Code Change Summary: The actual methods of conductor grouping have been deleted and replaced with a cross reference to the section where they are now located.

Section 210.4(D) is all about grouping of conductors in a multiwire branch circuit. A multiwire branch circuit consists of two or more ungrounded conductors that have a voltage between them, and a grounded neutral conductor that has equal voltage between it and each ungrounded conductor of the circuit. The neutral conductor is a shared return path for current returning back to the source.

The previous code language required ungrounded and grounded circuit conductors of each multiwire branch circuit to be grouped by cable ties or similar means in at least one location within the panelboard or other point of origination. That wording had been deleted and replaced with a reference to follow the rules in 200.4(B).

According to 200.4(B), “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”. The following exceptions are permitted:

• Grouping or identifying is not required if the branch-circuit or feeder conductors enter from a cable or a raceway unique to the circuit that makes the grouping obvious.
• Grouping or identifying is not required 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.

The grouping and identification requirement applies to any enclosure where more than one neutral and more than one circuit exists. This means junction boxes, panelboards, disconnect switches and the like. Any time there is more than one grounded neutral conductor present in the same enclosure with ungrounded conductors of other circuits, grouping or identification is needed in order to know which circuit each grounded neutral serves.

When troubleshooting or tying into existing circuits, it can be difficult to know which neutral to use. Generally, neutral conductors are not disconnected by the circuit breaker where the branch circuit originates. This can often result in the roll of a dice to decide which neutral to tie into in a junction box downstream of the circuit breaker.

Opening a neutral under load can result in electric shock. If the circuit arrangement is evident, then when a circuit is switched off for servicing, the electrician can remove a wire nut for a group of neutrals and be assured that there is no return current flowing when the wire nuts are removed.

Below is a preview of Article 210. See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2017 NEC^® edition of NFPA 70.