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The most common wire gauges used in U.S. residential buildings are 14, 12 and 10.

This bottle was a mere ordinary bottle, with a common cork in its neck, into which a common wire had been inserted.

When all the hooks are down, each call bell is connected between the lower common wire and the tip side of the talking circuit individual to the corresponding station.

The ringing buttons at each station are connected between the tip of the plug at that station and the upper common wire.

Ignoring at first the pilot relay and the pilot lamp, it will be seen that each of the tip-spring anvils of the jacks is connected to a common wire 1 which is grounded.