Multiwire circuits require 2 pole breaker ?

S

Stevenfyeager

Senior Member
Location
United States, Indiana
Occupation
electrical contractor
My employee says a 2 pole breaker is required by NEC for a multiwire circuit. I always used to just make sure the two hot wires from a 12-3 cable are on opposite phases as to not possibly overload the shared neutral. (which a 2 pole breaker does insure). He says it is safer when working on one of the circuits in that, turning off one circuit ensures the other one is turned off too. NEC ?
 
roger

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
Your employee is correct, disconnecting all ungrounded conductors of a MWBC has been been a requirement for a number of code cycles, multi pole breakers are only one way to achieve this. 240.15(B)
 
T

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
Stevenfyeager said:
My employee says a 2 pole breaker is required by NEC for a multiwire circuit. I always used to just make sure the two hot wires from a 12-3 cable are on opposite phases as to not possibly overload the shared neutral. (which a 2 pole breaker does insure). He says it is safer when working on one of the circuits in that, turning off one circuit ensures the other one is turned off too. NEC ?
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He is somewhat correct. 210.4(B) requires MWBC to be disconnected together. Note that this does not mean common trip. While you can use a 2 pole common trip breaker if desired only handle ties of 2 single pole breakers is compliant and often preferable. Ditto for 3 phase.
Also see 249.15(B0 as Rodger pointed out as there are some cases where a common trip would be required.
 
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