Liftmaster K21-5230 Transformer, 208/240V, 24VAC, 40VA 21-5230 Commercial Opener
The LiftMaster K21-5230 transformer provides low-voltage control power in select LiftMaster commercial door operators. It is commonly specified as a 208/240V primary transformer with 24VAC output and a 40VA rating. In a compatible operator, the transformer steps incoming line voltage down to the control voltage used by the logic circuit, relays, controls, or accessory circuits depending on the operator design.
Transformer fitment and safety depend on the electrical box design. The primary voltage, secondary voltage, VA rating, terminal layout, mounting, and wiring diagram all need to match. A failed transformer can be caused by age, surge damage, shorted low-voltage wiring, failed accessories, incorrect incoming voltage, or a control circuit problem. If the new transformer fails quickly, the low-voltage circuit should be checked for shorts or overload.
Compatible With
- Select LiftMaster commercial door operators
- Commercial operator electrical boxes that specify K21-5230 or 21-5230
- Applications requiring a 208/240V primary and 24VAC 40VA secondary transformer as listed by the operator diagram
- Not intended for 115V-only transformer applications unless specifically listed by the manufacturer
- Not a universal transformer for every LiftMaster gate or garage opener
Features and Specifications
| Manufacturer | LiftMaster |
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| Product Type | Transformer |
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| Part Number | K21-5230 |
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| Application | Commercial door operator control power |
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| Compatible Operator Type | Select LiftMaster commercial door operators |
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| Input Voltage | 208/240V |
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| Output Voltage | 24VAC |
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| Power Rating | 40VA |
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| Also Known As | 21-5230 |
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Also Known As / Related Part Numbers
Technician Note
If the transformer is burned, open, or repeatedly failing, inspect the low-voltage circuit, accessory wiring, photo eyes, control stations, and board inputs for shorts before installing another transformer.
Before Ordering
- Confirm the operator diagram calls for K21-5230 or 21-5230.
- Verify the primary voltage is 208/240V.
- Verify the secondary output requirement is 24VAC at 40VA.
- Compare terminal layout, wire colors, and mounting location.
- Inspect low-voltage wiring for shorts before energizing the operator.
Important Ordering Warnings
- Do not install this transformer on the wrong input voltage.
- Do not bypass fuses, overloads, or protective devices after transformer failure.
- High-voltage service must be performed by qualified personnel.
Professional Advisory
Transformer replacement inside a commercial operator involves high-voltage wiring and control circuit testing. Disconnect power before replacement and use a qualified technician if voltage testing or wiring repair is required.
Product Questions and Answers
What is the output of K21-5230?
It is commonly listed as a 24VAC, 40VA transformer.
What input voltage is this transformer for?
It is commonly listed for 208/240V input applications.
Is 21-5230 the same related number?
Yes. 21-5230 is the common related number for K21-5230.
Can this replace a 115V transformer?
No, not unless the operator parts diagram specifically calls for this transformer and the input voltage matches.
Why did my transformer fail?
Transformer failure can be caused by surge damage, incorrect input voltage, shorted low-voltage wiring, failed accessories, or a control circuit fault.
