How many amps do I need for detached garage?

[frankd]

So we just built a 20x32 garage/storage building and I plan on installing a sub-panel in the next few weeks. Thing is, I need around 125-150 feet of wire to run from the main panel to the sub-panel.

Copper 8/3 UF-B wire is going to cost $300+. if I co with 10/3 it'll be about half of that. I was also looking into aluminum but it doesnt seem to be readily available at the big box stores. I can call some electrical supply places in the area to see if they carry it.

If I go with 10/3 then I'm limited to 30 amps. The over-achiever in me wants to install a 40-50 amp panel but I think that might be overkill. I plan on installing Lights and outlets and thats about it. There will be no heat/AC. Might get a small compressor that would plug into a regular 20a outlet. And maybe a welder down the road. We also have a really old table saw that will usually trip a 15 amp breaker when it powers up, but runs fine on 20

So I just wanted to get some opinions. I'd like to keep the cost down as much as possible.
I've never worked with Aluminum before. if I end up going that route for the underground run, are there any drawbacks aside from it being stiffer/harder to work with?

 

[The Cobbler]

it entirely depends on what you will be doing out there, now & in the future.
It would be wise , in my opinion, to put more power out there then less .

 

[frankd]

it entirely depends on what you will be doing out there, now & in the future.
It would be wise , in my opinion, to put more power out there then less .

That's the thing...I have these grand dreams of doing all sorts of stuff in the garage but experience tells me that just a couple of 20a outlets and some lighting will be sufficient.

 

[alfredeneuman]

I've never worked with Aluminum before. if I end up going that route for the underground run, are there any drawbacks aside from it being stiffer/harder to work with?

Aluminum is not as stiff as Copper and is much easier to work with.

 

[theoldwizard1]

60A is pretty common

2-2-2-4 MHF should be good for that distance. It should be <$2/foot.

 

[frankd]

60A is pretty common

2-2-2-4 MHF should be good for that distance. It should be <$2/foot.

Thanks. I'll look into this

 

[frankd]

Aluminum is not as stiff as Copper and is much easier to work with.

Sorry. Meant stiffer in the sense that I'd need a larger gauge aluminum wire vs copper for the same amperage.

 

[AP514]

that $300 bucks only hurts once.....You might want to run at least 50-60 Amps

 

[dcg9381]

I had a 42 x22 or so.. 50A was more than I ever needed.

 

[frankd]

Thanks for the replies. Is there any reason why I wouldn't be able to use the wire below, and just run 4 lengths of it?
I found some for sale on amazon and after seeing the name of the place I realized they're in the same county ad me so I can just go there and pick it up this week

https://www.nassauelectrical.com/products/single-conductor-aluminum-urd-cable-600-volts

 

[mike93lx]

Either 2-2-2-4 MHF or the same sizes in aluminum xhhw. Will be about 1.30ish a foot and give you 60a,no problem.

Running copper uf in that size is crazy, IMO

 

[Gunfixr]

I've got a 120ft temporary 30 amp extension cord run to mine now, until I can actually wire it. It has a 4 gang outdoor box at the end with a 20 and a 15 amp outlet.
Yes, I know I can't fully load both at once........
But it will run a few lights, radio, belt sander, or welder, or plasma cutter, side grinder.....

Kind of a pain to roll it up every time I cut the back yard......

 

[alfredeneuman]

Thanks for the replies. Is there any reason why I wouldn't be able to use the wire below, and just run 4 lengths of it?
I found some for sale on amazon and after seeing the name of the place I realized they're in the same county ad me so I can just go there and pick it up this week

https://www.nassauelectrical.com/products/single-conductor-aluminum-urd-cable-600-volts

It can not be used inside of a building (not fire rated)
"it can be used as a direct burial wire which involves direct insertion in to the soil with the use of a conduit or duct for protection."
You're better off with XHHW if you have to use use conduit

 

[mike93lx]

Thanks for the replies. Is there any reason why I wouldn't be able to use the wire below, and just run 4 lengths of it?
I found some for sale on amazon and after seeing the name of the place I realized they're in the same county ad me so I can just go there and pick it up this week

https://www.nassauelectrical.com/products/single-conductor-aluminum-urd-cable-600-volts

Urd can't go inside a structure, even for an inch. It is not the right wire for this application at all

 

[brewchief]

Thanks for the replies. Is there any reason why I wouldn't be able to use the wire below, and just run 4 lengths of it?
I found some for sale on amazon and after seeing the name of the place I realized they're in the same county ad me so I can just go there and pick it up this week

https://www.nassauelectrical.com/products/single-conductor-aluminum-urd-cable-600-volts

Same company has 2-2-2-4 mobile home feeder wire for 1.26 foot, it can go inside a building if inside of conduit.

Sent from my SM-T510 using Tapatalk

 

[BillK]

You already mentioned a compressor and a welder. That alone would tell me you need more than a 30 amp box. I ran a 100 Amp sub panel when I built my 24x24 detached. I will probably never need it but the cost difference was not that much and its there if I decide to buy a piece of equipment that needs it.

Also, if you start using the garage regularly you will almost certainly want heat and maybe ac.

 

[jeepxj]

highly suggest mobile home feeder. good for 90a.

solid place to get wire from:
https://www.wireandcableyourway.com/mobile-home-feeder

air comp, welder, ac and you're well above 50a

future is electric cars as well. need to buy once, cry once here.

 

[frankd]

Thanks for all the replies. Looking like the mobile home feeder is probably the way to go.

 

[mike93lx]

Thanks for all the replies. Looking like the mobile home feeder is probably the way to go.

Just make sure it is in conduit everywhere above grade.

 

[frankd]

Do they make smaller gauge mobile home feeder wire? Never worked with 2 gauge wire. Will it even fit in the neutral and ground bars or will I need some sort of adapter?

 

[nadogail]

Those who "Cheap Out" on electrical installations often regret their decision.

Upgrades after the cheapest possible installation are usually more expensive than doing it generously the first time.

 

[mike93lx]

Do they make smaller gauge mobile home feeder wire? Never worked with 2 gauge wire. Will it even fit in the neutral and ground bars or will I need some sort of adapter?

No, not smaller MHF, but you can get smaller xhhw.

Whether it will fit fine entirely depends on your panel and breaker sizes

 

[Yankeefarmer]

#2 Aluminum in MHF is surprisingly easy to work with. You will probably need to purchase lugs to connect it to your ground and neutral bars.

 

[NUTTSGT]

Do they make smaller gauge mobile home feeder wire? Never worked with 2 gauge wire. Will it even fit in the neutral and ground bars or will I need some sort of adapter?

If you buy something like a 100A box (I'd make it to the brand you have in the house, unless that is junk) with plenty of circuits. This will allow to split everything up and put on it's own circuit.

Using a larger breaker box rather than a small box, will allow the MHF to fit in the neutral bar. I believe the box I used, I had to buy an adapter for the ground lug. A couple of extra bucks, no big deal for what you're getting.

MHF may be rated for direct bury, but I'd spend the money to put it in conduit for some future protection, or especially if your area has rocky ground. Around here, many use 4" corrugated field tile to run wire.

 

[frankd]

Thanks again for all the replies. Lost of great info as usual! I'm still torn between copper/aluminum and wire size but you've all given me alot to think about.

I'm generally one that overdoes things..so that's probably what I'll end up doing.

 

[frankd]

No, not smaller MHF, but you can get smaller xhhw.

Whether it will fit fine entirely depends on your panel and breaker sizes

Can xhhw be buried (in conduit)? I can't seem to find an answer. It seems like this would be the best of both worlds. I can save on the cost of the wire and don't have to worry about whether or not the 2 gauge wire will fit in the existing panel in the house.

 

[alfredeneuman]

Can xhhw be buried (in conduit)?

Yes.
In fact conduit is required

 

[mike93lx]

Can xhhw be buried (in conduit)? I can't seem to find an answer. It seems like this would be the best of both worlds. I can save on the cost of the wire and don't have to worry about whether or not the 2 gauge wire will fit in the existing panel in the house.

Yes, and to add to what Alfred said, conduit is required for the entire run, above and below grade.

Make sure you run 4 conductors, and you need two ground rods at the shop

 

[frankd]

Yes, and to add to what Alfred said, conduit is required for the entire run, above and below grade.

Make sure you run 4 conductors, and you need two ground rods at the shop

Thanks. Yes I would be running 4 conductors and will be adding grounding rods at the garage.

Turns out I actually need to add a grounding rod at the house as well. We had some work done at the house several years ago including some excavation. The electrician never installed a new grounding rod. Although it does look like he attached a ground wire to the plastic water pipe entering the home. Lol

 

[WisJim]

And spend a little more on conduit and get a size or two bigger than minimum required.

 

[AP514]

Do not cheap out...you will regret it later

And while you are at it.... Drop another 3/4-1" conduit in that trench for future runs....internet/low volt circuit ect

 

[sky jumper]

you can use thwn. I think all #2 thhn is dual rated thwn. its a little cheaper than xhhw-2 and easier to pull. buy your wire from a local supply house it'll probably be cheaper than the box store and they'll spool up 4 spools for you.

also, to make life easier run the outside conduit up the exterior wall and LB directly into the panel. I put my LB way down low, and then had to do another LB on the inside to get the wire up to the panel. pulling through back-to-back LBs with large guage wire is a pain. xhhw-2 made it even harder. i'd use 2" conduit and 2" LBs, minimal extra cost vs 1-1/4" and will make life easier.

 

[mike93lx]

you can use thwn. I think all #2 thhn is dual rated thwn. its a little cheaper than xhhw-2 and easier to pull. buy your wire from a local supply house it'll probably be cheaper than the box store and they'll spool up 4 spools for you.

also, to make life easier run the outside conduit up the exterior wall and LB directly into the panel. I put my LB way down low, and then had to do another LB on the inside to get the wire up to the panel. pulling through back-to-back LBs with large guage wire is a pain. xhhw-2 made it even harder. i'd use 2" conduit and 2" LBs, minimal extra cost vs 1-1/4" and will make life easier.

Copper thwn is not cheaper than AL xhhw

 

[sky jumper]

Copper thwn is not cheaper than AL xhhw

who said anything about cu?

 

[mike93lx]

who said anything about cu?

My bad, I automatically associate thwn with copper

 

[theoldwizard1]

You already mentioned a compressor and a welder. That alone would tell me you need more than a 30 amp box. I ran a 100 Amp sub panel when I built my 24x24 detached.

The size of the sub panel does not matter much. What does matter is the size of the feeder wire and the size of the breaker coming off the main.

 

[theoldwizard1]

Copper thwn is not cheaper than AL xhhw

FYI, MHF is basically 4 AL XHHW conductors.

 

[frankd]

Do not cheap out...you will regret it later

And while you are at it.... Drop another 3/4-1" conduit in that trench for future runs....internet/low volt circuit ect

I actually do plan on running cat5 or cat6 to the garage in a separate conduit but thanks for the tip!

I know people are saying not to cheap out and normally I would agree but I just cant see any scenario where I'd be drawing more than maybe 30 amps. There will be no heat/AC. maybe a 120v compressor and we have some 120v saws but its not like they'd all be running at once.
This is a storage building near our summer/hunting cabin. its normally vacant. But I do want to have a little extra for the future.

I feel like 4 gauge or 6 gauge aluminum xhhw seems to fit the bill. The 4 gauge should be good for 50-60 amps. 6 gauge should be able to handle 40-50, right? I cant imagine ever needing more than that.

 

[sky jumper]

I know people are saying not to cheap out and normally I would agree but I just cant see any scenario where I'd be drawing more than maybe 30 amps.

pretty soon gasoline cars will be outlawed and you'll be forced to drive EVs. then you'll want the 90A service in your garage.

 

[NUTTSGT]

. This is a storage building near our summer/hunting cabin. its normally vacant.

Well, that bit of info was never shared. When you mentioned storage building/ garage, being GJ, I think most assumed this was at your residence or home.