NEC Article 210 Branch Circuits pt1

NEC Article 210 Branch Circuits

Article 210 provides general requirements for branch circuits.
Covers any circuit protected by a breaker that supplies power to other parts of a circuit.

Table 210.3 lists references for specific equipment and applications (not in Chapters 5, 6, and 7) that amend or supplement the requirements in Article 210.
Specific circuits have their own amendments and specific requirements.
Examples of specific purpose branch circuits from Table 210.3:
- Air conditioning and refrigerating equipment: Sections 440.6, 440.31, and 440.32
- Busways: Section 368.17
- Central heating equipment (other than fixed electric space heating equipment): Section 422.12
- Fixed heating or fixed electric heating equipment for pipelines and vessels: Section 427.4
- Fixed electric space heating equipment: Section 424.3
- Fixed outdoor electrical deicing and snow melting equipment: Section 426.4
- Infrared lamp industrial heating equipment: Sections 422.48 and 424.3
- Motors, motor circuits, and controllers: Article 430
- Switchboards and panel boards: Section 408.52
This table provides a quick reference to find information regarding installation and amendments for special purpose branch circuits.

Branch circuits recognized by this article are permitted as multi-wire circuits.
Multi-wire circuits can be considered as multiple circuits.
All conductors of a multi-wire branch circuit must originate from the same panel board or similar distribution equipment.
Typical branch circuit consists of a hot (ungrounded) and a neutral (grounded) conductor, plus a grounding conductor.

In 3-phase 4-wire Y connected power systems supplying non-linear loads, the power system design may need to account for high harmonic currents on the neutral conductor.
Delta and Y type transformer configurations exist for 3-phase systems.
A delta transformer looks like a triangle, while a Y transformer looks like a Y, with the neutral coming from the center point.
Unbalanced loading in a Y configuration can cause unbalanced current on the neutral, creating harmonics or noise.
Circuit design should balance loads to avoid unnecessary noise on the circuitry.

See 300.13(B) for continuity of grounded conductors on multi-wire circuits.
300.13(B) states that the continuity of a circuit should not rely on a device. The grounded circuit needs a solid mechanical connection that doesn't rely on a device.

Multi-wire branch circuits should only supply line to neutral loads.
Exception 1: A multi-wire branch circuit can supply only one utilization equipment, such as an electric oven or clothes dryer, using two phases.
These appliances require extra power for heating elements.
Exception 2: Where all ungrounded conductors of the multi-wire branch circuit are opened simultaneously by the branch circuit overcurrent device.
Multiple hots can share the same neutral if a handle tie is used.
A handle tie is a breaker that trips or shuts off both loads mechanically at the same time.
If Circuit 1 and Circuit 3 share a neutral, and Circuit 1 is turned off while Circuit 3 is on, the unbalanced load on the neutral can backfeed through the neutral on Circuit 1 and shock the person servicing the equipment.
Breaker tie rule became an actual requirement around 2008.
Previously, multiple circuits sharing one neutral was called