Running Power to the Garage Subpanel

Ted

Ted

The pilot formerly known as Twin Engine Ted
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With the Cobra build starting at some point, I'm thinking I might get around to finishing some of the garage projects I started.

One of them involved running a subpanel to the garage. I have the panel installed in its desired location, along with a bunch of the conduit and boxes run to their desired locations. The question is getting power to the subpanel.

The garage currently has two circuits going to it with a total of 8 outlets. One circuit provides power to 3 2-outlet boxes along the back wall. The first of those 3 boxes also happens to be a couple feet away from where I placed the subpanel.

I'm wondering about just running the required wiring into that box and then to the subpanel. Would that be an option or is there a better way? The main panels are in the basement.
 
I am unclear what you are trying to achieve. If you need more outlets, then just add more to the existing two circuits. If you need more current, then you need another circuit. Adding a subpanel to an existing circuit is not going to improve capacity.
 
Ted DuPuis said:
With the Cobra build starting at some point, I'm thinking I might get around to finishing some of the garage projects I started.

One of them involved running a subpanel to the garage. I have the panel installed in its desired location, along with a bunch of the conduit and boxes run to their desired locations. The question is getting power to the subpanel.

The garage currently has two circuits going to it with a total of 8 outlets. One circuit provides power to 3 2-outlet boxes along the back wall. The first of those 3 boxes also happens to be a couple feet away from where I placed the subpanel.

I'm wondering about just running the required wiring into that box and then to the subpanel. Would that be an option or is there a better way? The main panels are in the basement.
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Is there conduit from your existing panel to the box in question? How big is it? How much power (how many circuits? How much amperage each?) do you need in the sub panel?

Current required an distance will drive the wire size required and that will drive the conduit size which will determine if the existing conduit and box can be used.

John
 
sarangan said:
I am unclear what you are trying to achieve. If you need more outlets, then just add more to the existing two circuits. If you need more current, then you need another circuit. Adding a subpanel to an existing circuit is not going to improve capacity.
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It's a combination of needing more outlets (and for that, the existing circuit really would be fine as I'm never going to run too much at once) but also adding 220 so I can power my compressor and infrared heaters. Those (especially the heaters) I will run more continuously.

jsstevens said:
Is there conduit from your existing panel to the box in question? How big is it? How much power (how many circuits? How much amperage each?) do you need in the sub panel?

Current required an distance will drive the wire size required and that will drive the conduit size which will determine if the existing conduit and box can be used.

John
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Currently there is no conduit running from the existing panel to the box in question. Right now the box in question just is a standard 2-outlet with plastic cover. I could remove those and add a box and conduit, though, that's easy enough.

The idea behind the subpanel was more than anything to make it easier to run a bunch of outlets and then that also makes it easier to add the 220. Our house in Ohio had this setup in the garage and I really liked it.
 
Ted DuPuis said:
It's a combination of needing more outlets (and for that, the existing circuit really would be fine as I'm never going to run too much at once) but also adding 220 so I can power my compressor and infrared heaters. Those (especially the heaters) I will run more continuously.



Currently there is no conduit running from the existing panel to the box in question. Right now the box in question just is a standard 2-outlet with plastic cover. I could remove those and add a box and conduit, though, that's easy enough.

The idea behind the subpanel was more than anything to make it easier to run a bunch of outlets and then that also makes it easier to add the 220. Our house in Ohio had this setup in the garage and I really liked it.
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Sure. You need the panel for the 220. But how will you get wiring from your existing electrical panel to the new panel? That's what I thought you meant about using the existing box.

How much current will the heaters draw (they're probably the big load item)? You'll need to put a 2 pole breaker in some existing panel to feed your new sub panel. Then get wire from there to the new panel. How big the breaker and wire need to be is determined by 1) current draw (not 100% of all possible, there's a formula) and 2) distance (if it's long enough, say more than 50' you need to account for voltage drop. Again, there's a formula).

John
 
jsstevens said:
Sure. You need the panel for the 220. But how will you get wiring from your existing electrical panel to the new panel? That's what I thought you meant about using the existing box.

How much current will the heaters draw (they're probably the big load item)? You'll need to put a 2 pole breaker in some existing panel to feed your new sub panel. Then get wire from there to the new panel. How big the breaker and wire need to be is determined by 1) current draw (not 100% of all possible, there's a formula) and 2) distance (if it's long enough, say more than 50' you need to account for voltage drop. Again, there's a formula).

John
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Your first question is exactly what I'm trying to figure out. :)

I should take a picture to illustrate this. Basically there's an existing outlet about 2 feet from where I put the box. So I'm thinking of trying to snake wiring into that outlet box, and then run it to the subpanel. Does that make sense?

The formulas for wires, etc. I can do and figure all that out. I'm just trying to figure out how is best to get the wire to the subpanel.
 
I have on the side of my house a service box with 2 100A breakers. One goes to my house panel, the other goes to my second garage. Dug a trench to the garage. 3" sch 80 and ran the wiring through that. 100A/220V service in the garage. Was pricey since that was 100' run or so of #0 (I think, it's been a few years might be 1/0 or 2/0), but I did it right the first time. I don't expect to ever need 3 phase out there.
 
Ted DuPuis said:
Your first question is exactly what I'm trying to figure out. :)

I should take a picture to illustrate this. Basically there's an existing outlet about 2 feet from where I put the box. So I'm thinking of trying to snake wiring into that outlet box, and then run it to the subpanel. Does that make sense?

The formulas for wires, etc. I can do and figure all that out. I'm just trying to figure out how is best to get the wire to the subpanel.
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Maybe. Without knowing anything about the construction and locations., I can't help much. Also, if the box is not big enough, that may not work. Any pictures and floor plans with construction notes (i.e. block, frame, etc.) would help. If I was local I'd be happy to come look, and even help. But I'm in Florida...
 
Is an attached or detached garage? The cable you're going to have to run to power your subpanel probably isn't going to fit in the existing conduit, and my guess would be what's in there is probably sufficient for a 15-20 amp household circuit. Why not just bore some holes and run orange Romex from your main to the sub and leave the rest as is? Do you have an open slot on your main?
 
I guess the question is - do the existing wires have enough poop capacity? Seems likely not. Perhaps 12 gauge? About 20 amps? You want to run the two legs of the 220 in two separate used to be 110 circuits and re-combine at the sub-panel?

Dig/ pull some #1ish wire for a 100 amp 220 volt sub panel and be done with it.
 
The first question I would want answered is whether your existing service (from the pole to the current main panel) is sufficient to allow for an added branch. Odds are, it is, but you should check.

As Chip asked, we really need to know whether the garage is attached to the house, or geographically remote.
 
And what you're gonna want to run. A 220v welder is going to need 30-50 amps. A compressor, probably 30.
I'd pull new cable, from what we know. I hope you have 200amp main service panel.
 
We have 400 amp main service, two 200 amp panels.

I was planning on running new wire, I just thought it would be easier through an existing outlet.

If that's not the case, maybe not. The thing is that I'll be going through a wall so I think it'll need a box of some sort.
 
I'd recommend installing this.
Install #2 copper conductors. (these are oversized as I have no idea of distance..)
Attach #2's to 100 amp breaker in house panel...

Distribute as required from subpanel.
 
Kelvin said:
I'd recommend installing this.
Install #2 copper conductors. (these are oversized as I have no idea of distance..)
Attach #2's to 100 amp breaker in house panel...

Distribute as required from subpanel.
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That's more or less what I bought, I forget the exact box.
 
in addition to the #2 common wire....don't forget to have a ground wire for safety.
 
Checkout_my_Six said:
in addition to the #2 common wire....don't forget to have a ground wire for safety.
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Yeah, I ended up running 4 pieces of copper the diameter of my finger to my garage. Pain the the butt since I had to make 4 90 degree turns and 2 45 degree turns to get it there.
 
Details:
The wires (and any conduit) currently existing ain't close to being big enough based on what you have posted. Start over on that part.
Ground and neutral need to be run along with power from the main panel
100 amp breakers in the main and as disconnects in the sub.
The connection between ground and neutral need to be disconnected inside the sub panel.
If it's a separate building, you probably need a ground rod as well.
Don't try to pull romex through conduit. Individual stranded wires.
If the garage is attached, you probably don't need conduit and can run Romex - just cut holes in the walls as necessary to run the wire. Drywall is easy to fix.
 
Little tip. If you decide to pull multiple conductors through conduit, a little liquid dish soap makes a great lubricant.
 
(MSEE here with lots of home wiring experience) Ted, with respect, your post shows a serious lack of understanding about what you need and how to accomplish it. People are trying to help here, but even a consensus of a bunch of guys on the internet is a very risky basis for a wiring plan. In addition to understanding your needs for planned loads like a welder and electric heat, there is also a need to understand and plan for GFI (ground fault interruption) outlets. I suggest that you find a local electrician or electrically savvy engineer friend to look over your situation and advise. There is also a marvelous and inexpensive book, "Wiring Simplified" that you can get from Amazon: https://www.amazon.com/Wiring-Simplified-Based-National-Electrical/dp/099790531X or IIRC Home Depot also sells it. The book is guaranteed to teach you a lot, but not enough to eliminate the need for some local expert advice.

For reference, we gutted and rebuilt our home which has an attached garage. I put a 60 amp panel in the garage. It easily supports my Miller DialArc 250HF welder, an 11 inch Logan lathe, and a 3HP compressor. It would support some electric heat (maybe not while welding) as well. (My garage heat is natural gas.) I have two GFI breakers in the panel to support maybe ten duplex outlets plus a 220 outlet for my compressor. Don't cheap out on the ampacity of your service. The downside of too much service is a little extra cost for wire. The downside of too little is being unable to accomplish what you need to do. From what you're saying my guess is that 40 amp service would be the minimum to consider.

BTW, they sell lubricant designed specifically for pulling wires. No need to mess with home remedies.
 
Checkout_my_Six said:
He’s an engineer.... what could go wrong? :D
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I've seen my father get shocked numerous times and he's a very knowledgeable and competent engineer! :D

The best was last spring helping him change out a broken bathroom heater/vent. As I'm pulling the cover panel off I asked him if the power was off. Yeah yeah was his reply. Well being a good son I stopped and went downstairs to grab the Fluke as he always instructed me growing up. On my way back up the ladder I heard a few curse words followed by a "BOY did you bring the Fluke???".
 
I have a shop/barn/workshop with a big 220v 5hp air compressor, welder, a 220v window air conditioner, a forced air wood furnace, a stock tank deicer, tons of lights, a computer, network equipment, and a TV. All this is run from a 100-amp panel that is fed from the main breaker box in my house via a 100 amp breaker. We were a little concerned about 100amp service being sufficient but after doing some math it seemed like it would be fine and it has been. I can have a the air conditioner, air compressor, and industrial fan going then strike an arc with my welder and the lights don't dim or flicker.

The buildings are about 300' apart and we ran conduit burried in a 6' trench. There was a whole laundry list of reasons why this was the best way to it starting with the alternative being to run new electrical service 500' through woods and a hill too steep to drive up and ending with an extra monthly fee just for having the second meter. It took one heck of a thick cable to make that run, I let the contractor handle that part. I'm competent with household wiring but I don't have a trencher or crimping/stripping tools to handle wire as thick as my thumb.
 
airdale said:
BTW, they sell lubricant designed specifically for pulling wires. No need to mess with home remedies.
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Yeah, you never have it when you need it, and then it's an extra trip to the store, which probably doesn't have it in stock either. Soap works just as good, as explained to me by the licensed electrician who asked to borrow some.
 
Start with a kite and a key, you're an engineer and you can derive the rest from there. Seriously, get a copy of the local code. When you know what you can do figuring out how is the easy part. When I wired up the shed I built, I ran wires from the box in the garage under the crawlspace using backer boards so I didn't have to drill every joist and then trenched the final part to the shed.

If I was in your place, I would figure out which 110 circuit breaker is powering the garage and disconnect it. Then I would run a 220 line to the garage and run everything out there already from the new box. I would even run my 110 outlets and lights from different sides of the 220 so I could run a couple of things with heavy draws. Put different colored outlets and switches in for each side.
 
Capt. Geoffrey Thorpe said:
I guess the question is - do the existing wires have enough poop capacity? Seems likely not. Perhaps 12 gauge? About 20 amps? You want to run the two legs of the 220 in two separate used to be 110 circuits and re-combine at the sub-panel?

Dig/ pull some #1ish wire for a 100 amp 220 volt sub panel and be done with it.
Click to expand...
and then decommission the exising circuit out there.

Ted, the only way you can avoid running new cable is if the existing wire is heavy enough to be upsized. can you peek in the box and see? i'm guessing it's 12 gauge, 2 conductor wire. so you're out of luck. if by chance they ran heavier wire to it than that, then it MAY be possible to safely convert it to 240v service to your subpanel (with obvious changes in your home panel). if you can report back, we can give you better answers.

Additionally, if the garage is attached or detached will determine some issues around grounding in the garage. easy either way, but important to do it correctly.
 
It seems I did a very bad job explaining what I was asking for help on.

I wasn't talking about reusing the existing wire going to the 20A GFCI breaker. That would obviously not handle a 100A box.

What I was talking about was more just reusing that box as a convenient location to run the wires since it was right near the subpanel. I've taken a closer look at things in the basement and now have a better idea of how to go about routing.

I was strictly talking about the aspect of getting wiring to the panel, not the rest of it. I've already planned for GFCIs on all the circuits (which is a requirement here for garages), and wiring it for 20A on the 120V outlets that I'm adding. I forget the amperage I was going to run for the 220V but I want to say it was 30A. I planned that out a year or two ago. Still have some conduit to run, I basically went until I ran out of conduit and stopped.
 
You won't be happy with 30 amps. I have a farm shop with 30amp service, and running a compressor and 208v tombstone welder simultaneosly is asking a lot...I have a barrel stove for heat.
 
Chip Sylverne said:
You won't be happy with 30 amps. I have a farm shop with 30amp service, and running a compressor and 208v tombstone welder simultaneosly is asking a lot...I have a barrel stove for heat.
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Agreed. I was never happy with the 30A 220V circuit at my old house to the detached garage. Unfortunately there I was limited by the main pole drop, which was old and 100A total. Or maybe slightly higher, I forget, but adding up everything in the main panel, the garage couldn’t go higher when we had a storm destroy the underground conduit and replaced it with an overhead drop to the garage.

Anyway, 30A isn’t enough for gear-heads with real shop tools. It runs out real quick if you feel like sticking a temporary electric heater in the garage for not freezing to death in a winter repair job on something, too.
 
Ted DuPuis said:
Your first question is exactly what I'm trying to figure out. :)

I should take a picture to illustrate this. Basically there's an existing outlet about 2 feet from where I put the box. So I'm thinking of trying to snake wiring into that outlet box, and then run it to the subpanel. Does that make sense?

The formulas for wires, etc. I can do and figure all that out. I'm just trying to figure out how is best to get the wire to the subpanel.
Click to expand...

What you propose will work fine. I suggest replacing existing two gang outlet box with a deep four gang box to facilitate pulling wires through it and to the panel.

Use NEC Table 310-16 to determine maximum wire size that can be pulled through the existing conduit. I'm assuming the conduit already exists, you haven't specifically said that.

I have a license for doing this stuff.
 
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