Need Help Planning New Garage Wiring

[SliderJack]

Wow, reading the forum some great info and contributors. Just wanted to say thanks in advance!

I've read a little about wiring but really could use some direction and help planning. I'm planning a 28x32 detached garage 12:12 roof with attic trusses. Right now attic plan is unfinished and just for storage.

I did a load calculation using a form from a book and came up with 120A needed for the current house and electronics. Let me know if you want details.

Main breaker appears to be a Siemens 225A service. Only 3 spots left. Not too concerned with that. Don't plan on adding much to current house and if I had to I could combine a couple with 1/2 width breakers?

So, I was thinking a subpanel would be the way to go for the detached garage. Need a grounding rod? Not sure how deep yet I have to dig a trench, but the idea would be to bury the feed wire. Our house doesn't have a basement, but instead a crawl space. Our main panel is mounted in a finished external wall in our attached garage. I'm not sure if I would run the feed to the crawl space and dig through the block underground or cut a hole through the outside wall and brick and mount conduit. The feed to the subpanel would be between 35' and 40'.

So far for the garage I have the following:
AC Unit (have to buy yet figured in-window with heat 230V at 9A Example HD AC Unit)
Air Compressor (current is 115v 15A motor)
Garage Door Opener
Smoke Detectors
Welder (current is 115v 20A)
Fullsize Fridge ~2500watt
Saws
Vacuum
Lights
Outlets

I have no immediate plans to upgrade the welder or air compressor. I figured I'd run one 230 for the AC and I could maybe use that plugin later for an air compressor or welder. I don't think I'd ever use more than one at a time. Would it make more sense to wire a different outlet now? I wasn't sure if it was just more for the inspector to check. I originally didn't plan on finishing the garage but now I'm thinking I would with OSB instead of drywall. And I haven't considered insulation yet.

Not sure how to handle the attic. If it is unfinished, should I put all those outlets? Can I leave it unfinished and just use cable?

Could you take a look at my wiring diagram and let me know what you think? Should I combine circuits? Is it all wrong?

Not sure if it is legible or not but I was planning on 3-way switches for all except for outside lights beside the garage door. There would be only one switch for that by the font door. Let me know if you need more detail.

Would i use a dual-pole breaker to feed the subpanel? What size subpanel based on current service and current load? Suggestion on subpanel? Suggestion on feed wire and routing?

Thanks!

 

[FordTruckWench]

So, I was thinking a subpanel would be the way to go for the detached garage. Need a grounding rod?

Your ground and neutral will be bonded in your main panel in the house. This means they cannot be bonded in the garage sub panel, hence you will have to run a ground from the house to the garage. Someone else will have to answer the question of whether you need a ground rod at the garage.

Could you take a look at my wiring diagram and let me know what you think? Should I combine circuits? Is it all wrong?

Split the green circuit onto two breakers. Add a dedicated outlet/breaker for the fridge.

You don't need to connect loads linearly. You can branch out in a tree configuration. This reduces the number of splices any given load has to go through. This affects your orange, dk blue, and lt blue circuits.

Your present white circuit will need several segments of 12-3 (or 14-3) wire. If you set it up to go out and back (panel -> switch -> lights) you can use 12-2 (or 14-2). This saves you the trouble of getting some oddball wiring. It also gives you a light circuit power source at the upstairs back door - perhaps you will need to add an external light someday. The "out" run might even best be in the attic floor / ground level ceiling. (There's a new code requirement that neutral be present in the junction box with the switch.)

The wiring for the 3-way switches almost needs to go panel -> switch -> switch -> lights. You can't simply insert switches into either end of the circuit.

Would i use a dual-pole breaker to feed the subpanel? What size subpanel based on current service and current load? Suggestion on subpanel?

Yes, you'd use a double-pole breaker. Get as big a panel as you can afford. Given the size of your garage, I might suggest 200A - even if you only feed it with 100A to start with. If your house panel is a reputable brand/model, suggest getting the same brand for the garage.

Edit: Add an outdoor outlet between the vehicle and man doors. The inside of that same wall segment is a good place for a welder outlet. Don't worry about making more work for the inspector. I doubt the inspector would actually spend additional time. Having it all installed on the original permit means nobody can come back and cite you for later additions.

 

[SliderJack]

Thanks for much for the info!

Your ground and neutral will be bonded in your main panel in the house. This means they cannot be bonded in the garage sub panel, hence you will have to run a ground from the house to the garage. Someone else will have to answer the question of whether you need a ground rod at the garage.

Ok. I've got a lot to learn about wiring the subpanel, I'm just to point where I figured out that was the way to go. The subpanel however is probably the most important since I'll need to at least determine if I'm going to put some type of conduit through the slab.

Split the green circuit onto two breakers. Add a dedicated outlet/breaker for the fridge.

Good idea! Will do!

You don't need to connect loads linearly. You can branch out in a tree configuration. This reduces the number of splices any given load has to go through. This affects your orange, dk blue, and lt blue circuits.

Thanks! Great point. I'll fix!

Your present white circuit will need several segments of 12-3 (or 14-3) wire. If you set it up to go out and back (panel -> switch -> lights) you can use 12-2 (or 14-2). This saves you the trouble of getting some oddball wiring. It also gives you a light circuit power source at the upstairs back door - perhaps you will need to add an external light someday. The "out" run might even best be in the attic floor / ground level ceiling. (There's a new code requirement that neutral be present in the junction box with the switch.)

Great idea, especially the light at the top of the stairs.

The wiring for the 3-way switches almost needs to go panel -> switch -> switch -> lights. You can't simply insert switches into either end of the circuit.

Ah, the pattern I was trying to use made use of two sets of wires between the fixtures. I see how your suggestion would make things a lot easier. Thanks! I'll change that too!

Yes, you'd use a double-pole breaker. Get as big a panel as you can afford. Given the size of your garage, I might suggest 200A - even if you only feed it with 100A to start with. If your house panel is a reputable brand/model, suggest getting the same brand for the garage.

Siemens.

Edit: Add an outdoor outlet between the vehicle and man doors. The inside of that same wall segment is a good place for a welder outlet. Don't worry about making more work for the inspector. I doubt the inspector would actually spend additional time. Having it all installed on the original permit means nobody can come back and cite you for later additions.

Thanks! Sat down with the inspector today and he seemed like a really nice, helpful, and level minded guy.

 

[Falcon67]

The wiring for the 3-way switches almost needs to go panel -> switch -> switch -> lights. You can't simply insert switches into either end of the circuit..

You can have switches at both ends

http://diy.stackexchange.com/questi...th-two-lights-into-two-3-way-circuits-that-co

Also IMHO, I would move that panel down to near the fridge location. As it is, you are going to run a buttload of romex/wire/whatever to reach your far circuits. I made that "error" in my shop, putting the panel close to the house to reduce the power pull. Ended up using over 750' of 12 gauge just for common outlets.

 

[SliderJack]

Thanks Chris!

You can have switches at both ends

http://diy.stackexchange.com/questi...th-two-lights-into-two-3-way-circuits-that-co

Yeah, that's the pattern I was using originally. I took the suggestion as it might be better use of wire and maybe more simple with two switches at one end and fixtures at the other.

Also IMHO, I would move that panel down to near the fridge location. As it is, you are going to run a buttload of romex/wire/whatever to reach your far circuits. I made that "error" in my shop, putting the panel close to the house to reduce the power pull. Ended up using over 750' of 12 gauge just for common outlets.

I'm not sure whether it would improve much. Since I have switches at each end, I have all that wire. And the outlets run the perimeter, so either way one side would be longer. I would save on the 230, but now I added a 230 by the garage door. I don't have to do that.

I changed up the wiring based on FordTruckWrench's suggestions and attached it. Not sure it saved much. I did add an outdoor light top left. Looks like a lot of cable.

 

[SliderJack]

Seems most people are suggesting to use the same brand of subpanel as the main panel. Since my main is a Siemens should I get something like this?

Siemens 40-Circuit 30-Space 200-Amp Main Breaker Load Center

It's a lot more than I think I'd ever need.

 

[SliderJack]

Your ground and neutral will be bonded in your main panel in the house. This means they cannot be bonded in the garage sub panel, hence you will have to run a ground from the house to the garage. Someone else will have to answer the question of whether you need a ground rod at the garage.

Okay, I think I understand this now. In the new panel if the two are connected, I'll remove the tie.

Subpanel should be grounded with the ground bar mounted directly to the panel and neutral bar should be set off the box?

 

[FordTruckWench]

Siemens 40-Circuit 30-Space 200-Amp Main Breaker Load Center

It's a lot more than I think I'd ever need.

AC (back): 2 spaces
Welder (front): 2
Receptacles: 4 (green, yellow, fridge, orange)
Lights: I'd spread the load across 2 breakers

That's 10 spaces out of 30 used in the panel. The Lowes' website showed they carry a 20 space panel for a little less $.

Subpanel should be grounded with the ground bar mounted directly to the panel and neutral bar should be set off the box?

Yup!

Something for you to research: What's recommended for AC powered smoke detectors? Might they need a separate circuit? Maybe a lighting circuit would be a better choice than a receptacle circuit? (You could power the downstairs detector from the white circuit as it runs to the back upstairs door.)

 

[SliderJack]

AC (back): 2 spaces
Welder (front): 2
Receptacles: 4 (green, yellow, fridge, orange)
Lights: I'd spread the load across 2 breakers

That's 10 spaces out of 30 used in the panel. The Lowes' website showed they carry a 20 space panel for a little less $.



Yup!

Something for you to research: What's recommended for AC powered smoke detectors? Might they need a separate circuit? Maybe a lighting circuit would be a better choice than a receptacle circuit? (You could power the downstairs detector from the white circuit as it runs to the back upstairs door.)

I'll look into the smoke detectors. Thanks!

 

[theoldwizard1]

Yes, you will need 2 ground rods. You will also have to buy a ground bar as most panels do not come with them.

You always want overhead lighting on a separate (possibly 2) circuit(s).

I will disagree with FordTruckWrench only because I am frugal (some people say cheap). I don't think you will ever use anywhere near 40 circuits. I would go with the Siemens 100A 20 circuit $57 or the Siemens 100A 24 circuit $70

(IMHO) You really can not go wrong with any of these. But the difference in price is more than just a couple of cases of beer.

 

[SliderJack]

Yes, you will need 2 ground rods. You will also have to buy a ground bar as most panels do not come with them.

You always want overhead lighting on a separate (possibly 2) circuit(s).

I will disagree with FordTruckWrench only because I am frugal (some people say cheap). I don't think you will ever use anywhere near 40 circuits. I would go with the Siemens 100A 20 circuit $57 or the Siemens 100A 24 circuit $70

(IMHO) You really can not go wrong with any of these. But the difference in price is more than just a couple of cases of beer.

Thanks!