By Mike Holt, NEC Consultant

Article 408 provides the requirements for switchboards, switchgear, and panelboards that control power and lighting circuits.

In this industry, some people use the terms switchboard and switchgear interchangeably. But this practice can lead to misunderstanding because these are not the same things.

Switchgear is manufactured and tested to more exacting standards than switchboards. And switchgear is configured differently from the way switchboards are.

For example, in switchgear there are physical barriers between breakers, and also between the breakers and the bus. Switchgear is more durable and fault resistant, and is commonly selected for larger applications where low-voltage power circuit breakers and selective coordination are applied (e.g., data centers, manufacturing, and process facilities).

High-leg

Panelboards supplied by a 4-wire, delta-connected, 3-phase (high-leg) system must have the high-leg conductor (which operates at 208V to ground) terminate to the “B” (center) phase of the panelboard [408.3(E)].

There’s an exception to this rule. Namely, the high-leg conductor can terminate to the “C” phase when the meter is in the same section of a switchboard or panelboard.

And some cautions apply:

• Orange identification, or some other effective means, is required for the high-leg conductor [110.15 and 230.56].
• The ANSI standard for meter equipment requires the high-leg conductor (208V to neutral) to terminate on the “C” (right) phase of the meter socket enclosure. This is because the demand meter needs 120V and it gets it from the “B” phase.
• When replacing equipment in existing facilities that contain a high-leg conductor, put the high-leg conductor back in its original location. Prior to 1975, the high-leg conductor was required to terminate on the “C” phase of panelboards and switchboards. Failure to re-terminate the high leg where it came from can result in 120V circuits being inadvertently connected to the 208V high leg. Such a connection will almost certainly be disastrous.

Identification

Switchboards, switchgear, and panelboards must meet identification requirements. One of those is the high-leg caution label [408.3(F)(1)]. This label:

• Can’t be handwritten.
• Must be permanently affixed and be of sufficient durability to withstand the environment involved [110.21(B)(3)].
• Must say, ““Caution _____ Phase Has _____ Volts to Ground”

Circuit identification is another requirement [408.4(A)]. All circuits and circuit modifications must be legibly identified as to their clear, evident, and specific purpose.

Identification must include enough detail to allow each circuit to be distinguished from all others. And it can’t be based on transient conditions of occupancy, such as Brittney’s bedroom. Spare positions that contain unused overcurrent devices must also be identified. The identification must be on a circuit directory, which must be on the face or inside of the door of the panelboard.

Source of supply is yet another labeling requirement [408.4(B)]. All switchboards, switchgear, and panelboards supplied by a feeder in other than one- or two-family dwellings must be marked as to the device or equipment where the power supply originates.

Clearances and openings

If raceways enter a switchboard, switchgear, floor-standing panelboard, or similar enclosure, the raceways, including end fittings, must not rise more than 3 in. above the bottom of the enclosure [408.5].

Don’t leave unused openings for circuit breakers and switches open. Close them using identified closures (or other means approved by the authority having jurisdiction) that provide protection substantially equivalent to the wall of the enclosure [408.7].

This same provision exists generally for all enclosures [110.12(A)]. Note the language there, which says the closure must be “substantially equivalent to the wall of the equipment.”

Panelboards

Part III of Article 408 provides the requirements for panelboards. Each panelboard must be provided with overcurrent protection located within (or at any point on the supply side of) the panelboard. The overcurrent device must have a rating not greater than that of the panelboard [408.36].

But individual overcurrent protection isn’t required for panelboards used as service equipment where the service disconnecting means consists of up to six circuit breakers mounted in a single enclosure per 230.71 [408.36 Ex 1].

When a panelboard is supplied from a transformer (as permitted in 240.21(C)), the overcurrent protection for the panelboard must be on the secondary side of the transformer [408.36(B)]. The required overcurrent protection can be in a separate enclosure ahead of the panelboard, or it can be in the panelboard.

Plug-in circuit breakers that are back-fed from field-installed conductors must be secured in place by an additional fastener that requires something other than just a pull to release the breaker from the panelboard [408.36(D)].

The purpose of the breaker fastener is to prevent the circuit breaker from being accidentally removed from the panelboard while energized, thereby exposing someone to dangerous voltage.

Circuit breakers marked “Line” and “Load” must be installed per their listing or labeling instructions [110.3(B)]; therefore, these types of devices must not be back-fed.

Damp or wet locations

The enclosures (cabinets) for panelboards must prevent moisture or water from entering or accumulating within the enclosure, and they must be weatherproof when located in a wet location [408.37]. In a wet location, the enclosure must be mounted with at least ¼ in. air space between it and the mounting surface [312.2].

Equipment grounding conductors

Locate the terminals for neutral and equipment grounding conductors (EGCs) so someone connecting to those terminals doesn’t have to reach past uninsulated live parts [408.3(D)].

Metal panelboard cabinets and frames must be connected to an EGC of a type recognized in 250.118 [215.6 and 250.4(A)(3)]. Where a panelboard cabinet contains feeder or branch circuit EGCs of the wire type, a terminal bar for the EGCs is required and that terminal bar must be bonded to the metal cabinet [408.40].

But there’s an exception. Insulated EGCs for receptacles having insulated grounding terminals (isolated ground receptacles) [250.146(D)] can pass through the panelboard without terminating onto the equipment grounding terminal of the panelboard cabinet.

EGCs aren’t permitted to terminate on the neutral terminal bar, and neutral conductors aren’t permitted to terminate on the equipment grounding terminal bar, except as permitted by 250.142 for services and separately derived systems [408.40].

Most panelboards are rated as suitable for use as service equipment, which means they’re supplied with a main bonding jumper [250.28]. This screw or strap must not be installed except when the panelboard is used for service equipment [250.24(A)(5)] or a separately derived system [250.30(A)(1)].

Also, a panelboard marked “suitable only for use as service equipment” means the neutral bar or terminal of the panelboard has been bonded to the case at the factory. This panelboard is restricted to being used only for service equipment or on separately derived systems according to 250.142(A).

Neutral conductor terminations

Each neutral conductor within a panelboard must terminate to an individual terminal [408.41].

Why this rule? If two neutral conductors are connected to the same terminal and someone removes one of them, the other neutral conductor might unintentionally be removed also. If that happens to the neutral conductor of a multiwire circuit, it can result in excessive line-to-neutral voltage for one of the circuits plus undervoltage for the other circuit.

This requirement doesn’t apply to EGCs, because the voltage of a circuit isn’t affected if an EGC is accidentally removed.

Specifications

Part IV provides construction specifications. These are primarily for the manufacturer, but reviewing them against your actual equipment is never a bad idea. It’s also good to understand these requirements before going too far into a project.

For example, a panelboard must prevent the installation of more overcurrent devices than the number for which the panelboard was designed, rated, and listed [408.54]. When applying this rule, a 2-pole circuit breaker is considered to be two overcurrent devices, and a 3-pole circuit breaker is considered to be three overcurrent devices. If your existing panelboard is already at its design limits for the number of breakers, you’ll need to add another panelboard or replace the one you’ve got if you need to add another circuit.

Points to remember

When applying Article 408, keep these three points in mind:

• One objective of Article 408 is that the installation prevents contact between current-carrying conductors and people (or equipment).
• The circuit directory of a panelboard must clearly identify the purpose or use of each circuit that originates in the panelboard.
• You must understand the detailed grounding and overcurrent protection requirements for panelboards.

And don’t forget that switchgear does not mean switchboard or vice-versa.