiring on cleats
a) Braided vulcanized-rubber-insulated cables or PVC-insulated braided or unbraided cables uncased and unarmoured, may be used only where approved, and subject to any special conditions which the engineer may specify for the particular installation, in addition to those set out in this regulation.
b) The cables shall be open to view throughout their length except where protected in accordance with clauses (f) and (h) below, and, in particular, they shall not be buried in plaster nor installed under floors or within partitions, nor within a roof space in any position where the working height is less than two feet six inches.
c) The cables shall be carried on and suitably fixed to rafters, purlins or tie beams, and where there are no ceilings shall be not less than ten feet from floor level.
d) Cables shall be supported on effective insulators which are so spaced as to prevent the cables from coming into contact with each other or with walls, ceilings, or any other part of the structure of the building, or with any fixture. The insulators shall have smooth or rounded edges that will not indent nor damage the braided, and if tough-rubber insulators are used, they shall be provided with suitable protection where they are likely to be permanently exposed to direct sunlight. (For the purpose of this paragraph, sunlight which has passed through ordinary window glass shall not be deemed to be direct sunlight).  The minimum distance between the centres of cables shall be one and one-half inches and the insulators shall be secured by screws.
e) Where the cables pass into a tube they shall not be strained, and shall be
Supported by bobbins or cleats within six inches of the tube. The tubing shall project from the wall or above the tie beam by only a sufficient length to enable The bush and earth clip to be installed.
f) If passing through floors, walls, partitions or ceilings, they shall pass through directly and shall be protected by being enclosed in metal or other non-absorbent, non-combustible conduits, the ends of which are bushed or so finished as to prevent abrasion of the cables ; and, in the case of walls and floors, the holes through which the conduits pass shall be made good with cement or similar non-combustible material to the full thickness of the material of the wall or floor, no space through which fire might spread being left around the conduits.
g) All crossing cables shall cross at right angles and shall have a clear space of at least one and one-half inches between them.
h) In damp situations and in any position in which the cables would be liable to mechanical damage, and wherever they are within reach of any person standing at floor level, they shall be adequately protected by enclosure in conduit or casing.
i) Under thatched or wood-shingle roofs, the cables shall be protected by enclosure in screwed conduit.
j) Cables shall be run so as to leave a fair gangway in the neighbourhood of trapdoors, tanks, pipes and other apparatus liable to frequent inspection, use and maintenance.
k) Roof space wired in this manner shall not be used for the storage of goods or lumber nor for similar purposes.
So back in the bad old days open wiring was a system of wiring with cleats and bobbins which is not a recommended installation method for new installations today. And if anyone can find cleats and bobbins out there I would appreciate a sample to add to my collection of the way things were!
Brian Bilton