Wiring Options for 14/3 NM-B Cable and Two Single Pole 15 Amp Circuit Breakers

Question

A 14/3 NM-B cable is run from the main breaker panel. The black wire is connected to one 15 amp single pole circuit breaker and the red wire is connected to a second adjacent 15 amp single pole circuit breaker. Are any of the following acceptable according to the National Electric Code? If so, do the handles of the two circuit breakers need to be tied together using a handle tie approved by the manufacturer of the circuit breakers?

1. Single duplex receptacle in a one-gang electrical box
   • Black wire to the top brass screw terminal
   • Red wire to the bottom brass screw terminal
   • White wire to one of the silver screw terminals
   • Ground wire to the green screw terminal
   • Tab connecting the two brass terminals broken
   • Tab connecting the two silver terminals intact
2. Two duplex receptacles in a two-gang electrical box
   • Black wire to the top brass screw terminal of the first duplex receptacle
   • Red wire to the top brass screw terminal of the second duplex receptacle
   • White wire to the top silver screw terminal of the first receptacle
   • Separate insulated white wire from the bottom silver screw terminal of the first receptacle to the top silver screw terminal of the second receptacle
   • Ground wire pigtailed to the green screw terminal of both receptacles
   • Tab connecting the two brass terminals intact on both receptacles
   • Tab connecting the two silver terminals intact on both receptacles
3. Two duplex receptacles in a two-gang electrical box
   • Black wire to the top brass screw terminal of the first duplex receptacle
   • Red wire to the top brass screw terminal of the second duplex receptacle
   • White wire pigtailed to the top silver screw terminals of both receptacles
   • Ground wire pigtailed to the green screw terminal of both receptacles
   • Tab connecting the two brass terminals intact on both receptacles
   • Tab connecting the two silver terminals intact on both receptacles

Please reference and/or quote the National Electrical Code.

Reason for question: I recently assumed responsibility for maintenance in a small office building that was constructed in the late 1990s or early 2000s. While adding a new outlet, I noticed that the existing panel makes extensive use of 14/3 NM-B cable where the black wire is connected to one 15 amp single pole breaker, the red wire is connected to a second 15 amp single pole breaker, and the handles of the two breakers are not tied together. Based on other issues I have found, I have a suspicion that the wiring is not compliant with the current National Electrical Code.

Answer 1

(NB: All quotes here are from the 2014 NEC, but I know of no significant changes to these passages between 2014 and 2017.)

Methods 1 and 3 are fine...

For a 15A MWBC, both wiring method 1 and wiring method 3 will work and are Code-compliant as described, insofar as the receptacle wiring goes.

but Method 2 isnt...

Method 2, however, violates NEC 300.13(B) as described:

(B) Device Removal. In multi wire branch circuits, the continuity of a grounded conductor shall not depend on device connections such as lampholders, receptacles, and so forth, where the removal of such devices would interrupt the continuity.

as removing the first receptacle of the circuit leaves the second receptacle sans neutral. Fortunately, this mistake won't fry any equipment, but that's only because the second receptacle only gets the second leg's hot.

And all three of these need handle tying to be compliant

In any case, identified handle ties need to be used in order to provide the "common disconnecting means" required by 210.4(B):

(B) Disconnecting Means. Each multiwire branch circuit shall be provided with a means that will simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates.

Informational Note: See 240.15(B) for information on the use of single-pole circuit breakers as the disconnecting means.

and 240.15(B) (specifically, 240.15(B)(1)):

(B) Circuit Breaker as Overcurrent Device. Circuit breakers shall open all ungrounded conductors of the circuit both manually and automatically unless otherwise permitted in 240.15(B)(1), (B)(2), (B)(3), and (B)(4).

(1) Multiwire Branch Circuits. Individual single-pole circuit breakers, with identified handle ties, shall be permitted as the protection for each ungrounded conductor of multi-wire branch circuits that serve only single-phase line-to-neutral loads.