Can conductors of different voltages share a panel enclosure?

Yes, per NEC 300.3(C)(1), provided every conductor in the enclosure has an insulation rating at least equal to the maximum circuit voltage present. Standard 600 volt rated building wire satisfies that for 480 volt and 208 volt systems.

Do feed through conductors need a label?

Yes. NEC 312.8(A)(3) requires a warning label complying with 110.21(B) on the enclosure identifying the closest disconnecting means for any feed through conductors.

Do I have to identify voltage systems in a building with both 208 and 480 volts?

Yes. NEC 210.5(C) and 215.12(C) require ungrounded conductors of each system to be identified, with the identification method posted at each panelboard or otherwise documented and readily available.

Can 480 volt conductors pass through a 120/208 volt panel?

Feed through conductors are permitted, and conductors of different systems can share an enclosure, but there are conditions on both counts and one of them is easy to miss.

Feeding through the enclosure

Section 312.8(A) of the 2023 NEC permits enclosures for switches or overcurrent devices to contain splices, taps, and conductors feeding through, subject to three conditions. Conductors alone at any cross section cannot exceed 40 percent of the cross sectional area of the wiring space. Conductors, splices, and taps together cannot exceed 75 percent. And a warning label complying with 110.21(B) must be applied to the enclosure identifying the closest disconnecting means for any feed through conductors. That label requirement is the one people forget. If you pass a set of 480 volt feeders through a 208 volt panel gutter, that panel has to carry a label telling the next technician where those conductors are disconnected.

Different systems in the same enclosure

Section 300.3(C)(1) states that conductors of alternating current and direct current circuits rated 1000 volts nominal or less shall be permitted to occupy the same equipment wiring enclosure, cable, or raceway, provided all conductors have an insulation rating equal to at least the maximum circuit voltage applied to any conductor within the enclosure, cable, or raceway. Standard building wire types such as THHN and XHHW are rated 600 volts, so a 480 volt circuit and a 208 volt circuit both qualify, and the mix is permitted.

If the higher voltage system exceeds 1000 volts, Part II of Article 300 does not apply and you go to 300.37 and the medium voltage rules, where the mix is not permitted with the low voltage systems.

Identification and working space

Section 210.5(C) and Section 215.12(C) require branch circuit and feeder ungrounded conductors to be identified by system where a premises has more than one nominal voltage system, with the method of identification posted at each branch circuit panelboard or documented in a readily available manner. On a building with both 208 volt and 480 volt systems, that identification is mandatory, not optional.

Section 110.26 working space still applies, and Section 312.7 requires the wiring space to remain usable. A bundle of feeders crossing the gutter of a branch panel eats the space you need to dress the branch circuits and often makes the deadfront hard to reinstall. Section 110.12 lets an inspector reject the work on workmanship grounds alone.

Field takeaway

It is legal. Verify the fill math, use 600 volt rated insulation for everything in the box, apply the 110.21(B) warning label naming the disconnect for the feed through conductors, and post the voltage system identification legend. If the gutter is tight, run a separate wireway instead. It is cheaper than a failed inspection and a re-pull.