I think you need to be a groupie… Grouping of conductors in MWBC

I think you need to be a groupie… Grouping of conductors in MWBC- Wenatchee Home Inspections

It is very common to find multiwire branch circuits (MWBC) in homes, especially newer homes.  A multiwire branch circuit is where you have two or more hot/line conductors (ungrounded conductors) sharing a common neutral (grounded conductor).

We can argue the merits of this type of wiring in residential, you find those who like them and those who do not.

But as home inspectors and electrical inspectors it often hard to tell if  the hot conductors (ungrounded conductors) have been properly landed on opposing buses.

What leg are they on?

This is important because if both hot conductors are on the same buss/leg the currents on the neutral conductor will add up versus canceling each other out which could possibly overload the neutral conductor.

We do not want a neutral looking like this

The Code requirement of grouping of conductors came into effect in the 2008 NEC code cycle to help address identification of conductors associated with a circuit.

From the 2014 NEC

210.4 Multiwire Branch Circuits

(D) Grouping.

The ungrounded and grounded circuit conductors of each multiwire branch circuit shall be grouped by cable ties or similar means in at least one location within the panelboard or other point of origination.

Exception: The requirement for grouping shall not apply if the circuit enters from a cable or raceway unique to the circuit that makes the grouping obvious or if the conductors are identified at their terminations with numbered wire markers corresponding to the appropriate circuit number.

In the 2014 NEC  there was an new addition to grouping requirements.

200.4 Neutral Conductors

(B) Multiple Circuits.

Where more than one neutral conductor associated with different circuits is in an enclosure, grounded circuit conductors of each circuit shall be identified or grouped to correspond with the ungrounded circuit conductor(s) by wire markers, cable ties, or similar means in at least one location within the enclosure.

Exception No. 1: The requirement for grouping or identifying shall not apply if the branch-circuit or feeder conductors enter from a cable or a raceway unique to the circuit that makes the grouping obvious.

Exception No. 2: The requirement for grouping or identifying shall not apply where branch-circuit conductors pass through a box or conduit body without a loop as described in 314.16(B)(1) or without a splice or termination.

This requirement expands on the requirements in section 210.4 that grounded conductors must be grouped with ungrounded conductors of the same circuit.

2014 NEC section 200.4 requires the neutrals (grounded conductor) to be grouped with the Hot/Line (ungrounded conductors) of the same circuit in any enclosure. This may be a wireway, gutter or junction box. NEC Section 210.4 applies only to panelboards or where the circuit originates.

Proper identification makes it easier for those evaluating these circuits.

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Red Adair

NCW Home Inspections, LLC  is a Licensed Washington State Home Inspection service located in Wenatchee Washington serving Chelan County, Douglas County, Kittitas County, Okanogan County and Grant County Washington and the cities of Wenatchee, Leavenworth, Cashmere, Oroville, Cle Elum, East Wenatchee, Quincy and many more…  

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