This doesn’t seem to apply to 110v what what I’ve been able to tell, unless they are adding an extension cord.
But level 2 or DC chargers appear to have a requirement of about 3-6 feet. Why is this?
What is the importance of the length of cable?
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The power drop, or power lost in a cable, depends on the cable length, cable size and the current through the cable. Larger cables have less resistance and can therefore transmit more power without large losses. Losses in smaller cables remain low if the amount of power transmitted is small, or if the cable is not very long. Engineers have to design the power system so that the power loss in the cables is acceptable for the length of cable required to supply the load
There is technically no difference between an EV charging cable a regular cable with regards to length and size. In fact the EV charging cables carry the same 110V as your regular cables and the charger is just a smart power switch. What makes EV charging so special is that it draws close to maximum current for a long time. You do not have many appliances which do and if they do then you are not putting them on a regular extension cord. The problem is that the cable will generate heat when you pass a current through it. So when drawing maximum current for an extended period of time you will heat up the cable quite noticeably. This will use up power, deteriorate the rubber insulation and in the worst case might catch fire. So you need to keep the cable as short as possible and make sure it is well ventilated and not coiled up under some rags or something.
Along with current drop as others mentioned, customers would be tempted to leave a longer cable coiled under the vehicle. The natural resistance of cable produces heat and when coiled that heat becomes trapped and can easily set fire to insulation. This is a very common problem with cable reels and electric hook ups on camp sites especially in countries with 240v supplies where a 13 amp connection is fully loaded.
Running electricity over a cable always drops the voltage at the end, but a fat cable can help keep the loss down. This is why we have various thicknesses of extension cables and lengths. You might be able to run 15 feet with a thinner cable to power your table saw, but you need a thicker cable to run 50 feet so you’re not under voltage.
The same would apply to car chargers, which are pushing a lot more electricity than your 110V extension cord is. .
If the cable was longer you would role it in to a neat pile. It would get hot and create a fire.
tl;dr you need big cables to use big charging amps, and big cables weight a lot. you have a maximum length because you have a maximum weight you can support with a cheap plastic clip.
the resistance of a wire is more or less constant, for a given length/cross section.
if you double the cross section of the wire, you halve the resistance (more or less).
if you double the length of it, you also double the resistance.
if you want to send 110v, 8 amps 15 meters, 2mm twin and earth is a perfectly acceptable size of wire to use (that’s standard 14 gauge household wire, for people that use freedom units).
if you want to send 220v, 20 amps 15 meters, you can still use that same 2mm cable.. but by the other end of the cable, you’ll probably only have 212volts.. and slightly warm cable. as a minimum you’ll want to use 2.5mm (14 gauge), or even 4 or 6mm (that’s 12 or 10 gauge). .
more cross section = less resistance to current.
when you’re talking about level 2 vehicle chargers, you’re talking about 240 volts, and **40** amps of current… which means that in order to still have 240 volts at the other end, you need to use 10 or 12mm cross section cable (8 or 9 guage)..
the problem with 12mm cross section wire (and bear in mind that that’s the measure of just the conductor, not including insulation, then a ground layer, then an outer layer of insulation).. is that it weighs quite a lot.
a meter of 12mm level 2 charging cable weighs in at roughly 2lbs (slightly less than a kilo).. so 2 meters of it (about your limit of 6 feet) weights roughly 4 lb .. and you have to support that weight with the clip on the end of the charging socket.. usually at some extension, because the cable is attached to the car at one end, and the charging station at the other, and usually not supported at any point over it’s entire span. … and that puts a lot of strain on what is basically just a plastic plug and a plastic retaining clip. you could make the retaining clips stronger, but they have to be weak enough to break off if your car is hit whilst it’s charging, or if you try to drive off without unplugging it.
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