Grundfos CUE Variable Frequency Drive — Selection & Sizing Guide
How to size and specify a Grundfos CUE pump VFD — the dedicated variable frequency drive built around pump-specific control modes.
The Grundfos CUE is a variable frequency drive built specifically for pumps. Where a generic VFD is a blank motor controller, the CUE arrives with constant-pressure, proportional-pressure, constant-flow, pipe-fill, dry-run-protection and pump-specific commissioning wizards already loaded. It is the right choice for retrofitting fixed-speed CR, CM, MTR and BM pumps to variable-speed control, or for new builds where a separate VFD cabinet is preferred over an integrated E-Pump.
CUE at a Glance
| Property | Range |
|---|---|
| Power range | 0.55 – 250 kW (about 0.75 – 335 HP) |
| Voltage | 1×200–240 V, 3×200–240 V, 3×380–480 V, 3×525–600 V, 3×525–690 V |
| Frequency | 50/60 Hz input, 0–200 Hz output |
| Enclosure | IP20 indoor / IP55 mech-room / IP66 outdoor |
| Built-in control modes | Constant pressure, proportional pressure, constant flow, constant level, constant temperature, open loop |
| Pump protection | Dry-run, motor overload, pipe-fill, low/high pressure, sensorless |
| BMS interface | Modbus, BACnet, PROFIBUS, PROFINET, EtherNet/IP, LON, GRM via CIM |
Five Steps to Specify a CUE
- Read the motor nameplate — record rated kW, voltage and current. The CUE is matched to the motor, not the pump frame.
- Select voltage class — single-phase 200–240 V for residential / small commercial, three-phase 380–480 V for industrial, 525–600 V for North American medium voltage industrial.
- Pick IP rating — IP20 in a clean electrical room, IP55 in a mechanical room with wash-down, IP66 for outdoor or chemical exposure.
- Choose control mode — constant pressure for booster sets, proportional pressure for HVAC primary loops, constant flow for irrigation or process feeds, open loop for retrofit-of-throttle-valve scenarios.
- Add a sensor or two — 4–20 mA pressure transducer for booster control, VFS flow/temperature sensor for constant-flow mode, or run sensorless using the CUE's pump curve.
Worked Example — Replace a 10 HP Throttled CR 5
- Existing: CR 5-15, 7.5 kW motor, 3×460 V, throttle valve controls discharge pressure.
- Bottleneck: pump runs at full speed regardless of demand; throttle valve wastes ~40 % of energy.
- Spec: CUE 7.5 kW 3×380–480 V IP55, constant-pressure mode with a discharge-side RPS pressure sensor at 60 psi setpoint.
- Result: roughly 45 % energy reduction, plus extended pump life from soft-start and reduced cycling.
Specifier tip: If the application has any chance of dead-heading (closed discharge valve), enable the CUE's pipe-fill and high-pressure shut-off functions in addition to dry-run protection. The CUE handles both natively.
CUE vs Generic VFD vs E-Pump
| Criterion | Generic VFD | Grundfos CUE | Grundfos E-Pump |
|---|---|---|---|
| Pump control modes | Build your own | Built in | Built in |
| Dry-run protection | Manual logic | Native | Native |
| Footprint | External cabinet | External cabinet | None (in motor) |
| Motor efficiency | IE3 typical | IE3 typical | IE5 |
| Cost | Lowest | Mid | Highest |
| BMS integration | Variable | CIM plug-in | CIM plug-in |
| Best for | Existing PLC programs | Pump retrofits, BM/CR upgrade | New install with variable demand |
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Frequently Asked Questions
What is the difference between CUE and a generic VFD?A generic VFD is a general-purpose motor drive. The Grundfos CUE is a pump-specific VFD: built-in algorithms for constant pressure, constant flow, proportional pressure, pipe-fill, dry-run protection and sensorless operation that a generic drive does not natively provide.
What size CUE do I need?Match the CUE kW rating to the motor rated power, then check the voltage range (1×200–240, 3×200–240, 3×380–480, 3×525–600 V) and IP rating (IP20 indoor, IP55 wash-down, IP66 outdoor). ForeverPure runs the selection from your motor nameplate.
Does the CUE replace an external pressure controller?Yes. The CUE has on-board PI control for constant pressure or proportional pressure with a single 4–20 mA pressure transducer. No external PLC or PI controller required for typical booster applications.
Is the CUE compatible with Grundfos E-Pumps?E-Pumps (CRE/CRIE/CRNE/CME/MTRE) already have an integrated drive (the MLE/MGE FCC unit). The CUE is for fixed-speed Grundfos pumps (CR/CM/MTR/BM) and for non-Grundfos induction motors.
Can the CUE communicate with a BMS?Yes. Plug a CIM module into the CUE for Modbus RTU, Modbus TCP, BACnet MS/TP, BACnet IP, PROFIBUS DP, PROFINET, EtherNet/IP, LONworks, or Grundfos Remote Management (GRM cellular).
What IP rating should I order?IP20 for indoor electrical rooms with controlled environment. IP55 for mechanical rooms with wash-down or condensation risk. IP66 for outdoor mounting or harsh chemical environments. The CUE comes in all three ratings across the full kW range.