orm.

The reference figures are similar to those in the preceding diagram,
and all conditions are also alike except that a central compensating, or
balancing, conductor, PN, is here introduced. This is technically termed
the "neutral" wire, and in the discharge of its functions lies the
solution of the problem of economical distribution. Theoretically, a
three-wire installation is evenly balanced by wiring for an equal number
of lamps on both sides. If all these lamps were always lighted, burned,
and extinguished simultaneously the central conductor would, in fact,
remain neutral, as there would be no current passing through it, except
from lamp to lamp. In practice, however, no such perfect conditions can
obtain, hence the necessity of the provision for balancing in order to
maintain the principle of independent control of each unit.

It will be apparent that the arrangement shown in Fig. 2 comprises
practically two circuits combined in one system, in which the central
conductor, PN, in case of emergency, serves in two capacities--namely,
as negative to generator G<1S> or as positive to generator G<2S>,
although normally neutral. There are two sides to the system, the
positive side being represented by the conductors P and PN, and the
negative side by the conductors PN and N. Each side, if considered
separately, has a potential of about 110 volts, yet the potential of the
two outside conductors, P and N, is 220 volts. The lamps are 110 volts.

In practical use the operation of the system is as follows: If all the
lamps were lighted the current would flow along P and through each pair
of lamps to N, and so back to the source of energy. In this case the
balance is preserved and the central wire remains neutral, as no return
current flows through it to the source of energy. But let us suppose
that one lamp on the positive side is extinguished. None of the other
lamps is affected thereby, but the system is immediately thrown out of
balance, and on the positive side there is an excess of current to this
extent which flows along or through the central conductor and returns to
the generator, the central conductor thus becoming the negative of that
side of the system for the time being. If the lamp extinguished had been
one of those on the negative side of the system results of a similar
nature would obtain, except that the central conductor would for the
time being become the positive of that side, and the excess of current