NEC 495 — Equipment over 1000 Volts (Washington)

NEC 490 — Equipment over 600 Volts (Washington Journeyman)

Learning Objectives

1.1 Scope (495.1)

Article 495 covers the general requirements for equipment operating at more than 1000 volts ac, 1500 volts dc, nominal. The thresholds are asymmetric — ac arcs are harder to extinguish at a given voltage, so the ac value sits lower — and an option that swaps or equalizes the pair is testing whether you read the scope line.

The "over 600 volts" wording in this chapter's title is the legacy grouping from older editions. The 2026 NEC contains no Article 490; those equipment rules now live in Article 495, so an answer built on a 600-volt threshold is quoting an obsolete arrangement.

The scope is a floor, not a ceiling: nothing in 495.1 caps the voltage at which the article stops applying, and the 15,000-volt and 52,000-volt figures appearing later are listing thresholds in 495.2, not scope limits. Informational Note No. 1 points to NFPA 70E and Note No. 2 to ANSI Z535.4 for hazard signs and labels; notes are explanatory, but an option that dresses a note up as a rule is still wrong.

1.2 Listing, Reconditioned Equipment, Enclosures (495.2 through 495.4)

495.2 splits by voltage: switchgear and industrial control assemblies operating not over 15,000 volts ac or dc, nominal shall be listed effective January 1, 2029, and the same equipment over 15,000 volts but not over 52,000 volts ac or dc, nominal shall be listed effective January 1, 2032.

495.3 permits reconditioned switchgear or sections of switchgear, with two limits: equipment damaged by fire, products of combustion, corrosive influences, or water must first be specifically evaluated by its manufacturer or by a qualified testing laboratory, and reconditioned equipment of any other type may not be installed.

495.4 requires enclosures in damp or wet locations to be weatherproof; in a wet location, raceways or cables entering above the level of uninsulated live parts must use fittings listed for wet locations. Damp-location fittings, drain fittings, and sealing compound do not satisfy that rule.

1.3 Isolating Means (495.20 and 495.22)

495.20 says the requirements of Article 495 Part II apply to all equipment — no voltage sub-threshold, no equipment-class filter. A stem narrowing Part II to switchgear over 15,000 volts, to reconditioned equipment, or to equipment over 52,000 volts invents a restriction.

495.22 requires means to completely isolate an item of equipment from all ungrounded conductors other than service conductors connected to the service disconnect. Only service conductors are excepted; equipment grounding conductors are outside the rule because they are not ungrounded, and grounded neutrals and control conductors are not the named exception.

The section then removes a burden: isolating switches are not required where other ways of de-energizing the equipment for inspection and repairs exist, such as draw-out-type switchgear units and removable truck panels. The test is whether the alternative really de-energizes the equipment; lockable doors, portable grounding sets, and infrared inspection windows do not.

Non-load-break isolating switches shall comply with one or both of the following: (1) interlocking with a circuit interrupting device in series such that the interrupting device must be open before the isolating switch is opened or closed; or (2) field marking with a warning against opening or closing under load, signs or labels complying with 110.21(B). Either option satisfies the section, so the cure for a missing interlock is the marking — not a barrier, a load-break replacement, or a ground-fault detector (a battery-circuit provision in 480.13). A fuseholder and fuse identified for use as an isolating switch is permitted as an isolating switch; the identification is the only condition.

1.4 Voltage Regulators (495.23)

Regulator switching sequence shall be ensured by one of three methods: mechanically sequenced regulator bypass switch(es); mechanical interlocks; or a switching procedure prominently displayed at the switching location. Any one satisfies the section. The distractors are real code elsewhere: the single-line diagram is 495.25(B), the interlocked grounding switch is 495.26(A), and the backfeed warning sign is 495.25(A).

1.5 Minimum Space Separation (495.24)

In field-fabricated installations, the minimum air separation between bare live conductors, and between such conductors and adjacent grounded surfaces, shall not be less than the values given in Table 495.24. The table is keyed to nominal voltage rating and basic impulse level (BIL), with separate indoor and outdoor values for phase-to-phase and phase-to-ground clearances.

The exception is narrow and often tested: the values do not apply to interior portions or exterior terminals of equipment designed, manufactured, and tested in accordance with accepted national standards. A flat 6 inches regardless of voltage is not what the code specifies. Check the table number too: Table _490.24_ is a legacy designation that no longer exists in the 2026 NEC, and Table 495.2(A) is the listing provision for equipment rated not over 15,000 volts.

1.6 Backfeed (495.25)

Where the possibility of backfeed exists, the installation shall comply with 495.25(A) and 495.25(B) — both, not either.

495.25(A). A permanent sign complying with 110.21(B) shall be installed on the disconnecting means enclosure or immediately adjacent to the open disconnecting means with the following words or equivalent: DANGER — CONTACTS ON EITHER SIDE OF THIS DEVICE MAY BE ENERGIZED BY BACKFEED. "Or equivalent" gives latitude in phrasing, not in substance: both sides of the device can be live from backfeed. "DANGER — DO NOT OPEN UNDER LOAD" describes a different hazard, and "DANGER — HIGH VOLTAGE — KEEP OUT" is the marking 495.35(A) requires on doors giving access to energized parts.

495.25(B). A permanent and legible single-line diagram of the local switching arrangement, clearly identifying each point of connection to the high-voltage section, shall be provided within sight of each point of connection in accordance with 110.39. "Within sight of" means visible and not more than 15 m (50 ft) away.

1.7 Grounding Switches (495.26)

Where grounding switches are installed, they shall comply with 495.26(A) and 495.26(B).

495.26(A). Grounding switches shall be interlocked with the disconnecting means for all sources of power to the location where the grounding switch is applied, so that the disconnecting means must be open prior to moving the grounding switch to the grounded position, and cannot be closed while the grounding switch is grounded. The interlock stops the switch being closed on a live line and stops a grounded section being re-energized. Interlocking with only the nearest upstream overcurrent device fails, and a sign never substitutes for the interlock. Exception: interlocking is not required under single management where documented safe switching procedures are established and maintained.

495.26(B). A sign complying with 110.21(B) shall be installed at the grounding switch location indicating that a grounding switch is present and the designation and locations of all disconnecting means which must be opened prior to moving the grounding switch to the grounded position. It may be field or factory installed. Ampacity is not required content — presence, designations, and locations are.

Exception. No sign is required where the grounding switch is interlocked with a disconnecting means in accordance with 495.26(A) and there is no other source of power to the grounding switch location. A fault-current rating, a warning label, and supervision by a qualified person do not remove the sign requirement.

1.8 Marking and Location Rules the Article Relies On (110.21(B), 110.16, 110.39)

110.21(B) Field-Applied Hazard Markings. Where caution, warning, or danger hazard markings such as labels or signs are required by the code, they must be of sufficient durability to withstand the environment involved and must warn of the hazards using effective words, colors, symbols, or any combination of these. Article 495 leans on this section repeatedly — the isolating-switch warning in 495.22, the backfeed sign in 495.25(A), the grounding-switch sign in 495.26(B), the locked-door marking in 495.35(A).

110.16 Arc-Flash Hazard Marking has a different job. In other than dwelling units, a permanent arc flash marking is applied, field or factory, to service equipment and feeder-supplied equipment such as switchboards, switchgear, enclosed panelboards, industrial control panels, and motor control centers likely to be worked on energized; its content is the nominal system voltage, the arc flash boundary, the available incident energy or the minimum PPE level, and the date of the assessment. When a stem asks which section governs a warning label on an isolating switch, 110.16 is the planted distractor. Older keys also cite _490.21_ for switchgear markings; that section no longer exists in the 2026 NEC.

110.39 In Sight From. Where the code says equipment shall be "in sight from", "within sight from", or "within sight of" a building, structure, or other equipment, the equipment must be visible and not more than 15 m (50 ft) from it.

1.9 The Rest of the Article: Parts III through VII

Part III — Switchgear, Substations, Industrial Control Assemblies (495.30 through 495.48) applies to substations, assemblies of switchgear, and industrial control equipment (495.30), and covers arrangement of devices, guarding of energized parts, enclosures, inspection windows, fused interrupter switches, breaker locking, and the service-equipment ground bus. Part IV — Mobile and Portable Equipment (495.60 through 495.66) covers skid-mounted substations, shovels, draglines, cranes, hoists, drills, dredges, compressors, pumps, and conveyors. Part V — Boilers (495.70 through 495.74) requires supply from a 3-phase, 4-wire solidly grounded wye system or isolating transformers providing one, with control circuits not exceeding 150 volts (495.71). Parts VI and VII (495.80 through 495.97) cover equipment other than transformers with more than 38 L (10 gal) of insulating fluid in a single volume, and vaults for it, which must ventilate to outside air without flues or ducts wherever practicable (495.91).

Code Navigation

Common Exam Traps

Practical Field Points

Summary

Article 495 holds the 2026 NEC's requirements for equipment operating at more than 1000 volts ac, 1500 volts dc, nominal; the "over 600 volts" label from the older Article 490 arrangement describes nothing in the code, so scope answers built on 600 volts, or on the listing bands of 495.2, are traps. Part I sets the frame with listing dates (495.2), a limited permission for reconditioned switchgear (495.3), and weatherproof enclosures with wet-location fittings (495.4). Part II is where the exam dwells. Section 495.20 applies it to all equipment; 495.22 requires complete isolation from ungrounded conductors other than service conductors connected to the service disconnect, and gives non-load-break isolating switches two substitute conditions — interlocking with a series circuit interrupting device, or a field marking against operating under load complying with 110.21(B). Section 495.23 lists three ways to ensure a regulator switching sequence, and 495.24 ties air separation to Table 495.24. For backfeed, 495.25(A) fixes the sign wording and 495.25(B) the diagram within sight, which 110.39 defines as visible and not more than 15 m (50 ft). Grounding switches bring 495.26 into play: interlocking for all sources of power, a location sign, and two narrow exceptions. Parts III through VII extend the same discipline to switchgear, mobile equipment, boilers, insulating liquids, and vaults.

Section 495.24 then settles the field-fabricated air separations, and 495.20 keeps every one of these requirements applying to all equipment in the article's scope.