24A vs 32A vs 40A: which amperage do you need?

The decision rule: take the breaker rating on the circuit, multiply by 0.8, and buy a charger that can be set to that number or below. Everything else on this page is why that rule exists and what each answer means in miles.

The 0.8 comes from the continuous-load rule in the National Electrical Code. A load running for three hours or more is continuous, and a circuit may carry no more than 80% of its rating continuously. EV charging runs all night, so it is continuous by any definition.

Look at the last column before the third. Every 240V row already returns more range overnight than almost anybody drives in a day. The difference between 24 amps and 40 amps is real on paper and mostly invisible in a life where the car sits still for twelve hours.

Whenever your 240V comes from a 30 amp circuit — which for renters is most of the time, because the 30 amp circuit in a rental building is the dryer. 24 amps is not a compromise there, it is the correct number, and a charger that cannot be set to it simply cannot use that circuit at all.

A splitter switch enforces this in hardware, which is a meaningful safety property: it carries its own 24 amp breaker rather than relying on you to configure the charger correctly.

On a 40 amp circuit, which is less common in residential buildings but does appear — some older range circuits and some purpose-installed EV circuits are 40 amps. It is also the sensible setting on a 50 amp circuit whose wiring you are not certain about, because it leaves headroom without costing you meaningful range.

On a genuine 50 amp circuit behind a NEMA 14-50 receptacle. This is the fastest AC charging available to a renter without electrical work, and it is worth having when you can reach it. It is not worth buying a 40 amp charger for a circuit you have not found yet.

Quick picks

Ranked, with the reasoning underneath. Tap any row to jump to that write-up; tap the price to check it on Amazon. Prices come from the live layer, never from this page.

#	Product	Best for	Type	Price
1	Grizzl-E Mini Connect Portable ChargerAdjustable from 7 to 40 amps and shipped with four plug adapters, which is the closest thing to a unit that fits whatever outlet you turn out to have.	Not knowing your outlet yet	Adjustable Level 1 and 2 EVSE	Check price#ad
2	Lectron Portable Level 2 J1772 Charger (40A, NEMA 14-50)The plainest answer to a NEMA 14-50 outlet you can reach: 40 amps, a plug on the end, and nothing screwed to a wall you do not own.	A reachable 14-50 outlet	Plug-in Level 2 EVSE	Check price#ad
3	Splitvolt Splitter Switch (NEMA 10-30, 240V, 24A)The one device that makes a shared older dryer outlet a legitimate EV circuit — it switches automatically and carries its own breaker.	An older 3-prong dryer outlet	Automatic 240V splitter	Check price#ad

#1 · Not knowing your outlet yet

Grizzl-E Mini Connect Portable Charger

Adjustable from 7 to 40 amps and shipped with four plug adapters, which is the closest thing to a unit that fits whatever outlet you turn out to have.

Published specifications for the Grizzl-E Mini Connect Portable Charger, each linked to its source

Adjustable current	7A to 40A (9.6 kW maximum)source
Voltage	Automatically detects 120V (Level 1) or 240V (Level 2)source
Cable length	25 ft (7.6 m)source
Plug and adapters	NEMA 14-50 plug plus four included electrical adapterssource
Connector	J1772 or Tesla (NACS) versionssource
Enclosure	UL Type 4 / IP67 ratedsource
Certification	UL tested and certified, Energy Star certifiedsource

What those numbers mean

The adjustable current is the feature that matters to a renter, and it is not a convenience. A 30 amp dryer circuit legally supports 24 amps of continuous EV load; a unit that can be set to 24 amps can use that circuit, and a fixed 40 amp unit cannot.

25 ft of cable is nine feet more than the common 16 ft, and nine feet is frequently the difference between reaching the car and not.

IP67 and a UL Type 4 enclosure describe the unit's own weather tolerance. They say nothing about the outlet it plugs into, which is usually the part that is not weather-rated.

What it does well

• 7-40A adjustment means one unit fits a 15, 20, 30 or 50 amp circuit
• 25 ft cable is among the longest on a portable unit
• Four plug adapters included, so an outlet change does not mean a new charger
• Available with either a J1772 or a NACS connector

What it does not

• Costs meaningfully more than a fixed-amperage unit that does one job
• The bundled adapters make it easy to plug into a circuit you have not actually checked

Skip this one if: You know exactly which outlet you have, it is not changing, and you would rather put the money into a longer cable than into adjustability you will set once and never touch.

Check price on Amazon

#ad · how this is funded

#2 · A reachable 14-50 outlet

Lectron Portable Level 2 J1772 Charger (40A, NEMA 14-50)

The plainest answer to a NEMA 14-50 outlet you can reach: 40 amps, a plug on the end, and nothing screwed to a wall you do not own.

Published specifications for the Lectron Portable Level 2 J1772 Charger (40A, NEMA 14-50), each linked to its source

Input	240V, 40A maximumsource
Output power	Up to 9.6 kWsource
Cable length	16 ftsource
Plug / connector	NEMA 14-50 plug, J1772 connectorsource
Certification	UL 2594 / UL 2231 certifiedsource
Manufacturer charge-rate claim	Roughly 30 miles of range per hour of chargingsource

What those numbers mean

9.6 kW is the ceiling this unit can deliver, not what your car will take. A vehicle with a 7.2 kW onboard charger draws 7.2 kW from it and no more, and that is a car limitation no charger fixes.

The 16 ft cable is the number to check before anything else. Measure from the outlet to where your charge port sits when the car is parked as it will actually be parked, not as you would like to park it. Sixteen feet disappears faster than people expect once it has to route around a wall.

A 40 amp unit needs a 50 amp circuit behind the outlet to run at 40 amps continuously. If the outlet is on a smaller breaker, the answer is a lower-amperage charger, not this one turned down.

What it does well

• Plugs in and unplugs — it leaves with you at the end of the lease
• UL 2594 and UL 2231 certified, the two standards that matter for EVSE
• 40 amps covers the fastest charging any renter-reachable outlet realistically supports

What it does not

• 16 ft of cable is short for a parking space that is not directly beside the outlet
• No amperage adjustment, so it is the wrong unit for a 30 amp circuit

Skip this one if: Your only 240V outlet is a 30 amp dryer receptacle. This unit expects a 50 amp circuit behind a NEMA 14-50, and derating it is not an option it offers.

Check price on Amazon

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#3 · An older 3-prong dryer outlet

Splitvolt Splitter Switch (NEMA 10-30, 240V, 24A)

The one device that makes a shared older dryer outlet a legitimate EV circuit — it switches automatically and carries its own breaker.

Published specifications for the Splitvolt Splitter Switch (NEMA 10-30, 240V, 24A), each linked to its source

Input plug	NEMA 10-30 malesource
Output sockets	Two NEMA 10-30 female outlets — one for the dryer, one for the EV chargersource
Rating	240V ~ 60Hz, 24A AC maximum loadsource
Protection	Integrated 24A circuit breaker with easy resetsource
Switching	Automated power switching between the dryer and EV power socketssource
Certification	Conforms to UL 60730-1, certified to CSA E60730-1, cETLus listed Intertek 5021938source
Installation	No electrical installation required — plug and playsource

What those numbers mean

24A is the number to design around, and it is not the manufacturer being cautious. A 30 amp circuit supports 24 amps of continuous load under the 80% rule, and continuous is exactly what EV charging is.

Automatic switching is what makes this a device rather than a Y-splitter. Both loads on one 30 amp circuit at once would trip the breaker at best; the switch guarantees only one draws at a time.

The integrated 24A breaker is the part that earns the trust. It means the splitter protects the circuit itself instead of relying only on a panel breaker you cannot see and wiring you cannot inspect.

What it does well

• Plugs in — genuinely no electrician, no permit, no landlord construction
• Its own 24A breaker rather than trusting the panel alone
• cETLus listed with the Intertek file number published
• Automatic switching, so the dryer keeps priority without anybody replugging anything

What it does not

• 24A caps charging at roughly 5.7 kW, well below a NEMA 14-50's ceiling
• NEMA 10-30 is an ungrounded three-wire configuration, which is a real caveat rather than a formality
• Only useful if you can physically reach the laundry outlet from the car

Skip this one if: Your dryer outlet is the modern four-prong NEMA 14-30. Buy the four-prong splitter instead — this one will not fit, and forcing the fit is exactly the wrong instinct.

Check price on Amazon

#ad · how this is funded

It caps the top end and nothing else. A car with a 7.2 kW onboard charger draws 7.2 kW from a 9.6 kW supply, so on that car a 40 amp charger and a 32 amp charger perform identically. Check the vehicle's specification before paying for amperage the car cannot accept — it is a genuinely common overspend.