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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:
- 3-phase, 4-wire, wye-connected systems may experience high harmonic currents on the neutral conductor due to nonlinear loads.
- Continuity of grounded conductors on multiwire circuits is addressed in 300.13(B).
- 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.
- 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.
- Multiwire branch circuits should only supply line-to-neutral loads.
- Exceptions:
- Circuits supplying only one equipment can supply line-to-line loads.
- 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).
- Ungrounded and grounded conductors of each circuit must be grouped as specified in 200.4(B).
- 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.