The insulators are planted on creosoted oak arms, 21 in.
In diameter, charged to a negative potential of at least 2000 volts, is supported between insulators in the open, usually at a height of about 2 metres.
The advantage of the high conducting power which copper possesses Over- is of especial value in moist climates (like that of the United Kingdom), since the effect of leakage over the surface of the damp insulators is much less noticeable when the conducting power of the wire is high than when it is low, especially when the line is a long one.
Under the action of the same or identical electric forces the intensity of this state in various insulators is determined by a quality of them called their dielectric constant, specific inductive capacity or inductivity.
The climatic conditions in the British Islands are such that it is not possible to maintain, in unfavourable weather, a higher standard than that named, which is the insulation obtained when all the insulators are in perfect condition and only the normal leakage, due to moisture, is present.