LiftMaster 21-5575 575V to 24VAC Commercial Door Operator Transformer
The LiftMaster 21-5575 transformer is a service replacement transformer used in select industrial and commercial door operators wired for 575V incoming power. Its job is to step the high-voltage operator supply down to the 24VAC control voltage used by the operator control circuit, control stations, and low-voltage command wiring. In the field, this is the kind of part a technician checks when a 575V commercial operator has line voltage present but the control circuit is dead, weak, or inconsistent. Correct voltage matters here: LiftMaster commercial operators often use different transformers for 115V, 230V, 460V, and 575V configurations, and the physical operator model alone may not prove which transformer is inside the electrical box. Match the existing transformer label, operator voltage, phase, and wiring diagram before replacing this part.
Common Replacement Reasons
- No 24VAC control voltage at the operator control circuit on a 575V unit.
- Burned, overheated, or open transformer winding in the electrical box.
- Control station and accessory inputs are inactive even though incoming power is present.
- Transformer replacement after confirmed power surge or electrical-box failure.
Compatible With
Used with select LiftMaster and Chamberlain commercial door operators built for 575V service and a 24VAC control circuit. Commonly associated with 575V versions of industrial-duty operator families where the parts diagram calls for 21-5575.
- Select LiftMaster / Chamberlain GH commercial gearhead hoist operators with 575V electrical boxes.
- Select LiftMaster / Chamberlain T trolley commercial door operators with 575V electrical boxes.
- Select LiftMaster / Chamberlain GT gearhead trolley commercial door operators with 575V electrical boxes.
- Select Logic 3, Logic 4, and similar commercial door operator assemblies only when the wiring diagram lists 21-5575.
- Commercial door operators using 575V primary voltage and 24VAC control-voltage transformer placement.
Do not use this part on 115V, 230V, 460V, or residential opener applications unless the parts diagram specifically calls for 21-5575.
Features and Specifications
| Manufacturer | LiftMaster / Chamberlain Group |
| Product Type | Commercial door operator transformer |
| Part Number | 21-5575 |
| Application | 575V commercial door operator electrical box |
| Input Voltage | 575V primary |
| Output Voltage | 24VAC control voltage |
| Compatible Operator Type | Select industrial-duty commercial door operators |
| Notes | Match original transformer and wiring diagram before ordering |
Also Known As / Related Part Numbers
- 21-5575
- K21-5575
- LiftMaster 21-5575
- Chamberlain 21-5575
- 575V transformer
- 24VAC transformer
- 21-5115 - related 115V transformer, not interchangeable
- 21-5230 - related 230V transformer, not interchangeable
- 21-5460 - related 460V transformer, not interchangeable
Technician Note
This is a high-voltage commercial operator component. A failed transformer may be the result of a shorted control circuit, damaged accessory wiring, or incoming power problem, so the cause of failure should be checked before installing the new part.
Before Ordering Checklist
- Confirm the operator is actually a 575V model.
- Match the existing transformer label to 21-5575.
- Compare the wiring diagram inside the operator cover or manual.
- Check for shorted low-voltage wiring before energizing the new transformer.
- Do not substitute a similar transformer from another voltage operator.
Professional Advisory
High-voltage commercial door operator service should be handled by a qualified commercial door technician. Disconnect power and follow the operator wiring diagram; do not bypass control-circuit protection or safety devices.
Product Questions and Answers
What does the 21-5575 transformer do?
It steps 575V operator power down to the 24VAC control voltage used by select LiftMaster and Chamberlain commercial door operators.
Is 21-5575 used on every LiftMaster commercial operator?
No. It is for select 575V operator configurations only. Other voltage versions use different transformer part numbers.
Can I use this on a 460V commercial operator?
No. 460V applications commonly use a different transformer, such as 21-5460, when specified by the parts diagram.
What should I check before replacing the transformer?
Confirm incoming voltage, check for shorted control wiring, and verify the original transformer number against the operator wiring diagram.
Is this a residential garage opener transformer?
No. This is a commercial/industrial door operator transformer for specific high-voltage applications.
