TSLA in my hands

After reading what @Trollbait and @DavidA wrote, I think they both make good points. If you already have a 40A circuit, you could just make sure the car doesn't draw more than 32A. But if I was needing to install a circuit, a 50A doesn't cost that much more. And since I could do it myself, I would probably upgrade a 40A to 50A to get the most out of the system. If you have to hire someone to do the upgrade, then that takes some extra motivation.

 

We should all just crownfund a big road trip for Jerry to come help all of us with electrical upgrades!

 

Thank you for your professional electrician view on this.

 

Just saying what I would do. Previous posters had it covered pretty well.

 

Some people were questioning the 20% headroom circuit buffer.

 

I would do this myself, if the faster draw wasn't needed to cover daily driving use. The question I have is, would such a set up need to be 'fixed' before home renovations or selling?

The max amperage draw of an appliance can vary a little from what the label states. Likewise, the breaker could be tripped at lower than stated. So the closer expected appliance draw to the breaker rating, the more likely of the breaker tripping.

Then there is a fire concern for the wiring. Pulling 39 amps continuously on a 40 amp circuit will heat up the wiring more than on a 50 amp circuit. The entire reason for fuses and breakers in a home is because a fire will start if a wire is carrying more amperage than it is rated for.

 

Thanks Jerry, this is consistent with my understanding. I installed a 50A breaker for my UMC (Universal Wall Connector) with a NEMA 14-50 outlet, even though my model 3 can only draw 32A with this connection, by design. The reason I did this is because the cost of materials was only about $10 more than a 40A circuit AND I wanted the flexibility of a larger circuit if needed in the future with Tesla upgrades. My car charges very happily on this 32A system at the rate of about 30 m/h. If my car was capable of charging at 40A, it would charge at about 37 m/h. But that is a moot point because I usually need way less than 100 mile recharge per day which means only 2 to 3 hours of charging at night under either system.

 

I agree. I just thought a licensed electrician chiming in would add credibility to the discussion.

 

Even more important is that a 40 amp breaker "might" only be accurate to within 5% (I don't know what the actual code says about tolerances). So it might not trip until 42 amps. And a 39 or 40 amp device might not draw exactly that and might consume 41 amps, for example. So your whole end-to-end wiring could be over current, continuously.

The required standard wires sizes are supposed to account for a combination of tolerances that are at the edges, I would think. But still not a good idea to test it.

Mike

 

The size of the breaker is based on the ampacity of the wires. It's not to protect the load, but the wires. Otherwise you would be unsafe plugging in a night light in a 15 amp circuit.

The general rule of thumb, to protect the breaker from failure or false trips, is to not put more than 80% of the tripping point amperage on that breaker.

So, if the charging device is hard wired, you size the wires to carry that load plus a safety margin and then size the breaker so it will trip before the wires can overheat if something increases the current too much.

But, just to be clear, I am not a licensed electrician. I have quite a few years of industrial electricity experience and was trained by some really smart guys in addition to the electronics degree. But no actual license.

 

Sorry. In my state you need to be a licensed electrician if you are paid for doing electrical work. I thought that was a widespread law.

 

The EEs that design the circuit don’t have to be

 

If you're a contractor, yes. In the manufacturing facilities, the employers are responsible. I could not legally go hire myself out to wire someone's house, but my former employer could hire me back to work again in one of their factories if they were crazy enough to hire someone my age and I was crazy enough to work that hard again. LOL! In fact, about 30 years ago, I did work at one of our plants in VA for six weeks helping with a major project there.

 

I believe the model 3SR is limited to 32A on L2 charger no matter what you do. I suspect trying to over-ride the on board systems could void the warranty and Tesla return policy. And Tesla will know because the car automatically uploads all the logs.

I have tested my model 3MR on several longer road trips (300 mi. - 800 mi.) I find the on-board computer remaining range prediction (either percent or miles) to be accurate to within ~1%. The computer is constantly re-calibrating subject to current speed, terrain, and wind conditions. Obviously, the closer you get to your programmed destination, the more accurate it is. I have charged to as high as 100% (just minutes before leaving on a longer trip) to as low as 7% when returning home. I usually keep my charge at between 20% to 80% for daily use.

 

After viewing this video - Tesla Wall Connector vs. NEMA 15-40 - comparing a 50amp circuit to a Tesla Wall Connector on a 60amp circuit. The Tesla Wall Connector appeared more efficient.

 

That is probably a reflection of the different design goals of the EVSE's.

A NEMA 15-40 outlet will be using the portable EVSE that came with the car. it is going to get tossed around, dropped, possibly left out in the elements, plugged into circuits of questionable quality, etc. It needs a degree of robustness in order to be reliable. It also comes with every car, so cost is a factor.

The Wall Connector will be wired to a dedicated circuit in a protected location, and has a hard shell giving better protection to its innards. That, and the higher price tag, justifies using more efficient components. Whereas for the portable one, maximum efficiency is below reliability and cost.

 

I gave that video a firm thumbs down, mostly because he doesn't know the difference between a NEMA 14-50 and a NEMA 15-40. Hint: One of those doesn't exist, even though he mentioned it and printed it onto the video like, 15 or 40 times.

All Teslas come with a J1772 to TESLA pass through converter. A M3 limits AC charging to 32A and 240v (except for the LR model which is 40A). A L2 home charger on a 40A circuit should do just fine vs. the 50A TESLA branded L2 hardwired charger, which is overkill for all 3's except the LR version.

I'm interested in Bob's findings, as my eMotorWerks L2 is 40A 240v, same as his.