On Amazon they sell all these different cables for different kW ratings (7, 11, 22) and 1 phase or 3 phase, but does it actually matter?
Yes, it certainly does, or it can. As does the power of the EVSE (AC "charger").
The worst combination, as
@Tight Git mentioned, is an 11 kW EVSE with a 7 kW vehicle. Each phase of the three-phase source can only deliver 16 A (3.6 kW), and the vehicle can only charge on one phase. So 3.6 kW max.
The other problem is if you have a 16 A cable. The cable will have a resistor in it that tells the vehicle how much current it can draw. If you use a 16 A cable (1 phase or three phase) and the vehicle is 7 kW (one phase, 32 A), then you'll again only get 3.6 kW.
The other combination of interest is a 7 kW EVSE (32 A single phase) and an 11 kW On-board charger (as found in the MG4 Extended Range, and the MG4 Xpower). The car has three 3.6 kW on-board chargers, usually connected to L1, L2, and L3. In order to use the 32 A that the EVSE has available, and assuming that a 32 A cable is used, one of the on-board chargers has to switch itself from say L2 to L1, after detecting that power is available only on L1 and not on L2 or L3. Most vehicles with an 11 kW On Board Charger will do this detecting and switching, but if they don't, then once again the power limit is 3.6 kW. I have yet to check that my MG4 ER (called the long range in Australia) will do this, but I'm 99% sure that it will.
I ended up buying a 22 kW, 3 phase cable, just because it was the most reasonably priced cable that was 7 metres long...
But a 22 kW cable should cover all cases: up to 32 A, at up to 3 phases.
A 22 kW 7 metre cable will be quite bulky and heavy. I don't know the weight off hand, but it will be awkward to pull out of the boot or froot (frunk). It may be that you accidentally or my sleight or hand ended up with a 16 A 3-phase cable (11 kW). As above, this will limit you to 3.6 kW, which can be painfully slow unless it's overnight, and even then it might be too slow.
Unless the cable is totally fraudulent, you should be able to check the cable from the Cross Sectional Area of the main conductors. A single phase cable will have 3 of these (L1, N, and PE); a three phase cable will have 5 (all these plus L2, L3). It's possible that the earth conductor has a lower cross sectional area than the others; this is OK, as long as it's at least 2.5 mm² (2.5 square millimetres in area).
32 A wire is generally about 5 mm² or a little larger; 16 A wire is generally about 2.5 mm² or a little larger. So stamped on the side of the cable you should see something like 5 x 5 mm² + 1 x 0.5 mm²; sometimes they use a capital G in stead of the x for multiplication. For example, here is the cable on my 16 A single phase EVSE (I have a 32 A EVSE as well, this was more convenient to photograph):
This part of the rating of the cable (temperature, voltage, other things) and the CSA that I mentioned above. This cable has two 0.5 mm² wires, one for the control pilot, and as far as I can tell, one spare. The proximity pilot doesn't connect from end to end.
One possibility is that the site may have been short on power, and was throttling the EVSEs, but throttling down to 3.6 kW seems a bit extreme.
Another possibility, though remote, is that the cable is rated for 32 A, but has the resistor saying that it's 16 A:
| Current capability | Resistance |
| 13 A | 1.5 kilo ohms |
| 20 A | 680 ohms |
| 32 A | 200 ohm |
| 63 A (3 phase) / 70 A (single phase) | 100 ohms |
So you might have a 680Ω resistor that should be a 200Ω resistor. This resistance can be measured with a multimeter between protective earth (middle thick pin) and the proximity pilot pin. It will line up with the longer of the two thin pins in the vehicle.
Finally, the car might be reading that resistance incorrectly, though I've never heard of that.
Edit: Thinking about all these cases, the most likely scenario is the first one I mentioned: 11 kW EVSE, and your 7 kW car. 7 kW vehicles are the most common at present, so that's why 11 kW EVSEs are a poor choice. Few vehicles can use all the available power, and most vehicles can only charge at half the rate that they are capable of. In eastern Australia, all EVSE's that I've seen are 22 kW.
