Wiring for Transfer Switch & Generator Installations

One of the most common questions we hear from electrical contractors at Wolter is:

“What wires do I need to run between the generator and transfer switch?”

You’ve likely been on jobs where wiring details weren’t clear until late in the project—costing time, coordination, and sometimes, callbacks. This outlines the most required control wires and cable types so you can plan, install efficiently, and ensure code compliance from day one of your generator installation.

Transfer Switch to Generator: Control Wiring
For most automatic transfer switch (ATS) installations, you’ll need 7 control wires between the ATS and the generator:

• (2) Start Wires – These wires tell the generator when to start running.
• (3) Position Feedback Wires – These provide feedback to let you know whether the ATS is in utility, off, or generator mode.
• (2) DC Power Wires – These supply control power to and from the ATS.

Tip: Always confirm voltage specs & terminal assignments with Generac’s wiring diagram.

Remote Annunciator Cabling

When a remote annunciator panel is part of the installation (common in commercial applications or NFPA 110 setups), the recommended cable is:

• (2) #14 AWG stranded wires
• (1) 18/2 shielded stranded cable – Belden 3105A is a commonly used reference here.

Shielded cable is critical to avoid signal interference, especially when long cable runs are involved or the wire is routed near power circuits.

Remote Emergency Stop (E-Stop) Wiring

If the system includes a remote E-Stop (per NEC or customer request), the wire count will depend on the generator’s size:

•  <100kW units: Run (6) #12 AWG stranded wires
•  >100kW units: Run (4) #12 AWG stranded wires

E-Stops should be tested during commissioning to ensure safe shutdown across all locations.

Always Verify with the Manufacturer and AHJ

While this information reflects industry norms, you should always:

• Reference the generator and ATS manufacturer’s installation manual
• Verify requirements with your local Authority Having Jurisdiction (AHJ)
• Account for site-specific factors like distance, conduit fill, and grounding requirements

Need Help or Have a Complex Site-Specific Scenario?

If you’re working on a complex installation or need to verify compatibility with a Generac generator model, Wolter is here to assist. We’ll help you select the correct wire types and routing strategies to streamline installation and ensure compliance.

Get a quick, easy-to-follow guide on wiring for transfer switch and generator installation. Download our Flyer today and ensure your business keeps running smoothly!