Wiring colours

Extensions or alterations to existing single-phase installations do not require marking at the interface between the old and new fixed wiring colours. However, a warning notice must be fixed at the consumer unit or distribution fuse board which states ... 

Caution - this installation has wiring colours to two versions of BS 7671. 

Caution - this installation has wiring colours to two versions of BS 7671. Great care should be taken before undertaking extensions, alterations or repair that all conductors are correctly identified. 

If the iodide is deeply coloured, it may be decolourised with a little sodium bisulphite. A perfecUy colourless product can be obtained by distilling in the dark or in dilfusod light from a little silver powder. The iodide should be preserved in a bottle containing a short coil of copper wire made by wrapping coppor wire round a glass rod or tube. 

Push one end of a length of 20 cm. of stout copper wire into a cork (this wUl serve as a holder) at the other end make two or three turns about a thin glass rod. Heat the coil in the outer mantle of a Bunsen dame until it ceases to impart any colour to the dame. Allow the wire to cool somewhat and, while still warm, dip the coil into a small portion of the substance to be tested and heat again in the non-luminous dame. If the compound contains a halogen element, a green or bluish-green dame will be observed (usually after the initial smoky dame has disappeared). Before using the wire for another compound, heat it until the material from the previous test has been destroyed and the dame is not coloured. 

If an appreciable amount of residue remains, note its colour. Add a few drops of water and test the solution (or suspension) with htmus or with Universal indicator paper. Then add a httle dilute hydrochloric acid and observe whether efiervesceiice occurs and the residue dissolves. Apply a flame test with a platinum wire on the hydrochloric acid solution to determine the metal present. (In rare cases, it may be necessary to subject a solution of the residue to the methods of qualitative inorganic analysis to identify the metal or metals present.) If the flame test indicates sodium, repeat the ignition of the substance on platinum foil. 

For easy identification and prompt maintenance it is mandatory to segregate all control wires when they are carrying more than one control supply (e.g. at different voltages and both a.c. and d.c.), and run them in separate bunches. The control wires must also be of different colours for different control supplies. The colour codes have been standardized for different control supplies (refer to lEC 60445). 

Rapid purification Check for peroxides (see Chapter 1 and Chapter 2 for test under ethers). Pre-dry with CaCl2 or better over Na wire. Then reflux the pre-dried solvent over Na (1 % w/v) and benzophenone (0.2% w/v) under an inert atmosphere until the blue colour of the benzophenone ketyl radical anion persists. Distil, and store over 4A molecular sieves in the dark. 

Chemical deposition Simple immersion deposits of copper may be obtained on iron and steel in a solution containing, for example, 15 g/1 of copper sulphate and 8 g/1 sulphuric acid, and on zinc-base alloy in a solution containing copper sulphate 300 g/1, tartaric acid 50 g/1 and ammonium hydroxide 30ml/l . Such deposits are thin and porous and are mainly plated for their colour, e.g. for identification, or for their lubricating properties, e.g. in wire drawing. 

Flammable atmospheres can be assessed using portable gas chromatographs or, for selected compounds, by colour indicator tubes. More commonly, use is made of explos-imeters fitted with Pellistors (e.g. platinum wire encased in beads of refractory material). The beads are arranged in a Wheatstone bridge circuit. The flammable gas is oxidized on the heated catalytic element, causing the electrical resistance to alter relative to the reference. Instruments are calibrated for specific compounds in terms of 0—100% of their lower flammable limit. Recalibration or application of correction factors is required for different gases. Points to consider are listed in Table 9.10. 

Lunch came and went, and it was time to return to school. Charlie passed the old house once more, but this time noticed that the lamp post outside had been vandalized and the metal cover over the wires had been broken. Coloured wires were sticking out and looked damaged. He thought this could be a dangerous situation. (E)... 

The brain could be likened to a television set in which the amino acids are providing the basic positive and negative power lines, while the other NTs (the multi-coloured wires) control the colour, contrast and brightness. All are required for a perfect picture but some are obviously more important than others. 

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