Safely wiring up a 1916 Garage

[waldosgone]

Garage Journal,

I've searched through the mighty Google and now I'm turning to Garage Journal for some advice. I've got a detached, 1916 garage. It's 16x18 and I currently have electric run out there (from the previous owners) and here's the setup.

15 amp circuit split from an existing circuit (no boxes just open splices!) Heads out of the basement/crawlspace through 3/4'' conduit into a metallic junction box. This then goes down under the "new" driveway, in PVC conduit, and terminates ~25 feet away in the garage. The wire that was fed through the PVC conduit was UF-B (I think based on what it looks like but I can't find any markings) and I'd like to run two circuits out there.

I've basically narrowed it down to two different ways to accomplish this.

1. Dig a new trench (at least 18'' down) from the panel (it's on the outside of the house) to the garage (~30 feet) and run new 3/4'' conduit and 2 12g THWN circuits (2x hot, 2x neutral, 2x ground for each) in the new conduit. Additionally, this would allow me to run another conduit for CAT 5e for Internet.

2. Use the existing conduit and UFB to pull the THWN through the existing conduit. I have no idea what the previous owner did with the conduit once it was laid under the driveway…

My end state is this:

I'm looking to have one 20 amp circuit for electrical (I use the garage as a wood shop with a miter saw, table saw, sander, shop vac for dust collection) and another 20 amp for lighting and some additional outlets in the rafters. This isn't our forever house, I'm in the military, and the most we'll be here is another ~ 2 years but I want to be able to use my table saw and the vacuum without one or the other slowing down.

What say you?

Thanks in advance, Waldosgone

 

[jwh]

Waldo, welcome to GJ and thank you for your service!

I had a similar situation with a detached garage at our present house: Circuit branched off house circuit, underground run, 1 outlet (not grounded), 1 pull chain light, (originally 2 but on removed and box blank-plated for overhead door.) UF cable buried from house to garage. Looked like was in conduit. In reality, only the out of the ground portion was in conduit.

I did basically what you are proposing to do. I ran 10/3 with ground in 3/4" conduit. Good idea on the Cat 5 cable in a separate conduit, wasn't around when I did this job.

Was fed off main panel in basement. Originally 1 circuit with GFCI in house basement. Had lights and outlets on that circuit. Lights were tripping GFCI. (Sodium vapor on dusk-dawn photocell.) Wound up hooking up second hot for lights and moving GFCI outside of garage for outlet circuit. (no service door - only overhead on opener). I know, should have had a second neutral.

That garage is now history, we built a new attached garage a couple years ago.

Sounds to me like you're doing it right, I'm sure someone else will chime in with more opinions.

Good luck!

John in Rochester NY

 

[wyliesdiesels]

Whats your location? If youre in the US, u cant have more than one electrical feed to a detached structure!

Your best bet is probably MHF #2 AL feeding a subpanel...

 

[alfredeneuman]

If you are in the US,

If you only need 2 - 20amp circuits, in order to comply with the 1 circuit to a detached structure rule, the only way to do this is with a multiwire branch circuit.

If you run separate neutrals, it will count as 2, whereas the MWBC counts as 1.

A MWBC shares the same neutral between the 2 circuits. They must be placed on opposite legs in the panel, and the breaker must have handle ties, or be a 2 pole.

You only have to run 1 ground wire no matter how many circuits in the conduit.

 

[bczygan]

Temporary or permanent?

Permit?

What do you need to power and light?

Budget?

Skill level?

 

[bczygan]

What's the thinking behind no more than one feed to a detached structure?

 

[Norcal]

What's the thinking behind no more than one feed to a detached structure?

Would be a nightmare having multiple circuits to a detached structure, there needs to be a simple way to disconnect all power easily.

 

[waldosgone]

Temporary or permanent?

Permit?

What do you need to power and light?

Budget?

Skill level?

Permanent.

Permit if required. I live in Oklahoma.

I was planning on digging the trench and hiring an electrician to run the wire. I figured there was no reason to pay his rate to dig a trench…

Currently have 3x T8, 2 bulb fixtures. Two in the main area and one over the work bench; I figure that's enough light for my needs but I only have one 2 gang set of outlets. Leads to many extension cords all over the garage. As far as tools I don't plan on powering more than my current miter saw (10'' Dewalt), Ridgid table saw (R4512), couple of smaller circular saws, sanders, and possibly a small Rockler dust collection (.75hp) system.

Budget is about $300 to run the wire from the service to the garage and wire up another 2 gang outlet on the wall with the workbench and one on each wall. I'd also like to add 1 outlet (on the light circuit) in the rafters to install a pull down extension cord (to run power to my assembly table).

 

[waldosgone]

If you are in the US,

If you only need 2 - 20amp circuits, in order to comply with the 1 circuit to a detached structure rule, the only way to do this is with a multiwire branch circuit.

If you run separate neutrals, it will count as 2, whereas the MWBC counts as 1.

A MWBC shares the same neutral between the 2 circuits. They must be placed on opposite legs in the panel, and the breaker must have handle ties, or be a 2 pole.

You only have to run 1 ground wire no matter how many circuits in the conduit.

Thanks, is a MWBC something that an electrician should be able to do? Is a MWBC a good idea with high draw (table saw and small dust collection) running on it?

I've attached a picture to give everyone a rough idea of what I'd like to do. I'd like this to meet code as there are so many parts of our 1916 hours that don't I figure it's time to start chipping away at it piece by piece.

 

[alfredeneuman]

Thanks, is a MWBC something that an electrician should be able to do? Is a MWBC a good idea with high draw (table saw and small dust collection) running on it?

If he doesn't know how to wire a MWBC, which is a basic circuit, you've hired the wrong electrician.

A MWBC will have no effect whatsoever on the performance of high draw items.

 

[waldosgone]

If he doesn't know how to wire a MWBC, which is a basic circuit, you've hired the wrong electrician.

A MWBC will have no effect whatsoever on the performance of high draw items.

Thanks for the info! Now if only it can stop raining (I'm sure I'll change my tune in August) so I can dig the trench.

 

[wyliesdiesels]

With the stuff u listed and a 20a MWBC, u could probably only run the dust collector on one leg and a saw on the other at the same time with some lights...

 

[waldosgone]

With the stuff u listed and a 20a MWBC, u could probably only run the dust collector on one leg and a saw on the other at the same time with some lights...

With that said sounds like a small panel would be the better choice? What would we be looking to run a 50 amp panel? The panel is 30 ft from where the garage is currently. It'd give the future owners some room to grow or knock the thing down and start over fresh….

 

[wyliesdiesels]

With that said sounds like a small panel would be the better choice? What would we be looking to run a 50 amp panel? The panel is 30 ft from where the garage is currently. It'd give the future owners some room to grow or knock the thing down and start over fresh….

Theres several ways to go about it. Either use direct bury wire such as UF-b or MHF(though i would recommend conduit anyways), or conduit and THHN wire. U already kinda of know this.

U will need 2 ground rods and a main breaker panel if u have more than 6 breaker handles. Also will need to isolate the neutral bar from the enclosure and ground bar.

the way u go kinda depends on how much u have or want to spend on it.

For #8 THHN/#10 THHN grn(for ground), a panel, breakers, rods, etc youre probably looking at about $200....hopefully u wont need a trencher...

 

[waldosgone]

Theres several ways to go about it. Either use direct bury wire such as UF-b or MHF(though i would recommend conduit anyways), or conduit and THHN wire. U already kinda of know this.

U will need 2 ground rods and a main breaker panel if u have more than 6 breaker handles. Also will need to isolate the neutral bar from the enclosure and ground bar.

the way u go kinda depends on how much u have or want to spend on it.

For #8 THHN/#10 THHN grn(for ground), a panel, breakers, rods, etc youre probably looking at about $200....hopefully u wont need a trencher...

Only trencher I was planning on using was a shovel and a day or so worth of labor. Either way (MWBC or sub panel) I was planning on THHN.

 

[wyliesdiesels]

Only trencher I was planning on using was a shovel and a day or so worth of labor. Either way (MWBC or sub panel) I was planning on THHN.

So i would go with 1" PVC. U will need 3 #8 THHN with a #10 THHN green(must be green jacked), 2 8' ground rods, some solid bare #6 cu wire, 2 acorn clamps, etc. 50a breaker for your main panel. Dont forget to isolate the neutral bar in your subpanel. Depending on what u buy, u may need to buy a ground bar kit!

BTW any circuit that is 120v/240v is considered a MWBC...

 

[waldosgone]

So i would go with 1" PVC. U will need 3 #8 THHN with a #10 THHN green(must be green jacked), 2 8' ground rods, some solid bare #6 cu wire, 2 acorn clamps, etc. 50a breaker for your main panel. Dont forget to isolate the neutral bar in your subpanel. Depending on what u buy, u may need to buy a ground bar kit!

BTW any circuit that is 120v/240v is considered a MWBC...

So just making sure I have all the material correct (run from house panel to sub panel will be ~35 feet)

100 ft black #8 stranded….$47.00 (2 hot runs from house panel to sub panel)
50 ft white #8 stranded…..$26.00 (1 neutral run from house panel to sub panel)
50 ft green #10 stranded…$15.00 (1 ground from house panel to sub panel)
25 ft solid bare copper…….$17.00 (attach grounding rods to new panel)
2x 5/8''x8' grounding rod…$22.00 (need to be placed 6 feet apart?)
2x 5/8'' grounding clamps..$5.00
Square D 100 amp (6 space) Outdoor Panel….$29.00
GE 40 Amp Double Pole Breaker…$12.00 (main panel)
4x 20 Amp single pole breakers….$16.00 (sub panel)
--------------------------------------------
$189 (good estimate!)

12-2 wire and outlets as required

Anything I'm missing?

 

[wyliesdiesels]

With #8 THHN u can use a 50a breaker...

"Anything missing?"

Yes. Check the panel youre buying to see if it comes with a ground bar. If not then u will need to purchase one separately!

Also, i would run a separate conduit for any communication wire u might wanna run out there in the future. With how cheap conduit is, its easier and cheaper to run it now while u have the trench dug...