The old subpanel in the garage question

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Old 08-07-09, 09:22 AM
J
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The old subpanel in the garage question

I've read as many of the threads I can find on installing a subpanel in my garage, but I still have some questions. I apologize in advance for the length of this post, but I'm hoping to get all my questions and detail out there at one time.

I'd like to install a subpanel to support some woodworking equipment in a detached garage, about 25' from the main house and a total of about 75' from the main panel in the basement.

I was thinking a 50 amp double pole breaker at the main box would support my needs. The max load would be 13.6 amps for a planer, a 12 amp dust collector, and 3 amp air filter. So, not including lights, that's about 29 amps. All the other tools are rated much less in terms of amperage.

I was planning on running 6-3 romex w/ grd from the main panel through the crawl space to a J-box at the back of the house where I'll switch to thwn (3, #6 plus 1, #10 ground) and then run that in 1" conduit (or larger if I want to make pulling easier) at least 18" below grade until hitting the garage. I figure the romex will be easier to struggle with in the crawlspace than fighting with conduit the whole way. There's not a lot of room to work in there. Is it okay to just staple the romex to the bottom of the floor joists or are there special hangers with this larger-sized wire? I read that I have to use color-coded thwn because less than #4 cannot be run in conduit and then re-coded at the ends. I'm assuming that I can run two blacks, a white and a green for my colors, and there's no need to distinguish between the hots. If I didn't have to buy the different colors, I would probably just buy a big spool of the thwn and run that the whole way in conduit with no intermediate connections. It would be a lot cheaper and make fighting with the conduit in the crawlspace worth my while.


The J-box I found is pvc with no holes. I'm assuming that I create my own openings and then find a fitting that will connect the J-box to the small run of conduit through my wall to outside. Is there a recommended size box to use? Anything I should know about the fitting that connects the box to the conduit? Is there a special way to make up the ends between romex and the thwn? I've never worked with #6 gauge before and it seems pretty big for a standard (albeit larger) wire nut connection. After making up a connection, do you guys wrap tape around the wire nut and a bit of the wire? I've seen that done and have gotten into the habit of repeating it on #12 or #14 connections, but I was curious as to what other folks might do.

To have enough space for different circuits, I was planning on using a 100 amp subpanel. I'll probably have at least five circuits to start with two of them being 220v, so I just thought it easier to go with the 100 amp panel.

The neutral bus bar should not be connected to panel with grounding screw or strap.

Because it's a detached garage, I would need a grounding rod and would run #6 copper from the rod to the panel, connecting the wire to the rod with an acorn nut.
  • Do I use solid or stranded wire for grounding rod wire?
  • Should I use bare or shielded wire?
  • Do I need to protect the grounding wire somehow?
  • Use a different conduit to run from rod to panel?
  • Do I sink the rod below grade? By how much?
  • Does the grounding rod get protected somehow or just driven into the ground as is?
  • How do you know if you need more than one rod?
  • If more than one, do you just drive a second near the first and wire them together and then to the panel?
I've read that you place the panel at working height with the top of the panel no higher than 6'6", making sure you have ample room in front of and to the side of the panel to work on it.

The most convenient place for my panel is immediately upon entering the garage. The main garage door is on the front of the garage with 4 feet to the left of it. The side door to the garage is toward the front with 3 feet to the right of it, creating a corner in the front of the garage between the doors that's 4' x 3'. I'd like to place the panel on the 3' wall, just inside the side door. Is there an issue with doing that? There wouldn't be anything in front of it.

There has to be GFCI protection because it's a garage. If I bought a 50 amp double pole GFCI breaker for the main panel, would that protect everything all at once and then I could just wire the rest of the breakers and circuits without worrying about GFCI? That breaker is pricey, so is there a more efficient way to get GFCI protection in the garage? I know I can run my standard outlets through a GFCI receptacle to get protection on the whole run, but do you have to do that with lights as well? Is there such a thing as a GFCI 220v receptacle if I don't buy the special circuit breaker? I thought I read somewhere that 220v did not need GFCI protection. I'm not sure of the best option in terms of cost and still meeting code. Also, if I trip the GFCI, I'd also rather not have to run into the house to reset it.

When rewiring the garage, I'm assuming that I can use 12 gauge romex through the walls for all receptacles and 14 gauge for lights. 12/3 romex is adequate for a 220v receptacle that will see about 14 amps from the planer, right? By code, do I need to seal up the walls with drywall or pegboard or something like that if I just run the wire through the walls? Or, are the rules a bit different because it's an unfinished garage?

I've been searching around the posts and reading a few basic books, so I'm hoping that most of what I have here is right and just needs a bit of confirmation. I'm a bit fuzzy on the details about the panel placement, GFCI, and the grounding rods, though. Again, sorry about the length of the post...
 
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Old 08-07-09, 12:52 PM
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Originally Posted by JJ Ronk View Post
where I'll switch to thwn (3, #6 plus 1, #10 ground)
The THWN portion can be done with (3) #8 + (1) #10 to save a little money. The temp ratings are different for THWN so a smaller size is okay.

I figure the romex will be easier to struggle with in the crawlspace than fighting with conduit the whole way.
You might want to consider 3/4" or 1" ENT ("smurf tube" because it's bright blue) which is a flexible PVC conduit -- not really any more difficult to work with than cable. It can glue directly into your rigid PVC LB fitting at the transition from inside to outside.

Is it okay to just staple the romex to the bottom of the floor joists or are there special hangers with this larger-sized wire?
Yes, check the electrical aisle at the hardware. There will be a variety of staple sizes with the supported cables listed on the package.

I read that I have to use color-coded thwn because less than #4 cannot be run in conduit and then re-coded at the ends.
True, however I have never run into a situation where the inspector wouldn't allow recoding of a black #8 or #6 with a few wraps of white tape. Spooled black wire is often quite a bit cheaper than colors by the foot, so ask the inspector upfront. It will probably be okay. The ground must still be green or bare though.

The J-box I found is pvc with no holes. I'm assuming that I create my own openings...Is there a recommended size box to use?
That's right, 6x6 should be plenty.

Is there a special way to make up the ends between romex and the thwn?
Big blue wirenuts. Set screw connectors are also available, but much more expensive. Although if you go with conduit method you replace the splice and the j-box with just an LB fitting.

After making up a connection, do you guys wrap tape around the wire nut and a bit of the wire?
No, it's not necessary. When properly installed, the nut should be tight enough to hold itself firmly in place on the wires.

The neutral bus bar should not be connected to panel with grounding screw or strap. Because it's a detached garage, I would need a grounding rod and would run #6 copper from the rod to the panel, connecting the wire to the rod with an acorn nut.
Correct.

I'll answer these in place:[LIST][*]Do I use solid or stranded wire for grounding rod wire?

Either.
[*]Should I use bare or shielded wire?

Either.
[*]Do I need to protect the grounding wire somehow?

Not for #6
[*]Use a different conduit to run from rod to panel?

Not required.
[*]Do I sink the rod below grade? By how much?

Just a little. It can be up into the mulch if it's landscaped.
[*]Does the grounding rod get protected somehow or just driven into the ground as is?

As-is.
[*]How do you know if you need more than one rod?

With an expensive meter. Simpler to just install two.
[*]If more than one, do you just drive a second near the first and wire them together and then to the panel?

At least 6' apart, use one continuous wire from panel to rod to rod.

I've read that you place the panel at working height with the top of the panel no higher than 6'6", making sure you have ample room in front of and to the side of the panel to work on it.
Technically the top breaker handle can't exceed 6'7". Required clear working space is 30" wide by 36" deep floor to ceiling. The panel doesn't need to be centered in the 30".

Is there an issue with doing that? There wouldn't be anything in front of it.
Sounds okay as long as the door can be swung to provide the necessary clearance.

There has to be GFCI protection because it's a garage. If I bought a 50 amp double pole GFCI breaker for the main panel
It's only mandatory on 15A and 20A 120V receptacles. While the single breaker would meet the code it is not recommended because you have a greater chance of false trips and you would lose lighting if a power tool malfunctioned which may be a very dangerous situation with blades still spinning.

is there a more efficient way to get GFCI protection in the garage?
GFCI receptacles as the first device on each circuit.

but do you have to do that with lights as well?
Only if you use fluorescent shop lights which plug into receptacles on the ceiling. That makes it easy though because you can still use a GFCI receptacle.

I'm assuming that I can use 12 gauge romex through the walls for all receptacles and 14 gauge for lights.
If the walls are drywalled or otherwise enclosed. You generally can't have exposed romex in the garage walls, although some jurisdictions do allow it. The ceiling exposed is okay. Some inspectors may require conduit sleeves down the wall or the use of AC or MC cables if you leave the walls open. 3/8" Drywall or OSB sheathing might be cheaper and less hassle than bothering with cable protection though. The wire sizes are appropriate for 20A and 15A circuits respectively.

12/3 romex is adequate for a 220v receptacle that will see about 14 amps from the planer, right?
12/2 is okay for that application. A 240V circuit doesn't use the neutral. Remark the white wire with red or black tape.

Again, sorry about the length of the post...
No problem; I got my typing workout for the day. I'd rather get all the details done in one post than go back and forth for a week playing 20 questions.
 
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Old 08-07-09, 03:22 PM
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This is awesome....thank you so much for all the information!!
 
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Old 02-01-10, 11:30 AM
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I need clarification, pleae

Originally Posted by ibpooks View Post
If the walls are drywalled or otherwise enclosed. You generally can't have exposed romex in the garage walls, although some jurisdictions do allow it. The ceiling exposed is okay. Some inspectors may require conduit sleeves down the wall or the use of AC or MC cables if you leave the walls open. 3/8" Drywall or OSB sheathing might be cheaper and less hassle than bothering with cable protection though.
If I surface mount the panel and the wires run through the sides, then into the walls, do the wires have to be protected? In my basement they are not protected. Most enter the floor above, so they are exposed for several feet, while a few that service the basement are exposed for less than one foot.
In my pole-building I plan to use OSB for wall covering and surface mount the breaker box/panel board/load center.
 
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