Power to new detached garage

[77broncodriver]

Hey Guys,

New to the forum here. Well Ive been reading for a few years but first time posting.

We are building a 30' x 40' red iron detached garage on our property, just signed the papers and getting the permits set up now.

While we are waiting for the building to show up I am going to start trenching and laying conduit to run the main power to the new garage.

We have a 200amp main panel but we can not easily access it without tearing up 10' of our driveway concrete which isn't an option. When the house was built the builder added a junction box about 10' from the main box and has 6 gauge aluminum cable (still needing to be confirmed) going to it from the main box which we are planning on connecting to.

The junction box is ~120' from where the sub panel is going to be located in the new garage. Is there any way that we will be able to feed 60amp with what we have? Is 50amps even possible at that distance or are we stuck with using a 40amp breaker in the main panel?

If we can not get enough power from this junction box location we have another junction boxed wired the same on the other side of the house that we can pull power from and add a second sub panel at the garage. This one probably has 80' of 6 gauge aluminum cable from the main panel to the junction box and then we would have to add another 90' from the junction box to the garage.

I plan on eventually getting an electrician out to help but for now I would like some advice on what options we have here in the mean time.

Thank you,

Evan

 

[wyliesdiesels]

Hey Guys,

New to the forum here. Well Ive been reading for a few years but first time posting.

We are building a 30' x 40' red iron detached garage on our property, just signed the papers and getting the permits set up now.

While we are waiting for the building to show up I am going to start trenching and laying conduit to run the main power to the new garage.

We have a 200amp main panel but we can not easily access it without tearing up 10' of our driveway concrete which isn't an option. When the house was built the builder added a junction box about 10' from the main box and has 6 gauge aluminum cable (still needing to be confirmed) going to it from the main box which we are planning on connecting to.

The junction box is ~120' from where the sub panel is going to be located in the new garage. Is there any way that we will be able to feed 60amp with what we have? Is 50amps even possible at that distance or are we stuck with using a 40amp breaker in the main panel?

If we can not get enough power from this junction box location we have another junction boxed wired the same on the other side of the house that we can pull power from and add a second sub panel at the garage. This one probably has 80' of 6 gauge aluminum cable from the main panel to the junction box and then we would have to add another 90' from the junction box to the garage.

I plan on eventually getting an electrician out to help but for now I would like some advice on what options we have here in the mean time.

Thank you,

Evan

You cannot have more than one feed to a detached structure

What loads do you plan on having?

 

[77broncodriver]

I will have about 4 - 220v items (welder, air compressor, 2 post lift, table saw) which are all rated at 30amps or less. I do not think that I would have to run any of these at the same time, though it would be nice not having to remember to turn off the compressor when I go to use any of those other items.

Other than that there will be the basics; charging battery powered tools, LED lights, 120v tools (bench grinder/chop saw/drill press), stereo, and garage door openers.

 

[AP514]

50Amp or 40 Amp C/B to feed that much stuff. ummm
Just to run my 1 stage HD Compressor with an intercooler is 25Amp C/B(21Amp max draw)Add Shop lighting and security lights ..your cutting it Close.

Your Not going to be able to run things as you like....going to be a Big PITA IMHO.
No chance to bore under Drive ? or Saw cut for the trench ?

But I am sure a real Sparky will be along shortly to give you real hands on advice.

 

[Colorado Squarebody]

Evan
So # 6 AWG Aluminum is rated for 50 Amps or 55 depending on the insulation. Not including the voltage drop you can only Use 80% of that. So before voltage drop you would be at 40 AMPS. Given a distance of only 120' using Aluminum at 240V and 40 Amp load the voltage drop would be about 6 volts. just about 234 Volts. And the drop is just about 2.5 %.
IF you could change the existing wire to Copper then you could get 50 Amps, But It might be better to up size to a larger feed.
These are just rough numbers. to give you an idea.
Hope that this helps.
Landon

 

[77broncodriver]

Evan
So # 6 AWG Aluminum is rated for 50 Amps or 55 depending on the insulation. Not including the voltage drop you can only Use 80% of that. So before voltage drop you would be at 40 AMPS. Given a distance of only 120' using Aluminum at 240V and 40 Amp load the voltage drop would be about 6 volts. just about 234 Volts. And the drop is just about 2.5 %.
IF you could change the existing wire to Copper then you could get 50 Amps, But It might be better to up size to a larger feed.
These are just rough numbers. to give you an idea.
Hope that this helps.
Landon

Thank you Landon.

I am going to have to go back to the drawing board to see if there is anyway to run a new larger feed cable to the main panel without having to tear out the driveway.

 

[sberry]

You really dont have to turn off the air comp,,, just dont turn the others on while its running.

 

[Terry D]

There are company's that can bore under that driveway. Probably not the cheapest thing, but maybe better than saw cutting the concrete. I would put in at least a #2 alum. to get you 90 amps out there.

 

[77broncodriver]

There are company's that can bore under that driveway. Probably not the cheapest thing, but maybe better than saw cutting the concrete. I would put in at least a #2 alum. to get you 90 amps out there.

I agree, from the beginning I wanted to put a 90-100amp panel but then ran into the issue of not being able to get the cable ran.


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[Don1357]

I'm about to do what to do are doing minus the under the slab.

Use 2-2-2-4 service wire. Cheap, is what mobile homes use, 100amp capacity? Can be direct buried without conduit. That will buy you the option of one day pumping more amps.

Get at least a 20 slot electrical service panel. Believe it or not you are bound to run out of slots before you run out of power, and the difference is a few bucks.

For now put 60amp breakers. Compared to bigger ones they are dirt cheap.

This setup is actually pretty cheap while buying you a lot of room for growth. You could spend a lot more for less capacity copper, or save five bucks one a smaller panel that you'll outgrow in a hurry.

 

[pattenp]

#2 MHF used as a branch feeder to an out building is 90A, not 100A.

 

[77broncodriver]

I am going to look into how I can get a new 2ga cable into the main panel. Can I use a 100% continuous duty 90amp breaker to avoid only being able to use 80% of the power?

If it is not worth bringing the 2ga cable to the main panel can I use a 50amp 100% continuous duty main breaker to get as much power as possible?

We use these at work for light systems in comercial greenhouses but do not know if they are allowed in residential use.


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[Don1357]

I am going to look into how I can get a new 2ga cable into the main panel. Can I use a 100% continuous duty 90amp breaker to avoid only being able to use 80% of the power?

If it is not worth bringing the 2ga cable to the main panel can I use a 50amp 100% continuous duty main breaker to get as much power as possible?

We use these at work for light systems in comercial greenhouses but do not know if they are allowed in residential use.


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Why would it not be worth it to use 2-2-2-4 wire? That stuff is not that expensive.

Chances are a 60amp breaker will be enough. If that's not the case your 90amp capable wire and your 100amp capable electric box would let you unpaint yourself out of that corner.

I'm eventually using 80 amp breakers. I'm not an electrician so i like to over engineer the solution, make sure that this leg of the grid trips that breaker before the cable gets a chance to even get warm.

 

[77broncodriver]

Why would it not be worth it to use 2-2-2-4 wire? That stuff is not that expensive.

Chances are a 60amp breaker will be enough. If that's not the case your 90amp capable wire and your 100amp capable electric box would let you unpaint yourself out of that corner.

I'm eventually using 80 amp breakers. I'm not an electrician so i like to over engineer the solution, make sure that this leg of the grid trips that breaker before the cable gets a chance to even get warm.

I will post a picture of where the main panel is located later today to show the dilema of running a new cable. Maybe you guys will think of a solution that I haven’t thought of yet.


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[AP514]

Also if your Conduit is limited(size) you might consider paying the extra and run Copper.
I think with copper you can go up 1 size (4-4-4-6)??
I am sure one of the real electricians will Correct me on this...

Also if you do go the Trench way make sure they add extra conduit you never know when your going to add some CAT 6 cable or some other stuff that can not go in the same Conduit as high volt electrical.

 

[johnnyradiant]

If cutting a trench in the concrete driveway is out of the question is boring under it also out of the question?

 

[benjy]

Anyone ever try a water jet under a slab? I'm planning on this to go diagonally under a sidewalk for 10' or so for my feeder.

 

[77broncodriver]

Here is what I am working with. I guess I can take up all the pavers and get close enough to get under there.

Then I have to figure out how to get into the box from below as I assume there was a single conduit set in the concrete pad when the house was built.

On the other side of the fence is where the junction box is where I am planning on tapping into if I can’t get into the main panel.

The garage will be to the right of this picture 120’




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[Awag]

How big is the conduit going to the junction box with the 6 gauge cable? Could you use the #6 to pull a bigger sized wire into the box? Since its only 10' would it be legal to pull a #4 copper into the junction box and change to the cheaper #2 aluminum for the rest if the run? I'm not a sparky thats why I'm asking in the form of a question.

 

[77broncodriver]

How big is the conduit going to the junction box with the 6 gauge cable? Could you use the #6 to pull a bigger sized wire into the box? Since its only 10' would it be legal to pull a #4 copper into the junction box and change to the cheaper #2 aluminum for the rest if the run? I'm not a sparky thats why I'm asking in the form of a question.

I thought about doing that but it looks like the cable is not in a conduit. It looks like a SE type cable that is probably ran through the wall studs.

Can I have exposed conduit on the side of the house above ground? I am thinking of punching a piece of conduit into the side of the stucco bump out below the box to the left of the door and run it below the door right above the concrete. Once I get past the concrete and to the pavers I can remove the pavers and run the conduit underground the rest of the way to the garage?

 

[wyliesdiesels]

Yeah theres no prohibition on surface mounted above ground conduit.

BTW SE type cable is not permitted underground

 

[sberry]

Dont you love the dum azzws that design stuff like that. Figure no one will even need to get in to it. I was in a garage, 100A panel, great, 1 15A circuit in it and drywall tight as a nun cunny.