Bosch Level 2 EVSE Charging too fast?

[QueenBee]

Hey everyone. Thought that you might like to know that my charger is finally legit! Ran new 8AWG wire on a 2-Pole 40AMP circuit. Charger is plugged in and wired to an 8AWG Nema 14-50 cord. So we are good to go. Just noticed that the Bosch charger that plugs into the car is actually 10AWG? WTF? So code requires 8AWG everywhere else, but the Bosch can use a 10AWG? How does that work?

The conditions are different. The J1772 cord set is used in free air while house wiring is installed in enclosed insulated spaces. The NEC has some extra safety margins built in as well. As an example if house wiring were to overheat a fire starting in the walls might pose a bigger fire risk than the J1772 cordset. The connections in house wiring are all field installed so the quality of the connections might be lower. House wiring is used for decades while appliance wiring is a lot less. The wiring in the house can be a lot longer than appliance wiring generally is. To make things simple the three most common wire sizes have a basic max limit of 15,20,30 amps for #14, #12, #10 respectively as a simple requirement even though the actusl rating of a specific wire at those sizes might be higher. Anyways, lots of different things go into the NEC requirements to make wiring as safe.

Good for you for upgrading your install!

 

[johnrhansen]

Another interesting thing to note is that the EVSE is tested and listed specifically as it is built. The connections inside might be rated for a higher temperature, the wire insulation rated for a higher temperature, all kinds of things. But it has been tested and proven safe. Household wiring codes on the other hand are more general in nature, not designed for any specific circumstance. Therefore a larger safety factor is built in. I suppose if you wanted to draw up a specific installation plan, and take it down to a PE licensed electrical engineer and convince him to stamp it, you could have maybe gotten away with using 10 gauge wire. A lot cheaper just to buy #8 wire though.

 

[pchilds]

Most J1772 cables are rated at 105°C, and the manufacturer has control over the connections. Most house wiring connections are rated at 70°C, so you can't even take advantage of the 90°C wire rating.

 

[alanlarson]

If you have a 14-40 with a 40A breaker, that is allowed but you should label it 40A.

Tony Williams feels that every 14-50 should be wired for 50A. I feel this is un-necessary.

The NEC appears to agree with you.
210.21 (B) Receptacles Receptacles.
(1) Single Receptacle on an Individual Branch Circuit. A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit.

"not less than". 50 is not less than 30 (or 40), so it should be legit.

Of course, your local codes may vary, so checking them is a good idea.

 

[davewill]

Hey everyone. Thought that you might like to know that my charger is finally legit! Ran new 8AWG wire on a 2-Pole 40AMP circuit. Charger is plugged in and wired to an 8AWG Nema 14-50 cord. So we are good to go. Just noticed that the Bosch charger that plugs into the car is actually 10AWG? WTF? So code requires 8AWG everywhere else, but the Bosch can use a 10AWG? How does that work?

The wiring in the wall has to be good for the entire 40a that the circuit breaker allows. The EVSE only has to handle the 30a max the EVSE is rated for. It's a side effect of the 80% rule for continuous loads. It only applies to the premise wiring, not the EVSE itself.

 

[tkdbrusco]

Yeah I thought about the 14-50 plug situation but the 14-50 plug was the only 10 footer I could find (I needed 10ft to get to the EVSE installation point, and I wanted the wire to be at least 8AWG for safety reasons. I put a sticker on the breaker box that told people 40A max, just in case they wanted to plug some 50A item into the outlet, although unless they are plugging in a welder or a Tesla charger, I doubt this will be a problem.

 

[GlennD]

Personally I doubt this will be a problem. I have total control over my house. In the future event that I die if the purchaser can not read, then reset that breaker.