About Us

Our journey started when one of us, just like you, purchased an electric vehicle and needed to charge it at home. The house already had an 240VAC, 30A outlet that was used for an electric dryer. To safely add another 240VAC, 30A (or higher amperage) outlet for an EVSE (EV supply equipment) Level2 necessitated the upgrade of the 100A electric circuit-breaker panel which could cost several thousand dollars.

You can find the Electric Panel Upgrade Cost here :

    Electric Panel Upgrade Cost

Using many years of experience in designing high-reliability electronics, we built a line of EV-Switch tm 240VAC Switch Products that can time-share the existing 240VAC outlet and thus eliminated the need for such costly upgrade.


TF Instruments 's mission is to provide the best-in-class 240V AC Switch Products that can safely time-share an existing 240VAC outlet for 2 or more electric devices / AC loads.

We offer a complete line of smart design and quality AC switch products.

TF Instruments understands the paramount importance of safety --for both the users and their properties-- so we use robust components and build safety and reliability into our products to minimize any risk to the users and their properties whereas some/most of our competition chooses low-cost parts and does not put as much effort into reliability and safety issues. We also provide product details so the user can know all about their specifications, safety features and operating conditions before making the decision to buy. This way, the user can avoid the trial-and-error/buy-first-then-find-out-later buying experience that can be quite frustrating. 

In a high current 240VAC application such as this AC Switch product, the lack of safety precautions may lead to fire hazards.


Our flagship product (EV-Switch/TFI-1xx) employs a fast microcomputer and solid-state electronics to constantly monitor the AC input at the higher priority side/port then swiftly, safely and automatically switch off the electric device / AC load on the lower priority side/port whenever the higher priority side is active.

To safeguard against hazard and failure conditions, we put in many safety features which minimize risks to both the user and their property :

    i. fast AC switching to preclude overlapping currents.

    ii. diagnostic LED to indicate normal operation (or not).

    iii. thermal shut-down in case of over-heating during EV charging ; automatic recovery after ~60 minutes.

    iv. safety shut-down when EV charging current exceeds ~27A (90% of outlet 30A rating) ; automatic recovery after ~2 minutes.

    v. fuse to protect against short-circuit in AC meter (if used).

The result is a safe and reliable AC switch using proven and quality USA and Japanese technologies that fits in an attractive and compact ABS or polycarbonate plastic box.

In addition, the patented (patents)design process also allows the product customization to support operating temp >50C (122F) at 24A load. Please contact us about the customized products.

You can find the details of our AC switches here :

    Automatic AC Switch User Guide

    Manual AC Switch User Guide

All our products are made in the USA. Our office is in Orange County, CA.

There are several models (automatic, manual, 3-prong for pre-1996 outlets, 4-prong for after-1996 outlets) for every budget and user 's preference.

Please browse through to select the switch that fits your need the most. Click on this link for Buyer's Guide.

Here are examples of the very simple set-ups : TF Instruments AC Switch Set-up Examples.

Since a portion of our income/profit goes to various worthy causes, your purchase helps in the efforts to make our world a little better.

Thank you for visiting our website.