Planning new sub panel and have a few questions.

[SNS]

Hey everybody, been lurking for a while and digging through old posts and I'm finally getting ready to start wiring my garage this winter. Compared to some of the garage wiring projects I've seen, I think mine seems relatively simple. I've got 200 amp service into the main panel which is in the attached garage, and this is completely full. In the garage I've got a single 15 amp gfci outlet, and really need more power. I'm considering this panel, since my main is also a homeline and the breakers should be the same.

http://www.homedepot.com/p/Square-D...th-Cover-Value-Pack-HOM2448M100PCVP/204836362

My plan for now is to wire the panel into the main fairly close, somewhere on the same wall as the main (garage is only 20x30) and run 5 separate 20amp 120 circuits (3 dedicated for 2 air compressors and a third near the front corner where my mig is run 90% of the time) with 2 general power circuits with a total of 13 receptacles (9 on one, 4 on the other) I've also got a 220v stick welder that I need to run that has a nema 6-50 plug, so I'd like to run a couple 50amp circuits for this as well.

I guess my questions so far are:

1. Will a load calculation be required for the new 240v circuits?

2. I'm planning on running 12/3 romex for the 120v circuits and 6/3 romex for the 240v. The longest 240 will be approximately 60ft. Does this sound right?

3. I'm planning on running everything through the walls without conduit. Do I need to worry about derating the cables? Everything I've seen so far refers to thhn

4. What size cable would y'all recommend? I'm considering #3 copper for the 10-15 foot run.

and 5. Most of what I've seen has talked about running a sub panel to a detached garage. Is there any code issues with running a separate sub so close to the main?

The county I'm in uses the 2011 version of the NEC. Thanks in advance for any info you guys can provide.

 

[pattenp]

1- Load cals in your case are most likely not needed. Just be mindful of what you are powering up along with other equipment that may cause a breaker to trip.

2- Why are you running **/3 wire, typically you only need **/2? The **/3 wire is used when a device is 240V but also needs 120V for controls such as clocks, etc. **/2 is 2 conductors with a ground and **/3 is 3 conductors with a ground.

3- If you are running SER from the main panel to the sub-panel and then using NM-b (Romex) from the sub-panel for your circuits then there should be no derating issues. THHN is individual wires that's normally run within conduit. Just don't tightly cram too many cables through a bored hole.

4- #3 Cu SER will work for a full 100A feed at 75 degree C. Be mindful that if SER is within insulation it's temp rating drops to 60C which means #3Cu is 85A max. Aluminum SER will need to be #1 for 100A @t 75C and 85A @ 60C.

5- A sub panel can be right next to a main panel, no code issue. Sub-panels have an isolated neutral meaning the grounds and neutrals are not bonded together as they are in the main service panel.

 

[SNS]

Thanks for the info! I think I'll go with some #3 Cu SER if there's no insulation in the walls, and #1 if there is, just so I can run the full 100 amp breaker without a huge difference in cable cost for the short run. Even at 85 amps I don't think I'd ever come close to tripping the main. The biggest loads I have are a big stick welder which has run off a 10 guage extension cord to the dryer outlet just fine for years, and the air compressors. I've got a pair of 2hp, and the only time they get ran at the same time is when the sandblaster's going, which requires another extension cord to the laundry room. Both of them will trip the 15amp breaker in the garage if there's anything else running on that circuit, so I'm assuming if they both kicked on at the same time I'd have a spike around 30 amps.

12/3 may not be typical, but I have a buddy that has about 150 feet left from his remodel that's free if I need it. Not sure if I really want to mess with running MWBCs with the GFIs, but the thought has definitely crossed my mind.

I guess the next step is to call the county and get rolling on the permit. That's the part that has me nervous, never had to file for one before...