Could someone help me, i wanted 50amps installed and only received 30amps

Question

Could someone Please help I had a 30amp receptacle installed when I paid and was expecting 50amps he came back and said I only have 100amp service and cant do 50amps because there wasn't room however i have 2 free receptacles that at one point one was connected to a stove/oven and the other a dryer and both are gas now freeing uo those receptacles, so am wrong to think that he isnt correct telling me that i can't safely run a 50amp receptacle to charge at, atleast 40kWh?

Answer 1

There are a LOT of issues here. But the key is right at the end:

50amp receptacle to charge at, at least 40kWh

which tells me that you are:

• Installing a receptacle for EV charging instead of hardwiring
• Are confused about A vs. kW vs. kWh - 50A would actually be 12 kW and 9.6 kW actual. So maybe the 40 kWh is how much you want to charge each night? That is a lot, but doable. Or maybe you meant 40A, which is the actual charge rate on a 50A circuit.
• Likely don't realize that 30A (5.7 kW actual) is more than enough for most people most of the time
• Don't know about options for adjusting the EV charging rate as needed

First of all, receptacle vs. hardwiring:

A receptacle is an extra point of failure. In fact, many receptacles are not designed for the heavy usage required for EV charging. In addition, in many places (varies depending on NEC adoption and sometimes local code amendments) a receptacle requires a GFCI protection but a hardwired connection does not. (This is actually currently up for debate for the next NEC cycle. Stay tuned.) So there are a bunch of advantages to hardwiring EVSE instead of using plug/cord/receptacle.

In most locations in the US, the key values are:

• Volts - usually 240V, some buildings 208V (all calculations below based on 240V)
• Amps - this is the "circuit size" as determined by wire and breaker. The circuit breaker must be sized to protect the wire, so larger wire (lower AWG) is always OK. If you are working with long distances then you want everything to match exactly. If you are working with short distances (e.g., breaker panel is in or near garage/driveway) then it may make sense to oversize the wire - e.g., 6 AWG copper cable or 8 AWG individual copper wires will work for 50A - even if due to service size/load calculation you can only use 30A, as I suspect is your current (pun intended) situation.
• Watts - Commonly listed as kW for kilowatts. Generally (ignoring load factor adjustments and inductive loads, etc.) V x A = W. But you also have to limit the Amps to 80% because this is a continuous (> 3 hours) load. Which means that at 240V:
  • 20A = 20 x 240 x 0.8 = 3,840W
  • 30A = 30 x 240 x 0.8 = 5,760W
  • 40A = 40 x 240 x 0.8 = 7,680W
  • 50A = 50 x 240 x 0.8 = 9,600W

Multiple by hours to get Wh and divide by 1,000 to get kWh.

These numbers may not seem like much if you have, for example, a 60 kWh battery. But most people don't run their 60 kWh battery to 0 every day. If you use half of it - 30 kWh, and add a bit for conversion losses, etc. then you will find that:

• 20A - Charge in 8 hours
• 30A - Charge in 5.5 hours
• 40A - Charge in 4 hours
• 50A - Charge in 3 hours

When you also consider that most people leave their car sitting in one place for 8 to 10 hours every night, it is clear that 30A is more than enough for most people. Increase a bit for 40 kWh and you are still OK with a 30A circuit.

Hopefully your electrician did a Load Calculation. This includes the size of your house (for general loads), HVAC, large electric appliances, etc. If you have 100A and an all-electric house then you likely don't have any room to spare for EVSE. If you have gas for cooking and heating then you likely have some room, but very likely not 50A. If a proper Load Calculation showed between 30A and 39A available then 30A is the correct circuit size.

However, there are a number of different systems available that will monitor the usage of the rest of the house and then give your EVSE the balance. If you are running HVAC and clothes dryer and lots of other stuff then the EVSE might get 20A or less. But in the middle of the night when you aren't running much else - and when your car has many hours to charge - it could easily get 30A or 40A or more. But doing this right requires some additional equipment. If 30A is legitimate then it may be best to leave it as is - just switch to hardwired instead of plug/cord/receptacle. If 30A is purely a guess by the electrician then a proper Load Calculation is the next step.