Been updating circuits in my basement and I'm horrified at the previous work that has been done. Improperly routed cables, overloaded junction boxes and, in two separate instances, 12-3 cable feeding completely different circuits but with single-pole breakers. Aside from the obvious problem with the breakers, I am wondering why anyone would use 12-3 in this way. Seems to me it's just laziness during cable routing but I'd be interested in hearing if there are legitimate reasons to do so.

1 Answer 1

  • To reduce material costs of the job.
  • To reduce the number of holes bored through framing.
  • To reduce the number of cables that have to be pulled.
  • A request for clarification: my read of the OP suggested that there were 2 circuit breakers and that everything was coming back on 1 neutral. Is that legal? (My notion is that the 2 circuits could be running at a full 20A, concievably on the same leg, which could have 40A returning on the neutral...) Feb 21, 2015 at 23:01
  • @AloysiusDefenestrate If the ungrounded conductors are on the same leg, then it's no longer a code compliant multi-wire branch circuit. The OP does not specifically address this, so I'd have to assume the circuits are wired to code.
    – Tester101
    Feb 21, 2015 at 23:05
  • Appreciate the clarification, Tester101. Feb 21, 2015 at 23:42
  • The OP mentioned that the 12/3 is connected to "single-poll breakers". Doesn't code require dual-poll or handle-tie breakers for MWBC?
    – DoxyLover
    Feb 22, 2015 at 5:10
  • @DoxyLover Not until the 2008 version of the code. Up until that point, you only had to simultaneously disconnect all ungrounded conductors if they supplied multiple devices on the same yolk NEC 2002 210.4 (B) Dwelling Units. In dwelling units, a multi-wire branch circuit supplying more than one device or equipment on the same yoke shall be provided with a means to disconnect simultaneously all ungrounded conductors at the panelboard where the branch circuit originated.
    – Tester101
    Feb 22, 2015 at 5:37

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