Read the manual thoroughly and understand all of the instructions, cautions, and warnings before using this equipment. If any section of the manual is not understood, contact your nearest authorized dealer, or contact Generac Customer Service at 1-888-436-3722 (1-888-GENERAC), or www.generac.com with any questions or concerns. 

Main line circuit breaker (MLCB)

Most Generac air cooled and liquid cooled home standby generators feature a 2-pole main line circuit breaker (MLCB), also known as a generator disconnect. This article explains the most important things to know about the MLCB including its purpose, real-life applications, and safety considerations.

 

Environment

This article applies to air-cooled and some liquid-cooled generators.

Note: 3-phase XG liquid-cooled models do NOT include the MLCB on the generator. Single-phase XG liquid-cooled generators do have the MLCB. All RG liquid-cooled models also include an MLCB.

MLCB Location

Depending on the age and model of the home standby generator, the location of the MLCB may vary:

Next Generation Air-Cooled Standby Series generators (2025-Present)

For Next Generation Series 10-28 kW air-cooled standby generators, the MLCB is located under the lid in the upper right-hand corner.

 

10 kW-26 kW Guardian Series Air Cooled Home Standby Generators (2016-present)

For 10 kW-26 kW Guardian Series air cooled home standby generators manufactured from late 2016-present, the MLCB is located under the lid:

 

 

Air Cooled Home Standby Generators (2016 and earlier)

For air cooled home standby generators manufactured prior to October 2016, the MLCB is located inside a compartment on the generator's side panel:

  

 

Liquid Cooled Generators

Applicable models

• 3-phase XG liquid-cooled models do NOT include the MLCB on the generator.
• Single-phase XG liquid-cooled generators do have the MLCB.
• All RG liquid-cooled models also include the MLCB.

For applicable liquid cooled generators, the MLCB (A) is located inside the viewing window (B) on the generator's side panel. 

Note: Due to large variation in size and models, the exact location of the MLCB may vary. Consult your owner's manual for specifics.

 

Purpose of the MLCB

The MLCB is a circuit breaker, usually located inside the generator, similar to those found in a home's electrical panel. If there is too much electrical load on the generator, the MLCB trip, and interrupt the electrical current to prevent damage or overload to the generator. The amperage of the MLCB varies based on the size, or power rating, of the generator. Consult the generator owner's manual or spec sheet for details: Where can I find a user manual or other documentation for my home standby generator?

If the MLCB is set to OFF, the flow of electricity stops. The circuit is open.

If the MLCB is set to ON, the flow of electricity is live. The circuit is closed.

If desired, the MLCB (A) can be locked in the OFF position for safety when the generator is being serviced, or if not in use for a period of time.

To do this, turn the MLCB to OFF, and use an appropriately sized padlock (not included) with a shackle long enough to pass through both lock tabs (B).

 

Note: Do NOT leave the generator MLCB locked in the OFF position during normal generator operation. Leaving the MLCB in the OFF position will prevent the generator from powering the home in the event of a power outage.

Applications & safety related to the MLCB

In general, whenever maintenance (such as an oil change) is being performed on the generator, or if the generator is being shut down during an outage:

• The generator should be set to OFF.
• The MLCB should be set to OFF. 
• The 7.5-amp fuse should be removed.

An example of a procedure that requires the MLCB to be turned OFF is when powering down a home standby generator under load: How Do I Shut Down My Generator When It’s Powering My House (During an Outage)?