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.
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!