Multi-Wire Branch Circuits Code Requirements Explained - NEC 2023

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Guide to Multiwire Branch Circuits in the 2023 NFPA 70 NEC 210.4​

210.4 Multiwire Branch Circuits​

A. General

• Multiwire branch circuits are permitted and can be considered as multiple circuits.
• All conductors must originate from the equipment with the branch-circuit overcurrent protective device, except as specified in 300.3(B)(4).
• Informational Notes:
  1. 3-phase, 4-wire, wye-connected systems may experience high harmonic currents on the neutral conductor due to nonlinear loads.
  2. Continuity of grounded conductors on multiwire circuits is addressed in 300.13(B).

Enhanced Content:

• Multiwire branch circuits can serve dual purposes, such as providing two appliance circuits in kitchen countertops.
• Issues with harmonic currents may arise from devices like computers and printers which may exceed the load current itself.
• Refer to 310.15(E) for guidelines on neutral conductor ampacity.

B. Disconnecting Means

• A means to simultaneously disconnect all ungrounded conductors must be provided at the circuit origin.
• Informational Note: Single-pole circuit breakers as disconnecting means are discussed in 240.15(B).
• Options for disconnecting include:
  • For single-phase: two single-pole breakers with a handle tie or a 2-pole breaker.
  • For 3-phase: a 3-pole breaker, three single-pole breakers with a handle tie, or a 3-pole switch with protection.

C. Line-to-Neutral Loads

• Multiwire branch circuits should only supply line-to-neutral loads.
• Exceptions:
  1. Circuits supplying only one equipment can supply line-to-line loads.
  2. Permitted line-to-line loads if a device opens all ungrounded conductors simultaneously.
• Enhanced Content:
  • Common configurations include 120/240-volt, single-phase systems often found in residential applications.
  • Benefits include reduced wire use, easier balancing, and less voltage drop.
  • Care must be taken with high-leg delta systems, especially with phase B (marked orange).

D. Grouping

• Ungrounded and grounded conductors of each circuit must be grouped as specified in 200.4(B).

See Also:

• 210.19, 210.4(A), 240.15(B)(1), 300.13(B) for further reading on voltage drop, 3-phase system neutrals, and circuit protection specifics.