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

[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/prod...e681745a&_ss=r

[Chris Parks]

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

Attachment 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

[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/prod...e681745a&_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)

3A78E2A7-B98B-48C2-B6A7-20ABD88A833D.jpg

[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.