LiftMaster K21-36793 Control Transformer — 208/230/460V, 20VA

The LiftMaster K21-36793 is the 20VA control-transformer service reference listed for documented LiftMaster commercial-door operator electrical boxes with 208/230/460V supply configurations. It belongs to the operator’s control-power circuit and must be selected using the exact model, installed electrical arrangement and transformer label. The multiple listed supply voltages do not mean that the transformer automatically selects a voltage or that replacing it converts the complete operator to another supply. Verify the specified connections and the remaining equipment ratings before ordering.

Compatibility — Models, Versions and Exclusions

Match the Electrical Configuration Before Selecting the Transformer

A commercial operator family can be offered with multiple electrical configurations. Record the complete operator nameplate and transformer label, and inspect the actual wiring diagram inside the equipment. A model name without its supply details is insufficient for selecting a power component. Do not infer the required secondary connections from the 20VA rating or from the voltage used by a nearby accessory.

Have qualified personnel diagnose the incoming supply, control wiring and connected load before replacing the transformer. A shorted circuit or excessive load can remain after a new part is installed. The 20VA rating describes the transformer’s apparent-power capacity; it is not a motor horsepower rating or permission to add arbitrary accessories to the control circuit.

Specifications and Product Identification

Before Ordering

• Record the full model, supply voltage and complete transformer markings.
• Find K21-36793 in the applicable electrical-box parts drawing.
• Confirm the specified primary and secondary connections with the exact diagram.
• Inspect the control load, protective components and wiring for the cause of failure.

Package Contents and Separate Requirements

This offer identifies the control transformer. A logic board, motor, contactor, fuse set, wiring harness and complete electrical box are not promised as included. Confirm the current package for mounting or connection pieces and retain only hardware approved for reuse. Other parts shown in the same electrical-box illustration remain separate service items unless expressly included in the supplier’s offer.

Safety Warnings — Read Before Installation or Service

• WARNING: Commercial-door electrical boxes contain hazardous supply voltage. Transformer diagnosis, connection and replacement require qualified electrical personnel.
• Disconnect and secure all applicable power before service, and secure the door against unexpected movement according to the operator instructions.
• Do not energize an unverified connection, improvise voltage taps or treat the transformer as a whole-operator voltage-conversion kit. Preserve grounding and protective devices.
• Restore covers and verify control operation, travel, reversal and required monitored protection before the door returns to normal use.

Related Products and Important Differences

• CPS-U monitored commercial photo eyes — a separate protection component for approved operators and environments; not supplied with this mechanical accessory.
• TDC12X1BMC MAXUM trolley operator — a complete-operator comparison; verify accessory selection against its own documentation.

Frequently Asked Questions

Does this transformer automatically switch among 208, 230 and 460 volts?

Do not assume automatic selection. Follow the specified connections for the actual supply and transformer label.

Is 20VA a motor power rating?

No. It is the transformer’s apparent-power rating for its specified control-power role.

Can it replace the separately listed 575V transformer?

No interchangeability is established. Use the service reference specified for the equipment’s actual electrical configuration.

Will a new transformer fix a shorted control circuit?

No. The connected circuit and reason for failure must be diagnosed and corrected separately.

Need Help Confirming the Right Product?

Contact Garage-DoorParts.com before ordering. Send the full equipment model, readable part labels and photographs of the installed assembly. Include the dimensions, electrical configuration or accessory details relevant to your project so the listing can be checked against the actual installation.