I am going to post the presentation in text in here so it is searchable by future people (like me).
This is the first of what is likely to be many presentations on the topic of the serious charging infrastructure build I am doing at my house.
Acquire materials (at a discount)
Upgrade house service to 400 A (320 A cont.)
Install conduit to garage and panels
Install conduit and disconnects for stations
Build and install stations
Continuous vs rated, rated*.8=continuous=charging rate
I would like to charge 2 Teslaís 75A and 2 cars 35A
- Off peak and as fast as possible (real time pricing)
Chargers are more efficient at full power
Cheap rates only last so long each night
Four family members, and friends who drive EVís
Three car garage and one outside at the end of the garage
Considering Electrically heated driveway
- 150+ amps at 240V
Puts demand way beyond existing 200A service
Cheaper to put in stuff now compared to rebuilding later
Can use the power to charge cars when it isnít snowing
75+75+35+35 =220 amps continuous!
I would like to just park where convenient
All chargers the same 75 amp capability
This makes electrician headís explode
They do load calculations and assume
All 4 100 A circuits are in use 100% continuous
80 A cont *4 =320A = the complete service of the house!
House also has E-Oven and E-AC, everything else big is NatGas
While I wonít have four Teslaís all charging normally
I need to prevent bad things, and convince inspector all is well
There need to be limits
- Charging stations can be set manually
Disconnects can have smaller fuses
JuiceBox and new Tesla charging stations can agree on a current that doesnít break things (inside brand only)
Not perfect, as they canít account for other large loads
like a heated driveway
Scouring the internet I have found enough to make me believe I can get a system working with OpenEVSE
That is another presentationÖ
Just set them all to 50A while I work out the details
How am I going to do this?
- Breaker boxes above 225A that work for home service donít seem to exist
Normal implementation is to put in 400A meter and then run 2 200A main breaker panels from it.
My service is on the other end of the house in the basement
Put second panel in garage direct from meter?
Put in a meter box with breakers?
Put another meter on the garage itself?
Service upgrade time!
- In my case I am adding a second 200 A panel just like the existing one in my basement and using a plain meter base without breakers
This requires the main breakers be very close to the meter
I also plan to move the E-Oven to the new panel to balance the load when AC and oven are on.
Only one problem, how I am going to run all of those charging stations when I have my service split in two halves which are in the basement?
- Plural sub panels
Two of them, one off of each main panel in the basement to the garage.
Gain access to more power than a single 200A panel could provide, so long as I can convince inspectors
I have 150, 125 and 100 amp breakers to run to the subs, and will run the biggest I can get approved.
The sub panels are 225A capable 42 slot monsters
The slots arenít required, but space to turn the big wire for the charging is very nice (they were cheap too)
- Someone in the audience has just realized:
My job of balancing load across charging stations has just gotten harder
I lose the ability to truly park anything anywhere
I add enough total power that I am not losing sleep
Originally the best I could hope for was 100A continuous shared across four stations
Now I am looking at 240A continuous, with each pair of charging stations sharing 120A continuous
Two Teslaís on one sub panel would limit them to 60A each, not ideal, but not worth chasing
Charging station connectivity
- With OpenEVSE I can connect conduit many ways and with large wire size, but what if I need to change a charging stations in five years?
So instead of wiring from the breaker to the charging station I decided to put in a disconnect
There are more than a few places that this is a requirement
This will be right at the charging station and for added safety I bought fused disconnects
I can run any size charging station by changing the fuses
Proper fuses are more likely to break DC than an AC circuit breaker, they are also faster
Could DC back feed in to the charging station?
In theory if the charger in the car breaks in just the wrong way it could connect the DC battery pack directly the 100 Amp AC circuit feeding the charging station. Depending on the relative voltage and exactly how it went wrong we are either going to be backfeeding DC in to the grid, or doing some very quick charge, discharge cycles to the battery pack. These are both bad, backfeeding DC in to the grid could damage many things in the rest of my house, and since circuit breakers are designed to break AC current only it is likely that it will try to open, only to be fused shut / catch fire by the high current DC voltage flowing through it. This will result in further damage. The resistance of the grid is possibly enough to keep the EV fuses intact as they can provide lots of amps for the car to drive. It is possible that the fuse for charging is different than the controller, we hope so in this situation. Putting fast blow high DC current breaking fuses in line offers additional protection to my house, car, and family. Possibly the reputation of EV's across the world. Before you say that could never happen, lightning strikes routinely cause exactly these types of scenarios in computer power supplies. I also had a car battery charger that died just like this during a storm. When I took it apart the transistor was shorted through, and the 1 amp fuse was predictably blown. Scaling up for a standard 12V car battery to a traction battery, and the circuit breaker is the only external protection as most installations. I will be putting surge protection in the breaker boxes, but they are no guarantee, and since they are parallel, not in line with the car, they can't even blow open to prevent a surge.
Maybe I am paranoid, but compared to the money spent of the rest of this stuff this has the best chance of stopping anything truly bad from happening for a reasonable cost.
Determining wire gauge is easy, except it isnít really.
I have bought for 150A, and 100A connections
Wire insulation is THHN which is 90C ratedhttps://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm
So can I carry 150A on #1? The NEC310.15(B)(16) table says I can
No, the breakers only allow 75C load rating, and requires a minimum of 75C rated wirehttp://www2.schneider-electric.com/resources/sites/SCHNEIDER_ELECTRIC/content/live/FAQS/175000/FA175147/en_US/Wire%20Terminations%200110DB9901R2-02.pdf
So why is THHN the most readily available?
Temperature Derating, my garage is above the ambient temp which is allowed to run 75C wire at full rated current
What I need wire
1/0 copper THHN for 150A breaker to subpanel 300 ft
#6 bare copper earth ground main to sub run 100 ft
#3 copper THHN for 100A breaker to disconnect 450 ft
#8 bare copper earth ground from sub to disconnect 150 ft
I also got a deal on some #4 copper so I picked that up to cover the ground to the mains and the ground rod for the main panel upgrade 25 ft
I could use the #4 to run to 50A outlets if I want
Ft lengths are what I calculated I needed
Now that we know what wire is going where, we can calculate the conduit size. http://conduitfillcalculator.com/
They donít include bare wire for ground, so I have used to THHN to estimate that.
For runs with 3 or more wires, you have to be below 40%.
I am using Electrical Metal Tubing (EMT) as it is thinner and lighter than Rigid Metal Conduit (RMC)
By picking 3 #3 and 1 #8, we get 38% fill on 1 inch EMT
By picking 3 1/0 and 1 #6, we get 29% fill on 1.5 inch EMT
Dropping to 1.25 inch EMT yields 40.5% fill
The runs from the basement to the garage will be challenging enough to pull the wire through that I donít want to make it harder by trying to go with a borderline fill ratio
There are adjustments that can be made for the total amount of bends in a run of conduit
No more than 360 degrees of bends in any one cable pull. You can insert a pull box to break the pull in more than one part.
My basement to garage run will have about 300 degrees of bends, so having a 29% fill will help make that pull much easier
The sub panel to disconnect pulls will only have about 200 degrees so higher fill worries me less
What I bought
4 100A 240V 1ph 3wire fused safety disconnects, I chose SquareD D223N, D223NRB for outdoor
2 150A+ 240V 1ph 3wire main lug breaker boxes, I chose the 225A SquareD 42 slot as they were cheaper than anything else I found
Additional main panel 200A 240V 1ph 3wire, I chose a matching one with what I already have
Meter base 400A 240V 1ph 3wire, 2 sets of lugs, I chose Milbank U1748-O for underground wire
Comed has an approved meter base list, this is one of the few 400A on it, and it seems to be the most common
I kept the same brand and type of breaker boxes so that I could move breakers around at will
SquareD QO series in my case, and they are readily available at more than your local store
Nothing better than retail on Craigslist after monitoring for 6 months
Bought them on Ebay for deep discounts compared to other sources
QO are going through a product changeover which the old models are phasing out, but the feature they added doesnít matter for my purpose
I paid 89 for the 225A and 95 for the 200A panels
I spent 6 months monitoring Craigslist, ebay and Amazon for SquareD QO breakers 100A and above.
100A breakers 2 pole, $31 avg cost delivered
125A breakers 2 pole, $26 avg cost delivered
150A breakers 2 pole, $175 avg cost delivered
200A Main breaker, $45 delivered
The 150A breakers are much more expensive and they also consume four slots in the box instead of two
I went for the SquareD D223N (3) indoor and D223NRB (1) outdoor
Nothing good local for 3 months on Craigslist
Ebay yielded results on New or close enough to new units to meet my needs,
To my door costs 151.57 for all 3 D223N, and 65.24 for the D223NRB
300ft of 1/0 THHN craigslist $205
1000ft of #3 THHN craigslist $400
250ft of #6 ground craigslist $80
500ft of #8 ground craigslist $100
161ft of #4 THHN craigslist $45
$830 in copper cable!
I have serious excess in #3/8 which will get resold
Retail for that is about $1600, and that is shopping around for it.
Thoughts on Juicebox
I was talking to JuiceBox and their 75A charging station has a 6 gauge whip to connect to the service provided by a 100A breaker.
They were quite confident in their solution and suggested using a junction box to connect to larger wire.
You canít wire it direct to a breaker, or even a service disconnect (which was my plan) as breakers and service disconnects are only rated for 75 C wire, and this would be 90C+ to run 100A service through a #6 wire.
I wasnít impressed as their documentation didnít point out this detail or reinforce the junction box suggestion as the requirement that it is.
An electrician should know this but why take that chance.
I reorganized this content compared to my presentation order, and added some written notes to fill in for my verbal stuff. Feel free to ask questions.