I have two new 12/2 romex in the garage for outlets for woodworking. Is it acceptable to wire quad receptacles with both circuits with 12/3 from an accessible junction box containing the two 12/2's? I know these outlets have to be GFI protected.

 

Yes. The neutral will be pigtailed and you need either two single pole breakers with a handle tie or a two pole breaker.

 

You may have 12-3 (or 14-3 etc.) coming from the panel to a junction box where the (multiwire branch circuit) x-3 continues on as two (non-MWBC) x-2 cables.

You may not have two x--2 cables coming from the panel and bringing power to a junction box where they merge into one x-3 cable to continue on.

Two x-2 cables each supplying power may enter the same junction box but the neutrals must be kept separate. If the two cables serve the halves of the same duplex receptacle then the tabs on both sides of the receptacle are to be broken off.

The load side of a ground fault circuit interrupter receptacle unit and any different circuit or subcircuit (such as the other half of a MWBC) may not continue on down the same x-3 cable.

 

I f I read correctly pcboss and AllanJ disagree. Who's right?

AlLanJ each duplex receptacle in the quad receptacle will be on one of the 12/2 circuits and the other duplex on the remaining one. If I understand you correctly I cannot merge the two 12/2's into a 12/3 and wire a series of outlets, the first one being GFI outlet protecting the others downline. So then I would have to run the two 12/2's into each quad box maintaining separate neutrals. I was trying to avoid the added difficulty but if it's not permitted I won't do it.
ALSO IN THIS SCENARIO HOW MANY OUTLETS PERMITTED DOWNLINE FROM A 20A GFI?

 

I'm not jumping in as a referee, by any means. You will start at the panel with a double breaker, or two singles with handle ties, connecting your white to the neutral buss and the red to one side of the breaker and the black to the other side. At your receptacle box, run your neutral to both receptacles via pigtail, the red to one hot screw and the black to the other hot screw on the other receptacle.

NOW, Why do you see the need for this? You are not technically limited by code to the number of receptacles on a circuit. That is where common sense comes to play. You must determine the use of the receptacles and their potential amperage draw.

 

I think the issue is whether you bring power in on the xx-3 or use the xx-3 between boxes and the number of gfis used.

 

I do not have a 12/3 from the panel I have two 12/2's.
The sales guy at Home Depot just told me it is not code to have 2 circuits in the same receptacle box since for service ,one could be live and the other not but this should be a non issue if handle ties are used.

 

Two circuits in one junction box is not prohibited by the electrical code.

One should always ensure the power is off before doing any work in a junction box.

 

I cannot count on both hands the times I have heard similar stories about the guy at the big box. I am not picking on any particular store, but big boxes in general. It just amazes me how they hire people who really don't have a clue yet they allow them to dish out advice like they know what they are talking about when they don't.