NEMA 14-50 vs NEMA 14-30

[eprosenx]

Thanks for your thoughts/input.

The short response from the electrician that finally installed the circuit is that given my house setup (A/C, electric oven/range, normal small appliances, LED lights) I would never pull the 100a my box is rated for. The 50a circuit for the car would be okay.

I know now about the NEC formula but I'm assuming that given the electrician's experience he was well aware what that formula would yield. The circuit has been working fine. I charge in the middle of the night (ComEd hourly pricing generally $0.015 - $0.02 /kW - sometime negative so they pay me! - drawing 8kW during charge) and wake up to a fully-charged car. I was very pleased with the quality of the installation - would recommend him to anyone in south/west Chicago area.

Nice!

That is an amazing non peak usage rate! What is it during peak time?

It is crazy the different rates in different parts of the country. I was blown away by a recent thread on power costs in San Diego.

 

[rsomrek]

Nice!

That is an amazing non peak usage rate! What is it during peak time?

It is crazy the different rates in different parts of the country. I was blown away by a recent thread on power costs in San Diego.

To be fair there are other charges added to this basic rate. So even at $0.02 there are other charges that appear to add another $0.05 to the charge for electricity. The hourly rates the past 6 weeks have varied from -$0.02/kWh to as high at $0.145/kWh during hot afternoons when everyone is running their air conditioners. Generally, daylight hours run about $0.03 to $0.06/kWh. Right now the rate is $0.028; the max tomorrow is projected to be $0.043 plus the additional charges; tonight's overnight min is $0.019. Without hourly pricing the flat rate is ~$0.05 plus another $0.05 for additional charges.

 

[Roverman318]

You are right, I get 22 mph on my 14-30. Works fine with my 45 mile commute.

My 10-30 socket charges 23 miles per hour on my 3. Not the same plug as 14-30 but same amps.

 

[tivoboy]

My 10-30 socket charges 23 miles per hour on my 3. Not the same plug as 14-30 but same amps.

Same here, I sometimes even get 24-25 mph charging. I have a 10-30 dyer socket and simply bought one of those dryer buddy devices on ebay for 170$ shipped. It has a 10-30 cord and two 10-30 sockets. It will switch back and forth if they dryer is running.

I could have gotten one with a 10-30 socket and a 14-50 socket, but since I didn't have a 50 amp breaker there, I wasn't sure if it would work.

Saved me having to put in a new plug.

 

[—Miguel—]

1. Disclaimer: I'm not an electrician; if it looks like I know what I'm talking about, I probably don't
2. Background: We have a 30 amp two-pole circuit breaker in our garage subpanel that was originally intended for an 220V RV outlet outside the garage. It was wired with 10g copper running in the garage wall (unknown exact length, depends on which path they took) that terminated in an outdoor electrical box without a receptacle. An electrician subsequently installed a NEMA 14-50 outlet there to allow us to charge.
3. Question 1: What is the maximum amperage that can safely be drawn from this outlet? From what I've surmised from Tesla's info, it seems to be no more than 80% x 30A = 24A. 4. Question 2: What could be expected to happen if it were set to draw 30A?

 

[linkster]

Just call your electrician (fail) back and have him install a proper 14-30 receptacle and spend the 35 bucks on a MC 14-30 adapter for safe trouble free charging. No need to get into the what if’s when safety and personal property damage could be at stake for this very simple do-over.

Good luck!

 

[TexasEV]

Or maybe call a different electrician. I wouldn’t trust someone who put a 14-50 outlet on a 30A circuit.

 

[brkaus]

Question 2: What could be expected to happen if it were set to draw 30A?

The wire will be overloaded. You may get lucky or the magic smoke & fire manufactured into the wire might escape. It might share that smoke & fire with combustibles around it. Things like houses.

 

[eprosenx]

1. Disclaimer: I'm not an electrician; if it looks like I know what I'm talking about, I probably don't
2. Background: We have a 30 amp two-pole circuit breaker in our garage subpanel that was originally intended for an 220V RV outlet outside the garage. It was wired with 10g copper running in the garage wall (unknown exact length, depends on which path they took) that terminated in an outdoor electrical box without a receptacle. An electrician subsequently installed a NEMA 14-50 outlet there to allow us to charge.
3. Question 1: What is the maximum amperage that can safely be drawn from this outlet? From what I've surmised from Tesla's info, it seems to be no more than 80% x 30A = 24A. 4. Question 2: What could be expected to happen if it were set to draw 30A?

Sorry to be pedantic, but technically it is 240v, not 220.

10 awg is good for a 30a circuit. All EVSE’s are considered continuous load devices and so you are not allowed to draw more than 24 amps.

Technically a 14-50 is allowed to be installed on a 30a circuit , but only if the intended load won’t overload the circuit. In this case your UMC with a 14-50 adapter will draw 32 amps (it does not count if you manually set the draw down in the car - that has been known to reset itself sometimes to the max). But a 14-30 is really really the right way to go.

As others have said, I STRONGLY recommend you have a 14-30 installed instead and you get the right Tesla adapter for $35. This really and truly is the correct and safe way to do it.

To answer your second question: Technically the wire is rated for a full 30a, but it is not intended for use with a continuous load (over 3 hours now of draw). Derating it by 20% provides some safety headroom. Also, it is complicated, but the breaker is likely to blow at some point of drawing 30a. It all depends on how hot your breaker panel gets and what other breakers are installed next to it. There is a bimetallic strip in the breaker that’s heats up and causes it to blow. It all depends on temperature.

So most likely all that would happen is you would blow the breaker but I absolutely in no way recommend you running over 24 amps for the car charger. The NEV has layered protection mechanisms for good reason. Sometimes breakers fail. Sometimes connections are not tightened enough. Sometimes receptacles heat up due to bad contacts.

It is not worth burning your house down over and endangering lives.

 

[Glamisduner]

the downside for me is that I would not be able to dry cloths when on super off peak hours if I had to use my 14-30

 

[Brenzo]

I say just go with the 14-30 ran on the 30 amps. While I don't know your specific daily use / needs, I can almost guarantee that for 98% of drivers the charge rate provided by the 14-30 (20-22 mph) is more than sufficient for your daily use with the long range model.

Personally, I went with 14-30 over 14-50 because the thicker gauge wire necessary to run 50 amps wouldn't fit through the existing conduit running from the panel to the detached garage. I've got a great electrician who has done previous installs for Tesla owners (outlets and HPWC) and he said that with the separate conduit, which he was only going to charge me a couple hundred bucks extra to do despite it requiring a second guy to help with digging up 8' trench in my backyard and poking through two mason block walls, that I could go with a 100 amp config to support the HPWC. I'm in a condo and probably only here for another 2-3 years, so I didn't want to make that investment. I also have a tight parking spot in a shared garage so I was worried about the thicker cable included with the HPWC sticking out from the vehicle too much.

Anyways, I then thought about the recharge rate afforded by the 14-30 and said that if he could fit the 10 gauge wire through the existing conduit, to go with that. I have it scheduled to recharge to 70% beginning at midnight and could car is ready with plenty of time to spare. It's rare that there is ever an evening when the time between when I would get home and when I would need the car the next day is less than 9 hours, more than enough time to recharge.

 

[mikeshyu]

1. Disclaimer: I'm not an electrician; if it looks like I know what I'm talking about, I probably don't
2. Background: We have a 30 amp two-pole circuit breaker in our garage subpanel that was originally intended for an 220V RV outlet outside the garage. It was wired with 10g copper running in the garage wall (unknown exact length, depends on which path they took) that terminated in an outdoor electrical box without a receptacle. An electrician subsequently installed a NEMA 14-50 outlet there to allow us to charge.
3. Question 1: What is the maximum amperage that can safely be drawn from this outlet? From what I've surmised from Tesla's info, it seems to be no more than 80% x 30A = 24A. 4. Question 2: What could be expected to happen if it were set to draw 30A?

As eprosenx mentioned, 24A is the safest your circuit should be able to handle with a continuous draw on 30A breakers. Your electrician did you a disservice by installing a NEMA 14-50. While you theoretically could be safe by manually setting the charge in your car to charge at 24A, you're still exposing your home to a potential hazard by having that NEMA 14-50 plug there. What happens if the manual setting gets reset, or if someone else tries plugging into your outdoor plug and drawing a higher current. With a 14-50 plug, a device could theoretically try to draw 50A. 10 AWG wire is good for 30A. For a conservative 14-50 install, the wire should be 6 AWG.

Best case scenario in case something goes bad is that it trips the breakers and all is well. Worse case scenario is that it causes an electrical fire.

1. Either swap out the cable gauge and breakers to 6 AWG and 50A if you want to stay with the 14-50 plug or;
2. Swap out the outdoor receptacle with a 14-30 or 10-30 receptacle and buy the Tesla mobile charging adapter for a 14-30 or 10-30 plug.

If the cable that connects from the panel to outside box is routed through conduit (metal tube), it would be relatively easy to pull new 6 AWG cable. If there is no conduit, then it would be more work and therefore more expensive.

 

[eprosenx]

As eprosenx mentioned, 24A is the safest your circuit should be able to handle with a continuous draw on 30A breakers. Your electrician did you a disservice by installing a NEMA 14-50. While you theoretically could be safe by manually setting the charge in your car to charge at 24A, you're still exposing your home to a potential hazard by having that NEMA 14-50 plug there. What happens if the manual setting gets reset, or if someone else tries plugging into your outdoor plug and drawing a higher current. With a 14-50 plug, a device could theoretically try to draw 50A. 10 AWG wire is good for 30A. For a conservative 14-50 install, the wire should be 6 AWG.

Best case scenario in case something goes bad is that it trips the breakers and all is well. Worse case scenario is that it causes an electrical fire.

1. Either swap out the cable gauge and breakers to 6 AWG and 50A if you want to stay with the 14-50 plug or;
2. Swap out the outdoor receptacle with a 14-30 or 10-30 receptacle and buy the Tesla mobile charging adapter for a 14-30 or 10-30 plug.

If the cable that connects from the panel to outside box is routed through conduit (metal tube), it would be relatively easy to pull new 6 AWG cable. If there is no conduit, then it would be more work and therefore more expensive.

Totally agree, just a couple clarifying points on the moving up to larger gauge wire:

• Conduit is also allowed to be plastic (PVC) in some cases (does not always have to be metal).
• You would need to verify (with a conduit fill calculator) that 6 AWG would not exceed the wire fill limits in whatever conduit was available (this all assumes it is in conduit, which is unlikely - I thought we were talking NM - Romex - here)?
• 50a circuits are actually allowed on 8 AWG, though it is right at the limit of that cable and so if you need to "derate" due to ambient temp being over 86 degrees F or any other reason then you are forced to 6 AWG. So 6 AWG is often recommended and many consider it best practice (Tesla says to use 6 AWG - but I mostly think that is to simplify the instructions).

 

[mikeshyu]

Here's my charging stats for a NEMA 14-30.

The receptacle is in my garage. I also have a 25 foot 10 AWG NEMA 14-30 extension cord between the garage receptacle and the mobile charging cable. https://www.amazon.com/gp/product/B01MRC08Q8/

234V @ 24 amps. Around a 3% voltage drop under load. Not terrible considering the extension cord. 20 miles/hour.

 

[timk225]

I've been charging my 3 on a 6-20 at 15 mph for months, it is almost always enough charge rate.

I just built a new driveway and just finished running power to it. 100 feet of 6/3 cable from the breaker box to the 14-50 and a 50 amp breaker. In 3/4" PVC conduit as specified by my electrician, buried underground in clay/soil dirt about 8 inches for 20 feet of the run.

The 3 will only pull 32 amps so I should be very safe with this setup.

 

[eprosenx]

I've been charging my 3 on a 6-20 at 15 mph for months, it is almost always enough charge rate.

I just built a new driveway and just finished running power to it. 100 feet of 6/3 cable from the breaker box to the 14-50 and a 50 amp breaker. In 3/4" PVC conduit as specified by my electrician, buried underground in clay/soil dirt about 8 inches for 20 feet of the run.

The 3 will only pull 32 amps so I should be very safe with this setup.

Nice! That will double (or slightly more) your charge rate.

Technically that conduit should be deeper, but probably fine. ;-)

You could actually plug a different EVSE into that and get 40 amps of capacity (like a UMC Gen 1).

If if you put a Wall Connector on it (if 100% of the run is in conduit) then you could put it on a 60a breaker and charge at the full 48a rate that the M3 LR supports. ;-)

But it sounds like if a 6-20 was mostly enough then doubling that from 16a continuous to 32a continuous will probably be sufficient. ;-)

I personally really like the Wall Connectors (*especially* outdoors), but that is just me. ;-)

 

[Rocky_H]

If if you put a Wall Connector on it (if 100% of the run is in conduit) then you could put it on a 60a breaker and charge at the full 48a rate that the M3 LR supports. ;-)

Depends on what was used, which wasn't really specific. He did say "6/3 cable". That sounds like bundled Romex cable, not separate wires. If it's really cable, then that's only rated up to 55A, so you can't do a 60A circuit with it.

 

[linkster]

Rock

I have used bundled XHHW-2 for certain applications which would have the same ampacity as THHN @ 75A. Even though this is often used as an SEC, some electricians will use this In a variety of situations. My $.02.

Btw, I have (3) classic HPWCs, but I charge my 3 on a 6-20 (due to its increased mph charge rate over big sis S) nearly every night.

 

[eprosenx]

Rock

I have used bundled XHHW-2 for certain applications which would have the same ampacity as THHN @ 75A. Even though this is often used as an SEC, some electricians will use this In a variety of situations. My $.02.

Btw, I have (3) classic HPWCs, but I charge my 3 on a 6-20 (due to its increased mph charge rate over big sis S) nearly every night.

Hah, wow! So if the S gets one HPWC, what do the other two Wall Connectors get used for?