Over the last 13 months, we dove deep into many critical requirements in Article 250 to build out an effective grounding and bonding system. Now it is time to switch gears and look at the requirements for the backbone of the premises wiring system, i.e., branch circuits and feeders, with a focus on systems under 1,000V. The National Electrical Code separates branch circuits and feeders above 1,000V in separate articles to make it easy for those installing high-voltage systems to find the necessary requirements easily.

For this discussion, the focus will begin in the Code. The NEC covers branch circuit requirements in Article 210 and feeder requirements in Article 215. Within these articles, we can find sizing, overcurrent protection and branch-circuit outlet requirements. Understanding how the NEC guides the installation of branch circuits and feeders is critical to installing a system that is safe to use and minimizes the risk to the building from electrical fires.

Article 210

So, let’s unpack Article 210 and discuss the requirements for branch circuits. The article’s scope is very broad and simply states that it covers branch circuits operating at less than 1,000V AC and 1,500V DC. However, in true NEC fashion, Article 210 is not all-encompassing and there are specific articles that contain branch circuit requirements that override or supersede those in Article 210. A list of these specific instances can be found in Section 210.3, “Other Articles for Specific Purpose Branch Circuits.” 

A table in this section lists where users will find the requirements for branch circuits that serve a specific purpose. Typically, this has to do with what they are supplying, such as with motor branch circuits and certain types of heating and air ­conditioning equipment. Notice that this does not include anything in chapters 5, 6 or 7. The latter chapters in the NEC are, by their very nature, going to modify what can be found in Article 210, as we covered in the series on navigating the NEC (starting with “A Beginner’s Journey” in the November 2023 issue of ELECTRICAL CONTRACTOR).

Next, Article 210 spells out which types of branch circuits are permitted to be installed. Article 100 defines a branch circuit as: “The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s).” 

In other words, Article 210’s definition means the circuit conductors downstream from the circuit breaker or fuses up to the equipment being supplied or the device where a connection will be made to supply power to the equipment. The overcurrent protective device (OCPD) referenced in the definition does not include those integral to electrical equipment, since those are downstream from the outlet, which is defined as “a point on the wiring system at which current is taken to supply utilization equipment.” 

So, how do we deliver electrical current from the OCPD to the outlet? One way is to install an individual circuit to each system outlet. Depending on the equipment being installed, this might be the only choice. The range in my house is a great example of an individual branch circuit. We might also put several outlets on the same branch circuit. This is often the case with branch circuits supplying receptacle outlets installed for convenience within a building.

Multiwire branch circuits 

There is also an option that allows us to minimize the material used and still supply multiple outlets on multiple branch circuits using a multiwire branch circuit. The NEC defines a multiwire branch circuit as: “A branch circuit that consists of two or more ungrounded conductors that have a voltage between them, and a neutral conductor that has equal voltage between it and each ungrounded conductor of the circuit and that is connected to the neutral conductor of the system.” 

Simply put, this is multiple branch circuits using a shared neutral, since the neutral conductor is going to carry the imbalance of current between the ungrounded conductors. Therefore, several circuits can use the same neutral without overloading the conductor above the allowable ampacity. 

However, there are some stipulations that come along with using this type of branch circuit. Those stipulations are in Section 210.4, and it is clear that multiwire branch circuits can be considered multiple circuits, even with the same neutral conductor. The first major requirement is that all conductors of the multiwire branch circuit must originate in the same equipment. Therefore, we can’t pull the A and B phase from one panelboard and the C phase and neutral conductors from a second. They must all be supplied from the same panelboard. This helps ensure the safety of those working on these circuits. 

Another critical safety requirement for these circuits is that they must be supplied with a means that disconnects all ungrounded conductors at the same time. This can be a physical switch or a circuit breaker acting as the disconnecting means. This also ensures the safety of personnel working on multiwire branch circuits, because if you shut off one leg of the multiwire circuit, you shut them all off. This is important due to the shared neutral conductor being possibly still energized if there are energized ungrounded conductors in the multiwire circuit. 

Finally, multiwire branch circuits are only permitted to supply line-to-neutral loads and are required to be grouped in accordance with the rule for grounded conductors with the corresponding ungrounded conductors for easy identification. The requirement to only supply line-to-neutral loads prevents overloading circuit conductors. 

However, there are two exceptions. The first deals with multiwire branch circuits that supply a single piece of utilization equipment that has line-to-line and line-to-neutral loads and is designed not to overload the circuit conductors. A great example of this is a new electric range that uses 240V to supply the heating elements and 120V for the controls. 

The second exception is that a multiwire circuit can supply line-to-line loads if the OCPD opens all conductors at once. If one piece of equipment overloads the circuit or one branch of the multiwire has a fault, the OCPD opens all ungrounded conductors. This means a two-pole or three-pole circuit breaker must be used.

As you can see, there is a lot to consider when deciding what kind of branch circuit you will run to the equipment. Ultimately, the installer has options that best suit the projects’ needs. Each option comes with its own pros and cons. 

Next month, we’ll explore branch circuit conductor identification and voltage limitations for branch circuits. Until then, stay safe and always remember to test before you touch!

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