3-Phase Plug (CEE / Industrial) Symbol
Definition: The 3-Phase Plug (CEE / Industrial) symbol represents an industrial polyphase electrical connector—drawn as a circle or plug-face diagram with four or five contact positions labelled L1, L2, L3, PE/Earth, and optionally N—standardised under IEC 60309 (CEE 17) for safe, keyed, colour-coded connection of three-phase power at voltages up to 500 V AC and currents up to 125 A.
Also known as: CEE plug, IEC 60309 plug, industrial plug, 3-phase commando plug, 3-phase connector, CEE 17 plug, three-phase plug.
What the 3-Phase Plug (CEE / Industrial) symbol means
The 3-Phase Plug (CEE / Industrial) symbol denotes a heavy-duty, weatherproof, keyed electrical plug used to connect three-phase machinery, generators, and portable equipment to a three-phase supply. The CEE (Commission on the Rules for the Approval of Electrical Equipment) design is standardised in IEC 60309, making plugs and sockets internationally interchangeable regardless of manufacturer.
In electrical wiring and installation diagrams, the plug symbol shows the four or five contact positions with their terminal labels: L1 (first phase), L2 (second phase), L3 (third phase), PE (protective earth/ground), and N (neutral, present in 5-pin variants). The symbol also conveys, through its position keying angle and colour coding, the voltage class: red = 400 V (most common for three-phase industrial), blue = 200–250 V single-phase, and yellow = 100–130 V.
How to identify the 3-Phase Plug (CEE / Industrial) symbol
The three-phase plug symbol is drawn as a circle (representing the plug face) with four or five smaller circles or dots arranged around the interior at specific clock positions representing the individual contacts. The contacts are labelled L1 (at approximately the 12 o'clock or keyed position), L2, L3, PE (earth, typically at the keyway position at 6 o'clock for 400 V types), and N (for 5-pin versions). The overall circle may be filled or have an arc indicating the plug body. IEC 60309 mandates a colour coding: the plastic body of the plug is red for 380–415 V 3-phase, blue for 200–250 V, and yellow for 100–130 V.
Function in a circuit
The IEC 60309 three-phase plug provides a safe, polarised, and mechanically keyed connection between a portable three-phase load (motor, welding machine, generator, portable tool) and a fixed power outlet (socket). The keying mechanism (a raised rib on the plug face at the earth-pin position) ensures the plug can only be inserted at the correct angular orientation, preventing wrong-voltage connection. The protective earth (PE) pin is the longest, making first contact on insertion and last to break on removal, ensuring the equipment chassis is always earthed. The locking collar prevents accidental disconnection under vibration.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60309-1 and IEC 60309-2 specify CEE industrial plugs and socket-outlets for industrial use (formerly called CEE 17). IEC 60309-1 covers general requirements; IEC 60309-2 covers dimensional requirements for interchangeability. The standard defines current ratings (16 A, 32 A, 63 A, 125 A), voltage classes, pin configurations, and colour codes. The schematic symbol follows IEC 60617 conventions for connectors. |
|---|---|
| ANSI/IEEE 315 | In North America, the equivalent for three-phase industrial connectors is NEMA locking plug standards (e.g. NEMA L15-30 for 3-phase 250 V, NEMA L21-30 for 3-phase 120/208 V). IEC 60309 plugs (CEE) are also used in North America for industrial and entertainment industry applications. ANSI/IEEE 315 defines the general connector schematic symbol. |
| Key difference | IEC 60309 (CEE) plugs are used globally and are physically interchangeable across manufacturers. NEMA locking connectors are standard in North American electrical installations. CEE plugs use a round body with angular keying; NEMA locking connectors use a twist-lock mechanism with blades. In schematics, both are shown as circle/plug symbols with labelled pins, but CEE symbols show L1/L2/L3/PE while NEMA symbols may show X/Y/Z/W/G. |
Terminals / pins
| Pin | Name |
|---|---|
| l1 | L1 |
| l2 | L2 |
| l3 | L3 |
| pe | PE/Earth |
Typical values
Standard current ratings: 16 A, 32 A, 63 A, 125 A. Voltage ratings: 100–130 V (yellow), 200–250 V (blue), 380–415 V (red), 500 V (black). Pin configurations: 3-pin (3P: L1, L2, L3), 4-pin (3P+E: L1, L2, L3, PE), 5-pin (3P+N+E: L1, L2, L3, N, PE). IP rating: IP44 minimum, IP67 available for wet environments.
Where the 3-Phase Plug (CEE / Industrial) symbol is used
- Industrial machinery connections — CNC machines, injection moulding equipment, and compressors connected to plant 400 V three-phase supply via 32 A or 63 A CEE plugs
- Construction sites and outdoor events — temporary power distribution using CEE 16 A or 32 A plugs from spider-box distribution units
- Generator connections — portable generators with CEE outlets for connecting to site distribution boards
- Stage and entertainment industry — 63 A and 125 A CEE plugs powering lighting rigs, sound systems, and stage machinery
- Electric vehicle (EV) charging infrastructure — IEC 60309 plugs used in some non-domestic EV charging points (industrial installations)
- Marine and caravan hookups — 16 A blue single-phase CEE connectors for shore power; red three-phase for larger vessels
Example
In a construction-site temporary-power wiring diagram, a 400 V three-phase spider-box distribution unit shows its three-phase input as a red 63 A IEC 60309 plug symbol with terminals L1, L2, L3, and PE; six output sockets are shown as 32 A red CEE socket symbols (4-pin, L1/L2/L3/PE), each protected by a 32 A MCB, supplying portable tools and site lighting.
Key facts
- The 3-Phase Plug (CEE / Industrial) symbol is drawn as a circle with four or five internal contact positions labelled L1, L2, L3, PE (and N for 5-pin variants), following IEC 60309 terminal conventions.
- IEC 60309 (CEE 17) mandates colour coding by voltage: red body = 380–415 V three-phase (most common industrial), blue = 200–250 V single-phase, yellow = 100–130 V.
- The plug is mechanically keyed by an angular offset (the 'h' position, e.g. 6h = 0–50 V, 9h = 380–415 V) that physically prevents cross-voltage connection between incompatible outlets.
- The PE (Protective Earth) pin is the longest pin in a CEE connector, ensuring the equipment chassis is earthed before L1, L2, and L3 make contact on insertion.
- Standard current ratings under IEC 60309 are 16 A, 32 A, 63 A, and 125 A; the plug body size increases with current rating, preventing a lower-rated plug from fitting a higher-rated socket.
- A 3P+E (4-pin) CEE plug supplies three-phase power without neutral, suitable for balanced three-phase motor loads; a 3P+N+E (5-pin) plug adds the neutral conductor for three-phase systems supplying single-phase loads.
- The minimum IP (Ingress Protection) rating for IEC 60309 plugs is IP44 (protected against solid objects >1 mm and water splashing); IP67-rated versions are available for submersible or high-pressure wash-down environments.
- North American NEMA locking connectors serve the equivalent purpose to CEE plugs but use a different physical form (blade-based twist-lock) and are not physically interchangeable with IEC 60309 devices.
Frequently asked questions
What does the 3-phase plug symbol look like in a wiring diagram?
The 3-phase plug (CEE/industrial) symbol is drawn as a circle representing the plug face, with four or five smaller circles or dots inside representing the individual contacts, labelled L1, L2, L3, PE (and N for 5-pin versions). The circle may have an arc or filled segment indicating the keying direction. Red colouring or a 'red' label indicates a 400 V three-phase plug under IEC 60309 colour conventions.
What standard governs industrial 3-phase plugs (CEE plugs)?
IEC 60309-1 and IEC 60309-2 govern the design, dimensions, and requirements of industrial CEE plugs and socket-outlets (formerly CEE 17). These are the globally recognised standards for industrial electrical connectors. In North America, the equivalent connectors follow NEMA locking connector standards, which are different in physical form.
What is the difference between a 4-pin and 5-pin CEE 3-phase plug?
A 4-pin CEE plug (3P+E) carries three phase conductors (L1, L2, L3) plus a protective earth (PE), without a neutral — suitable for balanced three-phase motor loads. A 5-pin CEE plug (3P+N+E) adds a neutral conductor (N), making it suitable for three-phase systems that also supply single-phase loads (such as a combination of 230 V lighting and 400 V machinery on a 400/230 V TN system).
What do the colours of IEC 60309 plugs mean?
IEC 60309 mandates specific body colours by voltage class: yellow = 100–130 V, blue = 200–250 V (single-phase, most common for domestic-style CEE connectors), red = 380–415 V three-phase (the standard industrial colour for 400 V three-phase), and black = 440–500 V. The colour coding allows quick visual identification of the voltage class without reading markings.
What is the PE pin on a 3-phase plug?
PE stands for Protective Earth (also called Safety Earth or Ground). On a CEE plug, the PE pin is deliberately made longer than the L1, L2, L3, and N pins so that it makes contact first when the plug is inserted and breaks contact last when it is withdrawn. This ensures that the equipment chassis is always connected to earth before any live voltage is applied, preventing electric shock if a fault develops.
What current ratings are available for IEC 60309 (CEE) three-phase plugs?
IEC 60309 defines four standard current ratings for three-phase plugs: 16 A, 32 A, 63 A, and 125 A. Each rating has a physically larger body diameter, so a 16 A plug cannot be inserted into a 32 A socket, preventing overloading of smaller connectors. For most industrial machinery and construction-site use, 16 A and 32 A plugs are the most common.
Can a CEE (IEC 60309) plug be used in North America?
CEE (IEC 60309) plugs are physically different from NEMA locking connectors used as standard in North America and are not interchangeable. However, IEC 60309 connectors are widely used in North American industrial, film/entertainment, and temporary power applications alongside NEMA connectors. Adapters between CEE and NEMA are available but must be rated for the appropriate voltage and current.
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