Symbols

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HVAC Industry Standards

In order to read and understandan electrical diagram you need toknow how different controls andloads are drawn.

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SYMBOLS

SINGLE POLE SINGLE THROW

SPST

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SYMBOLS

SINGLE POLE SINGLE THROWNORMALLY OPEN

SPST - NO24

SYMBOLS

SINGLE POLE SINGLE THROWNORMALLY CLOSED

SPST - NC25

SYMBOLS

DOUBLE POLE SINGLE THROW

DPST – 2 NO

26

SYMBOLS

SINGLE POLE DOUBLE THROW

SPDT

27

SYMBOLS

DOUBLE POLE DOUBLE THROW

DPDT28

Relays

Normally Closed Contact

Normally Open Contact

Relay Coil

Relays or Contactors

Contactors

R

R

C

C

Contactor Coil29

24v

120vM

L2

c

Relays

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24v

120vM

L2

Small Current

Large Current

c

Relays

31

Relays or ContactorsTHE CONTACTS OF A RELAY OR CONTACTOR ARE DRAWNIN A DE-ENERGIZED CONDITION

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SPST Opens on Rise(Safety Control)

SPST Opens on Drop(Safety Control)

High-PressureSwitch

Low-PressureSwitch

Pressure Switches

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SPST Closes on Rise(Operating Control)

Air PressureSwitch

Fan CyclingPressure Switch

SPST Closes on Drop(Operating Control)

Pressure Switches

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SPST Opens on Rise(Differential)

SPST Closes on Rise(Differential)

DifferentialAir Pressure Switch

DifferentialRefrigerantPressureSwitch

Pressure Switches

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Pressure SwitchesTHE CONTACTS OF A SAFETY CONTROL ARE DRAWN IN THE NORMAL RUNPOSITION, USUALLY CLOSED

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SPST Closes on Drop(Operating Control)

HeatingThermostat

Defrost Thermostat

Return WaterTemperature ControllerCooling Thermostat

SPST Closes on Rise(Operating Control)

Temperature Switches

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SPST Opens on Drop(Safety Control)

SPST Opens on Rise(Safety Control) Discharge Gas

ThermostatOvertemperature

Limit Switch

Freeze Protection Thermostat

Temperature Switches

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SPDT Temperature(Safety or Operating)

Bi-Metal Temperature(Safety)

Low-Water Temperature Cutout Control

Klixonâ

OvertemperatureCutout Control

Temperature Switches

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THE CONTACTS OF AN OPERATING CONTROL ARE DRAWN OPEN, WITH NO CALLFOR COOLING, HEATING

Temperature Switches

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SPST De-HumidistatCloses on Rise

(Operating Control)

SPST HumidistatCloses on Drop

(Operating Control)

Humidity Control

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Time Delay RelayDelays Closing

(Mechanical/Thermal)(Electronic)

Time Delay RelayDelays Opening

(Mechanical/Thermal)(Electronic)

Time Delay

Time Delay Relay(Mechanical)

Time Delay Relay(Thermal)

Time Delay Relay(Electronic)

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Time DelayTHE CONTACTS OF A TIMER ARE DRAWN IN THE

READY-TO-START POSITION OR AT TIME ZEROON A BAR CYCLE DIAGRAM

NOTE: BLACK DENOTES CLOSED CIRCUITS

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Manual Switches

Momentary Push Button

SPST Normally OpenManually Operated

Push Button

SPST Normally ClosedManually Operated

Push Button

SPDT Switch Single-PoleDouble-Throw

Switch44

Flow Switches

SPST Flow SwitchCloses on Rise

(Safety and Operating)

SPST Flow SwitchOpens on Rise

(Safety Control)

Flow Switch

Sail Switch

Thermal DispersionFlow Switches 45

Enthalpy Switches

ElectronicEnthalpy Control

SPDT Enthalpy Control(Operating Control)

MechanicalEnthalpy Control

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Run Capacitor(Marked Terminal)

Start Capacitor

Capacitors

Dual RunCapacitor

StartCapacitor

Run Capacitor

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Fuses

Fuse- Fusible Link

One Time Fuse(Fusible Link)

One TimeFuse

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Transformers

49

NF F

230 VAC

24 VAC

Fused & Non FusedSecondary

Multi Tap Primary

COMM

C575 480 380 230 200

24 VAC

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Dual SecondaryTransformer

Dual SecondaryWith

Center TappedTransformer

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AMPS3.124V

75VAVOLTAGESECONDARY

RATINGVACIRCUITAOFDRAWAMPTOTAL

==

=

Volt AmpsSecondary

Voltage

Transformers

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