Buyer 's Guide
What is the correct TF Instruments AC Switch For Me ?
Basically, there are two types of electric dryer outlets : 3-prong NEMA 10-30R (pre-1996), or 4-prong 14-30R (after-1996), and two types of switches : Automatic (for two or more electric devices / AC loads), or Manual (for two electric devices / AC loads).
Step #1 : Determine which outlet you need. If your house/property was built before 1996, you most likely need the 3-prong 10-30R. If after 1996, you most likely need the 4-prong 14-30R.
Step #2 : Decide how many EV you plan to charge in one [overnight] charging session. If only one total, choose either the Manual (lower cost) or the Automatic Switch. If you plan to charge two or more EV total, get the Automatic Switch. You can always get the Manual Switch first, then cascade another Automatic Switch later when the 2nd EV is purchased. With the Manual Switch, you have to move the switch while the Automatic Switch does the switching by itself.
Note that the ability to charge more than one EV in one charging session can be especially beneficial to owners of multiple lower-cost EVs with shorter driving range that need frequent charging for daily use.
Automatic Switch Part Numbers : TFI-1xxManual Switch Part Numbers : TFI-2xx
Step #3A : 1. If you choose the Automatic switch, then decide whether you need the AC meter.
The AC meter provides Volt, Amp, Watt measurements (1% accuracy, Japanese technology) on the EV side and thus adds convenience and safety enhancement to the system but it is not required for normal system operation and is not specified to operate below 0 C (32 F).
2. Next, decide whether you need the option S to safely limit the maximum EV charging current to 27A +/- 5%. Note that certain charging units such as Tesla Mobile Units with NEMA 10-30P already limit the charging current to 24A maximum thus they do not need this option.
If your EV is not a Tesla and you do not know the charging current limit of your EVSE Level2 device or if you simply want peace of mind, then do consider getting option S for extra protection.
3. Next, decide the type of receptacles you want : industrial-grade Bryant or Hubbell (brand name, higher cost) or generic type. Note that the industrial-grade receptacles are more sturdy and reliable but cost significantly more than the generic ones.
Automatic Switch Without AC Meter, 3-prong Hubbell outlet : TFI-10H, TFI-10SH
Automatic Switch Without AC Meter, 3-prong generic outlet : TFI-10, TFI-10S
Automatic Switch With AC Meter, 3-prong Bryant outlet : TFI-100B, TFI-100SBAutomatic Switch With AC Meter, 3-prong Hubbell outlet : TFI-100H, TFI-100SH
Automatic Switch With AC Meter, 3-prong generic outlet : TFI-100, TFI-100S
Automatic Switch Without AC Meter, 4-prong Bryant outlet : TFI-14B, TFI-14SBAutomatic Switch Without AC Meter, 4-prong Hubbell outlet : TFI-14H, TFI-14SH
Automatic Switch Without AC Meter, 4-prong generic outlet : TFI-14, TFI-14S
Automatic Switch With AC Meter, 4-prong Bryant outlet : TFI-104B, TFI-104SBAutomatic Switch With AC Meter, 4-prong Hubbell outlet : TFI-104H, TFI-104SH
Automatic Switch With AC Meter, 4-prong generic outlet : TFI-104, TFI-104S
You can find the Automatic Switches here :
Step #3B : If you choose the Manual switch then also decide whether you need the AC meter and the type of receptacles you want : generic, industrial-grade Bryant, or industrial-grade Hubbell, (brand name, higher cost). Note that the generic receptacles are not as sturdy and reliable as the industrial-grade ones.
In below 2 pictures, the rightmost receptacle is the generic type.
Manual Switch Without AC Meter, 3-prong Bryant outlet : TFI-20B
Manual Switch Without AC Meter, 3-prong Hubbell outlet : TFI-20H
Manual Switch With AC Meter, 3-prong generic outlet : TFI-200Manual Switch With AC Meter, 3-prong Bryant outlet : TFI-200B
Manual Switch With AC Meter, 3-prong Hubbell outlet : TFI-200H
Manual Switch Without AC Meter, 4-prong generic outlet : TFI-24Manual Switch Without AC Meter, 4-prong Bryant outlet : TFI-24B
Manual Switch Without AC Meter, 4-prong Hubbell outlet : TFI-24H
Manual Switch With AC Meter, 4-prong generic outlet : TFI-204Manual Switch With AC Meter, 4-prong Bryant outlet : TFI-204B
Manual Switch With AC Meter, 4-prong Hubbell outlet : TFI-204H
You can find the Manual Switches here :
Step 4 - Thermal Considerations :
Due to inherent resistance in the enclosed electronic components and high (24A to 27A) current, there is heat accumulation during operation of all high current AC Switch devices. The generated heat inside the switch box will be higher than the ambient temperature. By contrast, some components, e.g. mechanical switch, display etc., may not work well at low temperature.
Always select the AC switch model that is able to operate safely at the worst-case ambient temperatures. (Note : Ambient temperature is the air temperature where the AC switch is installed which most likely is in the garage).
Ex. : For ambient temperature less than -10C (14F), do not select any product model that has either the manual switch or the AC meter since the mechanical switch and AC meter are not specified to operate below -10C (14F) and 0C (32F) respectively.
Note that among the TFI AC Switches, the TFI-1x Automatic Switch has the lowest worst-case temperature specification (-20C or -4F) while the TFI-2x Manual Switch has the highest worst-case temperature specification (45C or 113F). Contact the factory regarding customization of the TFI-1x for operation to -40C (-40F) or to 50C (122F) in EV mode without thermal interruption.
Be wary of any [high current/power] 240VAC AC switch device that has skimpy safety features or no operating temperature specifications because of potential malfunction and/or fire hazards at high (> 40C or 104F) or low (< 0C or 32F) temperature !