Sub panel, feeder, underground conduit, garage wiring and electrical

[DHill]

Hey all,

So I built a garage. I'm in the process of painting it, and all along I've planned to run 2" conduit from the house.

Problem is, I've thought as far as digging the trench, putting in the conduit, and what it should look like. Now I'm starting to buy parts for wiring and I'm starting to get confused. A friend offered some 4/0 aluminum "Triplex" wire at the moment, but now I'm wondering if that's the right stuff. With 4/0 my drop should be less than 0.5%. I want the wire to be intentionally overdesigned in case I want to run more power later, and since this is the only time I'll have the ground all dug up, now is my only chance!

I've looked up gauges from here:
http://en.wikipedia.org/wiki/American_wire_gauge#Table_of_AWG_wire_sizes
I've calculated the drop from here:
http://www.csgnetwork.com/voltagedropcalc.html

Data:

Distance between house and garage: 50 feet
Expected load for garage: 100 A (with possibility for more?)
Conduit size: 2"
Voltage: 220/240 V
Conditions: underground, in conduit

Questions:
1) Grounding rod(s)? Is this necessary or do I ground to my main panel in the house?
2) Conductor type?
3) What does it look like at my main panel? I originally intended to have a 100A breaker in the house named "Garage" --- this breaker would then feed my garage sub-panel which would have yet another 100A main and then several circuits for 110V and 220V.

Garage will power lights, air compressor, saws and other power tools, and welder.

Pics:

rough idea of distance to garage (blank spot near bottom right of door will be service entrance from ground conduit)

entrance of conduit through garage wall

Mock up of LB fitting and service entrance

 

[yzair]

I just installed a 100 amp panel in my detached garage / shop finally found my best information on this site and did exactly as it said and it works perfect.

www.selfhelpandmore.com/homewiring-usa/acessory-structure

I wired mine "three or more circuit without grounding conductor 240 volt underground minimum 60 amps.

Should start on page 24

Hope this helps

 

[yzair]

Selfhelpandmore.com/home-wiring-usa/acessory-structure

 

[Stuart in MN]

http://www.selfhelpandmore.com/home...o-dwellings/wiring-a-detached-garage-2002.php

This is a pretty good page to use for reference. Note that it was written using the 2002 version of the National Electric Code; most parts of the country have adopted newer versions now so there may be some detail differences, but it's a good start.

There's nothing wrong with using larger wire than the minimum size required (as long as the terminals at the main and sub panels will accept it), but make sure the wire you use is rated for underground use.

 

[Charles (in GA)]

There's nothing wrong with using larger wire than the minimum size required (as long as the terminals at the main and sub panels will accept it), but make sure the wire you use is rated for underground use.

To emphasize this, the wire must be rated for use in a wet location even though it will be inside a conduit. A conduit, underground or in a cement slab, is considered a wet location by the code.

Triplex sounds like the three twisted wires that are used for direct burial and around here is commonly called "mobile home feeder". In your case, you need a fourth wire, a ground, carried back to your main panel, in addition to a ground system at the garage.

Charles

 

[muckyp]

I am in the middle of wiring a shop with almost the same parameters that you listed. The distance from the house to the shop was about 75 feet. I have a friend that is an electrician and his recommendation was actually the aluminum wire but a smaller wire than you mentioned. I ended up using copper two 3 awg wires, a 4 awg and a 6 awg. I got a deal on copper and still paid $1.00 a foot for the #3 wire. I thought copper was better so I used it. Now I have learned that the service from the street to my house is aluminum wire. So if I had it to do over, I think I would have saved the money and used the aluminum.
As far a grounding rods, I think code requires that you ground it at the shop as well as the house. Good luck and get ready to spend some $$$ on wire.

 

[Palmetto]

You're gonna have a hell of a time pulling (3) 4/0's through that 2" conduit!! But, I think you will be able to run 200amp service in there with 4/0.

My setup:
Dist. from main panel to shop: 175'
Conduit: 2" (3' deep)
Service: 100amp, 240v
Wire: 4-#3's, copper. This was a shielded, direct buirial kind of wire. They where all bundled together. Made it much easier to pull.
My main panel by my transformer has a 100a main breaker. there is also a 200a main that will go to my house when it gets finished.

Also, I put one grounding rod in at my main panel. I did not put one in at my sub panel.

 

[PeteW]

You may need to up the conduit size from 2" to 3" if you are going all 4/0 wire.
The NEC code only allows you to fill a conduit 60%, and those 4/0's will most likely be too large of a wire bundle for 2".

If I remeber correctly the latest NEC code book has a quick reference chart to tell the number of conductors arranged by guage that can be used in different sized conduits.

 

[timgr]

I did roughly the same thing in my garage, though I reused the 100A panel from my house service upgrade.

I dug the trench and I hired an electrician to run the wire and connect. Digging the trench is a significant job, especially here in rocky MA. Note the trench must be 18" deep - deeper than your typical small rental yard trenchers can go.

My electrician did all the electrical work except for hanging the panel in the garage. $600 including the materials, which I thought was a good price. He used 3 cond AWG2 - 1 cond AWG4 aluminum cable.

If I did it again, I'd bury a second conduit for later expansion in the trench, with pull twine. I had thought I wouldn't need phone or cable, but now I wish I had cable in particular. IIRC you aren't supposed to run these services in the same conduit as the power wires.

If you do a search, you'll find different opinions about how to ground the subpanel. My electrician ran a continuous #10 bare wire clamped to a grounding rod in my trench. I recall this was in addition to the ground conductor that went back to the main panel.

 

[muckyp]

That was a good point, always take the opportunity to bury a second conduit when you have a ditch dug. This may be common knowledge to most, but I was amazed at how well a shop vaccuum can pull a string through conduit. Even when with my ditch, which had several turns.

 

[W-Cummins]

You're gonna have a hell of a time pulling (3) 4/0's through that 2" conduit!!

At 50' it shouldn't be that bad as it's a straight run. I'm getting to pull about 45' with about the same number of turns ( of course we both will need a ECG too) With the proper pulling tools and lube it shouldn't be too bad. I will let you know how it goes when I do mine....

You may need to up the conduit size from 2" to 3" if you are going all 4/0 wire.
The NEC code only allows you to fill a conduit 60%, and those 4/0's will most likely be too large of a wire bundle for 2".

For rigid sec 40 pvc the max fill is 4 #4/0 (THHN /THWN) in 2" most other wires are 3 wires in 2". If he uses the triplex he will have to do a manual fill calculation.


William....

 

[DHill]

Thanks for all of the replies!

From what most of you are saying it looks like the 4/0 Triplex is missing a conductor and is a bit of overkill anyway. From some of you it looks like I could get away with a little smaller wire and still have 100-125A capacity.

Why are these naming conventions all over the place? When I'm standing at the bottom of the wire spool area at Lowes, their labels mix and match conventions and naming schemes. Argh. It's as bad as different names for threads and fittings.

 

[dipper]

First thing to do is do a load calculation to size your panel box and get the appropriate wire for the sub panel. I have a 100A sub panel for a 20x22 garage with a ton of lighting and outlets; and two 220v for a welder and plasma cutter etc. etc.
I'm 70' from the main panel, underground feeder thru 1.5" conduit, four #4 copper THHN.
4/0 aluminum is overkill for 100A i think. Don't know if you want to feed underground wire through conduit, usually you just use individual THHN conductors.

Do yourself a favor and not go to Lowes for the larger wire; you will save alot by going to an electrical supply house. Or figure out exactly what you need and keep an eye on craigslist and ebay.

 

[Palmetto]

4/0 aluminum is overkill for 100A i think............. .

I agree. But It sounds like he is getting it cheap.

Do yourself a favor and not go to Lowes for the larger wire; you will save alot by going to an electrical supply house. Or figure out exactly what you need and keep an eye on craigslist and ebay.

I was fixing to post this as well. Around here there is a Wholesale Electric Co. that has the best prices. They say the only thing they cant beat box store on prices are the rigged out breaker boxes for houses.

Later...

 

[yhprum]

I have been thinking of doing something like this. How deep would I have to go for the conduit in Phoenix?
Thanks

Steve

 

[BlueSOG]

I just put 100 amp service in my small (16x24) motorcycle shop. I took out a permit and did everything by code. 1st off, you can directly bury the conductors (2 ft. min. depth) or run through conduit (min. depth is 18"). the conductors MUST be marked for underground service (USE, USE-2, etc). You can NOT bury SE (sevice entrance) cable, not even in conduit. I used #2 Al USE conductors -2 hot and a common, plus a #4 AL for the ground. 1.5" Sch. 40 PVC conduit. Buy some cable lube if you intend to pull through conduit... A detached garage MUST also run a seperate ground. You must drive ground rods (2) at least 6 ft. apart. for equipment grounding. Use #6 bare copper for the ground rods. Wire attachment to the rods must be marked "for burial". The garage ground can NOT be tied to the common at the subpanel. That's what the seperate ground conductor is for...

 

[BlueSOG]

Oh, and as suggested earlier, I ran a seperate 3/4" conduit for RG6 and CAT 5. I did the "direct burial" (2 ft.) for power and put the conduit for cable in after backfilling approx 6-8 inches...

 

[jamm]

I just got finished wiring my 26x42 with a 100 amp service so I thought I'd mention a couple of things to keep in mind.

1) Limit your bends as much as possible if you are running the wiring in conduit underground. I believe that your total bends cannot equal more the 360 degrees without installing an LB or pull through. Make sure the electrical inspector approves the install prior to backfilling also.

2) Make sure to ground the service at the garage. Here in Michigan we have to install two ground rods a minimum of 10 feet apart.

3) If you're going to have your electrical service in-ground, it costs very little to add a second 1" PVC conduit at the same time to run cable/phone/etc.

Good luck.

 

[DHill]

I very much appreciate the suggestions to run a second conduit. This a great idea and I am doing that now - thanks for convincing me.

I am also very appreciative of the detailed responses. If I can find the materials, here is my recipe (I think):

Qty (2): Black 1/0 Copper (hots)
Qty (1) White/Gray 1/0 Copper (neutral)
Qty (1) Green or Bare 6 AWG copper (ground)

I am also running a 1" PVC conduit in parallel to my electrical 2". I will install an 8' ground rod at the shop with 6 AWG.

I'm thinking about the coatings on the wire - I suppose I should never intend on getting the wires as high as 90 C as some of the ratings suggest as that will surely be bad inside conduit, so do I just go with 60 C or what?

It also cracks me up that the gauge of the wire is based on number of passes through a die and it corresponds to cross sections and diameters measured in inches, but the coating rating is in degrees Celsius. I wish we'd just convert to metric and get it over with.

 

[DHill]

So I've got cable - Graybar did not have the copper I was looking for, so they gave me some 2/0 aluminum Alcan SEU XHHW-2 cable with two conductors and a braided neutral. For conduit I have been told this is fine, and the XHHW-2 apparently means it can be used wet up to 90 C.

So now I'm wondering how I can connect this up to my panel. There are two options:

1) In that www.selfhelpandmore.com page, there was a suggestion for a 325A meter base:

you can exchange your existing meter base to a larger meter base that is usually called a 325 amp meter base with double lugs on the load side in that meter base. These double lugs will allow one set of lugs in that meter base on the load side of the meter, to serve as your dwelling connection, and a second set of lugs in that meter base, on the load side of the meter, to serve as your detached garage connection.

2) Is there such a thing as a breaker with lugs in it, like the QO2200H shown below (am I interpreting this image correctly)? From what I have deciphered from the Square D online catalog, there is a part number QO2100H that is a 100A breaker.

 

[jamm]

I thought if aluminum wire was used (as most homes service from the pole to the house is) you have to step up the wire size (larger)? You originally figured 1/0 copper but now have 2/0 aluminum are you changing your power expectations?

Just curious as I just installed (3) #2 copper and (1) #6 ground in 1-1/2" conduit in a 250' run to my garage and I have a welder and compressor.

 

[DHill]

I ended up with 2/0 aluminum because it was the closest to 1/0 - actually bigger and higher capacity but all that Graybar had in stock at the time.

I am planning for larger upgrades in the main panel. I wanted to run something oversize to the garage so that when I upgrade the main panel I will already be suited to step it up in the garage.

This is probably way overkill but I stepped it down from 4/0 for a more realistic goal - and at the time I had less of a clue (not that I'm that much smarter now). But with such beefy wire I'm not sure how to connect to the main panel as the hot wires are too big for a normal sized breaker. How do other people connect their garage to the main panel?

As for your copper hot and neutral wires, were these all separate or were they collectively a multi-conductor cable? Buying cable is apparently like computer programming as the guy at the counter gave me a blank stare... junk in equals junk out.

 

[Ezzie]

You'll probably need a seperate disconnect box with lugs that are large enough to accommodate the 2/0 wire size. Does your subpanel not have a large breaker (100A) that is big enough?

 

[DHill]

The Square D breakers appear to accommodate wire with a maximum size of 3 AWG or 4 AWG (~0.20" or so). That's why I'm wondering if there is a different kind of breaker to use from the house panel.

I can't tell if that is a normal breaker or not, but look at this picture. The main feed is in the top, then the top left breaker is feeding something big, like an outbuilding:

Or this one... appears to have oversized inputs? The 60A breaker looks like it is not the main, but instead feeds a subpanel. As a result it expects a larger gauge wire. Are all large breakers sized accordingly? In my case, since I'm going bigger than I need to, how much room would I have?

 

[Charles (in GA)]

The breaker panel will have a paper inside the door or loose with it that will list all approved breakers for that panel. My Siemens panel has the paper glued in the door with a place to list all the circuits, but it also lists all combinations of breakers that are approved. You need to find the approved 100 amp breaker(s) for the panel and look at their specs.

Charles

 

[Aceman]

So I've got cable - Graybar did not have the copper I was looking for, so they gave me some 2/0 aluminum Alcan SEU XHHW-2 cable with two conductors and a braided neutral. For conduit I have been told this is fine, and the XHHW-2 apparently means it can be used wet up to 90 C.

The 2005 code is a little fuzzy on installing SE cable underground, it doesn't exactly say it's not allowed although I believe it was their intent when the article was made. The 2008 code was changed and cleared it up by stating it is not allowed underground. Also, if your area is under the 2008 code, it requires 4 wires to a detached garage and with an SE cable only having 3, you're outta luck.

Your best bet is to get ahold of your local electrical inspector and get the lowdown. Your area may be on an older code cycle or have the amendments that allow such an installation.

 

[DHill]

I read several different sections of the code regarding that cable. For direct burial it is not allowed, but for conduit it seem that it is (depending on the language). The "U" prefix after SE supposedly means "underground". The code is arcane - it is labeled "XHHW-2". Apparently if you read the label on the wire from left to right it translates to something like this:

"Rated to 90 C (X), no wait, derate it to 75 C (HH), also use it in wet conditions (W), oh sorry rate it back up to 90 C (-2)"

Ack.

As for the 3 conductors you are right I need a fourth. I will have green 6 AWG copper running along next to it in the conduit.

I buried the conduit yesterday and drove a ground rod next to the garage. Maybe I'll have pics up soon.

 

[Aceman]

From Alcan's website listing aboveground use only:

http://www.cable.alcan.com/alcancab...OY+Service+Entrance+Cable+Type+SE+Style+U.htm

If you fill in your info, this is a free access agreement to an online 2008 codebook:

http://www.nfpa.org/catalog/service...freecodes/free_access_agreement.asp?id=7008SB

These codes are worth looking up:

300.3(B)
338.10(B)2
338.12(A)2

I'm not trying to bust your chops, but if you're doing diy electrical you should be aware of the codes pertaining to your installation.

 

[IDASHO]

Im running a similar setup.

Ive got a main panel coming into the garage, with a subpanel in the house.

125A 220V breaker in the main box that feeds the subpanel.\

I used 1/0 copper. More expensive, yes, but I had a 40' section that had to be pulled thru conduit, and I didnt want to mess with the larger (aluminum) wire.

 

[DHill]

Aceman: thank you for the link to the code book. I will read those sections.

IDASHO: that picture is exactly what I was looking for. Thank you.

 

[sweeper716]

Usually if the cable is too large to fit into a breaker (for example 2/0 wire won't fit into a 60 amp breaker) it's simply because the breaker wasn't designed to be used with wire that large...

You should probably just put the larger panel in now and add the extra circuits as needed. Even a 20 space 100amp Square D Homeline panel only runs about 50 bucks, and it'll come with 5 15 or 20 amp breakers to boot! Then you can take out the 100 amp breaker and put in subfeed lugs and sell the main breaker on eBay or whatever. I'd assume 20 spaces will be more than adequate for a garage.

IDASHO's picture is a little different than you'll want to have. His main panel is out in the garage as I read it, and the house is run off of a subpanel. This is how your situation will vary (assuming your house's panel is the main panel, and the garage will be fed off of that):

If you're running a 100 amp 240v service out to the garage, then of course you'll want a double pole 100 amp breaker in the main panel. Out in the garage you won't have a main breaker for that panel. If you do, it has to be rated lower than 100 amps, and the next most common size is 60 (which would defeat the purpose of running wire as large as you did out there). But, you are not allowed to have two breakers of the same amperage on the same circuit. Also, since it's a subpanel, the ground and neutral bus have to be separate, so you WON'T put in the green bonding screw on the neutral bus You can see the green bonding screw at the main neutral connection in his picture. Since that's a Siemens panel, there's a copper bar bonding both buses on each side of the breakers...if it were a subpanel either that wouldn't be there and one would be neutral, and the other ground, or you'd have to install a separate ground bus on each side (which is what I'd recommend)
When you connect the grounding rod you already drove, that'll go only on the ground bus. Same with the #6 ground you're running in the conduit.

Aside from that it sounds like you have everything else pretty much figured out.

 

[pennsylvaniaboy]

Which of these should I run for a 100 amp feed to my garage, underground in 2" conduit-

http://www.lowes.com/pd_70262-295-28714401___?productId=3129329&pl=1&Ntt=mobile+home+feeder

http://www.lowes.com/ProductDisplay?partNumber=70203-295-13102915&langId=-1&storeId=10151&productId=4294349&catalogId=10051&cmRelshp=req&rel=nofollow&cId=PDIO1

http://www.homedepot.com/p/Southwire-2-2-2-4-Aluminum-Quad-****-Wire-By-the-Foot-55417399/205001803?keyword=55417399

 

[kmkalf]

I was told by my electrician that the 2 2 2 4 aluminum won't work for a 100a service but in copper it will, in aluminum he said to get the 0 0 0

 

[pattenp]

Which of these should I run for a 100 amp feed to my garage, underground in 2" conduit-

http://www.lowes.com/pd_70262-295-28714401___?productId=3129329&pl=1&Ntt=mobile+home+feeder

http://www.lowes.com/ProductDisplay?partNumber=70203-295-13102915&langId=-1&storeId=10151&productId=4294349&catalogId=10051&cmRelshp=req&rel=nofollow&cId=PDIO1

http://www.homedepot.com/p/Southwire-2-2-2-4-Aluminum-Quad-****-Wire-By-the-Foot-55417399/205001803?keyword=55417399

How far is the run? Of the 3 listed only the first one (#4/0) is large enough. The second one (SER) is not allowed under ground in conduit. The third one (#2) is only good to 90 amps. If you want the full 100A you can use aluminum THHN/THWN in single wires in the sizes of 1-1-1-6. The length of run will make a difference.

Edit: Forgot to say the third one (****) is a URD cable and is only USE rated and cannot be run inside of the structure. It has to be terminated outside.



*

 

[pennsylvaniaboy]

100' run tops, and i thought 2-2-2-4 was enough? and i want something that can be continuous from box to box....so does that narrow it down to #1? http://www.lowes.com/pd_70262-295-28714401___?productId=3129329&pl=1&Ntt=mobile+home+feeder

 

[pattenp]

The 2-2-2-4 MHF can go panel to panel and needs to be in conduit where above ground to the panel, but it's best to do conduit from panel to panel. #2 aluminum is limited to 90A as a branch feeder. If you know you need the full 100A then you could check with an electrical supply house to see if they have 2/0-2/0-2/0-1 MHF. The #4/0 MHF is way overkill for a 100A and will require reducing the ends to fit a 100A breaker. Don't get hung up on buying the wire from HD or Lowes.

 

[pennsylvaniaboy]

So this would work?

http://www.homedepot.com/p/Southwire-2-2-4-6-Aluminum-MHF-Wire-By-the-Foot-30163099/205001794

I wouldnt mind using lowes, but they dont seem to stock a 4 strand MHF. As for feed, 90amps should be fine.

And there is a local supply house, just trying to price out stuff online and they don't have a website. I guess I would call and ask for a 2-2-2-4 MHF or a 2-2-2-1 MHF?

 

[pattenp]

#2 MHF comes as either 2-2-2-4 or 2-2-4-6. I suggest using 2-2-2-4 since it does not have a reduced neutral. The 2-2-4-6 will work but I just prefer having the larger neutral. Lowes where I live has the 2-2-2-4 MHF in store for $1.49 a foot. Have you physically gone to a Lowes and checked what's in the store?

Also you should start your own thread instead of tacking on to this one.