What is the T1 fuse in my transfer switch?

The T1 circuit in Generac automatic transfer switches provides 120VAC power to keep the generator’s battery charged. In single-phase models, this circuit includes a fused T1 connection located inside the ATS and should only be serviced by trained personnel. Three-phase transfer switches do not have a T1 fuse and instead require a dedicated 120VAC protected circuit from the main panel.

  • Apr 22, 2026
  • Knowledge

Title
What is the T1 fuse in my transfer switch?
URL Name
Where-Is-the-T1-Fuse-on-My-Home-Standby-Control-Panel

Public Answer

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. 


T1 – Battery Charge Circuit (120VAC)

The T1 fuse is part of a circuit that originates in the automatic transfer switch (ATS) and powers the battery charger in the generator. The voltage for the T1 circuit originates in the transfer switch. If battery charging errors frequently appear, or if generator battery keeps dying, the T1 wire or T1 fuse should be inspected by an authorized service dealer: How Can I Find a Generac Service Dealer in My Area? This circuit must be connected to keep the battery charged whether the generator is running or not. 

The T1 fuse is located in the ATS, which should never be accessed by untrained or unauthorized individuals. The specific location, fuse size, and orientation may vary based on the transfer switch model. 
 

DANGER: Generac does NOT recommend untrained end users attempt to service fuses in transfer switches. The T1 fuse is always live with 120v, even when the generator is not running. To locate an authorized service dealer, see the How Can I Find a Generac Service Dealer in My Area? article.

Environment

This article applies to single-phase and three-phase automatic transfer switches.

  • If you have a single-phase transfer switch, see here.
  • If you have a three-phase transfer switch, see here.

Note: The vast majority of residential ATS' are single phase. To find out what transfer switch you have, enter the model number or serial number on the Generac.com product lookup page.

 

Single-phase transfer switches

This image shows the location of a T1 fuse in an ATS with an integrated SACM board. Transfer switch user manuals can be found on Generac.com.

Note: Next Generation automatic transfer switches may have a Fuse Control Module (FCM) installed instead of a SACM. See the owner's manual for additional information. 

 
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Three-phase transfer switches

Certain three-phase automatic transfer switches do not have a T1 fuse. Three-phase transfer switches without a T1/fused connection must utilize a dedicated 120VAC protected circuit from the panel board to power the battery charging circuit. (15/20 amp circuit)

To find more information on the three-phase ATS' battery charging circuit for your specific model, enter the model number or serial number of the ATS on the Generac.com product lookup page.

Implications for three-phase transfer switch installations

Three-phase transfer switches need to have a T1 up-fit kit added to the switch during installation. The kit should be installed by a Generac authorized service dealer or qualified electrician. See here to find a Generac dealer in your area.


See Also

 
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