Panel Thermostat Symbol
Definition: The Panel Thermostat symbol represents a temperature-sensing control device mounted inside an electrical enclosure or control panel — used in industrial wiring diagrams to indicate a bimetallic or electronic thermostat that switches a normally-open (NO) or normally-closed (NC) contact when the internal panel temperature reaches the setpoint, with terminals +24V (power), NO, and NC, used to control panel fans, heaters, and alarms per IEC 60947-5-1 switching device standards.
Also known as: enclosure thermostat, cabinet thermostat, panel temperature controller, enclosure temperature switch, panel climate control, bimetallic thermostat.
What the Panel Thermostat symbol means
The Panel Thermostat symbol represents a compact thermostat device mounted on the DIN rail or panel interior wall that monitors the air temperature inside an electrical enclosure. When the measured temperature reaches the configured setpoint, the thermostat switches its output contacts — opening or closing them — to activate cooling fans, heating elements, or alert signals to maintain the panel's internal environment within acceptable component operating limits.
In industrial wiring diagrams, the panel thermostat symbol is drawn with its three terminals visible: the +24V power input and two switching outputs (NO and NC). The NO contact is typically wired to a panel cooling fan circuit (fan runs when temperature exceeds setpoint), and the NC contact may be wired to a heater element (heater runs until temperature rises above setpoint). Panel thermostats protect sensitive electronics from overheating in summer and from condensation in cold environments.
How to identify the Panel Thermostat symbol
The Panel Thermostat symbol is drawn as a rectangular block with three labelled terminals: +24V (power supply input) at the top, NO (normally open contact output) on one side, and NC (normally closed contact output) on the other side. Inside or beside the block, a small thermometer or temperature symbol may indicate its sensing function. In some schematic styles, the thermostat is shown as a temperature-sensitive switch symbol — a switch contact with a temperature actuator — per IEC 60617 conventions for thermally actuated switches.
Function in a circuit
The panel thermostat continuously monitors the enclosure air temperature using a bimetallic strip or NTC/PTC thermistor sensor. When the temperature rises above the high setpoint, the NO contact closes (activating a cooling fan) and/or the NC contact opens (de-activating a heater). When temperature falls below the low setpoint (with hysteresis), the NO contact reopens and/or NC contact recloses. This maintains enclosure temperature within the operating range of installed PLCs, drives, and electronic components — typically 0 °C to 55 °C for standard industrial equipment.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60947-5-1 governs low-voltage control circuit switching devices including thermostats used in panel temperature control. IEC 60529 governs the IP rating of the thermostat housing (typically IP20 for DIN-rail mount, IP54 for panel-door mount). The thermostat's switching contact symbol follows IEC 60617-07 (thermally actuated make/break contact). |
|---|---|
| ANSI/IEEE 315 | ANSI/NEMA 250 governs panel enclosure types, which determine the required thermostat IP/NEMA rating. IEEE 315 represents the temperature switch as a thermally actuated contact with the temperature operating symbol (θ). UL 508A governs industrial control panel construction in North America, requiring appropriate thermostat ratings for panel thermal management. |
| Key difference | IEC and ANSI symbols for panel thermostats differ slightly: IEC 60617 uses a switch contact with a thermal actuator marker (small theta θ or the element symbol); ANSI/IEEE 315 uses a switch contact with a temperature control annotation. Both represent the same function. |
Terminals / pins
| Pin | Name |
|---|---|
| power | +24V |
| no | NO |
| nc | NC |
Typical values
Supply voltage: 24 V DC (typical), 115 V AC or 230 V AC (some models). Switching capacity: 6–16 A at 250 V AC (AC-1 per IEC 60947-5-1). Temperature range: -45 °C to +80 °C (adjustable setpoint). Accuracy: ±2–5 °C. Hysteresis: 3–10 °C (typically fixed). Contact configuration: 1 NO + 1 NC (changeover). IP rating (housing): IP20 (DIN-rail) to IP54 (door-mount). DIN rail: 35 mm TS35.
Where the Panel Thermostat symbol is used
- Cooling fan control: NO contact activates panel fan when enclosure temperature exceeds setpoint (e.g. 40 °C)
- Heater control: NC contact energises anti-condensation heater until panel temperature reaches low setpoint
- Overtemperature alarm: NO contact wired to PLC input or alarm lamp to indicate excessive panel temperature
- VFD enclosure climate control: thermostat maintains VFD ambient temperature within 0–40 °C rated range
- Outdoor telecom cabinet: thermostat controls cooling fan and heater cycle to manage wide ambient temperature swings
- Battery cabinet temperature management: thermostat protects lithium or lead-acid batteries from thermal extremes
Example
In a VFD control panel wiring diagram, a panel thermostat is shown on the DIN rail with its +24V terminal connected to the 24 V DC supply bus, its NO contact wired in series with the positive terminal of a 24 V DC panel fan (fan activates at 40 °C setpoint), and its NC contact wired in series with a 24 V AC anti-condensation heater element (heater runs below 10 °C setpoint), maintaining the VFD ambient temperature within its rated 0–40 °C operating range.
Key facts
- The Panel Thermostat symbol represents a DIN-rail or panel-mounted temperature switch that controls cooling fans, heaters, or alarms to maintain the electrical enclosure internal temperature within component operating limits.
- The panel thermostat has three terminals: +24V (power supply), NO (normally open contact — closes on high temperature), and NC (normally closed contact — opens on high temperature).
- IEC 60947-5-1 governs the switching performance of panel thermostats; typical contact ratings are 6–16 A at 250 V AC (AC-1 category).
- The NO contact is commonly wired to a cooling fan circuit (fan ON above setpoint) and the NC contact to a heater circuit (heater ON below setpoint), allowing a single thermostat to control both heating and cooling for year-round enclosure climate management.
- Typical panel thermostat setpoint range is -45 °C to +80 °C with adjustable setpoint and a hysteresis of 3–10 °C to prevent rapid on/off cycling.
- Panel thermostats are rated to IP20 (DIN-rail mount, IEC 60529) for installation inside standard industrial enclosures; door-mount models are rated to IP54 for direct panel door installation.
- The reference designator for a thermostat in schematics is typically T, TS (temperature switch), or TH per IEEE 315 (e.g. TS1, TH1).
Frequently asked questions
What does the panel thermostat symbol look like?
The panel thermostat symbol is a rectangular block with three labelled terminals: +24V (power input) at the top, NO (normally open output) on one side, and NC (normally closed output) on the other. In IEC 60617 schematics, it may be represented as a thermally actuated switch contact with a temperature actuator marker (θ symbol). Some diagrams include a small thermometer icon inside the block.
What does a panel thermostat do in an electrical enclosure?
A panel thermostat monitors the internal air temperature of an electrical enclosure and switches its NO and NC contacts when the temperature crosses the configured setpoint. Typically the NO contact activates a cooling fan above the setpoint and the NC contact activates a heater below the setpoint. This keeps the panel temperature within the operating range of sensitive components like PLCs, VFDs, and power supplies.
What are the terminal labels on a panel thermostat?
Standard panel thermostats have three terminals: +24V (or AC supply) for power input, NO for the normally-open switching contact (open below setpoint, closes above setpoint), and NC for the normally-closed switching contact (closed below setpoint, opens above setpoint). Some models include a common (COM) terminal used as the shared contact for both NO and NC outputs.
What temperature should a panel thermostat be set to?
For cooling fan activation, panel thermostats are typically set to 35–45 °C — below the maximum ambient operating temperature of the most sensitive component in the panel (often 40–55 °C for industrial PLCs and VFDs). For anti-condensation heater control, the setpoint is typically 5–15 °C to prevent moisture condensation on circuit boards during cold conditions.
What standard covers the panel thermostat?
IEC 60947-5-1 governs low-voltage control circuit switching devices including bimetallic and electronic thermostats used in panel climate control. IEC 60529 governs the IP protection rating of the thermostat housing. In North America, UL 508A governs industrial control panel construction and requires appropriate ratings for panel thermal management devices.
What is the designator for a panel thermostat on a schematic?
The standard reference designator for a thermostat or temperature switch is T, TS, or TH per IEEE 315 conventions. In industrial panel schematics it appears as TS1, TH1, or T1. Some drawings label it specifically as THERM to distinguish it from a timer (T) or transformer (T) designator, depending on the project's designator legend.
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