New Garage

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  #1  
Old 12-29-05, 08:23 PM
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New Garage

Hello guys,

I have a contractor building a new detached 24'x28' garage for us and it should be done mid-next week. I'm doing the electrical myself because I'm very comfortable doing it and thought it would be a great way to save some money and have the chance to overbuild it. I never plan on having any sort of welder, but it would be nice to at least have a 220 outlet just in case. Also, I plan on having great lighting and there will be a 1/2 HP garage door opener. Since the work will be inspected I want to follow the NEC codes to ensure it will pass inspection. That said here's my questions:

1) Do I need to install a sub panel box in the garage and how large of one do I need to install? How large of a supply will I need to bring to the garage?

2) How many feet apart will I need to install outlets?

3) I'm not finishing out the inside of the garage (at least not now) so do I need to install conduit or can I just secure the Romex to the studs (inside the stud cavity)?

4) Do I need to install a 220 outlet and if so how many/how many feet apart?

5) Is there a requirement for lighting the garage? Is there a minimum amount of lumens or wattage/design for lighting the garage will need to meet?

6) Since I'm planning on installing a subpanel box and having multiple circuits, what circuits will I need and what items should be kept off the same circuit?

7) What depth will I need to burry the supply to the garage? Is it OK to bring the electrical into the garage through PVC on the side of the garage (basically burry the wire then bring into the garage through PVC that is burried a few inches in the ground and also attached to the side of the garage)?

My goal is to take the minimum requirements and then go above and beyond that. Thanks for your input guys!
 
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  #2  
Old 12-29-05, 08:46 PM
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1. Based on your desires, you do need a subpanel. If you were content to power a few lights and an occasional hand tool, you could get by without the subpanel, but you have bigger eyes than that.

A typical supply to a garage without a large welder is a 60-amp subpanel, fed from a 60-amp double-pole breaker in the main panel, with 6/3 UF-B cable buried at least 24" deep and protected by schedule 80 PVC conduit up from the bottom of the trench and while above ground.

2. There are no outlet spacing rules for unfinished garages. Do whatever you want. Install as many or as few as you think you'll need.

3. If not prohibited by your city, you may run NM-B cable through bored holes in the studs. I would probably recommend you run the cable up rather high on the walls to minimize the possibilities of damage.

4. Again, install as many or as few 240-volt outlets as you want. Remember that unlike 120-volt outlets, 240-volt outlets are not "general purpose" and are normally designed and installed for one specific appliance. So you might want to delay putting in any 240-volt circuits until you actually have something that needs 240 volts. Then you can design a circuit spefically for that appliance.

5. There are no requirements. Install as much or as little light as you want. In order to gain the greatest flexibility, you probably want to put in a lot.

6. It's probably better to put the lighting and the receptacles on separate circuits. One lighting circuit is probably enough. How many receptacle circuits you need depends on what you plan to put in the garage, and how many tools you might run simultaneously. I would allocate individual circuits for any refrigerator, freezer, or garage door opener. Then a couple of circuits for tools would be good. I'd use all 12-gauge wire and all 20-amp circuits.

7. Covered above.

A 60-amp subpanel will provide up to 14.4 KW of power. That would be enough for most people. This is fairly easy for a DIYer, and going above that involves a significant increase in cost and difficulty.

You'll need a grounding rod at the garage. You'll need to keep the neutrals and grounding wires isolated in the panel (throw away the bonding screw or strap that comes with the panel). If you have more than 6 circuits, you'll need a main disconnect (you may want one anyway)--a second 60-amp double-pole breaker in the subpanel will serve. All 120-volt receptacles in the garage require GFCI protection, except the ceiling receptacle for the garage door opener and a dedicated receptacle for a refrigerator or freezer.
 
  #3  
Old 12-29-05, 08:56 PM
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I built a detached garage with an upper level workshop a couple of years ago. Here is what I did for the electrical.

I installed a 6 breaker subpanel in the garage fed through PVC from a 60A breaker in my house service entry panel. The feed cable is buried 24". I think the code limits a sub panel to 6 breakers but I could be wrong.

I installed a ground rod driven into the ground alongside the garage. The sub panel ground and neutral are not bonded at the panel.

I installed 5 separate circuits in the garage as follows:

Two, 20 Amp GFI protected circuits, outlets spaced so that there is no more than 4' from an outlet. The upper level outlets are individual GFI's providing power to typical woodshop tools. The lower level 20 Amp circuit has one GFI outlet serving the remaining outlets.

Two, 15 Amp, non GFI lighting circuits that include two outside receptacles that have GFI duplex outlets and an outside light. The lighting load on each circuit is around 500W.

One, 15 Amp non GFI circuit for two 1/2 HP garage door openers. Each door opener draws around 4-6 amps. If you only have one opener you may not need a separate circuit.

The omly issue I had with the inspector was not using a fire retardant caulk compound where the electrical cables penetrated the framing between the two levels.
 
  #4  
Old 12-30-05, 07:01 AM
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> It's probably better to put the lighting and the receptacles on separate circuits.

This will keep high current devices (such as a table saw) from drawing down the lights when the saw is turned on. Depending on the lighting you install, it may be sensitive to voltage dips and leave you in the dark..

> One lighting circuit is probably enough. How many receptacle circuits

I'd split the lighting to two circuits. If you need to replace a fixture on one of the circuits, you won't have to do it in the dark.

And label, label, label.
 
  #5  
Old 12-30-05, 07:41 AM
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Thanks for all your invaluable input guys! I'm still a little unclear regarding the whole conduit situation. Regardless of conduit or not I'll probably just use Romex for ease and success with it in the past. I'll be using 20 amp breakers and 12-guage wiring for the outlets. The outlets will be GFCI protected at the breaker. I'll hold off on the 220 for now until I determine the best placement.

1) If I use Romex do I need to use conduit since the garage will be left unfinished?

2) I'll be installing a ground rod for the garage. I'll be pulling electrical from a 6-breaker sub-panel box in an adjected garage that is connected to the house with 6-gauge 4-wire unground wire. Is it OK to connect the new garage to the old garage using 6-gauge underground wire and connect it to the old garage's sub-panel box on a 60-amp breaker or not? Otherwise to be safe should I install a 40-amp breaker in the old garage as not to stress the supply from the old garage to the house?

3) When I connect the garage to the old garage it's OK to connect the 2 hots and the nuetral but don't connect the ground, correct?

Thanks guys!
 
  #6  
Old 12-30-05, 08:19 AM
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Also, since the boxes will be exposed, should I use metal outlet boxes or are plastic (Carlson style) boxes OK?
 
  #7  
Old 12-30-05, 09:58 AM
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Exposed wiring must be protected. Generally this means that NM type wire cannot be exposed in an unfinished wall. It is usually allowed in the ceiling, even if exposed. You should probably run conduit down the walls and run the NM inside the conduit.

It is not generally recommended to run a sub panel off a sub panel. You would be better off to run the new garage all the way back to the main panel.

While it is okay to only run three wires to the sub panel, I would run four wires, two hots, a neutral and a ground. This will allow you, now or in the future, to run something else between the two buildings, such as a telephone, CATV or computer cable. To allow for this I suggest that you run two conduits to the garage, one for the sub panel wires and the other for low voltage lines. Even if you don't run any low voltage lines now, you will be able to in the future with minimal trouble if the conduit is in place. Keep the conduits at least twelve inches apart.
 
  #8  
Old 12-30-05, 10:06 AM
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It is not generally recommended to run a sub panel off a sub panel. You would be better off to run the new garage all the way back to the main panel.
Thanks for the input. What if I switch the subpanel in the old garage to a box with a main 60A switch and then just a standard subpanel box in the new garage. That way if the combined load between the two garages is greater than 60A then the main breaker throws. This way it will ensure that the 6-gauge that was run to the old garage will not overheat/be stressed?
 
  #9  
Old 12-30-05, 10:14 AM
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The box in the old garage is still a sub panel, whether it has a main breaker or not. You will be better off running the cable from the new garage all the way to the main panel.
 
  #10  
Old 12-30-05, 10:38 AM
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Originally Posted by racraft
The box in the old garage is still a sub panel, whether it has a main breaker or not. You will be better off running the cable from the new garage all the way to the main panel.
I understand that it would be ideal to run it directly and I would prefer that, but I don't want to spend the money to trench the wire from the house to the garage (roughly 50 ft) nor spend money on additional wiring when the old garage is ~12 ft from the new garage. I guess really I'm asking would it pass inspection to run it off the old garage or not.
 
  #11  
Old 12-30-05, 11:03 AM
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Originally Posted by sx460
...I don't want to spend the money to trench the wire from the house to the garage (roughly 50 ft) nor spend money on additional wiring when the old garage is ~12 ft from the new garage.
Not wanting to spend money is no reason to do a job in an inferior manner. Please reconsider your decision.

However, to answer your question, it is allowed to run a sub panel off a sub panel.

You stated that the sub panel in your attached garage is fed with four wire cable, but is not grounded ("unground"). If this is four wire cable, then it should be grounded. In fact, since it's in the same structure, it must be grounded back to the original panel.

To pass inspection, that sub panel in the attached garage (where you connect the feed for this new sub panel) will be examined as well as the new sub panel and wiring. Both sub panels will need to be correct to pass the inspection.

I recommend four wires from the old garage panel to the new garage panel, as well as four wires from the main panel to the first sub panel.
 
  #12  
Old 12-30-05, 08:30 PM
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Originally Posted by racraft
Not wanting to spend money is no reason to do a job in an inferior manner. Please reconsider your decision.

However, to answer your question, it is allowed to run a sub panel off a sub panel.

You stated that the sub panel in your attached garage is fed with four wire cable, but is not grounded ("unground"). If this is four wire cable, then it should be grounded. In fact, since it's in the same structure, it must be grounded back to the original panel.

To pass inspection, that sub panel in the attached garage (where you connect the feed for this new sub panel) will be examined as well as the new sub panel and wiring. Both sub panels will need to be correct to pass the inspection.

I recommend four wires from the old garage panel to the new garage panel, as well as four wires from the main panel to the first sub panel.
Thanks for the input. The existing garage is grounded with the house (I must not have been clear). I will be installing a ground rod next to the new garage. The house and the new garage will then have ground rods. Is it then OK to ground each building to each other, or should I not connect the ground between the two garages? Thanks.
 
  #13  
Old 12-30-05, 09:51 PM
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Originally Posted by racraft
Not wanting to spend money is no reason to do a job in an inferior manner. Please reconsider your decision.

However, to answer your question, it is allowed to run a sub panel off a sub panel.

You stated that the sub panel in your attached garage is fed with four wire cable, but is not grounded ("unground"). If this is four wire cable, then it should be grounded. In fact, since it's in the same structure, it must be grounded back to the original panel.

To pass inspection, that sub panel in the attached garage (where you connect the feed for this new sub panel) will be examined as well as the new sub panel and wiring. Both sub panels will need to be correct to pass the inspection.

I recommend four wires from the old garage panel to the new garage panel, as well as four wires from the main panel to the first sub panel.
If I do run a dedicated supply from the house to the garage, what gauge wiring should I use? 100A would be nice out there and the run is roughly 80 - 90 ft from the main panel in the house to the sub panel in the new garage. Should I build the electrical system for 100A or is that overkill. I have no plans for ever having a welder. The highest pulling tool I would ever use would be a high amperage saw or a 220 air compressor.

You're comment about money has got me thinking. Running a dedicated supply to the garage would only increase the whole project by $300 or so and considering the garage cost of around $21K it's not a lot of extra money relatively speaking. Thanks.
 
  #14  
Old 12-31-05, 05:05 AM
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Handy idea that works good is add a 50ft spring loaded cord on the wall with a dedicated circuit. I use mine all the time.
 
  #15  
Old 12-31-05, 10:12 AM
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New garage

I agree with John, don't skimp. You are eyeing a larger scenario than you realize. Having the 240 volt circuits are invaluable, even if you don't have a welder. I have converted all my larger tools (compressor, table saw, radial arm) to 240 volts, with the installation of proper jumpers in the peckerhead on the motors. You don't save anything on your electric bill, but spool up is alot quicker, and less bogging or blade slow down. So you will eventually want to plan on it happening.
There are many things you won't be "required" to do, but undercutting your dream isn't worth it. I planned my shop backwards from the tool to the power panel, that way I had what I wanted and did what I had to do in order to get it, for a minimal amount of money.
Good luck with the project. It will be rewarding.
 
  #16  
Old 01-01-06, 11:48 AM
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Originally Posted by orlando
Handy idea that works good is add a 50ft spring loaded cord on the wall with a dedicated circuit. I use mine all the time.
That's a great idea. I think I will do that.
 
  #17  
Old 01-02-06, 07:15 AM
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I'd call your inspector regardless on the whole sub panel/local ground topic. I've found about three different solutions in books/on the web, and I actually got two different opinions from the two different inspectors I spoke with. As you know, the opinion of the inspector that will visit you is the only one that counts.

/* Funny, here in MN no one has ever said anything to me about plugging the holes in the bottom/top plates between floors.... */

Good luck, have fun.
 
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