You're right, Table 408.56 in the NEC (National Electrical Code) primarily addresses clearances to ground. The NEC doesn't have a single, easy-to-find table that directly specifies air gap clearances between phases for 480V equipment. This is because the necessary clearance depends on several factors, including: The specific type of equipment

Panelboards, switchboards, motor control centers, etc., all have different construction standards.

The specific standards the equipment is built to

UL standards (e.g., UL 508A for industrial control panels) will dictate internal clearances.

Pollution degree

The environment the equipment is installed in affects required creepage and clearance distances.

Overvoltage category

Here's a breakdown of where you'll likely find the information and how to approach it:1. Equipment Listing and Labeling

The most reliable source for phase-to-phase clearances is the equipment's listing (e.g., UL) and labeling. Look for markings and installation instructions provided by the manufacturer. The equipment was tested to certain standards, and those standards will have clearance requirements. This is paramount, as the NEC generally requires listed and labeled equipment to be installed according to its instructions.2.

Manufacturer's Specifications

Consult the manufacturer's technical data sheets, installation manuals, and engineering drawings. They should provide the necessary clearance information specific to their product. Sometimes, they will refer to the specific UL standard they designed to.3.

UL Standards

If the manufacturer refers to a specific UL standard (e.g., UL 891 for switchboards, UL 508A for industrial control panels), you'll need to consult that UL standard directly. These standards are detailed and often expensive to obtain, but they contain the precise creepage and clearance requirements based on the equipment's voltage rating, pollution degree, and other factors.4.

NEC Article 110.26(A)(1) - Working Space

While this section doesn't give specific phase-to-phase clearance values, it mandates sufficient working space around electrical equipment. Adequate working space inherently requires clearances that prevent accidental contact and allow for safe operation and maintenance. Although it doesnt give an explicit phase-to-phase clearance, it is still critical that the "clear space" around the gear be maintained.5.

NEC Article 408 (Switchboards, Switchgear, and Panelboards)

As you mentioned, Article 408 is relevant. However, look beyond Table 408.56. Check the sections on construction specifications and installation, as they may indirectly refer to applicable standards.
6.

IEEE Standards

IEEE (Institute of Electrical and Electronics Engineers) standards may also offer guidance, especially for higher-voltage systems.

How to Find the Information in Practice


Identify the Equipment

Know the exact type of equipment you're working with (e.g., 480V panelboard, motor control center).2.

Find the Listing Label

Locate the UL (or other recognized testing laboratory) listing label on the equipment. Note the UL standard to which it is listed.3.

Consult the Manufacturer

Contact the manufacturer and request the technical specifications, installation manual, or engineering drawings. Specifically ask about phase-to-phase clearance requirements and the relevant UL standard.4.

Review Applicable Standards

If necessary, obtain and review the applicable UL standard or other relevant industry standards.

Important Considerations



Creepage vs. Clearance

Be aware of the difference between clearance (air gap distance) and creepage (distance along a surface). Creepage requirements are crucial for preventing tracking (surface arcing), especially in polluted environments.

Pollution Degree

The pollution degree of the environment significantly affects clearance and creepage distances. Higher pollution levels require greater distances.

Altitude

Higher altitudes require increased clearances.

Qualified Personnel

Determining the correct clearances and ensuring compliance with all applicable standards is best left to qualified electrical engineers and electricians. Improper clearances can lead to equipment failure, fire hazards, and electrical shock.

Example Scenario

Let's say you're working with a 480V industrial control panel listed to UL 508A.1. You would find the UL 508A listing mark on the panel.
2. You would contact the panel manufacturer and ask for the specific clearance requirements for phase-to-phase spacing within the panel, referencing the UL 508A standard.3. The manufacturer's documentation (or the UL 508A standard itself) would provide the minimum clearance distances based on the voltage, pollution degree, and other factors.

In summary, there is no single NEC table for 480V phase-to-phase clearances. The appropriate clearance is dictated by the equipment's listing, labeling, manufacturer's instructions, and relevant UL or other industry standards. Always prioritize the manufacturer's instructions and consult with qualified professionals. Flag for review