What size wire for detached garage?

[68rustang]

I am planning on running 60A out to a detached garage. The plan so far is to bury two runs of PVC conduit, one for data, one for power. The trench will be ~80' so each conductor will be ~100'.

If Cu, should I use 3 #6 and a #10 ground or 3 #4 and a #8 ground?

#4 or #2 if Aluminum?

It looks like #6 Cu is standard for 60A service until you get to/over 100' in which case you use #4?

There are plenty of threads on this but everyone's situation seems to be just a little different.

Am I on the right track?

 

[pattenp]

For the feed to your detached garage I recommend you use 2-2-2-4 AL Mobile Home Feeder. It's the cheapest way to go. It will give you the capability to go to a max of 90A, but the #2 will fit in a 60A breaker. Use no less than 1 1/2 PVC conduit, but I suggest 2".

 

[68rustang]

Can that legally be run in conduit?

 

[pattenp]

Yes it can legally be run in conduit. Above ground and inside the structure it has to be in conduit.

 

[68rustang]

What else would that cable be called? We don't have many mobile homes in this area and I am getting alot of blank stares when I ask for mobile home feeder cable.

 

[Kevin C]

My understanding is that 6 gauge at 60°C gets you 55 amps (2005 NEC, Table 310.16). While many wires are rated for 90°C (and a corresponding higher current) it must be derated to the max temp allowed at the termination points. Since most breaker panels are rated to 60°C, 55 amps is the max you can pull from 6 gauge copper.

Basically, you need to use the breaker box's termination temperature when sizing the wire.


At 100 ft you would also want to do a voltage drop calculation. If using copper, #4 would easily meet your requirements.

 

[68rustang]

Yes, I should have updated the thread. I am either using #4 Cu or #2 Al. I actually found some cable at the local HD but nobody there could tell me anything about it or how much it cost

The shelf label said 2/2/2/4 AL QUAD ****, jacket said AWG 2 AL type USE-2.

 

[cj7jeep81]

Yes, I should have updated the thread. I am either using #4 Cu or #2 Al. I actually found some cable at the local HD but nobody there could tell me anything about it or how much it cost

The shelf label said 2/2/2/4 AL QUAD ****, jacket said AWG 2 AL type USE-2.

that's the stuff. i'd also recommend checking with a local electrical house. i know here, the one I use is a good bit cheaper than home depot on bigger wire.

 

[68rustang]

I have a call in to two of my vendors to see what they can get me.

 

[wellpoison]

use UF cable- Underground Feeder, its labled for direct burial. i would use conduit if i was doing it though. that way if something happens to the cable, no digging required.

you can use USE cable (Underground Service Entrance) just make sure you get the four wire so you can pull a ground.

 

[pattenp]

68rustang it would help to know what your location is. Are you in the US?

The issue with using USE cable is it cannot be run inside the building it can only be used outside. So you need to use a junction box and switch to a cable rated for interior use when entering the building. If you get USE cable make sure it's rated RHH or RHW-2 which makes it suitable for interior use. The wire insulation for interior use needs to be fire resistant rated.

 

[68rustang]

I am in Cleveland, OH.

What ever I use I want to run from the main panel in the basement, through the wall, into the ground in conduit, through the garage wall directly to the subpanel.

This is the cable HD had. I don't see anything on the spec sheet about RHH or RHW. I think this is what I actually want.

Does RHH or RHW automatically cover USE but USE does not cover RHH or RHW?

 

[Charles (in GA)]

Should be marked like this.

Charles

 

[68rustang]

thanks for that, the HD wire was not marked like that, only USE-2.

 

[VHF]

One downside of using #2 AL cable end-to-end is it can be hard to terminate in your main panel... just too stiff to easily bend to connect to the breaker. But it is certainly the cheapest way to run up to 90A to your detached garage.

#6 CU (or even #4 CU) conductors would be much easier to work with.

 

[68rustang]

At 100' it looks like if running Cu I need to use #4 which I can get for $.79/ft (x3+ground) which isn't terrible. I am probably going to go that route since I can't find anybody around here that stocks or will order the Al stuff I am looking for.

 

[pattenp]

I can't say I've seen USE cable with just the RHH + RHW rating. I have seen it with just the USE-2 rating and with the USE-2 + RHH + RHW.

I am in Cleveland, OH.

What ever I use I want to run from the main panel in the basement, through the wall, into the ground in conduit, through the garage wall directly to the subpanel.

This is the cable HD had. I don't see anything on the spec sheet about RHH or RHW. I think this is what I actually want.

Does RHH or RHW automatically cover USE but USE does not cover RHH or RHW?

 

[pattenp]

Do you understand if you use cable such as Mobile Home Feeder or some other single wire that it also needs to be in conduit when run in the interior of the building.

I am in Cleveland, OH.

What ever I use I want to run from the main panel in the basement, through the wall, into the ground in conduit, through the garage wall directly to the subpanel.

This is the cable HD had. I don't see anything on the spec sheet about RHH or RHW. I think this is what I actually want.

Does RHH or RHW automatically cover USE but USE does not cover RHH or RHW?

 

[68rustang]

yes I do. What I don't want is to use something like the UF that isn't supposed to be run inside at all.

 

[Kevin C]

My understanding is that 6 gauge at 60°C gets you 55 amps (2005 NEC, Table 310.16). While many wires are rated for 90°C (and a corresponding higher current) it must be derated to the max temp allowed at the termination points. Since most breaker panels are rated to 60°C, 55 amps is the max you can pull from 6 gauge copper.

Basically, you need to use the breaker box's termination temperature when sizing the wire.

My bad, I just looked at my new breakers, they are combo rated for 60 / 75°C, so the derating 75°C with the right breakers should be OK. That gets you 65 amps of capacity from a 6 gauge system.

 

[Aceman]

yes I do. What I don't want is to use something like the UF that isn't supposed to be run inside at all.

UF is okay. USE is not.

 

[Charles (in GA)]

This is the cable HD had. I don't see anything on the spec sheet about RHH or RHW. I think this is what I actually want.

Does RHH or RHW automatically cover USE but USE does not cover RHH or RHW?

At 100' it looks like if running Cu I need to use #4 which I can get for $.79/ft (x3+ground) which isn't terrible. I am probably going to go that route since I can't find anybody around here that stocks or will order the Al stuff I am looking for.

The pic in my post #13 above is Southwire 2-2-2-4 Mobile Home Feeder that came from Home Depot.

As you can see, it has both USE and RHW/RHH on it. The USE allows you to use it underground (direct burial) while the RHW/RHH allows you to use it in the building. You can run it in conduit underground also. It is also called Quadplex.

If you look at using individual copper conductors, make sure they are OK to run in conduit underground (such as THWN) If it has the W in it, its acceptable in wet locations. Conduit underground is by code, a wet location.

Charles

 

[68rustang]

What size conduit would you guys recommend for running #4 copper (x3) and #8 ground? I bought fittings for 1.5" but now that the wire showed up I am concerned with pulling it through. The run itself is pretty straight with 90* elbows to come above ground at each end.

 

[royalton10]

For my detached garage I used your same wire configuration in 1.5" conduit. It worked fine, 2" might have been easier. I would not want less than 1.5" though. I used wire lub and pulled all 4 THWN wires (#4 copper but #8 for ground) at one time. Two of us did the pull. I was at the detached garage, pulling; my brother was at the house and panel end, lubed wire and pushed it into the conduit. It was done as a series of push, pull, stop; etc. It was not a continual pull until all wire was through.

I also had a 60 amp breaker. My total wire box to box was 130 feet.

I would suggest you also put in conduit for phone, wired network, etc. Oh, yes I see you already did that. In my trench I had 2 additional 3/4" conduit on top of the 1.5" conduit for electric. One conduit was for the phone. I also put in an extra 3/4" conduit just in case for something else down the road. An extra conduit is pretty cheap when the trench is already opened up. Down the road it means digging, back fill, and seeding the grass. Plus the aggravation of doing it the second time around.

 

[1967marti]

If you are going to go through all the trouble of laying conduit put in 2.5-3 inch... The extra cost is nothing big and it will make pulling easier. also the 90 degree bends should be the sweeping kind and not the elbo stuff you use with PVC. There are tables for the size of conduit to wire guages, just do a google search. BUT I would go bigger incase you want to upgrade to a larger size wire later. Also i know you didnt ask but while you have the trench open I would lay down a smaller pipe to run CAT5 cables and other data cables out to the garage...

 

[68rustang]

A second 1" conduit is going down for TV/LAN.

I spent a good bit of time looking for sweeping bends for 1.5" PVC and couldn't find anything. What I did come up with is something like this but obviously for 1.5":

http://www.homedepot.com/h_d1/N-5yc...angId=-1&keyword=pvc+conduit+90&storeId=10051

They had large radius or "long sweeps" for 2.5"

I just wanted to make sure the 1.5" isn't going to make pulling the wire overly difficult.

 

[pattenp]

You will be just fine pulling the #4's in 1 1/2" conduit with 2 90 deg bends. Should be easy.

Also be aware that exposed PVC conduit that may be subject to damage needs to be Sch80. Such as coming out of the ground up the outside of the structure where you could run your lawn tractor into it.

 

[68rustang]

Should be easy.

Great, now I'm screwed

Thanks for the heads up on the sch80.

 

[1967marti]

Also to help with the pipe that is out of the ground and exposed i wrap it with the silver "duct" tape. This seems to help with the UV damage issue.

You will also need a "pull box" at the end of each 90 degree bend.

 

[Aceman]

Also to help with the pipe that is out of the ground and exposed i wrap it with the silver "duct" tape. This seems to help with the UV damage issue.

Duct tape?!?! If I even recommended that to a customer I would get laughed off the job and never work for them again.

Painting it will accomplish the same thing.

 

[pattenp]

PVC electrical conduit is UV resistant. But painting it is the best option. Just be sure to wipe it down with some paint thinner or lightly sand for the paint to stick well.

 

[68rustang]

By "pull box" do you mean an LB box? There will be one at each end where it goes through the walls into the buildings.

 

[pattenp]

Any conduit body is considered to be a pull point. So a LB is a pull point/box.

 

[68rustang]

While thinking this project through I think it would be nice to put a switch in the house that controls a light on the outside of the garage. Is it legal to run the switched wires in the same conduit that contains the feeders from the house to the garage.

 

[pattenp]

Off hand I don't know of a reason you can't run a switch loop back to the house in the same conduit as the feed to the garage is in. As long as you don't exceed the fill rate of the conduit.

 

[68rustang]

Is this scenario covered in the second paragraph under 225.30 of the 2011 NEC?

EDIT:

Actually looks like it is 225.30 (D) found it here:

http://www.garagejournal.com/forum/showthread.php?t=140615

 

[pattenp]

225.30 is about multiple feeds or branch circuits serving other buildings. The switch loop you are asking about is not a branch circuit or feeder that will be serving power back to the original building. However, under 225.30 you are allowed to have one circuit that originates in the additional structure to provide power back to the original structure.

Code also requires that a neutral be available in a switch location so technically you need to pull 3 conductor wire to have a neutral available in the switch box. So it ends up being a circuit anyway.

 

[68rustang]

Thanks you. I really appreciate all your help.

A few posts back you mentioned sch 80 should be used where the conduit may be subject to damage. Lowes and HD don't appear to stock it. Is this a regional requirement or something that would normally have to sourced from an electrical house?

 

[pattenp]

The sch 80 is a NEC requirement (352.10(F)). Both Lowes and HD here stock it. You may need to get it from a electrical supply. Did you ask at the Lowes or HD if they had it? I know here it gets mixed in with the 40 sch and you may not see it.

 

[Aceman]

The sch 80 is a NEC requirement (352.10(F)). Both Lowes and HD here stock it. You may need to get it from a electrical supply. Did you ask at the Lowes or HD if they had it? I know here it gets mixed in with the 40 sch and you may not see it.

The sch. 80 requirement you keep quoting as code is up to the AHJ when he makes the determination whether the location is susceptible to physical damage or not.

I'm not saying it's a bad idea to do regardless.

I only use sch. 80 when coming out of the ground in free air(not against siding or wall, etc). For residential, I've never had an issue running sch. 40 up out of the ground to a panel or whatever. I can't say I see a whole lot of broken conduit either. Most of the time it's a poorly glued joint that came apart or a strap came loose that stressed a fitting and made it break, but not usually broken conduit.