30 November 1998
b. In the ladder diagram, the designer will:
(1) Show a section of the diagram for the HVAC control panel logic.
(2) Show a section of the diagram for each starter control circuit and interlock circuit for HVAC
(3) Label control devices and relays with their unique identifiers.
(4) Label magnetic starter coils.
(5) If multiple control devices of the same type (such as low temperature protection thermostats
or smoke detectors) are required, assign a unique identifier for each and show its contact.
(6) Show separate relays to control ac and dc circuits.
(7) Number the ladder diagram lines according to their control power source.
(8) Show a switch, located in the HVAC control panel, to override the clock (or EMCS) and to be
used to place the control system in continuous occupied mode (auto/auto override).
(9) Show a switch, located in the HVAC control panel, that can be used to shut down HVAC
equipment and interlocked equipment (off/enable).
c. The HVAC control panel section of the ladder diagram will be in accordance with the following
(1) Line numbers will start with 0 for the clock circuit and continue as required.
(2) Control system switches and contacts will be shown on the left of the diagram.
(3) Relay coils will be shown in the center of the diagram, centered below the clock circuit.
(4) Pilot lights will be shown on the right of the diagram.
(5) Contacts available to EMCS will be shown outside the ladder and to the right of the diagram.
d. Each section of the HVAC equipment starter control circuits and interlock circuits will be in
accordance with the following format:
(1) The line numbers of the first section will begin with 100, the second section with 200, and
subsequent sections with appropriate higher numbers in increments of one hundred.
(2) Magnetic starter circuits will show one phase powering a control circuit transformer, switches,
fuse, and overload relays.
(3) The panel ladder diagram will have a jumper shown for connection to EMCS of an economizer
enable and disable function. The panel ladder diagram will show terminal points for remote system
shutdown and remote safety override control of HVAC system fans.
(4) Starter ladder diagrams will have an off-enable switch to allow HVAC system motors to be
stopped from the HVAC control panel.
12. THE TYPICAL EQUIPMENT SCHEDULE.
a. An equipment schedule is required to show the control system parameters not shown on the
schematic and the ladder diagram. Not all HVAC control devices shown on the schematic and the ladder
diagram are included in the equipment schedule because it is not necessary to show parameters for
them. Control devices that are excluded from the schematic are relays, IPs, loop drivers, and signal
selectors. A typical equipment schedule is shown in figure 3-17.
Figure 3-17. Typical equipment schedule.