FAQ
Frequently Asked Questions :
Q1A. What is "Load Time-sharing a 240VAC Outlet" and how is it done ?
A1A. It is basically to use the same existing 240VAC outlet for more than one electric device / AC load. It can be done safely by using the automatic TFI-1xx or the manual TFI-2xx AC Switch to select an electric device / AC load for use one at a time. With the TFI-2xx AC Switch, the user needs to manually move a switch while the TFI-1xx employs a fast microcomputer and solid-state electronics to constantly monitor the AC input at the higher priority (dryer) side then swiftly, safely and automatically switches off the electric device / AC load at the lower priority (EV) side whenever the dryer side is active. This precludes any chance of an overload condition and/or a fire hazard. After the dryer side is inactive for more than two minutes, the EV side is automatically re-connected to the 240VAC source for EV charging task.
Click here TFI AC Switch Set-up Examples for set-up examples.
Since the electric dryer is typically used for only 2 to 6 hours per week, the 240VAC outlet can, through time-sharing, be used for electric vehicle (EV) charging or any other work during the remaining hours of the week.
Safety note: Time-sharing of 240VAC outlet is completely safe. On the other hand, "splitting" an outlet, i.e., using the same 240VAC outlet for two high current/power AC loads at the same time is NOT safe since it may lead to an overload condition and a fire hazard.
Q1B. What are the benefits of time-sharing a 240VAC outlet ?
A1B. After a homeowner buys one or more electric vehicle(s), they need to find a way to charge it/them at home during the hours when the utility rates are most favorable. Depending on the size of their house, their current electric usage and the electric panel (60A or 100A) of the house, the homeowner with an existing 240VAC that is already used for an electric dryer may have to upgrade the electric panel to safely add another 240VAC outlet to support an EVSE (EV supply equipment) Level2 for the additional EV charging need. Such upgrade tends to be costly and averages a few thousand dollars in USA markets. Click link for Electric Panel Upgrade Cost.
Time-sharing an existing 240VAC by using TFI AC switches can safely eliminate this upgrade cost entirely (when the existing 240VAC outlet is already used for an electric dryer) or minimize it by allowing the homeowner to only upgrade minimally (for example, a house with a gas dryer and no existing 240VAC outlet can just add one 240VAC outlet at minimal cost), then use the 240VAC outlet time-sharing approach to charge several electric vehicles in one session.
Note that load time-sharing between an electric dryer and one EVSE / EV charger is the exactly the same as load time-sharing between two EVSE / EV chargers.
The savings are more substantial when there are two or more electric vehicles to charge since the upgrade cost depends on the capacity of the new electric panel. Higher capacity electric panel to support several EVs costs significantly more.
In summary, load time-sharing the 240VAC outlet offers a simple, safe, and economical way to fill the EV home charging need and the TF Instruments AC switches are ready to help the users save their hard-earned money.
Q2. What is cascading of the TFI-1xx AC Switch and what is its benefit ?
A2. Cascading simply means to connect two or more TFI-1xx AC switches to allow the connection of more electric devices / AC loads.
To cascade, plug the cable of next unit into the EV side of the current unit etc.
See examples here : TFI AC Switch Set-up Examples .
Two units in cascade will support three electric devices / AC loads.
In general, n (n>=1) units in cascade will support (n+1) electric devices / AC loads.
When load time-sharing with an electric dryer, the 1st unit in the cascade can be either a TFI-1xx or a TFI-2xx but subsequent units need to be an intelligent TFI-1xx.
The TFI-1xx is an intelligent device that constantly monitors the AC input at the higher priority side/port and will safely switch off the lower priority side/port whenever the higher priority side/port becomes active. Therefore, only one AC load can be active at any given time in single or cascade mode. This insures safety in case of any scheduling conflict.
With multiple outlets available for load time-sharing, more useful work (i.e., clothes drying or EV charging) can be done than in the case of a single electric dryer connection.
Q3. Can the TFI AC Switch devices support more than three electric devices / AC loads ?
A3. Three TFI-1xx AC switches in cascade will support four electric devices/AC loads.
In general, n (n>=1) units in cascade will support (n+1) electric devices/AC loads.
In reality, since most household electric vehicle low-cost utility rates are limited to 12-16 [usually night time] hours per day, a time-sharing scheme for more than two or three vehicles may not have enough time to sufficiently charge all the vehicles to the recommended 70%-80% State of Charge at the [most] favorable utility rates.
Q4. What type/brand of electric vehicle can use the TFI AC Switch Products ?
A4. The TFI AC Switches safely turn the existing AC outlet (NEMA 10-30R or 14-30R) into 2 or more AC outlets. Any AC load or EVSE / EV charging set-up that can plug into these AC outlets can draw current/power from them. Most, if not all, EVSE (EV supply equipment) Level2 connect to NEMA 10-30R, 14-30R or 14-50R and use either the J1772 or a Tesla EV charging connector.
Below are adapters for the Tesla mobile (charging) unit. NEMA 10-30P and 14-30P (5th and 7th from left) mate to NEMA 10-30R (pre-1996 240VAC outlet) and 14-30R (after-1996 240VAC outlet) respectively.
Any electric vehicle charging set-up with a NEMA 10-30P or 14-30P adapter can use the TFI AC Switches with the mating NEMA 10-30R or 14-30R.
Q5. What is the maximum current load the TFI AC Switch devices can handle ?
A5. All current TFI AC Switch devices can handle up to 30A load. However, it is safer to limit the EV charging current to 24A (80% of household circuit breaker 30A rating) which corresponds to ~26 miles per charging hour for a 2021 Tesla Model 3. (Older Model 3 may get around 22 miles per charging hour).
Certain charging devices such as Tesla Mobile Units with NEMA 10-30P limit the charging current to 24A. For any charging circuit that allows more than 24A, the TFI-1xx Automatic Switch offers the option S to monitor and remove AC connection when the EV charging current exceeds 27A (90% of outlet 30A rating) +/- 5% to protect itself and the house 30A circuit-breaker.
The TFI-1xx is specified to operate at 24A, up to 40C (104F) ambient without thermal interruption. Due to tolerances, many units may indeed work fine at slightly higher ambient temperature than the 40C (104F) limit. In addition, lower temperature allows higher current load while higher temperature reduces the 24A current load specification. (Note : Ambient temperature is the air temperature where the TFI-1XX is installed which most likely is in the garage).
Contact TFI about the customized product TFI-1xxF that can operate at 24A, up to 55C (131F) ambient temperature without thermal interruption.
Future generation TFI AC Switches may support a higher current load (e.g., 40A at 45C (112F) ambient).
Q6. What information does the AC meter provide ?
A6. The AC Meter (Japanese technology) always provides measurements of Volts (1% accuracy), Amps (1% accuracy), and Watts (2% accuracy). There is also a fourth measurement of either Frequency (Freq) or Power Factor (PF) depending on the AC Meter availability.
The user just taps on SEL to scroll through the measurements. Press and hold SEL for three seconds for automatic scrolling of the measurements. Tap SEL again to return to manual scrolling mode.
After 60 seconds in a particular measurement, the AC meter will remember the setting and will power up to that setting after power cycling.
Q7. What support can I get from TFI ?
A7. All the information that a user needs to purchase, operate, and maintain the AC Switch is available on our website. Please read over the Documentation and FAQ sections for details.
Typically, after the initial installation which can be done in minutes (see examples here TFI AC Switch Set-up Examples ), the user can proceed to reliably use the TFI AC switch for both their electric dryer and EV charging need.
We pride ourselves in providing reliable products that completely fill the user' s need. In the rare case of an issue, the customer can contact us for service using the procedures in the Support section.
Please also familiarize yourself with our Return Policy and Terms and Conditions of Sale in the Policy section.
Q8. There are many models to choose from, what is the correct TFI-xxx AC Switch for me ?
A8. 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, 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 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 :
Q9. My outlet does not look like either 10-30R or 14-30R, can I still get a TFI-xxx AC Switch ?
A9. Short answer is YES. Most electric dryer outlets are either 10-30R (pre-1996) or 14-30R (after-1996). The '30' in the name denotes 30A capacity. However, some later outlets may have 50A or 60A capacity. See below table.
You may contact TFI regarding a custom TFI-1xx unit for most 240VAC outlets available on the market. But it is important to note that all TFI products currently support 30A outlet (i.e., 30A max AC load). The safe limit for electric dryer use or EV charging is 24A and the TFI-1xx Automatic Switch can optionally turn off the EV port [for two minutes] when the charging current is more than 27A +/- 5%.
In other words, when a high capacity (i.e., 50A, 60A) outlet is used with the TFI-1xx product, the EV charging current / AC load is still limited to about 27A to 30A max. Consult the factory for more details.
Note that the Tesla Mobile Unit with 14-50P limits the EV charging current to 32A.
Later generation of TFI products may support higher current load.
10. What about the 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 Automatic Switch TFI-1x 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 !