In stock items ship same day if ordered online before 12 EST

In stock items ship same day if ordered online before 12 EST


A Custom Manual Transfer Switch For Any Panel Any Amperage

Here at the Original Interlock Kit we understand better than anyone else that shopping for the perfect transfer switch can be hard. We make it easy, our expert team of kit designers will work with you step by step to create the perfect transfer switch for any electrical panel!

Custom kits are exclusively manufactured to prevent dangerous back-feeding scenarios in the following scenarios:

  • Solar: A main breaker and Solar breaker would need to be blocked while the generator breaker is on and vice versa.
  • Commercial: A main breaker larger than 225 amps.
  • Industrial:
  • Residential: older/obsolete residential panels (amperages 225 & below)


Residential/Commercial- Square D 400 amp panel: SU3040D400CB 🡢 compatible with K-3358: $250.00

To learn more about custom manual transfer switches, call or contact us today.


8 “gap between MAIN & generator breakers for custom Interlock Kits

Main Breaker On

Generator Breaker On


For this Square D 400 amp panel, Interlock Kit created the K-3358. This Interlock Kit successfully keeps the main breaker OFF while the generator breaker is ON and vice versa.

One of our Custom Interlock Kit designers will be assisting you throughout the process

Start by emailing a photo over to one of us. We will get right back to you with a dimensions form.

The dimensions form will be our way of determining a functional kit design specifically for your panel. It will also serve as a way for us to check our inventory to see if a design was already made for the panel!

Once we have your dimensions sheet expect a 2-3 week lead time to design, construct, & deliver your Interlock kit

How is pricing structured for custom Interlock Kits?

  • Pricing will fluctuate based on the amount of material used when building the Interlock Kit.
  • Another factor will be the complexity of the design or the amount of time needed to go into designing the perfect manual transfer switch for your panel!

Panels larger than 225 amps that we have worked with before: $250.00 + shipping

Panels 225-400 amps that we have NOT worked with before: $350.00-$450.00

Panels 400-600 amps that we have NOT worked with before: $450.00-$600.00

Panels larger than 600 amps that we have NOT worked with before: $600.00+