New 3 car detached garage: how big should the wire be

[Roger Feeley]

We are building a 3 car garage with living quarters above. I’m trying to think ahead to the day when cars will be electric and we might want to charge three at the same time. Really, the only decision I have to make now is the size of the wire from the main panel to the garage. If the wire is big enough, changing breakers at either end would be relatively cheap.

one thing I did ask the builder for is a 2” pipe from house to garage with a pull cord so we can add other kinds of wire in the future. Optical fiber, maybe. Who knows?

Suggestions?

[Tom M King]

How far, and direct bury or in conduit? Wire has to be derated when in conduit.

[Alan Lightstone]

Assuming that you are using NEMA 14-50 outlets for the cars (or the equivalent), 3 cars could be pulling 40 amps x 3 = 120 amps at 220V charging. Not a trivial amount of power. I don't think these cars have a current surge when starting a charge (my Tesla doesn't), so that's probably a reasonable steady state of charging current. But that's going with the 80% rule per outlet. So 3 NEMA 14-50 circuits at 50 amp rating a piece = 150 amp rated wire at 220V. An awful lot of current. Electric meters gonna spin like crazy with that one.

Not sure how big wire that would require. I've leave that up to more knowledgeable people. Gonna be big.

[Kendall Scheier]

Do 3 separate circuits so you don’t need 1 gauge wire. 3 40 or 50 amp circuits are better than one 120 amp circuit.

[Mike Henderson]

I put in a subpanel in my garage with two 50 amp NEMA 14-50 outlets. If I recall correctly, I use 6 gauge from the subpanel to the outlets but I don't remember what I used from the main panel to the subpanel.

Mike

[Kev Williams]

I would think 6 gauge should be plenty, but what you might also consider doing is upgrading your incoming service by 100 amps...

[Charlie Velasquez]

Three ev’s, figure 100-150 amps,
living quarters above… temps in Falls Church ranges from single digits to 90s so figure both heating and cooling will be necessary, refrigeration, cooking…

Even a 200 amp sub may be a stretch if you plan to charge all at once.

Looks like maybe 2/0 or 3/0 copper or 4/0 or 250mcm aluminum (my choice; and 4/0 is the max you can fit in 2” conduit if that is your plan.)

edit: the smaller of each of the copper and aluminum is only if your ahj lets you to use the 80% rule. It is not really applicable in this situation, but inspectors have been known to allow it.
? Is your main sufficient to handle this load?

[Mike Henderson]

Remember that an EV will only pull 80% of the outlet value, so on a 50 amp outlet, the max a car will pull is 40 amps. Most people do not charge their EV every night, and you can program the car to only charge at a certain time, so even if you have two EVs, you can arrange so that only one is charging at a time (if that's a concern).

Mike

[Bruce Volden]

]We are building a 3 car garage with living quarters above.[/B] I’m trying to think ahead to the day when cars will be electric and we might want to charge three at the same time. Really, the only decision I have to make now is the size of the wire from the main panel to the garage. If the wire is big enough, changing breakers at either end would be relatively cheap.

one thing I did ask the builder for is a 2” pipe from house to garage with a pull cord so we can add other kinds of wire in the future. Optical fiber, maybe. Who knows?

Suggestions?
Many fires from EV's!
I wouldn't even consider such an undertaking. Nothing against EV's.

Bruce

[Jim Becker]

Vehicle chargers typically utilize a 50 amp circuit, although they don't typically draw more than 40 amps or so. So if you want to support two chargers, you'll want a 100 amp subpanel minimum in the garage. That's if it's not being used as a shop, too. The additional living quarters are in addition to that. If you're putting in additional conduit and it will carry coms, it needs to be separated from the conduit that the electric service will pass through. I just pulled my Ethernet between the house and the new shop building today, as a matter of fact. (pre-terminated direct contact rated Cat 6 cable...even in a conduit, it needs to be rated for wet conditions. Conduits leak)

You may be able to get a tax benefit from preparing to support EV charging that will help with the cost of the subpanel, etc.

[Lee Schierer]

I would give the building separate metered service from the power provider into at least a 200 amp panel. That lets you charge the cars from separate outlets and still leaves some power for the living quaters, assuming it is not a 3 bedroom house.

[Roger Feeley]

Remember that an EV will only pull 80% of the outlet value, so on a 50 amp outlet, the max a car will pull is 40 amps. Most people do not charge their EV every night, and you can program the car to only charge at a certain time, so even if you have two EVs, you can arrange so that only one is charging at a time (if that's a concern).

Mike

Im betting that as electrics take over the chargers will get smarter about balancing multiple cars.

[Alex Zeller]

My biggest problem with EVs is charging time. But that's while traveling. For home charging speed isn't that important most of the time. For a 3 car set up I would do one dedicated level 2 charger and a second power sharing (also called dual charging) level 2 charger. That'll be two 50 amp circuits, not 3. So the question is how often do you plan on driving 200 miles a day in all 3 cars in multiple days in a row? Most likely never.

[Jim Becker]

I would give the building separate metered service from the power provider into at least a 200 amp panel. That lets you charge the cars from separate outlets and still leaves some power for the living quaters, assuming it is not a 3 bedroom house.

He can do things the same way I just did here and the billing is simpler...upgrade the service to a 320 amp meter and split just past the meter...200 amps to the house and 200 amps to the outbuilding. The power company here considers a separate meter for an outbuilding to be a commercial account and the extra charges for the privilege get put on the bill. The exception to my advice relative to the living quarters is that if it's going to be a rental, one has to decide whether to include electric in the rent (or have a private meter to track it) or have separate service and separate billing. The latter complicates having the garage with EV charging on the same meter as the rental living quarters.

[Mike Henderson]

My biggest problem with EVs is charging time. But that's while traveling. For home charging speed isn't that important most of the time. For a 3 car set up I would do one dedicated level 2 charger and a second power sharing (also called dual charging) level 2 charger. That'll be two 50 amp circuits, not 3. So the question is how often do you plan on driving 200 miles a day in all 3 cars in multiple days in a row? Most likely never.

It's better that that. Just like with gasoline, you don't (often) run it all the way down before you recharge. I'd expect that most people would recharge when they get down to about half charge. So if you had a 90kWh battery, you'd need to put about 45kWhs into it. At 40 amps and 240 volts, that's a bit less than 5 hours. If your electricity was $0.30/kWh, it would cost you about $13.50 to "fill the tank". That's quite a bit less than for gasoline.

Mike

[John K Jordan]

… The power company here considers a separate meter for an outbuilding to be a commercial account and the extra charges for the privilege get put on the bill. …

Same here.

[John K Jordan]

…

one thing I did ask the builder for is a 2” pipe from house to garage with a pull cord so we can add other kinds of wire in the future. Optical fiber, maybe. Who knows?

Suggestions?

When I built my shop (250’ from the meter) I dig a 24” wide trench and ran 3 consults. Two are 2”, one with the electrical conductors (#1 copper) and the second empty except for a rope. I added a 1” conduit on the other side of the trench with 2 cat6e ethernet cables, one for data and the second a spare, just in case.

I know nothing about EVs but calculate wire size according to the voltage drop tables based on the worst case of power use. I don’t see underground wiring runs as a place to try to save money. The cost of even big copper wire is insignificant relative to the total cost of the construction. I may never push the capacity but what about the next owner?

JKJ

[Jim Becker]

It occurs to me that there may be no good reason not to wire for 200 amp service to that building as the living quarters upstairs may even trigger that requirement in some jurisdictions. That will easily cover two EV chargers running simultaneously as well as the LQ including HVAC. As John noted, there's just no good reason to economize on what goes in the ground...

[Alan Lightstone]

My biggest problem with EVs is charging time. But that's while traveling. For home charging speed isn't that important most of the time. For a 3 car set up I would do one dedicated level 2 charger and a second power sharing (also called dual charging) level 2 charger. That'll be two 50 amp circuits, not 3. So the question is how often do you plan on driving 200 miles a day in all 3 cars in multiple days in a row? Most likely never.
A very good point. I don't know of any owners of three EVs right now, so never heard what any individuals do. I'll hopefully have a second EV next year or 2024 (whenever Tesla finally starts shipping Cybertrucks and my reservation number comes up), so I'll have to figure out a way to juggle 2EVs charging. But I would suggest the OP wire the house to be able to charge all 3 EVs at once. Frankly, having the space for all 3 EVs to charge at once (you would have to have 3 locations that fit your EVs with outlets close to them) to make this work. Not easy in many houses. Wouldn't work in mine, but with his new construction with a 3 car garage (you did spec out the wider garage door so that it really can fit two cars, right? I know many people who were burned by "two car garages" which really don't fit two cars side by side in the double door.)

The smart charger is an interesting idea, but I would save the money and just put three NEMA 14-50 outlets in three locations.

[Alan Lightstone]

It's better that that. Just like with gasoline, you don't (often) run it all the way down before you recharge. I'd expect that most people would recharge when they get down to about half charge. So if you had a 90kWh battery, you'd need to put about 45kWhs into it. At 40 amps and 240 volts, that's a bit less than 5 hours. If your electricity was $0.30/kWh, it would cost you about $13.50 to "fill the tank". That's quite a bit less than for gasoline.

Mike

Actually, talking with fellow EV owners, there is tremendous variation as to how people charge them. But I don't live in California, so time-of-day charges aren't in effect here.

I know owners who plug in their car every night. I know ones who charge when it's about half empty. I know ones who take the car down to about 20% capacity.

Personally, I tend to charge the car before the weekend, and usually do it in daytime with the solar panels running full. No real reason for that, it's just what I do.

With a Tesla, you are told not to charge the car more than 90%, or let it get down to 10% to maximize battery life.

In my case, I have a Tesla charger and charge at 48 amps. Usually takes about 4-6 hours to fully charge, depending on where we started. What I tell people is that as long as your car can be fully charged by morning, it's irrelevant how long that takes. So arranging for 80 amp charging with a Tesla charger is a silly waste of money. As it would be for other EVs assuming some can charge using that much current in the future. Most won't.

[Roger Feeley]

Many fires from EV's!
I wouldn't even consider such an undertaking. Nothing against EV's.

Bruce

Ive heard about the fires too. I found an article
https://www.autoweek.com/news/a38225037/how-much-you-should-worry-about-ev-fires/


A better way of looking at electric vehicle fires is to compare the number of fires per 100,000 vehicles sold. Researchers from insurance deal site Auto Insurance EZ (https://www.autoinsuranceez.com/gas-vs-electric-car-fires/) compiled sales and accident data from the Bureau of Transportation Statistics and the National Transportation Safety Board. The site found that hybrid vehicles had the most fires per 100,000 sales at 3474.5. There were 1529.9 fires per 100k for gas vehicles and just 25.1 fires per 100k sales for electric vehicles.
The reason why it's easy to think that electric car fires are so common is because EVs are still novel and still unknown to a large portion of the public. News and media outlets report on electric car fires more often because of its, which can make it seem like they are a common occurrence. What's more, when there are highway vehicle fires, they can require a tremendous amount of effort from emergency personnel to extinguish the blaze. A chain reaction inside the batteries—sometimes called thermal runaway—can occur when the battery generates more heat than it can dissipate.

[Mike Henderson]

Ive heard about the fires too. I found an article
https://www.autoweek.com/news/a38225037/how-much-you-should-worry-about-ev-fires/


A better way of looking at electric vehicle fires is to compare the number of fires per 100,000 vehicles sold. Researchers from insurance deal site Auto Insurance EZ (https://www.autoinsuranceez.com/gas-vs-electric-car-fires/) compiled sales and accident data from the Bureau of Transportation Statistics and the National Transportation Safety Board. The site found that hybrid vehicles had the most fires per 100,000 sales at 3474.5. There were 1529.9 fires per 100k for gas vehicles and just 25.1 fires per 100k sales for electric vehicles.
The reason why it's easy to think that electric car fires are so common is because EVs are still novel and still unknown to a large portion of the public. News and media outlets report on electric car fires more often because of its, which can make it seem like they are a common occurrence. What's more, when there are highway vehicle fires, they can require a tremendous amount of effort from emergency personnel to extinguish the blaze. A chain reaction inside the batteries—sometimes called thermal runaway—can occur when the battery generates more heat than it can dissipate.

I question the number of fires in hybrids - that would indicate that 3.5% of all hybrids sold catch fire each year. That's a LOT. If that many were catching fire, there would be a lot of action to address the problem.

MIke

[Lee Schierer]

Ive heard about the fires too. I found an article
https://www.autoweek.com/news/a38225037/how-much-you-should-worry-about-ev-fires/


A better way of looking at electric vehicle fires is to compare the number of fires per 100,000 vehicles sold. Researchers from insurance deal site Auto Insurance EZ (https://www.autoinsuranceez.com/gas-vs-electric-car-fires/) compiled sales and accident data from the Bureau of Transportation Statistics and the National Transportation Safety Board. The site found that hybrid vehicles had the most fires per 100,000 sales at 3474.5. There were 1529.9 fires per 100k for gas vehicles and just 25.1 fires per 100k sales for electric vehicles.
The reason why it's easy to think that electric car fires are so common is because EVs are still novel and still unknown to a large portion of the public. News and media outlets report on electric car fires more often because of its, which can make it seem like they are a common occurrence. What's more, when there are highway vehicle fires, they can require a tremendous amount of effort from emergency personnel to extinguish the blaze. A chain reaction inside the batteries—sometimes called thermal runaway—can occur when the battery generates more heat than it can dissipate.


Many fires from EV's!
I wouldn't even consider such an undertaking. Nothing against EV's.

Bruce

Be careful where the data comes from. Car and Driver has an article that says the NTSB and NHTSA don't collect car fire data. The National Fire Incident Reporting System (NFIRS) doesn't break their data down by vehicle type. It would appear that AutoInsuranceEZ may have data no one else does. (https://www.caranddriver.com/news/a40163966/cars-catching-fire-new-york-times-real-statistics/)

[Bill Dufour]

Co worker has a small rental house in the backyard. They installed a separate meter, fed from the main house. They bought their own meter and read it themselves. They charge the tenant based on their readings. The power company is not involved beyond the main house meter.
I believe it is minimum $25/month to have metered service plus charges for any power used. With more solar installations that minimum will be going up. I have read an extra $60 per month for solar. I have no idea how much an extra meter on one service drop would be.
Bill D

[Adam Herman]

distance and load are critical. sounds like you should hire an electrician. Car chargers can generally be set to different max charge levels, just did a ford lightning charger last week and we set it to 48 amps to use existing wiring and save the guy a bunch of money. You can overthink this stuff way too much with "what if".
pick a panel size, size the wire for that main breaker and distance keeping the voltage drop in spec.

I am studying for my journeyman.

with 3% voltage drop at 240 volts and 100 feet distance I get #1 CU or 3/0 alum.

for 300 feet i get 350kcmil alum or 4/0 CU

k=12 for CU
k=20 for AL

[Roger Feeley]

all,
Great advice. I won’t be doing this. I just want to be an informed consumer. We have a 400 amp service into the main house. There is a 120amp breaker supplying our “granny flat”. I’m thinking another 100 amps or so to the garage.

I should mention here that the living quarters electrical needs will be minimal. No stove. Just a mini-fridge, toaster oven and induction countertop hob. There will be a mini split type heat pump and a very modest HW heater. It’s really more of a guest quarters.

I agree with the consensus that charging three electric vehicles from nothing at the same time would be rare. If the tech doesn’t already exist, I would imagine that some means of juggling multi-car charging will come along.

[Kev Williams]

--from a March 2, 2022 article in Forbes:

he fire risk from electric cars appears to be less than for conventional vehicles, although Americans awaiting their new Volkswagens to be delivered from Europe could be forgiven for doubting that as their new cars were destroyed, apparently by a spontaneous lithium-ion battery fire on the Felicity Ace car transporter ship.

The ship sank Tuesday.
488602

Any firm conclusions on fire risks generally are not yet possible because there is not enough data to decide that pure electric cars are more prone to spontaneous fire than internal combustion engine (ICE) ones, or more likely to burst into flames after an accident.

As for the fire on VW’s car transporter from Germany to the U.S. carrying almost 4,000 vehicles, probably including battery-electric Porsche Taycans, Audi e-Trons and VW ID.4s, a report in Britain’s Daily Mail quoted the Felicity Ace’s captain Joao Mendes Cabecas saying lithium-ion batteries in the electric cars on board caught fire.

...Recent data whipped up a storm on both sides of the argument. Electric car enthusiasts liked the idea that National Transportation Safety Board (NSTB) data, analysed by AutoinsuranceEZ, showed BEVs were far safer than hybrids and ICE cars. AutoinsuranceEZ said the numbers showed electric cars were less prone to fire than other vehicles, with hybrids the most dangerous, followed by gasoline vehicles.

Hang on a minute said the doubters, the data shows no such thing. Graham Conway, principal engineer at the Southwest Research Institute in San Antonio, Texas, said there’s not enough information to decide if EVs are more prone to spontaneous fire than ICE ones.

“It is still too early to make any conclusions about EVs and spontaneity of fires. I just don’t think we have the sample size of data or the reporting structure for fires to say with any certainty. What is clear is that the fire is more difficult to deal with, the energy release during the exotherm of the electrolyte takes a lot of cooling to extinguish,” Conway said

Conway said the data didn’t allow for solid conclusions.

“The NTSB data said that after 41 fatal collisions involving BEVs, 1 caught on fire (2.44%). The NTSB data said that after 20,315 fatal collisions involving gasoline vehicles, 644 caught on fire (3.17%). The NTSB data said that after 543 fatal collisions involving gasoline hybrid vehicles, 12 caught on fire (2.21%),” Conway said.

“But 41 crashes vs 20,315 crashes vs 543 crashes make it statistically irresponsible to compare these numbers. For example, if there was a 42nd crash with an EV and it caught on fire then it would be 4.76% of EVs or double the rate of hybrids. Until the sample size is the same and significant we just can’t say which will be worse or not,” Conway said.

MY 'sketchiness' towards EV's are the number of spontaneous fires that seem to occur. Aside from its battery being the cause, I've never once heard of a gas vehicle just simply catching on fire. I have no desire for an EV, but should I ever get one, it will never be parked in a garage that's connected to the house...

[Alan Lightstone]

Co worker has a small rental house in the backyard. They installed a separate meter, fed from the main house. They bought their own meter and read it themselves. They charge the tenant based on their readings. The power company is not involved beyond the main house meter.
I believe it is minimum $25/month to have metered service plus charges for any power used. With more solar that minimum will be going up. I have read an extra $60 per month for solar. I have no idea how much an extra meter on one service drop would be.
Bill D

Duke Energy just started charging $30.00 plus tax down here as a minimum charge. Even if you use less (we have a surplus with solar panels). I'd imagine they'll keep trying to raise that in the future. That's just with one meter. Not sure how much they would add for a second meter. Not sure if you have Duke Energy in Virginia.

[Mike Henderson]

Duke Energy just started charging $30.00 plus tax down here as a minimum charge. Even if you use less (we have a surplus with solar panels). I'd imagine they'll keep trying to raise that in the future. That's just with one meter. Not sure how much they would add for a second meter. Not sure if you have Duke Energy in Virginia.

Here in CA, they started charging a "grid charge" to support the cost of maintaining the grid. That's fair because anyone who has solar depends on the grid and should pay a fair price for that.

I'm grandfathered in for a few years because I put solar in very early - so I don't know exactly what the monthly charge is. The grandfather is limited in time so I'll find out eventually,

Mike

[Ole Anderson]

Many fires from EV's!
I wouldn't even consider such an undertaking. Nothing against EV's.

Bruce Boy, that is a contradictory statement.

[George Yetka]

I would drop a new 200 amp service to the garage.

[Charlie Velasquez]

From the replies it is clear you will need more than 100 amps. Some have suggested 200 amps.

You have asked what size wire to run.
You seem to be good with over-sizing and switching out the sub panel breaker at a later date if need be.
2/0 Cu would allow a max of 175 amps, 3/0 would allow a max of 200 amps.
3/0 Al would allow a max of 175 amps, 4/0 would allow a max of 200 amps (and the max size you can fit in 2” conduit).
(need to clarify my previous edit- I was informed the 80% rule does not apply, but the “next size up” rule does. Aluminum ampacities have weird numbers. Circuit breakers are standard sizes. If there is no circuit breaker that matches the conductor ampacity you may use “the next size up”. I was told that is why the ahj will pass 180 ampacity 4/0 aluminum for a 200 amp panel.)

[Jim Becker]

If one is going to run wire capable of 200 amps, just put in 200 amps for the structure. The cost of electrical components is up there and there's little incentive to spend big bucks now for a smaller breaker for the disconnect and replace it later with a higher capacity breaker with more big bucks. The panel in the structure would need to be 200 amp rated anyway to support the upgrade and the cost for the panel is nearly the same, regardless of the amperage rating at this point. Copper is pretty much avoided like the plague at the moment for service and feeder cabling unless one wins the lottery. Even aluminum is "up there". The service to my shop that was just cut in was $1800 higher in materials alone from when it was originally quoted early summer.

[Tom M King]

This page has the wire dimensions for various aluminum direct burial service entrance wire. I'm getting read to run 487 feet of this.

https://nassaunationalcable.com/products/500-500-500-500-350-wofford-quadruplex-aluminum-conductor-underground-direct-burial-600v-urd?_pos=5&_sid=ce681745a&_ss=r

[Chris Parks]

--from a March 2, 2022 article in Forbes:

488602


MY 'sketchiness' towards EV's are the number of spontaneous fires that seem to occur. Aside from its battery being the cause, I've never once heard of a gas vehicle just simply catching on fire. I have no desire for an EV, but should I ever get one, it will never be parked in a garage that's connected to the house...

ICE cars do catch fire ferraris catch fire - Google Search (https://www.google.com/search?q=ferraris+catch+fire&oq=ferraris+catch+fire&aqs=edge..69i57j0i22i30l8.8874j0j1&sourceid=chrome&ie=UTF-8)

[Bill Dufour]

Porsche 911 with early electric fuel injection were known for catching the engine on fire while parked. A fuel hose would leak and the gas would catch on fire melting the hose so it leaked more. The fuel pump was always ready to come on if the pressure dropped so cold starts would not be a problem. The only way to turn off the fuel pump was to cut the battery cable. By the time the fire department got to the car the magnesium engine block might be burning. Few fire departments can put out a magnesium fire. Adding water just makes it burn hotter.
modern cars need you to turn the key to "Run" for a few seconds to start the fuel pump and pressurise the fuel rail. Then turn it to 'start". Takes a few seconds but much safer.
Bill D

[Rick Potter]

For what it's worth, Clipper Creek already makes a charger that handles two cars from one 50A circuit. It has two outlet cords, so you plug in two cars to it at the same time. It will charge one, then automatically switch to the second when the desired charge is achieved.

One fact that is never discussed is how many really cheaply made chargers are available. They don't last long and many are not UL approved. Just sayin'. Clipper Creek is one of the best.

[Charlie Velasquez]

This page has the wire dimensions for various aluminum direct burial service entrance wire. I'm getting read to run 487 feet of this.

https://nassaunationalcable.com/products/500-500-500-500-350-wofford-quadruplex-aluminum-conductor-underground-direct-burial-600v-urd?_pos=5&_sid=ce681745a&_ss=r

Tom, not sure of your application, but urd is a “utility” designation. He would have to inquire as to its NEC designation to find the allowable ampacities.
Additionally, I believe that chart shows ampacity at 90°C. As a feeder, conductors are limited to their 75° ampacity.

NEC 310.15(B)(16)

488689

[Tom M King]

To feed a 200 amp subpanel, but that subpanel will feed another 100 amp subpanel another 300 feet away. Don't really need a full 200 amps at that stop, but the end of the second one will feed a water pump to run an irrigation system pulling water out of the lake that draws 43 amps, and several boat lifts and some lights, but won't all operate at once. The pump will run after midnight, when everything else will not be operated.

The 200 amp panel will run a two bathroom building-the little brick house on the point in this picture. It's 487 feet from the 200 amp panel on one side of a 400 amp service on the end of this house. The pump will be in a large boathouse on the right side of the end of the point. The 200 amp panel will also power lights in white tents when the point is rented for weddings.

??? Haven't settled on that wire size yet.

[Adam Herman]

tom, what's the distance between each building?

for 43 amps continuous load at 487 feet I get 1/0 copper per code, but you would be fine with a touch more voltage drop to run #1. your breaker would be a 60 amp.
(12*2*487*(42*1.25) ) / 7.2

300 feet and 100 amps is easy, that is my barn and I am running 4/0 alum. 3/0 is barely good for 300 feet. you could use 1/0 copper as well

[Tom M King]

787' to the 43 amp load. 487' from main service 200 panel to 200 amp subpanel in that little bathroom house. That subpanel feeds another subpanel 300' to the boat house near the end of the point. The point if a lot longer than it looks in that picture. It covers 2 acres.

Water pump will be in the boathouse. Water heater and lights in bathroom house. Lot of lights in total, and three boat lifts in boathouse. I want to run enough capacity to be able for future additions at this point unknown. Probably will be an RV hookup near that bathroom house too. I'd like to get 200 amps into that bathroom house. There is a storage room across the near end of it.

I upgraded the overhead 200 amp service to 400 underground at that rental house. Box on right will feed the point. 487 from that box to the bathroom building.

[Adam Herman]

787' to the 43 amp load. 487' from main service 200 panel to 200 amp subpanel in that little bathroom house. That subpanel feeds another subpanel 300' to the boat house near the end of the point. The point if a lot longer than it looks in that picture. It covers 2 acres.

Water pump will be in the boathouse. Water heater and lights in bathroom house. Lot of lights in total, and three boat lifts in boathouse. I want to run enough capacity to be able for future additions at this point unknown. Probably will be an RV hookup near that bathroom house too. I'd like to get 200 amps into that bathroom house. There is a storage room across the near end of it.

I upgraded the overhead 200 amp service to 400 underground at that rental house. Box on right will feed the point. 487 from that box to the bathroom building.

ha. damn.

200 amps at 240 for 487 feet is 350kcmil copper or 600kcmil alum. about $10 000 for alum and $20 000 for copper. you may just want to do 100 amps? you can run a 100 amp sub panel from a 100 amp sub panel. no problem. lights are not much draw. 3/0 copper is good for 100 amps at that distance.

the utility may set a couple poles and a transformer for you for less cost.

[Tom M King]

That's why I linked the 500 mcm aluminum, which is bare minimum. Probably need to go up a size or two from that. Don't want poles. Power company charged 1800 to run the 400 amp underground wire 75', and that was after I dug the trench. I know it's not going to be cheap, but neither is the rental of the point.

[Bill Dufour]

Be careful about those distance tables some are one way some are two way distances.
Bill D

[Steve Demuth]

I would give the building separate metered service from the power provider into at least a 200 amp panel. That lets you charge the cars from separate outlets and still leaves some power for the living quaters, assuming it is not a 3 bedroom house.

Exactly. The difference between building for 100A, and building for 200A is entirely in the cost of the wire. Roger doesn't give the distance, but if going from 100A to 200A means the difference between 1/0 Al and 4/0 Al, that's about $3.00/ft. Unless the garage is very distant, that's going to future proof the electrical capacity for a fraction of the overall electrical cost of the build.

[Bill Dufour]

Used to have a neighbor who was a retired electrical engineer for utility companies. h
He started right after the war working in Tennesse and then California. He said he used slide rules for calculation so he always rounded up for loads and wire size. Once he knew what size service was needed he would add 20% for future growth. Yes this would cost extra millions for a neighborhood in San Jose but they never had to stop the growth in Silicon valley due to growing power demands.
Bill D.

[Scott T Smith]

all,
Great advice. I won’t be doing this. I just want to be an informed consumer. We have a 400 amp service into the main house. There is a 120amp breaker supplying our “granny flat”. I’m thinking another 100 amps or so to the garage.

I should mention here that the living quarters electrical needs will be minimal. No stove. Just a mini-fridge, toaster oven and induction countertop hob. There will be a mini split type heat pump and a very modest HW heater. It’s really more of a guest quarters.

I agree with the consensus that charging three electric vehicles from nothing at the same time would be rare. If the tech doesn’t already exist, I would imagine that some means of juggling multi-car charging will come along.

Roger, if I were you - irrespective of how much power you put into the garage right now, I'd run an empty 2" or larger conduit in order to easily allow you to pull new wires in the future. Conduit is cheap. If you run two conduits, you can pull current power needs in one, and Ethernet, camera coax, etc through the other. 2" conduit will allow you to pull up to three 3/0 wires, which is suitable for a future 200A service. You can run the ground wire in the second conduit with the Ethernet, etc.

The truth of the matter is that we don't know what the electric car charging needs will be in 15 years. Having a spare conduit will provide you with a lot of flexibility in the future, w/o having to cough up the $ now for a larger service that you may not need.

[Perry Hilbert Jr]

If you have natural gas or propane for heating and cooking you can lighten the load slightly for the living quarters, by using gas appliances. I had a natural water heater and furnace when I lived in Falls Church. I wanted to get rid of the electric range, but my wife didn't want a gas range then. She loves them now.

[Bill Dufour]

I am not sure if ground can be in a different conduit or not? I would think they must be all together. I belive ground is ignored for wire fill calculations?
Bill D

[Charlie Velasquez]

I am not sure if ground can be in a different conduit or not? I would think they must be all together. I belive ground is ignored for wire fill calculations?
Bill D

Kinda.. It counts in conduit fill, but it is ignored when computing if you have to adjust ampacity because of the number of conductors in the conduit.

[Bill Dufour]

Ground and all conductors for the circuit must be in the same conduit or same bundle of nm wire.
Bill D.

(B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4).

[Rollie Meyers]

How far, and direct bury or in conduit? Wire has to be derated when in conduit.

Not a true statement unless pulling a large number of conductors.

[Bill Dufour]

More then three conducting wires in one conduit they must be derated. Practically this means a max of only two 120 (shared neutral) or one 240 volt circuit, with neutral, before derating.
Bill D

[Charlie Velasquez]

How far, and direct bury or in conduit? Wire has to be derated when in conduit.



Not a true statement unless pulling a large number of conductors.

Probably talking about two different scenarios.
Utility companies operate under the National Electric Safety Code; most of us work under the NFPA National Electric Code for commercial and residential use.

The NESC allows utility companies to do things that are not allowed for residential customers, as they assume only qualified people would work on the infrastructure and conductors are seldom located in a place with flammables.
The ampacities of a specific gauge wire are significantly higher in NESC charts than in NEC.
But, there is often a difference in NESC ampacities between direct buried and ducted.

Tom was probably referencing that urd cable he posted a link to in a previous post. So again the confusion will be in the urd designation. If a utility company were to run that cable, they would indeed have to adjust the ampacity if in a conduit (click the link).
If he or a contractor were to run it, they would have to look up the NEC designation for that same cable and use the reduced ampacity allowed by the NEC. But then, they wouldn’t have to make an adjustment for being in conduit.

Doesn’t seem quite fair… same cable, but different ampacities.