EC-SWAP · schematic diagram

Retrofit of a two-speed fan: the existing control is retained. Five conductors and the protective earth arrive on the board, six with the optional voltage monitor; the board supplies and controls the EC motor. Two views: the circuit diagram and the installation overview. Reference diagram, revision v3.0 · complete diagram in seven sheets, of which sheets 4 and 5 are shown below.

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EC-SWAP wiring diagram, example with one fan, sheets 4 (control panel) and 5 (module and motor) — Wiring example with one EC fan: sheet 4, the control panel; sheet 5, the module and the motor. The five other sheets of the complete diagram are in the PDF to download. Open the sheet full size Download the complete diagram PDF · 320 kB · 4 Oct 2026 EC-SWAP wiring diagram, example with one fan, sheets 4 and 5. Sheet 4, inside the control panel: the L1, L2, L3 and PE supply from the 400 VAC distribution runs through circuit breaker -Q1, rated 16 A at most; contactors -KM1 (low speed) and -KM2 (high speed) are retained, the undervoltage monitor -A1 Schneider RM22TU23, optional, provides the fan fault contact; conductors U1, V1, W1, U2, V2, W2 and PE run to the module. Sheet 5, outside the panel: they arrive on the inputs of module -U1 EC-SWAP, whose LOW and HIGH potentiometers set the low and high speeds; on the output side, terminal block L1·L2·L2·L3·L3·PE·PE supplies the Ziehl-Abegg GR31C-ZIK.DC.CR EC motor -M1 on L1·L2·L3·PE, and terminals 24V, GND, D1, E1, CO and NC go to its control terminal block for enable, speed setpoint and fault contact; the enclosure dimensions and a photo of the board complete the sheet

Tags

Tag	Description	Note
Circuit breaker	Three-pole motor protection switch (existing)	The thermal setting must be adjusted to the EC motor current, which is lower than that of the induction motor.
PV	Low-speed contactor (existing)	Only one pole connected: it switches L3 onto W1.
GV	High-speed contactor (existing)	Only one pole connected: it switches L1 onto U2.
U1 · V1 · W2	EC-SWAP inputs	Connected to L1, L2 and L3 downstream of the circuit breaker: permanently energised.
Voltage monitor	Option, inside the cabinet	Monitors the voltages and provides the “fan fault” contact. The only fault signal source on the cabinet side.
EC-SWAP	Wellset interface board	Inputs U1·V1·W1 / U2·V2·W2 + PE · output L1·L2·L2·L3·L3·PE·PE · control 24V · GND · D1 · E1 · fault contact CO · NC.
LOW / HIGH	Setpoint potentiometers	LOW sets the low speed (PV), HIGH the high speed (GV), from 0 to 100 %. Marked LOW and HIGH on the board, PV and GV on the diagram.
EC fan	Ziehl-Abegg EC motor, M 3~	Supply 3 × 400 V – 16 A on L1·L2·L3·PE. Control is picked up on its terminal block 24V · GND · D1 · E1 · 11 · 12: 24V, GND, D1 and E1 go to the terminals of the same designation on the EC-SWAP, 11 and 12 to the CO and NC terminals of the fault contact. One EC-SWAP module per air stream.

Notes and points to confirm

A dual-flow air handling unit requires two EC-SWAP modules, one per fan, mounted as close as possible to the motor. The circuit diagram applies to one fan.
EC motor supply: 3 × 400 V – 16 A on L1·L2·L3·PE. The board also distributes the 24 V DC, the speed setpoint and the fault signal, on the motor's control terminal block.
Output terminal block of the board: seven terminals, L1·L2·L2·L3·L3·PE·PE; L2, L3 and PE are doubled for connecting a 400 V transformer. Check the marking on the board before wiring.
Contacts shown de-energised. Coils and control of the PV and GV contactors: existing, not shown.
Interlocking of PV / GV is mandatory: the two contactors must never be closed at the same time.
Speed setpoint: LOW for the low speed (PV), HIGH for the high speed (GV), adjustable from 0 to 100 % on the board.
Fault signalling on the CO and NC terminals of the board, volt-free contact. NC, normally closed, also detects loss of supply.
Voltage monitor as an option inside the cabinet: it provides the “fan fault” contact and does not replace the board's own fault signal.
Variant not shown: control via volt-free contacts DI1 / DI2, PLC connector and MODE jumpers on the board.
Replaceable fuses on the board: read the rating and breaking capacity before replacement.
Upstream type B residual current device if residual current protection is required, because of the DC leakage current of the EC motor.
PE runs through, never interrupted and never fused. Wait for the motor capacitors to discharge before any intervention.

Schematic diagram. To be validated against the EC-SWAP documentation, the EC motor instructions and the installation rules (NIBT / SN 411000) before execution. Back to the EC-SWAP part page.