My Nissan Leaf Forum

GRA wrote: if we're going to provide a couple of 32A L2s on a 25kVA (20 kVA usable) 208V transformer plus 4 L1s, they need to be 12A.

Who owns the transformers? Most service equipment is rated in terms of its allowable continuous load (unlike residential circuit breakers), so I would think you could draw 25kVA all day long from a 25kVA transformer. I also believe power companies will allow their transformers to be overloaded for a few hours a day, when they know that the load will be lower overnight, so that long term thermal behavior is acceptable.

Thus I would think that a dedicated 25kVA transformer could handle (3) 32A L2s and (3) 16A L1s, given that it will be rare to never that all 6 are in use flat out for more than, say, half a day. Also some consideration should be given to balancing the loads across all three phases, so multiples of 3 are good.

Cheers, Wayne

wwhitney wrote:

GRA wrote: if we're going to provide a couple of 32A L2s on a 25kVA (20 kVA usable) 208V transformer plus 4 L1s, they need to be 12A.

Who owns the transformers? Most service equipment is rated in terms of its allowable continuous load (unlike residential circuit breakers), so I would think you could draw 25kVA all day long from a 25kVA transformer. I also believe power companies will allow their transformers to be overloaded for a few hours a day, when they know that the load will be lower overnight, so that long term thermal behavior is acceptable.

Thus I would think that a dedicated 25kVA transformer could handle (3) 32A L2s and (3) 16A L1s, given that it will be rare to never that all 6 are in use flat out for more than, say, half a day. Also some consideration should be given to balancing the loads across all three phases, so multiples of 3 are good.

Cheers, Wayne

Thanks. For some reason I was thinking this might count as a feeder, and thus would need the de-rating. SCE provides power at Tuolumne Meadows, and PG&E covers the Valley, Wawona and presumably Badger Pass. I'll re-write the technical section accordingly. Unfortunately, my copy of the NEC dates from the early '90s, and the book I have that explains just what the hell the NEC means is also keyed to that edition, long before EV charging was an issue. It looks like I need to read Art. 240 (X-former feeder protection) and Art. 450 (X-former protection) of the 2014 NEC. The x-formers I was able to find a rating plate on in the T. Mdws area were all 208Y/120, as expected. The one @ Tioga Pass was 25kVA, that at the Tuolumne Meadows Lodge was 75kVA. The one at the gas station didn't have a plate I could find, but appeared to be identical to the Tioga Pass one. They're all pad-mounted, unlike some of those I saw at Curry Village which were pole-mounts, but those seemed to be related specifically to a cellphone tower set up in the parking lot.

GRA wrote: SCE provides power at Tuolumne Meadows, and PG&E covers the Valley, Wawona and presumably Badger Pass.

That doesn't necessarily mean that the POCO (power company) owns the transformers, in some case the "service point" is upstream of the transformers and the customer owns them. So you need to find out where the service point is and who owns the transformers.

If the customer installs loads that are larger than can be carried by the existing POCO-owned transformer, then sometimes the POCO just upgrades the transformer without charging the customer. Or sometimes the POCO wants to be paid by the customer for the upgrade. That's a question for the POCO in each case.

Of course, if the customer (the Park Service?) owns the transformers, then any cost of upgrading them is on the customer.

GRA wrote:I was thinking this might count as a feeder, and thus would need the de-rating.

Ratings tend to be continuous on the POCO side of the serivce point, while the NEC applies on the customer side of the service point. So if you have a 25kva 3 phase transformer at 208Y/120, that means the transformer can provide up to 25000/120/3 = 69.4 amps on each phase continuously. If the customer has a continuous load that draws 69.4 amps on each phase, then the NEC requires sizing the conductors after the service point with a factor of 125%, or a minimum of 86.8 amps. In practice you'd install a "100 amp" service (a standard size), using conductors sized for at least 100 amps under the NEC, all fed by that 25 kva POCO transformer.

In fact, the NEC load calculations are generally very conservative. So the NEC might tell you that you need a 200 amp 208Y/120 service, and you'd install 200 amp conductors from the service point to your main panel. But the POCO knows that calculation is conservative, so depending on your load type, it might choose to feed your 200 amp service with only a 25kva transformer. It knows that in practice your demand per phase will seldom exceed 69.4 amps, and that the transformer will be OK with occasional short term overloads.

If the load consists principally of EVSEs, that that is one case where the NEC calculation isn't overly conservative, other than the 125% multiplier for continuous loads. So three 32 amps 208V EVSEs really could draw 64 amps on each phase for a long period of time.

BTW, if you want to balance the EVSE loads across all 3 phases, another option is to install (2) 32 amp 208V EVSEs, one on, say, phase A and B, one on phase B and C, and then (4) 16 amps 120V EVSEs or (single) receptacles, two on phase A and two on phase C. When all 6 are then running flat out, the current on each leg will be 32 amps.

GRA wrote:They're all pad-mounted

Did you take photos of the name plates?

Cheers, Wayne

Here's my first try at the Suggested Charging Sites section. Constructive criticism is welcome.
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Suggested Charging Sites. [Note: the Technical section which immediately follows this goes into more detail about the types and numbers of charging stations recommended for each site, and the reasoning behind the recommendations]

I believe the most critical areas in the park for the initial expansion of charging are at concessioner-operated lodging, retail and activity centers, which have both grid-electricity and excess capacity. In decreasing order of priority:

1. Tuolumne Meadows: at the former gas station and at Tuolumne Meadows Lodge.

The Tuolumne Meadows area is furthest in both distance and elevation gain from existing charging sites in the Valley and outside the park, and also tends to see a higher percentage of environmentally-motivated visitors, who are more likely to opt for PEVs. The gas station already has power, and a transformer which appears to be going unused now. Charging stations located there can serve both the store/grill and campground guests.

Charging stations at the Lodge serve both overnight guests and those there just for breakfast or dinner.


2. The Valley: Yosemite Village, Yosemite Valley Lodge, Half Dome Village and the Majestic Yosemite Hotel.

An expanded number of stations in Yosemite Village will better serve short-term day-use visitors to the Village, who are currently restricted to just a single charger there. If it's in use they have to wait or go elsewhere and hope to find an available, working charger. If it's out of service they may well be out of luck, and will need to be towed to somewhere they can charge. Many BEV owners won't take that chance, and will just opt to drive their fossil-fuel powered vehicle instead. As is stressed in the Technical section, redundancy at each charging site is essential.


Charging stations at Yosemite Valley Lodge would serve overnight guests there as well as Camp 4 visitors, and also some day-use visitors visiting Yosemite Falls or the Merced River.

Half Dome Village would serve lodgers/dining guests, as well as the Pines Campgrounds and Happy Isles trail users.

The Majestic Yosemite Hotel sees a relatively large number of overnight users with higher-end PEVs, and expanding charging there will encourage that trend.


3. Badger Pass and Wawona.

Badger Pass needs charging in two areas, one for day skiers and one for wilderness permit overnight users in winter, and to encourage people to park and use the shuttle in summer.

The Wawona area is closest to existing charging sites in the Valley and outside the park, and can be left to last. Charging is needed at the Big Trees Hotel to serve overnight guests, and at the store/Pioneer Yosemite History Center parking for day use.


Once those facilities are provided for, follow-on charging sites should be aimed at NPS Visitor Information/Wilderness Permit Centers and trailheads with grid electricity either at them or nearby. Examples include the Big Oak Flat and Tioga Pass entrance stations; Happy Isles, Dog Lake/JMT, and Glen Aulin/Tuolumne Stables parking lots; Tuolumne Meadows and Wawona Visitor Centers, and Tuolumne Meadows Wilderness Permit Center.

wwhitney wrote:

GRA wrote: SCE provides power at Tuolumne Meadows, and PG&E covers the Valley, Wawona and presumably Badger Pass.

That doesn't necessarily mean that the POCO (power company) owns the transformers, in some case the "service point" is upstream of the transformers and the customer owns them. So you need to find out where the service point is and who owns the transformers.

If the customer installs loads that are larger than can be carried by the existing POCO-owned transformer, then sometimes the POCO just upgrades the transformer without charging the customer. Or sometimes the POCO wants to be paid by the customer for the upgrade. That's a question for the POCO in each case.

Of course, if the customer (the Park Service?) owns the transformers, then any cost of upgrading them is on the customer.

Don't know who owns them, but I think I can leave that to the park to handle.

wwhitney wrote:

GRA wrote:I was thinking this might count as a feeder, and thus would need the de-rating.

Ratings tend to be continuous on the POCO side of the serivce point, while the NEC applies on the customer side of the service point. So if you have a 25kva 3 phase transformer at 208Y/120, that means the transformer can provide up to 25000/120/3 = 69.4 amps on each phase continuously. If the customer has a continuous load that draws 69.4 amps on each phase, then the NEC requires sizing the conductors after the service point with a factor of 125%, or a minimum of 86.8 amps. In practice you'd install a "100 amp" service (a standard size), using conductors sized for at least 100 amps under the NEC, all fed by that 25 kva POCO transformer.

In fact, the NEC load calculations are generally very conservative. So the NEC might tell you that you need a 200 amp 208Y/120 service, and you'd install 200 amp conductors from the service point to your main panel. But the POCO knows that calculation is conservative, so depending on your load type, it might choose to feed your 200 amp service with only a 25kva transformer. It knows that in practice your demand per phase will seldom exceed 69.4 amps, and that the transformer will be OK with occasional short term overloads.

If the load consists principally of EVSEs, that that is one case where the NEC calculation isn't overly conservative, other than the 125% multiplier for continuous loads. So three 32 amps 208V EVSEs really could draw 64 amps on each phase for a long period of time.

BTW, if you want to balance the EVSE loads across all 3 phases, another option is to install (2) 32 amp 208V EVSEs, one on, say, phase A and B, one on phase B and C, and then (4) 16 amps 120V EVSEs or (single) receptacles, two on phase A and two on phase C. When all 6 are then running flat out, the current on each leg will be 32 amps.

Okay, thanks, I'll mention it, but I think I can probably leave most of that to the Park Engineer and maintenance people. I'll recommend some options, but they're the ones who know what kind of excess capacity they've got in many of the areas, load profiles etc.. I'm definitely going to recommend ToU pricing on any L2s with PoS systems, to keep them as free as possible during the day for short-term users.

wwhitney wrote:

GRA wrote:They're all pad-mounted

Did you take photos of the name plates?

Cheers, Wayne

Unfortunately not. My cell phone remains just that, and I haven't bothered to haul out my 35mm SLR in years. Besides, I had to check some of them out surreptitiously ("What, officer? You say the road is marked 'Closed to the Public' 1/2 mile back? I must have taken a path here that missed it. My apologies, and I promise not to do it again (until next time)." So, in the case of Tuolumne Meadows Lodge, which had closed for the season and was being dismantled, my inspection was somewhat hurried and had to make use of twilight. Meant to write the info down, but naturally I'd left my notebook in my other pack.

Just wanted to note that, a couple of weeks ago, we were able to take our new-to-us Tesla S-85 on a trip to Zion National Park in Utah. Getting there was a piece of cake - we maintained "normal" highway speeds and Supercharged only at Primm, NV and briefly at St. George, UT.

What's relevant here is that it really worked well to have access to L2 charging (ranged from 22-30 amps) during our time at Zion. The two charging stations by the main Visitor Center are right by the shuttle stop, so it was easy to charge while doing day hikes out of the main canyon. They are also walking distance to both of the canyon campgrounds (South and Watchman).

Why, one might ask, would we want/need to charge at or directly adjacent to a national park when the nearest Supercharger or fast charger is less than 50 miles away? Simple - to enable day trips and to enable skipping a charge stop on the way home. On one of our days camped at Zion, we took a day trip to Bryce Canyon National Park, away from any fast chargers. (The round trip to Bryce from Zion required nearly four hours of driving and was about 180 miles, which we completed on a single charge with about 75 miles of range to spare.) On another day, we drove up Kolob Terrace Road in Zion National Park and did a higher-elevation hike there. Plus, Zion Lodge (in the canyon) hosted a nighttime ranger program and the only way to travel there after hours was by private automobile. At the conclusion of our Zion visit, we drove directly to Valley of Fire State Park in Nevada without a charge stop (we paid for an RV site with electrical hookups at Valley of Fire and stayed one night).

So, while I'm a proponent of using shuttles to reduce congestion, and of encouraging people to get out of their vehicles and hike, it must be acknowledged that private vehicles will continue to play a key role in enabling the exploration of our most beautiful places. To the extent permitted by electrical infrastructure and park regulations, I hope to see more EV charging opportunities arise inside and around the parks. This will give EV driving visitors a level of freedom that's competitive with fossil fuel cars, as it did for us at Zion.

By the way, L2 charging at the Zion visitor center is a flat $5 for three days. Because we drew a significant amount of energy (over 100 kWh), I voluntarily paid extra! We only briefly saw one other EV (another Tesla) using the charging stations, and there are also some hotels near the park entrance that offer charging.

Thanks for the informative report. National parks are my favorite places to visit. For the first time, I am beginning to think I might eventually need a Tesla.

Here's a slightly redacted copy of a comment that I just provided to the park... (unfortunately ran out of time to turn in a handwritten comment before our departure)

We just returned from several days of camping and hiking at Tuolumne Meadows in Yosemite. Although we've enjoyed Yosemite's high country for years, this was our first time driving there in our Tesla Model S 85. Members of the park staff and other campers seemed genuinely pleased to see an EV up there, and it turned out that there was one other Model S at the campground during our visit.

Because of another commitment, we approached Yosemite from the north, and Supercharged to about 90% at Topaz Lake, NV, on US-395 at the state line. Driving up and over Tioga Pass was a pleasure, of course, and we arrived at Tuolumne with about 50% charge remaining. This was enough for some driving around, but not a whole lot, as we needed to reserve some charge to reach the Mammoth Lakes Supercharger in order to return home to the southland.

However, we ended up deciding we wanted to attend, for our first time ever, an evening/night presentation by "Ranger Bryan" down at Mono Lake South Tufa. So we ended up making an extra trip down to Mammoth and hanging out at the Supercharger for 40 minutes. This gave us ample range to visit Mono Lake (which was absolutely gorgeous in the light of the full moon in a partly cloudy sky), head back up to Tuolumne, and drive to various trailheads for day hiking.

Had we planned ahead, we could have added the needed range on a single 120V outlet by the parking lot at Tuolumne Lodge. I confirmed with lodge management that this outlet is available to all EVs during the evening, night, and early morning hours, which is great news! The downside is that the lodge is not exactly next door to the campground. It would have been a bit of a hassle to shuttle the car back and forth just to add 40-50 miles of range while taking the chance of the sole outlet already being occupied by another EV.

Thanks to Tesla's Supercharger network, it's great to experience using a Model S/3/X for visiting Yosemite's high country. However, this would be considerably tougher in a non-Tesla EV (think Chevy Bolt for now) or in a Tesla with a smaller battery pack. Even with larger battery Teslas, families are going to want to drive around some. Using shuttle buses outside the Valley isn't always practical due to schedule and stop limitations.

In the words of one of the rangers with whom we spoke, installing more EV charging stations within the park (in addition to the two in the Valley) would align well with the park's mission. Eliminating the gas station at Tuolumne Meadows was a good step to take, but it would be a mistake to preclude using that site for some EV charging.

Besides signaling to park visitors that EVs offer a way to travel to the park in a significantly more sustainable manner, offering EV charging in the Tuolumne campground area would reduce the likelihood of EV drivers needing to spend additional hours to charge their cars. It would help close the "convenience gap" relative to gasoline cars visiting the area, as fossil fueled cars can add hundreds of miles of range in mere minutes down in Lee Vining. Our entire society must transition away from fossil fuels, and the more we can all do to accelerate that transition, the better our planet's future will be.

Glad you made it up there. There are a couple of receptacles closer than the Lodge, although both are unofficial (I take it they're now officially letting people use the one by the shuttle bus stop at the Lodge?). One's on the southeast side of the Wilderness Permit building, and the other's back in the trees off the right side of the campground entrance road between the 'Employee parking area and the campground reservation office - both would require an extension cord, at least 50' and maybe 100' in the latter case.

I'm still wavering about whether or not to submit my proposal for inside the park charging, especially as there are plans to install Chargepoint dual-standard QCs at Oakdale, Groveland and Hardin Flat (Rush Creek Lodge) on 120, and at Oakhurst on 41. Look here: https://www.google.com/maps/d/viewer?mi ... 000007&z=9

and select GFO-15-603 Interregional corridors, or just look at the orange icons. Ideally, I'd also like to see one in El Portal (or at least Mariposa) and definitely Lee Vining. I'm unaware of any schedule as to when this is likely to happen, but at least they know where they intend to put them and the proposed awards were announced last October: http://www.energy.ca.gov/contracts/GFO-15-603_NOPA.pdf

GRA wrote:Glad you made it up there. There are a couple of receptacles closer than the Lodge, although both are unofficial (I take it they're now officially letting people use the one by the shuttle bus stop at the Lodge?). One's on the southeast side of the Wilderness Permit building, and the other's back in the trees off the right side of the campground entrance road between the 'Employee parking area and the campground reservation office - both would require an extension cord, at least 50' and maybe 100' in the latter case.

When we drove up to the kiosk at the campground entrance, I asked about outlets to charge our EV, and was directed to the Lodge. I don't know how "official" the Lodge charging is, but it seems that EV drivers are routinely being directed there, as confirmed by the manager at the Lodge. Yes, the outlet there is by the shuttle bus stop

Perhaps if I'd been a bit more persistent, I could have gained access to a different outlet, such as the ones you pointed out. Charging at 120V through a long extension cord may or may not be fruitful, however. I was also tempted to try an outlet on the back side of the old gas station, but didn't want to undermine the cause by charging without permission!

GRA wrote:I'm still wavering about whether or not to submit my proposal for inside the park charging, especially as there are plans to install Chargepoint dual-standard QCs at Oakdale, Groveland and Hardin Flat (Rush Creek Lodge) on 120, and at Oakhurst on 41. Look here: https://www.google.com/maps/d/viewer?mi ... 000007&z=9

and select GFO-15-603 Interregional corridors, or just look at the orange icons. Ideally, I'd also like to see one in El Portal (or at least Mariposa) and definitely Lee Vining. I'm unaware of any schedule as to when this is likely to happen, but at least they know where they intend to put them and the proposed awards were announced last October: http://www.energy.ca.gov/contracts/GFO-15-603_NOPA.pdf

Thanks for the links! Adding a few QCs on the west side of the park would be helpful for SoCal visitors heading for the Valley and for Bay Area visitors going anywhere in the park. This sort of mirrors what Tesla has already done by installing Superchargers in Groveland and Fish Camp. Indeed, QCs in these locations would probably do more good than adding more L2 charging in the Valley, simply because the Valley gets so congested and it could be tough to count on being able to access an EVSE.

Tuolumne Meadows, on the other hand, is comparatively isolated and much less congested. Other than Tesla Superchargers, US-395 is an EV charging desert, and there appear to be no plans to change that in the near future. I agree that CCS/CHAdeMO QCs in Lee Vining could be quite helpful, even for Tesla owners. Still, there's a lot of elevation change between Tuolumne and Lee Vining, so it's not exactly ideal to have to drive down to Lee Vining if you're in Tuolumne and you need to add more charge (unless of course you're going to Mono Lake for the evening anyway). People in gas cars now have to do this, but at least they generally have more range per "fill up". Also, compared to using a QC, it's more convenient and easier on the grid to charge on L2 while one sleeps, and it's always ideal if one can start the drive home with close to a full charge.

So, in view of Tuolumne's isolation and the large number of campsites there, I'd strongly encourage you to submit any EV charging proposal that includes L2 in Tuolumne Meadows. Even for through-travelers on CA-120, having some EVSEs in Tuolumne would provide range assurance on that long stretch of road.