Multiwire Connection - sort of...

Reply

  #1  
Old 01-02-18, 09:14 AM
J
Member
Thread Starter
Join Date: Apr 2012
Posts: 17
Received 0 Votes on 0 Posts
Multiwire Connection - sort of...

I am moving my kitchen from one room to another. I need to move the electrical connections, too. I have a question about a particular outlet box:

If a box has two outlets that are served by two separate 12-2 wires and two separate breakers (not next to each other or bridged), could I connect the two hots separately to the black and red of a 12-3 wire and use those to connect to the two separate outlets in the new location?

So the connection would be:

Wire 1:
12-2 Black => 12-3 Black => Outlet 1 Hot
Wire 2:
12-2 Black => 12-3 Red => Outlet 2 Hot
Neutrals from Wire 1 and Wire 2 tied together with 12-3 Neutral and branched in new box for both Outlet Neutral connections.
Grounds from Wire 1 and Wire 2 tied together with 12-3 Ground and branched in new box for both Outlet Ground connections.

The purpose for these two connections would be to drive the dishwasher and the garbage disposal (both on separate breakers not adjacent to each other).

I hope that is clear enough. Please advise. Thanks!
 
Sponsored Links
  #2  
Old 01-02-18, 09:50 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 56,394
Received 747 Votes on 702 Posts
No..... you want to turn two separate circuits into a multi wire branch circuit.
That you can't do. You would need to extend the two circuits individually.
 
  #3  
Old 01-02-18, 08:23 PM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 15,082
Received 63 Votes on 55 Posts
A multiwire branch circuit requires a common means of disconnect. The code also requires all conductors of a circuit be run together in the same sheath or raceway.
 

Last edited by pcboss; 01-03-18 at 08:58 AM.
  #4  
Old 01-02-18, 08:26 PM
A
Member
Join Date: Mar 2010
Location: USA
Posts: 3,926
Received 51 Votes on 49 Posts
In addition, the neutrals of those two circuits must not be connected together up in the house even where both circuits entered the same outlet box. this is an example of having two wire nutted clusters of neutrals in a box. If a duplex receptacle unit had the top half fed by one of those circuits and the bottom half fed by the other circuit then the bridging tabs between the terminal screws on both sides must be snapped off.
 
  #5  
Old 01-02-18, 08:33 PM
core's Avatar
Member
Join Date: Jan 2007
Location: Des Moines, IA
Posts: 1,127
Received 0 Votes on 0 Posts
They do make 12/2/2 if there's some physical reason that you only want to run one cable.
 
  #6  
Old 01-03-18, 05:37 AM
J
Member
Thread Starter
Join Date: Apr 2012
Posts: 17
Received 0 Votes on 0 Posts
Allanj, would you mind providing more detail on your neutral line management post? I'm curious to learn more. Why wouldn't you tie all the neutrals together? Don't they all go back to the same place?
 
  #7  
Old 01-03-18, 06:04 AM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
Parallel current-carrying paths are not allowed for both safety and overload reasons. The safety concern is that you would still have an energized neutral conductor if only one of the breakers was turned off, creating an electrocution hazard for an unwitting serviceman. The overload concern is that if the parallel paths are not constructed nearly identically (which is impossible in a branch circuit), one of the multiple paths will take the bulk of the current. In other words, the current doesn't split equally between parallel paths. If you combined the neutrals of two 20A circuits, one neutral might carry 35A and the other 5A producing an overload condition for #12 wire. The code only allows parallel paths in very specific panel feeder situations, never in branch circuits.
 
  #8  
Old 01-03-18, 06:53 AM
M
Member
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,947
Received 2 Votes on 2 Posts
If you combined the neutrals of two 20A circuits, one neutral might carry 35A and the other 5A producing an overload condition for #12 wire. The code only allows parallel paths in very specific panel feeder situations, never in branch circuits.
For my education, when you say "parallel paths" are you referring to two separate cables? Reason I ask is because we used to run 14-3 home runs all the time to feed two separate circuits in the same box with shared neutral, but used a duplex breaker with handle so neither leg would be on without the other. Over current wasn't the issue since the two circuits are 180 degrees out of phase and the currents subtract. For example, if one circuit was drawing 10A and the other 5A, the neutral would carry 5A. If one was 15A and the other 5A, the neutral would carry 10A. If both were drawing equal amounts of current, you'd essentially have zero current on the neutral. IOT you'll never have more than the maximum current of an individual circuit, if done properly of course. Doesn't sound like this is what the OP is trying to do though. I agree taking two separate 12/2, connecting to a 12/3, then back to two 12/2 would potentially be hazardous and against code.
 
  #9  
Old 01-03-18, 06:57 AM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
Yeah mossman, the OP question is sort of the opposite of a multiwire (shared neutral) circuit. They are asking about combining neutrals in two or more separate cables. Your understanding of additive current on a properly installed shared neutral circuit is correct.
 
  #10  
Old 01-03-18, 08:47 AM
A
Member
Join Date: Mar 2010
Location: USA
Posts: 3,926
Received 51 Votes on 49 Posts
All the neutrals are tied together at the panel (at the neutral bus bar within) where the breakers for their respective hots are located.

Neutrals for different branch circuits are not tied together in outlet boxes simply because they come togehter in an outlet box they share..

There must be exactly one neutral path from any outlet down to the panel for that branch circuit.

(Ground wires aka equipment grounding conductors from different cables or branch circuits are tied together wherever they come together.)
 
Reply
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: