Electrician's Guide20

The Institution of Electrical Engineers (lEE) has published an 'On-site guide' with the 16th edition of its Regulations, which is intended to enable the electrician to carry out 'certain specified installation work' without further reference to the Regulations. Publicity for this guide before its issue stated 'the electrician is generally not required to perform any calculations'. When printed, this was changed to 'to reduce the need for detailed calculations'.

In the opinion of the Author, this attitude is incorrect. It assumes that behind every electrician there is a designer who will provide him with precise details of exactly what he is to do. This is, of course, what happens in some cases, but totally ignores all those electricians (probably a majority) who are left to work entirely on their own, who have to do their own calculations and make their own decisions. These same electricians are subject to the law, so that a failure to implement the IEE Regulations which leads to an accident, may result (and has resulted) in a prison sentence.

It would be foolish to suppose that this Electrician's Guide could totally replace the complete Regulations, which are made up of over two hundred and fifty A4 pages, together with a total of eight associated 'guides'. Certainly, every electrician who does not have the advantage of expert design advice should equip himself with the complete Regulations and with the associated guides. However, it is the belief of the Author that this Electrician's Guide will help the average electrician to understand, and to implement, these very complicated Regulations in the safest and most cost-effective way possible.

Note on Supply Voltage Level
For many years the supply voltage for single-phase supplies in the UK has been 240V +/- 6%, giving a possible spread of voltage from 226V to 254 V. For three-phase supplies the voltage was 415 V +/- 6%, the spread being from 390 V to 440V. Most continental voltage levels have been 220/380V.

In 1988 an agreement was reached that voltage levels across Europe should be unified at 230V single phase and 400V three-phase with effect from January 1st, 1995. In both cases the tolerance levels have become -6% to +10%, giving a single-phase voltage spread of 216 V to 253 V, with three-phase values between 376V and 440 V. It is proposed that on January 1st, 2003 the tolerance levels will be widened to +/- 10%.

Since the present supply voltages in the UK lie within the acceptable spread of values, Supply Companies are not intending to reduce their voltages in the near future. This is hardly surprising, because such action would immediately reduce the energy used by consumers (and the income of the Companies) by more than 8%.

In view of the fact that there will be no change to the actual voltage applied to installations, it has been decided not to make changes to the calculations in this book. All are based on the 240/415V supply voltages which have applied for many years and will continue so to do.

In due course, it is to be expected that manufacturers will supply appliances rated at 230 V for use in the UK. When they do so, there will be problems. A 230 V linear appliance used on a 240 V supply will take 4.3% more current and will consume almost 9% more energy. A 230 V rated 3 kW immersion heater, for example, will actually provide almost 3.27kw when fed at 240 V. This means that the water will heat a little more quickly and that there is unlikely to be a serious problem other than that the life of the heater may be reduced, the level of reduction being difficult to quantify.

Life reduction is easier to specify in the case of filament lamps. A 230 V rated lamp used at 240 V will achieve only 55% of its rated life (it will fail after about 550 hours instead of the average of 1,000 hours) but will be brighter and will run much hotter, possibly leading to overheating problems in some luminaires. The starting current for large concentrations of discharge lamps will increase dramatically, especially when they are very cold. High pressure sodium and metal halide lamps will show a significant change in colour output when run at higher voltage than their rating, and rechargeable batteries in 230 V rated emergency lighting luminaires will overheat and suffer drastic life reductions when fed at 240V

There could be electrical installation problems here for the future!