Page 207 - Engineering drawing from first principles using AutoCAD

200 Engineering drawinq [rom first principles !

terminals marked Land N on the room thermostat cannot be shorted out when heat is not
required. The thermostat is electronic and is operated by relay. Without the neutral
connection the switch will remain open, and when the ambient temperature falls and
heat is required, no click would be heard.
The layout of a line diagram should hopefully enable the reader to follow the sequence of
events like a book.

Construction wiring

The wiring connections for the installation are shown on Fig. 9.13 Since the components
are positioned far from each other, a central terminal is now provided so thatwires for
each component can be run together from an accessible point where electrical opera-
tional checks may be made. The terminal numbers have also been added to the line
diagram so that tracing the wires is reasonably easy.
You will see on Fig. 9.13 that the wires from the white contacts on the valves are
connected to terminals 5 and 16. Signal lamps connected to these terminals and neutral
could indicate whether the valves were open or closed.

In large industrial installations, instrument panels with a wide variety of dials, gauges,
indicator lights and controls are individually designed and constructed.
Copy both of these diagrams so that each of them can be printed on A4 sheets of paper.
You will find that it is a valuable exercise in planning and layout work.