Shared Electrical Neutrals - Safety Concern

[Dave53]

Hi All,

Need some help to understand if shared neutrals are permitted by the NEC. I have heard conflicting reports where this electrical installation was common in many buildings prior to the early 2000s but may have been prohibited by the code for new or modified installations after 2010 or 2011 due to the potential electrical hazard not recognized by qualified electrical personnel. Any insight would be appreciated if this practice is still acceptable by the code.

 

[infinity]

It's a common misconception that MWBC's with shared neutrals are no longer permitted. That is not true even in the 2023 NEC. They can be less safe than a 2-wire circuit if a multi-pole circuit breaker or single pole breakers with a handle tie is not used.

Welcome to the Forum.

 

[roger]

Hi All,

Need some help to understand if shared neutrals are permitted by the NEC. I have heard conflicting reports where this electrical installation was common in many buildings prior to the early 2000s but may have been prohibited by the code for new or modified installations after 2010 or 2011 due to the potential electrical hazard not recognized by qualified electrical personnel. Any insight would be appreciated if this practice is still acceptable by the code.

MWBC's are an efficient wiring method and not a concern to "qualified people" I continue to use them when it's convenient.
To go another step forward, most all services in the USA are MWC's

 

[augie47]

The Code has taken steps to mitigate the "dangers" involved with MWBC by requiring simultaneous disconnect of all ungrounded circuits associated with a MWBC (210.4) and requiring a connecting means such as a wirenut be used where devices incorporated MWBC (300.13)

 

[infinity]

I always wondered who is spreading this false narrative about MWBC's being no longer permitted by the NEC?

 

[ramsy]

I always wondered who is spreading this false narrative about MWBC's being no longer permitted by the NEC?

Developer industry practice specify no MWBC's for their laborers, who come to this forum to learn electrical.

Labor is a variable cost in corporate accounting. Reducing cost with one less engineer on the train, is worth more than all the train wrecks it causes.

 

[Eddie702]

Nothing wrong with MWBC as long as the rules are followed. Each ungrounded conductor must be on different phases. The neutral must not be disconnected when the circuits are powered and a 2 pole switch or circuit breaker must be used or handle tys. Hots, grounds and neutrals should be pigtailed so that removal of 1 device does not affect the rest of the circuit.

There are issues with AFCI and GFCI on a MWBC

 

[xformer]

Developer industry practice specify no MWBC's for their laborers, who come to this forum to learn electrical.

Labor is a variable cost in corporate accounting. Reducing cost with one less engineer on the train, is worth more than all the train wrecks it causes.

IMHO.... Owners are tired of people who don't know how to properly install or maintain these.