Another Sub Panel thread...

[gsea]

After much deliberation and discussion, I've decided to this the right way and install a sub panel in the garage to supply a 30A heater and a 50A welder circuit. I wanted to run my plan by the garage journal brain trust first to make sure I'm not missing anything glaring.

- Install a 60A breaker in the main panel
- Run 6/2 wire to a small 70A sub (about 20 ft)
- Install a double gang box with a 6-50 and a 6-30 receptacle about 3 feet below the sub panel.
- Feed these two circuits with a 30A breaker and 10/2 romex and a 50A breaker with 6/2 romex.

Here are my questions...

1) The panel I'm looking at is a 70A with only 2 slots, which will be filled. Should I get something bigger in case I want to add a few 110V circuit later on?

2) Panel will be installed on a wall that is on the attached side of the house, shared wall with bathroom. Should I go with a surface mount panel so as not to cause an insulation void? Any code considerations there?

3) Being in the garage, do I have to care about GFCI on the 240?

4) Is there anything in the NEC I missed that says I can't install those two 240V receptacles close to the sub panel and in the same gang box?

5) None of these runs need to in conduit as they are in-wall, correct?



Thanks GJ!

 

[Aceman]

After much deliberation and discussion, I've decided to this the right way and install a sub panel in the garage to supply a 30A heater and a 50A welder circuit. I wanted to run my plan by the garage journal brain trust first to make sure I'm not missing anything glaring.

- Install a 60A breaker in the main panel (50 amp max on 6-2 Romex)
- Run 6/2 wire to a small 70A sub (about 20 ft)
- Install a double gang box with a 6-50 and a 6-30 receptacle about 3 feet below the sub panel.
- Feed these two circuits with a 30A breaker and 10/2 romex and a 50A breaker with 6/2 romex.

Here are my questions...

1) The panel I'm looking at is a 70A with only 2 slots, which will be filled. Should I get something bigger in case I want to add a few 110V circuit later on?

Yes. 100-125A main lug panel with at least 8-12 circuits, minimum. You also need 3 conductor wire. A 2 conductor wire will only give you 240v or 120v, but not both. I'd recommend #2 aluminum SER. For the price and capacity it provides, it's hard to beat. Plus, it's readily available.

2) Panel will be installed on an interior wall shared with bathroom)? Any reason to do a surface mount instead of a flush mount? NEC considerations or loss of insulation, for example?

NEC doesn't care.

3) Being in the garage, do I have to care about GFCI on the 240?

You don't need to GFCI your 240v circuit.

4) Is there anything in the NEC I missed that says I can't install those two 240V receptacles close to the sub panel and in the same gang box?

It's ok.

5) None of these runs need to in conduit as they are in-wall, correct?

Use Romex, if concealed behind wall finish.

....

 

[wyliesdiesels]

I agree with everything Aceman said

I would put in a larger panel that way u have room for expansion should u ever need it!

 

[pattenp]

....
Yes. 100-125A main lug panel with at least 8-12 circuits, minimum. You also need 3 conductor wire. A 2 conductor wire will only give you 240v or 120v, but not both. I'd recommend #2 aluminum SER. For the price and capacity it provides, it's hard to beat. Plus, it's readily available.

I suggest a main breaker panel. The main disconnect it nice to have if needed.

Also to clarify 3 conductor SER is actually 4 wires. The SER will be 2-2-2-4. #2 Al SER will give you up to 90A if the cable is not running within insulation. If the run of #2 SER is buried in insulation then it should be overcurrent protected to a max of 75A.

*

 

[theoldwizard1]

I would put in a larger panel that way u have room for expansion should u ever need it!

6 slot/12 circuit panels are cheap. I would not go with anything less.

I suggest a main breaker panel. The main disconnect it nice to have if needed.

Agreed !

On a panel that does not have a main, you can always feed the incoming wires to (typically) the first 240V breaker. This does only leave 4 slots/8 circuits open, unless you make that 240V breaker a tandem.

Make sure you have a separate ground bus bar. Many panels do NOT include these. Only a few $.

 

[wyliesdiesels]

6 slot/12 circuit panels are cheap. I would not go with anything less.


Agreed !

On a panel that does not have a main, you can always feed the incoming wires to (typically) the first 240V breaker. This does only leave 4 slots/8 circuits open, unless you make that 240V breaker a tandem.

Make sure you have a separate ground bus bar. Many panels do NOT include these. Only a few $.

If u use a backfed main then u need to buy a retention kit.

And a double pole 4 lug tandem breaker is called a quad

 

[jvitez]

Definitely get a bigger panel.

For my basement wood shop I carefully calculated I would only need a 4 slot panel with 30 amp feed. Then I thought harder, and changed that to an 8 slot panel. Then upon more persistent pensive perusal, my load calculation required a 40 amp feed, and I needed a 12 slot panel.

So now I have one 4 slot and one 8 slot subpanel panel sitting in it's cardboard in my basement. Maybe try and yard sale them?

Get a bigger panel, and feed it with 3 conductor wire. You never know when you might decide on an additional 120 circuit, and then kick yourself that you did all that work for a 240V only installation. And if you check, 6/2 Romex is probably more expensive that 6/3 as it's much less commonly used. A main breaker panel is also very convenient as you don't have to truck on down to the basement to shut off a breaker. Plus, they're not much more money.

 

[gsea]

Love GJ, thanks for all the input and info! I'm taking the suggestions to heart and am now going to go with a an outdoor surface mount main breaker panel with 8-spaces. Then I can shut the whole thing off and lock it up if I wanted when I have renters down the road. I'll also have 2 spaces left after my 2 240 circuits and 2 120 circuits, just in case.


Now, you guys have given me more questions...


1) If I go to a main breaker sub panel, I end up with 2 breakers: one on the main panel feeding the sub, and one as the main breaker in the sub itself, both rated for the same ampacity, right?

2) I only have 100A service. As I'll only have 60-70A breakers on the main and for the main breaker on the sub, why not just get a 60-70A panel?

3) If effectively the main breaker limits it to a 60-70A panel, then why not use 4/3 romex to feed the sub instead of aluminum SER (which I hear I need to downrate to 75A anyway)?


Thanks again!

 

[jvitez]

1. Yes and no. You calculate the maximum wattage of all loads you could possibly use now and in the future running off your subpanel, divide by 240, and that's the calculated amperage. You feed your subpanel with a cable capable of safely delivering at least that or better. You protect that cable with a circuit breaker sized for that cable. Practicality and NEC details make things a bit simpler, as there are only so many breaker sizes available.

The main breaker on your subpanel is acting only as a shutoff, so it has to be at the MINIMUM the same size as your feeder breaker in your main panel, but it can and often is higher.

2. No reason, except many main breaker panels are rated for 100 amps anyway, so again nothing wrong with installing equipment rated HIGHER than the feeder breaker.

You can feed your subpanel with a 60 amp breaker in your main panel, have a 100 amp main breaker acting as shutoff on your subpanel, with the subpanel itself rated for 100 or 125 amps.

I can't help you with #3 as SER is not easily available here. Our CEC rules mean we commonly use 3/3 copper NMD or 1 gauge aluminum cable to feed a 100 amp panel.