Adding Subpanel

[JoeyGee]

I am looking into adding a subpanel in my finished garage. The run between the main box and the new sub will be >50'. All wiring will be inside--through my basement/crawl.

I am thinking of using a 100 amp panel. These seem to be widely available, cheap enough and from what I read necessary if I want to run a 220 circuit--I don't now, but would like to be able to later on.

I know I would need a 40 amp double pole breaker in the main box, which I have room for. Now a few dumb questions. I know codes vary, and I will check, but just looking for basic info.

What wire do I need to run btw panels? I know I need 2 hots, neutral and ground--what size? This is all interior, so I don't need conduit, right? Can I get what I need in Romex?

I am putting the panel in a finished wall. When I run the wires to/from the panel, do I need to fasten them to the studs? I really don't want to open the whole wall.

These are the first of many questions, so I thank you all in advance. I can't wait. Right now I have one circuit I share with the house, and two bare light bulbs (plus garage door opener) for lights. That sucks.

[BigguyZ]

I think since it's not going external to the house, you don't need a separate grounding system (i.e. grounding rods and what-not). But make sure that the panel's ground is NOT bonded to the neutral (usually they ship not-bonded, but if it is remove the bonding). for 40 amps, you'd probably be fine with 8 gauge. I used 6 gauge, but I went with 60 amps.

Romex is fine, as long as it's not run under floor joists or in an area that could be damaged. If it's exposed, it'll need to be run through conduit, from my understanding.

BTW- I'm not an electrician, but I've wired several houses myself (and had everything passed with permits).

[toolguy1000]

I am looking into adding a subpanel in my finished garage. The run between the main box and the new sub will be >50'. All wiring will be inside--through my basement/crawl.

I am thinking of using a 100 amp panel. These seem to be widely available, cheap enough and from what I read necessary if I want to run a 220 circuit--I don't now, but would like to be able to later on.

I know I would need a 40 amp double pole breaker in the main box, which I have room for. Now a few dumb questions. I know codes vary, and I will check, but just looking for basic info.

What wire do I need to run btw panels? I know I need 2 hots, neutral and ground--what size?
8 wire for up to 50A.
This is all interior, so I don't need conduit, right? Can I get what I need in Romex?
these two questions vary from jurisdiction to jurisdiction. it's more of a code issue than anything else. if your permitting authourity accepts NM cable, that's what i'd run.

I am putting the panel in a finished wall. When I run the wires to/from the panel, do I need to fasten them to the studs?
yes

I really don't want to open the whole wall.
i'd be surprised if a permitting authority would let cables be run without proper stapling.

These are the first of many questions, so I thank you all in advance. I can't wait. Right now I have one circuit I share with the house, and two bare light bulbs (plus garage door opener) for lights. That sucks.

FWIW, i'd look into a 60A panel. pull 6/3 wires and you should be good to go. electrical requirements around here tailor all components to the wire and breaker size. your permitting authority may be different.

[Black wallnut]

Keep in mind future needs. The difference in breaker cost is not much. I'm not sure of current wire prices but always go bigger than you think you might need when installing a sub-panel so you only have to do it once.

[dbhost]

FWIW, I am putting my funds aside right now to do a similar job. I have decided to go with a 100 amp box / pull from the main. That will cost quite a bit more than just pulling 40 amps I know, but then again, I need at least 3 20 amp dedicated circuits as I figure it. I want at least 1 20 amp 220V circuit for future upgrade (In the long run, I want a SawStop 3HP PCS) and likely will want 2 20 amp circuits in 220V (the second for a 3HP cyclone).

For now the circuits needed would be...

#1. Dust collector / Air compressor. Simply put, I never do, and don't plan on starting now, run the air compressor and dust collector at the same time.

#2. HVAC. Simply put, I need a single, dedicated 20 amp 110V circuit between the garage doors to run the A/C, or heater as need be. With winters like this, I can almost throw my heater out as a space waster!

#3. Power tools. I'm one guy. I can't run the table saw, and planer at the same time, so why have separate circuits for them?

The worst part about it, I need to have my existing box redone, with a bigger box / higher rating. I need a 200 amp box coming in... Now you know why it is taking so long!

[woodturner]

II know codes vary, and I will check, but just looking for basic info.

NEC is adopted throughout the US. Municipalities can impose more stringent requirements, but (in theory) cannot reduce the requirements of NEC.

What you are proposing is a "branch panel" or sub-panel, if you want to look up the NEC section.

You will need to run four wires - two black hot wires, neutral, and ground. The neutral and ground will NOT be bonded at the sub-panel, and the only place the ground and neutral will be connected is in the service panel or meter socket (depending on your utility). There can only be one place where ground and neutral are connected, per NEC.

I don't think you will find NM-B (Romex) in a large enough cable. Without looking up the NEC table, off the top of my head you are probably looking at 2/0 cable, maybe 1/0. Typically SEC would be used, but you may have trouble finding it with the fourth wire. Be aware that wire this large is difficult to work with.


Conduit may be a better, easier option.

I am putting the panel in a finished wall. When I run the wires to/from the panel, do I need to fasten them to the studs?

The cable must be secured near the boxes (panel) and at roughly 2' intervals along the run. You will likely need to secure the wire within the wall, unless you run conduit. One option is to run conduit in the wall and transition to exposed wire in the crawl space.

[JoeyGee]

One more...do I need GFCI breakers for a panel in an attached garage? I might add some exterior outlets off this panel. I assume those would at least need to be GFCI.

[jdon]

40 amp breakers need 8 gauge copper wire; 50 amp need 6 gauge. I assume you've figured out how many circuits you would be using simultaneously, i.e. you probably wouldn't be running a table saw and jointer at the same time, while a dust collector might be run at same time as either.

You do need GFCI for garage 125V outlets (as well as any outdoor outlets).

My go-to reference for decades has been H.P. Richter's "Wiring Simplified": no-nonsense, practical; simplified but not simplistic.

[woodturner]

40 amp breakers need 8 gauge copper wire;

NEC specifies 8 gauge copper, 6 gauge aluminum at a minimum for 40A and short runs. For motor use, increasing the wire size one step will limit the light dimming and motor overheating.

For 50 A, 6 gauge copper or 4 gauge aluminum is required.

Keep in mind that a longer run (e.g. > 50') will require a larger wire size as well.

The 100 A, 50' service wire requires 1 gauge copper or 1/0 aluminum.

Here is a calculator:
http://www.paigewire.com/pumpWireCalc.htm

You do need GFCI for garage 125V outlets

GFCIs are a good idea in wet location, but tend to false-trip on motor circuits. It's best to wire the tools to separate circuits, then install GFCIs on the unassigned receptacles and lights.

[cabinetman]

My suggestion is to get advice from a certified electrician in your area that has experience with your project. What you are planning needs a responsible source of information. I've done my share of electrical work in the past and would not think of advising you on a project that could be a potential fire hazard or cause you or your family personal harm. Myself nor any other member won't assume responsibility for that liability. Members can say anything they care to, whether they are qualified or not to give such advice.

I wouldn't proceed with any work or the purchase of any materials without the counsel of an electrician...someone with a license that can stand in front of you. In the end you may decide it's a safer bet to let an electrician do the work, as he/she will have the liability.

.

[chopnhack]

If you are not intimately comfortable or experienced in wiring heed C-man's warnings. If you have done enough home wiring and understand and can use the NEC tables for conductor ratings, derating wire size when run in conduit, conduit fill calcs, box fill calcs and in general be able to do a UL install, then go for it otherwise its good to have the insurance hiring a pro provides.

[cabinetman]

If you are not intimately comfortable or experienced in wiring heed C-man's warnings. If you have done enough home wiring and understand and can use the NEC tables for conductor ratings, derating wire size when run in conduit, conduit fill calcs, box fill calcs and in general be able to do a UL install, then go for it otherwise its good to have the insurance hiring a pro provides.

+1. Taking it a step further, after getting information from all the sources...some by the book, and some by wannabe electricians, there may be conditions with existing wiring and proposed needs that would be eminently obvious to a seasoned electrician, but not to a lay person, or one that has done a similar project a time or two in the past and was lucky enough not to burn his house down.

It's a bit different getting advice or suggestions from a member who may be a desk jockey that has built a cabinet for the garage, and comes off as an expert, and gives advice on fabricating and installing kitchen cabinets.

.

[chopnhack]

LOL, beware the multiwire branch circuit!

I am not an electrician either.