National Electrical Code Top Ten Tips: Article 408 -- Switchboards and Panelboards
by Mark Lamendola
Based on the 2020 NEC
Please note, we do quote from copyrighted material. While the NFPA
does allow such quotes, it does so only for the purposes of education
regarding the National Electrical Code. This article is not a substitute
for the NEC.
These are the 10 NEC Article 408 items we deem most important, based
on the pervasiveness of confusion and the potential costs of same.
- Respect the "modular integrity" philosophy of switchboard and panelboard
installation. Donít use any vertical section as a wireway between other
vertical sections [408.3(A)]. Keep all wiring in its own section, and don't mix
wiring between sections.
- If used as service equipment, bond all sections together using a bonding jumper sized per Table 250.122
or Table 250.66 [408.3(C)]. If not used as service equipment, also bond all sections together even though this isn't explicitly required here. That will eliminate dangerous differences of potential.
- You must arrange the phases in a particular order. That order is A, B,
C--from front to back and from top to bottom (or left to right), when viewing
the cabinet from the front [408.3(E)]. Be sure each of these is correctly labeled. It helps also to color code on the panel. If the corresponding phasing tape is used on the conductor, the problem of phase mix-up during cable testing or other maintenance or repair operations is practically eliminated.
- On Delta systems, you must designate the phase with the highest voltage to
ground as the B phase [408.3(F)]. Make this stand out. For example, use a labelmaker that can print a strip that says "B phase" or simply a string of Bs.
- Fill out the circuit directory, and do so legibly with sufficient detail
[408.4(A)]. Rather than handwriting, use a professional-level labeler. The cleanest way to fill out the directory is to print the information on an overlay that you paste over the factory directory. Consult the manufacturer for more information on best practices for directories. An enhancement to this is to create a smartphone-compatible file that is stored on a server and create a QR Code that is affixed to the panel. This file could be a video, drawing, or photo. Its purpose is to identify each breaker (circuit). In a maintenance situation, this can help improve Lockout/Tagout by providing more information than might be on a drawing. For example, it could tell you which assets are supplied by each circuit in the panel.
- Close any unused openings [408.7]. Why violations of this requirement persist at such a high level is a mystery. If you install switchboards and panelboards, ensure you have a gear kit specifically for this purpose and a kit goes out on each job.
- If locating switchboards in wet locations or near combustible materials, follow the
rules in 408.16 and 408.17. These are mostly what we call common sense, but that doesn't mean you should wing it. Use the rules to ensure you don't overlook something.
- All panelboards must have a rating of at least the minimum feeder capacity required for the load calculated per Article 220, Parts III, IV, and V as applicable [408.30].
- Provide overcurrent protection on the supply side to each
panelboard. The rating of the OCPD cannot exceed the rating of the panelboard [408.36].
- Observe the minimum spacing requirements provided in Table 408.56. Please note that these are minimums. Actual conditions and common sense, not to mention sound engineering practices and maintenance needs, may require exceeding these minimums. Be sure to allow for maintenance carts, any lifting equipment that might be needed, and space needed to efficiently replace cables should the need arise.