Rewiring single car garage

[Powderm0nkey]

Hi guys, I've read many, many posts regarding wiring to a detached garage from our house, and I still have questions that I'm hoping someone here might be able to help me out with.

First some details:
- House has a new GE panel before we moved in, has about 12 empty slots. - Four pole 150A main breaker/cutoff for the house.
- Right now there are two 20A circuits running to the garage, unsure what else might be on those lines. But I know the lines to the garage come out of the roof below the shingles and above the gutter and have a swag over to the garage. Inside the garage it's a mess of wiring and I'm going to be removing all of the old wiring as it's not done correctly or safely, there's no insulation or conduit run, there are multiple outlets and light switches and it just looks like a hack job.
- Main house panel is at the back of the house, not too far from the garage.
- Garage is about 10' from the house, size is 14.5x24'. Poured concrete floor and foundation walls that are about 8" off the floor up to open stud walls and an open ceiling. Plans for insulation, a ridge beam to open up the ceiling for possible MaxJax or to be able to open and air out our VW van since we live in the PNW. A lot of inspiration has come from Woody and the Woody's Works Garage thread.
- The run will be somewhere between 30-40', I've run calculations for voltage drop for 50' to be safe.
- I'm wanting to run a 220V line to run a Lincoln TIG welder plus future air compressor and also one 110V for the lights and another 110 for the outlets in the garage. We are planning some backyard remodeling and I was hoping to have some lights on a pergola and maybe something for a future greenhouse heater/fan behind the garage.
- Inside the garage at this point I've got the welder (50-60A 220V) that will be occasionally used, a Porter Cable 8A 110V stand up drill press, a small 110V 1920s lathe, a small bench grinder, the four LED lights like these (48W output at 120V = 48/120 = 0.4A per fixture... is that right?), a shop vac that gets used occasionally and an Onkyo receiver I found at goodwill and saved. Once it gets insulated the little ceramic floor heaters I use should be more than enough for what I need, especially in NW Oregon and with the rubber horse stall mats covering the floor. It never really gets that cold here. Again, plans for a 220 double stage air compressor in the future, and possibly a few more lights.

Here is my plan:
- Install a 100A subpanel in the garage with a main cutoff and two ground rods at least 6' apart.
- 90-100A 2-2-2-4 Al wiring (opinions on this?) from our main panel out to the subpanel for the 220V supply to the subpanel. This will be down into the crawl space under the main panel of the house, in sch 80 1.5-2" conduit underneath the house out to the stem wall above the foundation about 8', down to an 18" deep trench to the garage 16' or so, up in conduit to the garage, inside and then up to the subpanel. I'm guessing 30' based on the bends and all the up/down. Voltage drop with the 2AWG AL is roughly 2.6V and 1.06% at 50', 240V and 100A. Based on the calculator I'm using here I can step down to 6AWG for the 50' run at 240V and 100A and still only have a 6.5V and 2.7% loss on the run. If it really is only 30' I can step down to 8AWG which gives a 6.2V drop at 240V/100A load which is 2.6%. So even though a 6 or 8 AWG might work, I think I'd like to use a 2 or 4AWG supply to be safe and to have some insurance the house/garage won't burn down. At least not from that wiring. The rest of the 1940s wiring and the yokels that have installed things before us, I don't want to talk about.
- From the subpanel run:
1. 50-60A 220 line for the welder.
2. A 30A 220 for the future compressor.
3. I'd like to run the lights on their own 20A circuit. I have 4 long LED overhead lights, probably add 2-3 more, and at least one light outside.
4. At least one, but ideally two 20(30?)A 110V circuits for the outlets around the garage. At least one of these will be powering an overhead roll-up door like one from Smart Garage.
5. At least one 15-20V 110V run outside and roughly 30-40' for an outdoor box to plug in our outdoor lights on a pergola.
6. Plan on having a second outdoor line 15-20A 110V from here to possibly run a heater or fan for a small greenhouse/hot house for the wifey to keep her happy.
- So a total of 6 planned circuits, 8 spots since there are two 220V double throw breakers.

I'm pretty doubtful all of these loads will be running at once, especially not all the time. Worst case scenario is lights on, welding something SUPER thick, compressor kicks on and the heater out in the greenhouse is on once it goes in. I'm a hobby builder, welder, machinist at best so I doubt I'll be welding anything much over 3/8", MAYBE 1/4", the machine will go up to 90A so I won't be running it too hard with what I do. It was a craigslist purchase from a manufacturing gig that was moving a few states away and didn't need it anymore, so it's quite over kill for my hobby uses but it's a quality machine and the price was right. There will be a cooling pump for the TIG torch running on one of the 110V lines when it's in use, but this could also be run off of the welder itself I suppose.


Long post, thanks for bearing with me, we're almost done on this journey...

Now here are my questions:
- From the experience of the board, is one 90-100A 220V line going from the house panel to the garage subpanel that is grounded properly, has the neutral and ground UNbonded from each other and has a main disconnect since I'll need 8-10 slots enough for what I'm looking to do?
- Is it possible to run a 220 75-90A service for the subpanel to power the garage tools and then also keep the current 20A circuits that are going out to the garage but just rewire them to go in the trench I'm going to dig? They would be in their own conduit, but how far away from the 220 line would they need to be to not have any inductance interference? Does having three lines coming into the garage make things too dangerous/confusing or does it break code? I haven't been able to find this out yet. Is there a way to add the 110 lines that are currently there into the subpanel? Should I just remove those two 20A circuits and put the double pole/throw 90-100A breaker in their place?
- I'd like to use GFCI breakers for both the 220 and the 110 circuits out in the garage subpanel. Should I use one in the house at the run from the main panel as well?
- The 20A 110 outlets around the garage, 8-9 of them, will be run in series, half and half. At least that's the plan and why I was going to do two separate circuits. Should I up this to 30A? Can it be run as one circuit, or is it safer/better as two?
- 90A is probably a LOT of overkill for my one car garage being used for hobby work, but I'd like to do it right the first time and not have to dig things back up. Any thoughts on downsizing the wiring and circuits, or do I have things about right? Am I going to run out of Amps with what I have planned? The only big thing we have left in the house is the dryer at 30A and the furnace at 15A. We just recently put in a gas stove with a gas convection oven, so no huge draw there. I suppose the water heater is electric too. But it's just me and my wife, ~1200 sqft cottage type Craftsman house. Our bills are typically pretty low.

The easiest thing would be to just run the one 220 line to the main cut-off/breakered, double grounded, UNbonded subpanel in the garage and then run my circuits from there. My head is swimming in numbers and acronyms and I think I'm confusing myself and over thinking things. Can anyone offer guidance or at least point me in the right direction? Thanks a million!
-Ryan

 

[pattenp]

Sorry but too much to digest, one easy comment is all existing circuits to the garage need to be abandoned. Only one feed is allowed.

 

[Powderm0nkey]

And here is a picture of what I have planned crudely drawn with crayon effect in paint.

 

[Powderm0nkey]

Sorry but too much to digest, one easy comment is all existing circuits to the garage need to be abandoned. Only one feed is allowed.

It's a lot, I know. Thanks for that tip though. I was planning on doing that anyways I think.

 

[wyliesdiesels]

Way too much to read.

You will lose everyone on here after the second or third paragraph.

Try breaking it up into sections and different posts.

 

[pattenp]

As your first grade crayon drawing shows is mostly correct. I'll just state some of the main things.
*Subpanel feeder is four wires, 2 hots, 1 neutral, 1 equipment ground.
*Subpanel neutral bar is not bonded to ground.
*Subpanel electrode system is needed, 2 ground rods on one continuous bare #6.
*Welder only needs 240V so no neutral is needed. Neutral is used for appliances that need both 120V and 240V.
*Put lights and outlets on separate circuits. Have multiple circuits for each if a lot of lights and outlets.
*Use 20A circuit for the 120V outlets.
*You can have more amperage in breakers in the panel than the amp rating of the panel. You need to determine amp load by what will be in use at one time, not by adding up breakers.
* 240V outlets above 20A should be dedicated single outlet circuits.
*Depending on compressor motor HP the compressor may need to be hardwired, not on a plug and outlet.
*if you use 2-2-2-4 Mobile Home Feeder (MHF) it's 90A max. Beware that some cable is listed as URD and is not allowed to run to the inside of the structure because it is not fire rated, MHF is allowed inside but has to be in conduit.
*GFCI is only required for 120V outlets in garage.

*

 

[arkieguide]

You are on the right track. However on the ground and neutral, keep them separate all the way back to the main panel then they join and go to the main ground rod. The sub panel, why 2 ground rods ? only one is needed.90 to 100 amp 4 wire feed is OK. Conduit can be PVC if you want. In your shop you probably, will never run all you tools at the same time. So delete the 2 circuits all ready there. 1 - 120 v /20 a, 1/p, circuit will run all your lights. ! 120 v - 20 a 1/p circuit to grinder and drill press, plus and additional 120 v 20 a outlet, 1 - 120 v 20 a 1/p circuit for misc outlets around shop.1- 220 v 40 a 2/p, circuit for welder, would be a good start. Add other circuits when needed. All ways connect the grd wire at all outlets and tools. Good luck on the project.

 

[wyliesdiesels]

You are on the right track. However on the ground and neutral, keep them separate all the way back to the main panel then they join and go to the main ground rod. The sub panel, why 2 ground rods ? only one is needed.90 to 100 amp 4 wire feed is OK. Conduit can be PVC if you want. In your shop you probably, will never run all you tools at the same time. So delete the 2 circuits all ready there. 1 - 120 v /20 a, 1/p, circuit will run all your lights. ! 120 v - 20 a 1/p circuit to grinder and drill press, plus and additional 120 v 20 a outlet, 1 - 120 v 20 a 1/p circuit for misc outlets around shop.1- 220 v 40 a 2/p, circuit for welder, would be a good start. Add other circuits when needed. All ways connect the grd wire at all outlets and tools. Good luck on the project.

The ground and neutrals go to the same bar in the main service panel, NOT the ground rods.

If you tie a neutral directly to a ground rod, you WILL have neutral current flowing on pathways that it shouldnt be on including the bare GEC. This creates a shock potential.

Also, 2 rods are required unless one can prove 25ohms or less of resistance between rod and earth.

 

[pattenp]

You are on the right track. However on the ground and neutral, keep them separate all the way back to the main panel then they join and go to the main ground rod. The sub panel, why 2 ground rods ? only one is needed.90 to 100 amp 4 wire feed is OK. Conduit can be PVC if you want. In your shop you probably, will never run all you tools at the same time. So delete the 2 circuits all ready there. 1 - 120 v /20 a, 1/p, circuit will run all your lights. ! 120 v - 20 a 1/p circuit to grinder and drill press, plus and additional 120 v 20 a outlet, 1 - 120 v 20 a 1/p circuit for misc outlets around shop.1- 220 v 40 a 2/p, circuit for welder, would be a good start. Add other circuits when needed. All ways connect the grd wire at all outlets and tools. Good luck on the project.

The need to delete the two existing circuits feeding the garage is not determined by how many tools the OP may run at one time. If a new feed is installed those two existing feeds must be abandoned.

Recommending a welder circuit size without knowing what size welder will be used is a shot in the dark.

 

[Powderm0nkey]

The need to delete the two existing circuits feeding the garage is not determined by how many tools the OP may run at one time. If a new feed is installed those two existing feeds must be abandoned.

Recommending a welder circuit size without knowing what size welder will be used is a shot in the dark.

Ok, sorry for the detail heavy post up top. Here's a slimmed down version.

- The two 120V lines running to the garage now have to go. Easy, peasy, done.
- Pop in a double pole, double throw 90A breaker in the spot these two just vacated.
- Using 2-2-2-4 MHF in conduit under the house, in the ground and while going up to the subpanel in the garage.
- In the subpanel the ground and neutral need to be unbonded. In the house both the ground and neutral go to the same bar?
- 60A 220 goes to the welder since it's a four wire hookup and has 120 output on the front, I have ~ 25' of power cord that is attached from the factory it was in.
- I'll need a 30A 220 for the air compressor eventually.
- 120V 20A for the lights.
- 120V 20A x2 for the outlets
- ?possibly a 120V 20a for the drill press and bench grinder.
- Two 8' ground rods linked by one #6 bare copper wire running to both with acorn nuts.

So I guess the questions will be how to connect the ground/neutral at the main panel, both to the same bar, or connect to their respective bars? Also, would it be unreasonable to link 4-5 of the 120V outlets together in series in the garage?

Sorry for all of the basic questions!

PS - pattenp, your detailed diagram that is floating around for the subpanel wiring is amazing.

 

[pattenp]

...
So I guess the questions will be how to connect the ground/neutral at the main panel, both to the same bar, or connect to their respective bars? Also, would it be unreasonable to link 4-5 of the 120V outlets together in series in the garage?

Sorry for all of the basic questions!

PS - pattenp, your detailed diagram that is floating around for the subpanel wiring is amazing.

I would think you have a couple of open holes in the existing neutral/ground bar, if not you may have to add a bar. Neutrals can only be one pre hole, grounds usually can be two per hole. If wire is too large for the bar then you can purchase a larger add-on lug that may take up a couple existing holes in the bar.

4 to 5 outlets on a circuit is fine. The outlets will be in parallel, not series.

The diagram was a web copy and paste. I didn't create it.