To be accurate, there is no such thing as a normal 240V 40A circuit. Nor is something like that small. Much of the confusion here comes from, like a few of you said, the thinking of ICE vehicle driving behavior (full--> dead --> back to full) as well as there being no standard in the EV industry. Rather than trying to understand "normal" or circuits, I like to break things down into what the industry uses and what is common. This way, you can understand your
actual needs. To preface, these is for US-based power. These are different elsewhere:
Battery Size: 60 kWh
I'm fully expecting the battery in the M3 to be 60kWh. There is a chance that it could be more, or less, but we'll use 60kWh for the sake of discussion since the Bolt is using a 60kWh battery, so it makes understanding this a bit easier.
Average Commute: 50 miles (or ~15 kWh)
Now, some people's averages are more, some are less, but considering that the research that GM did a few years ago leaned towards the average being 40-50 miles and used that for the Volt, it makes things easy.
EV Charging Recommendation: Every day
Unlike ICE cars which are driven from a full tank to empty and then back to full, EV's are designed to be charged every day. This is a change in behavior and change in habit. So, charging requirements are based on what you consume every day, not what it takes to go from dead to full, which will not be normal behavior.
Power: W=VA
When talking power, it is also important to know the equation that creates it. Power, measured in Watts, is the product of Electrical Potential, measured in Volts multiplied by the amount of current, measured in Amps.
Circuit Safety: 80%
When you are dealing with circuits and, specifically, fuses and circuit breakers, it is important to note that many of them are only rated for 80% continuous load. While electrical codes do allow for 100% rated circuits, there are conditions that have to be met for this to actually happen (wiring as well as environmental) and you will usually only find 100% circuits in newer builds. Thus, under most circumstances, a 15A circuit, for example, will only provide 12A of continuous load.
NEMA Receptacles:
The National Electrical Manufacturers Association (NEMA) is a company that sets the standards for AC plugs and receptacles in the United States. NEMA plugs have a type (the first number) and a current rating (the second number). The standard receptacle in the US is the NEMA 5-15R. NEMA 5 is what denotes the 2 vertical blades with the ground plug, 15 is the current rating (15A), and the "R" signifies whether it's a plug or a receptacle (if a plug, it would be 15P). So, a NEMA 5-15P plugs into a NEMA 5-15R.
Now that we have set the stage, let's talk about power. In the EV world, there are two types of power in the home:
Level 1 and Level 2.
Level 1:
Level 1 charging is described as using a standard 110V 15A circuit. These types of circuits use (typically) a NEMA 5-15R in the home (the standard wall socket). This receptacle can usually provide a maximum of 12A to the car. If there is nothing else on the circuit but the car, you are able to supply a maximum power of 1,320W (1.32kW) to the car. At that rate, it would take you approximately 46 hours to fully charge your EV. However, let's take the average commute into consideration. If all you did was your average commute, it would take approximately 11 1/2 hours to charge. If you are home by 6:00p and do not leave again until 7:00a the next morning, then Level 1 charging would provide you with enough power to perform your daily commute. The issue, however, comes when your travels are beyond your daily commute. For that, enter Level 2.
Level 2:
Level 2 charging is described as using
at least a 240V 15A circuit. And it is that last sentence that starts the confusion for just about everyone. Why? Let me ask you a question... What in your home uses a 240V 15A circuit? If you have an answer that isn't the word "nothing," you are probably in the less than 1% of the US homes that have anything using that. As it stands today, most homes that have 240V receptacles are for devices that are heavy in load, requiring 16A or more. Almost all of these circuits are dedicated, meaning that only one device connects to the circuit (but not always). In the US, there are 3 NEMA receptacles that are used for 240V power. They are: NEMA 6, NEMA 10, and NEMA 14.
NEMA 6 is a three-wire configuration that comes in four popular configurations:
- NEMA 6-15 (very uncommon today)
- NEMA 6-20 (common)
- NEMA 6-30 (common)
- NEMA 6-50 (uncommon in practice, but common for EV)
While the NEMA 6-15 does exist, most applications call for at least a NEMA 6-20. These circuits are commonly used with tools and heavy equipment (welders, compressors, etc). Most homes do not come with any NEMA 6 receptacles and are almost always installed later on. The interesting thing about these receptacles, however, is that they are
the receptacle of choice for use by most EV manufacturers. Most universal (J1772) wall charger companies that use plugs use a NEMA 6 and, specifically, the NEMA 6-50. There are a few that use the NEMA 6-20 (16A plug version of the Chargepoint Home Wall Charger), but most are on the NEMA 6-50.
NEMA 10 is also a three-wire configuration. However, because the NEMA 10 is ungrounded, its use has mostly been retired. You can still find them in older homes, but they are mostly replaced these days. The NEMA 10 is found in two popular configurations
- NEMA 10-30 (retired)
- NEMA 10-50 (retired)
The NEMA 10-30 was primarily used for dryers in the home. The NEMA 10-50 was primarily used for electric ovens. While they do provide 240V and 30-50A, because of their ungrounded nature, use of one of these plugs would probably
NOT work on your Tesla (I believe that the Tesla checks for grounding and will not charge if ungrounded).
NEMA 14 is a four-wire configuration that has replaced the use of NEMA 10 in the home today. They are found in two popular configurations:
Just as with the NEMA 10 that the NEMA 14 replaced, the NEMA 14-30 is primarily used for dryers and the NEMA 14-50 is primarily used for electric ranges. Most homes have at least one NEMA 14 receptacle somewhere in the home. The NEMA 14-50 is also very commonly used in RV parks and truck stops. Since it is common connector and most homes have at least one of them, it is likely the reason why Tesla uses it for Level 2 charging.
So, what does this all mean? The answer is actually quite simple. For your average commute, if you are using a common Level 2 source, you are going to replenish your car in as little as 2 hours. If you are completely dead, in as little as 8 hours. But, which one do you choose? After all, there are a bunch of common ones out there? The answer to that is simple too. What does your car recommend? Whatever that is, use that! There is a reason for this. Tesla recommends a NEMA 14-50. They recommend this because the cars' onboard charger, which is what does the actual charging of your car, is rated for 240V@40A input and the universal mobile connector comes with a NEMA 14-50P plug. So, use that. Could you use a NEMA 14-30, NEMA 6-50, NEMA 6-30, etc.? You sure could (for a NEMA 6, you would need an adapter). But, you will only get 240V@40A on a NEMA 14-50 or a NEMA 6-50. The others will still provide 240V, but the amperage will be less than 40 and require more time to charge, hence the "as little as" part above.
Wall Chargers:
So what about wall chargers? In addition to aesthetics, wall chargers are more convenient to use. With the exception of a few chargers that are plug based, most are directly wired to an electrical circuit. There are a few key things to note. Not all wall chargers provide the same output current. For example, the Chargepoint Home system comes in a 16A version. The Turbo Cord is also 16A. On average, most wall chargers provide anywhere from 30-40A. Considering that almost all of the generic ones are under $500 and provide around 30A, they are good alternatives and are priced fairly well.
Tesla Wall Chargers:
In addition to generic wall chargers, Tesla also makes one as well. In general, I only recommend the Tesla wall chargers in one of two situations:
1. You are committed to Tesla as an EV company and have no plans of using other brands of cars.
2. You have a need for more than 40A charging (i.e. dual charger vehicle).
Outside of those situations, I would stick to getting a plug (NEMA 14-50 or NEMA 6-50) or purchase a generic charger that provides 30 or more amps. The Tesla Wall Charger does allow for you to specify the output based upon what type of circuit you have. So, it is possible to limit a Tesla Wall Charger to any amperage you wish (up to 80A max).
Dual Charging and the Need For It:
Finally, there is dual charging. So, what is it exactly? Dual charging is a concept in which your Tesla is equipped with 2 x 240V@40A chargers internally. This second charger is what permits you the ability to Level 2 charge your vehicle up to 80A. Now, there are a couple of things to note. First, we are not sure if the M3 supports this or not. Second, and probably more important, this is a bit overkill for most situations. Now, that isn't to say that your situation doesn't have a need for it. Rather, for most people, you wouldn't. Here is a real world exception that I run into, on occasion. On some days, I end up doing a 16-18 hour day in which I have driven around 200 mi. In this type of situation, if I did this often or back to back, there is a good chance that a normal Level 2 charge would not completely fill the car by the time I needed to head out the next day. In a case like that, a dual charging unit would be beneficial.