Wiring design and protection

Under 1926.404(b)(1)(ii), GFCIs are required on all 120-volt, single-phase, 15- and 20-ampere receptacle outlets on construction sites that are not part of the permanent wiring and are in use by employees.

• Exceptions include receptacles on two-wire, single-phase portable or vehicle-mounted generators rated not more than 5 kW where the generator conductors are insulated from the frame and grounded surfaces.

(See 1926.404(b)(1)(ii).)

Yes. Under 1926.404(b)(1)(i), employers may use either approved ground-fault circuit interrupters or an assured equipment grounding conductor program to protect employees on construction sites.

• The employer must choose one of the two protective methods and comply with the detailed requirements for the chosen option.

(See 1926.404(b)(1)(i).)

Under 1926.404(b)(1)(iii)(A), the assured equipment grounding conductor program must include a written description of the program and the specific procedures the employer will use, and that written description must be available at the jobsite for inspection and copying.

• Keep the written program onsite so the Assistant Secretary and affected employees can inspect it.

(See 1926.404(b)(1)(iii)(A).)

Under 1926.404(b)(1)(iii)(B), the employer must designate one or more competent persons to implement the assured equipment grounding conductor program.

• A "competent person" is defined in 1926.32(f), and must have the knowledge and authority to identify hazards and take corrective action.

(See 1926.404(b)(1)(iii)(B) and 1926.32(f).)

Under 1926.404(b)(1)(iii)(C), each cord set, attachment cap, plug and receptacle of cord sets, and any cord-and-plug-connected equipment (except fixed cord sets/receptacles not exposed to damage) must be visually inspected for external defects before each day's use.

• Look for deformed or missing pins, insulation damage, or signs of internal damage; remove damaged equipment from service until repaired.

(See 1926.404(b)(1)(iii)(C).)

Under 1926.404(b)(1)(iii)(D), employers must test all equipment grounding conductors for continuity so they are electrically continuous, and test each receptacle and attachment cap or plug to confirm the equipment grounding conductor is correctly attached to its proper terminal.

• These tests verify that the grounding path is intact and correctly connected before use.

(See 1926.404(b)(1)(iii)(D)(1) and 1926.404(b)(1)(iii)(D)(2).)

Under 1926.404(b)(1)(iii)(E), required tests must be performed before first use, after repairs and before returning to service, after any incident that may have caused damage, and at intervals not exceeding 3 months (6 months for fixed cord sets and fixed receptacles not exposed to damage).

• Keep to the 3‑month testing interval unless the cord set or receptacle is fixed and protected, in which case test every 6 months.

(See 1926.404(b)(1)(iii)(E).)

Under 1926.404(b)(1)(iii)(G), employers must keep records that identify each tested receptacle, cord set, and cord‑and‑plug‑connected equipment that passed the test and show the last test date or interval. These records must be kept (e.g., logs or color coding) and maintained on the jobsite until replaced and made available for inspection.

• Use clear identifiers so each item’s test status and date can be verified quickly.

(See 1926.404(b)(1)(iii)(G).)

Under 1926.404(a)(1), a conductor used as a grounded conductor and a conductor used as an equipment grounding conductor must each be identifiable and distinguishable from all other conductors.

• This means using consistent color coding, marking, or other methods so workers can tell grounded conductors from grounding conductors and ungrounded conductors.

(See 1926.404(a)(1).)

Under 1926.404(a)(2), a grounded conductor shall not be attached to any terminal or lead in a way that reverses the designated polarity.

• In simple terms: do not connect neutral conductors to hot terminals or swap conductors in a way that changes intended polarities.

(See 1926.404(a)(2).)

No. Under 1926.404(a)(3), a grounding terminal or grounding-type device on a receptacle, cord connector, or attachment plug must not be used for purposes other than grounding.

• Never use the grounding point for carrying current or as a substitute for other conductors.

(See 1926.404(a)(3).)

Under 1926.404(b)(2)(i), a single receptacle installed on an individual branch circuit must have an ampere rating not less than that of the branch circuit.

• For example, a 20‑amp branch circuit should have a single receptacle rated at 20 amps.

(See 1926.404(b)(2)(i).)

Under 1926.404(b)(2)(ii), receptacle ratings for branch circuits supplying two or more receptacles must conform to the values in Table K-4.

• For example, a 20‑amp circuit may use 15‑ or 20‑amp receptacles; a 30‑amp circuit requires a 30‑amp receptacle.

(See 1926.404(b)(2)(ii) and Table K‑4 in 1926.404(c).)

Under 1926.404(c) and the related text, if individual overload protection for a motor is omitted, the rating of the attachment plug or receptacle used to connect the motor to a branch circuit must not exceed 15 amperes at 125 volts or 10 amperes at 250 volts.

• This rule prevents undersized plugs/receptacles being used where motors could overload unprotected conductors.

(See 1926.404(c).)

Under 1926.404(c)(1)(i) and 1926.404(c)(1)(ii), open conductors supported on poles must meet minimum horizontal climbing space and vertical clearances as follows:

• Horizontal climbing space: power conductors below communication conductors — 30 inches; power conductors alone or above communication conductors — 24 inches for 300 volts or less, 30 inches for over 300 volts.
• Vertical clearances above grade or platforms: 10 feet above finished grade or sidewalks, 12 feet over areas subject to vehicular traffic (not trucks), 15 feet over areas subject to truck traffic, and 18 feet over public streets, alleys, roads, and driveways.

(See 1926.404(c)(1)(i) and 1926.404(c)(1)(ii).)

Under 1926.404(c)(1)(iii), conductors must have a clearance of at least 3 feet from windows, doors, fire escapes, or similar openings. Conductors run above the top level of a window are considered out of reach and do not need the 3‑foot clearance.

(See 1926.404(c)(1)(iii).)

Under 1926.404(c)(1)(iv), conductors above roof spaces accessible to employees on foot must meet these vertical clearances: at least 8 feet for insulated conductors, 10 feet for covered conductors, and 15 feet for bare conductors, with specified exceptions for vehicular access, non‑normally accessible roofs, low-voltage situations, and short overhangs.

• Review the subsection’s exceptions to determine reduced clearance allowances for specific roof conditions.

(See 1926.404(c)(1)(iv).)

Under 1926.404(c)(2) and its related language, lamps for outdoor lighting must be located below live conductors, transformers, or other electric equipment unless those pieces can be locked open with a disconnecting means or adequate clearances or other safeguards are provided for relamping operations.

• This reduces the risk to workers replacing lamps by keeping them out from under energized equipment unless safe disconnect or safeguards are in place.

(See 1926.404(c)(2).)

Under 1926.404(d)(1)(i), there must be a means to disconnect all conductors in a building or structure from service‑entrance conductors, and the disconnecting means must clearly indicate whether it is open or closed and be installed at a readily accessible location nearest the point of entrance of the service‑entrance conductors.

• The disconnect must be obvious in position and easy to access for safety and emergency shutdown.

(See 1926.404(d)(1)(i).)

Under 1926.404(d)(1)(ii), each service disconnecting means must simultaneously disconnect all ungrounded conductors.

• This prevents situations where some ungrounded conductors remain energized while others are disconnected, reducing electrocution and equipment damage risks.

(See 1926.404(d)(1)(ii).)

Under 1926.404(d)(2), service‑entrance conductors over 600 volts must be guarded to make them accessible only to qualified persons and must have warning signs posted where unauthorized employees might come in contact with live parts.

• Guarding and signage help prevent unqualified employees from accidental contact with high-voltage conductors.

(See 1926.404(d)(2)(i) and 1926.404(d)(2)(ii).)

Under 1926.404(e)(1)(i), conductors and equipment must be protected from overcurrent in accordance with their ability to safely conduct current, and conductors must have sufficient ampacity to carry the load.

• Match overcurrent device ratings to conductor ampacity and equipment ratings to prevent overheating, fire, and damage.

(See 1926.404(e)(1)(i).)

Under 1926.404(e)(1)(ii), overcurrent devices shall not interrupt the continuity of the grounded conductor except for motor‑running overload protection, unless all conductors of the circuit are opened simultaneously.

• In practice, this means neutrals should not be disconnected alone by overcurrent devices unless the entire circuit is de-energized at once.

(See 1926.404(e)(1)(ii).)

Under 1926.404(e)(1)(iv), overcurrent devices must be readily accessible, not located where they could create a safety hazard by being exposed to physical damage, or located near easily ignitable material.

• Place fuses and breakers where workers can safely reach them without exposing themselves to hazards.

(See 1926.404(e)(1)(iv).)

No. Under 1926.404(b)(1)(iii)(F), employers must not make available or permit the use by employees of any equipment that has not met the requirements of the assured equipment grounding conductor program.

• Equipment that fails inspections or tests must be removed from service until it complies with the program.

(See 1926.404(b)(1)(iii)(F).)

Under 1926.404(b)(1)(iii)(E)(3), equipment must be tested before it is used again after any incident that could reasonably be suspected to have caused damage, such as when a cord set has been run over.

• Any event that may have compromised insulation, grounding, or connections triggers testing before reuse.

(See 1926.404(b)(1)(iii)(E)(3).)

Under 1926.404(b)(1)(iii)(E)(4), cord sets and receptacles that are fixed and not exposed to damage must be tested at intervals not exceeding 6 months.

• Portable cord sets and exposed receptacles require testing at intervals not exceeding 3 months.

(See 1926.404(b)(1)(iii)(E)(4).)

Yes. 1926.404(b)(2)(iii) indicates that receptacles used for connecting motors must meet the specific requirements described in the section, and related text in 1926.404(c) limits attachment plug and receptacle ratings for motor connections when individual overload protection is omitted.

• Check 1926.404(c) for the limits (e.g., 15 A at 125 V or 10 A at 250 V) when overload protection is omitted.

(See 1926.404(b)(2)(iii) and 1926.404(c).)

No. Under 1926.404(b)(1)(ii), the GFCI requirement applies to 120‑volt, single‑phase, 15‑ and 20‑ampere receptacle outlets on construction sites that are not part of the permanent wiring; receptacles that are part of the permanent wiring are excluded from this specific GFCI requirement.

• Permanent wiring is covered by other electrical code requirements but not this particular construction‑site GFCI mandate.

(See 1926.404(b)(1)(ii).)

Under 1926.404(e)(1)(iii), cartridge fuses accessible to unqualified persons and all fuses and thermal cutouts on circuits over 150 volts to ground must be provided with disconnecting means so the fuse or thermal cutout can be disconnected from its supply without disrupting unrelated equipment and circuits.

• This allows safe replacement or service of fuses without affecting other systems and reduces risks during maintenance.

(See 1926.404(e)(1)(iii).)

They must be located or shielded so employees cannot be burned or otherwise injured by arcing or suddenly moving parts. Employers should position fuse and circuit-breaker panels, guards, or barriers to prevent direct exposure to arcs and to keep employees out of the path of any parts that could fly or move during operation. See 1926.404(e)(1)(v).

Circuit breakers must clearly indicate whether they are in the open (off) or closed (on) position. Make sure breaker handles or faces have unambiguous markings or physical positions that show ON versus OFF so workers and maintenance personnel can tell the status at a glance. See 1926.404(e)(1)(vi)(A).

If handles operate vertically, the up position must be the closed (on) position. When installing or inspecting switchboards with vertical handles, ensure the mechanical orientation follows this rule so the ON/OFF positions are consistent and predictable. See 1926.404(e)(1)(vi)(B).

If a circuit breaker is used as a switch in 120-volt fluorescent lighting circuits, it must be marked "SWD." This marking identifies the breaker as serving a switching function in those lighting circuits. See 1926.404(e)(1)(vi)(C).

Yes. Feeders and branch circuits with nominal voltages over 600 volts must have short-circuit protection. Make sure over‑600V conductors are protected by properly rated protective devices to limit current during faults. See 1926.404(e)(2).

All three-wire DC systems must have their neutral conductor grounded. That means the neutral conductor of a 3‑wire DC power system supplying premises wiring must be connected to ground to meet the standard. See 1926.404(f)(1)(i).

Two‑wire DC systems operating over 50 volts but not more than 300 volts between conductors must be grounded unless they are rectifier‑derived from an AC system that meets the exemptions in paragraphs (f)(1)(iii) through (f)(1)(v). In short, most 50–300 V two‑wire DC systems need a grounded conductor unless they qualify under the listed rectifier‑derived exceptions. See 1926.404(f)(1)(ii) and the exemption conditions at 1926.404(f)(1)(iii)–(v).

AC systems rated between 50 and 1000 volts must be grounded if any of these conditions apply: grounding so the maximum voltage-to-ground on ungrounded conductors does not exceed 150 volts; the system is 480Y/277V 3‑phase 4‑wire where the neutral is used as a circuit conductor; the system is 240/120V 3‑phase 4‑wire using a phase midpoint as a circuit conductor; or if a service conductor is uninsulated. Verify which condition fits your installation and ground accordingly. See 1926.404(f)(1)(iv).

AC systems of 50–1000 volts that are separately derived from a transformer (with primary under 1000 V) may be left ungrounded when all of these are true: the system is used exclusively for control circuits; only qualified persons will service it (maintenance and supervision); continuity of control power is required; and ground detectors are installed on the control system. All four conditions must be met for the exemption. See 1926.404(f)(1)(v).

A portable generator's frame may serve as the grounding electrode when the generator supplies only equipment mounted on it and/or cord‑and‑plug equipment through receptacles on the generator, and all noncurrent‑carrying metal parts and the equipment grounding terminals of receptacles are bonded to the frame. For vehicle‑mounted generators, the vehicle frame must be bonded to the generator frame and the generator must supply only equipment on the vehicle or via receptacles on the vehicle/generator, with equipment metal parts and receptacle grounding terminals bonded to the generator frame; additionally, the system must meet all other grounding provisions and, if the generator is part of a separately derived system, the neutral must be bonded to the generator frame. See 1926.404(f)(3)(i)–(iii).

For grounded systems, connect the equipment grounding conductor and the grounded circuit conductor to the grounding electrode using a grounding electrode conductor, and make those connections on the supply side of the service disconnecting means (or on the supply side of the system disconnecting means/overcurrent devices for a separately derived system). For ungrounded systems supplied from the service, connect the equipment grounding conductor to the grounding electrode conductor at the service equipment; for ungrounded separately derived systems, make that connection at or ahead of the system disconnecting means or overcurrent devices. See 1926.404(f)(5)(i)–(ii).

The path to ground from circuits, equipment, and enclosures must be permanent and continuous. That means bonding and grounding conductors and connections must be installed so they provide an unbroken low‑impedance path for fault current at all times. See 1926.404(f)(6).

Metal cable trays, metal raceways, and metal enclosures for conductors generally must be grounded, but metal enclosures used only to protect cable assemblies from physical damage need not be grounded, and metal enclosures added to existing open‑wire, knob‑and‑tube, or nonmetallic‑sheathed installations need not be grounded if the runs are less than 25 feet, the enclosures are free from probable contact with ground or grounded metal, and the enclosures are guarded against employee contact. Check all these conditions before omitting grounding. See 1926.404(f)(7)(i).

Exposed noncurrent‑carrying metal parts of fixed equipment that may become energized must be grounded if they are within 8 feet vertically or 5 feet horizontally of ground or grounded metal and subject to employee contact, if located in wet/damp locations and subject to employee contact, if in electrical contact with metal, if in hazardous locations, if supplied by grounded metal raceways, or if equipment operates with any terminal over 150 volts to ground (with limited exceptions). Cord‑and‑plug equipment must be grounded in hazardous locations, when operating over 150 volts to ground (with some guarded motor exceptions), or when listed types (hand‑held tools, portable lamps, etc.) are used in wet or conductive locations unless exempted by double insulation or an isolating transformer under the specified conditions. Double‑insulated or equivalently listed portable tools need not be grounded but must be marked accordingly. See 1926.404(f)(7)(iii)–(iv).

Noncurrent‑carrying metal parts requiring grounding must be grounded with an equipment grounding conductor that is contained in the same raceway, cable, or cord, or that runs with or encloses the circuit conductors (for DC circuits the equipment grounding conductor may be run separately). The grounding conductor must have the capacity to safely conduct any fault current that may be imposed on it—select conductor size and type to carry potential fault currents without damage. See 1926.404(f)(8)(i)–(ii).

If a single grounding electrode (rod, pipe, or plate) has a resistance to ground greater than 25 ohms, you must add at least one more electrode and install it no closer than 6 feet to the first electrode. Also ensure made electrodes are free of nonconductive coatings and, if practical, embedded below the permanent moisture level. These steps lower overall ground resistance. See 1926.404(f)(10).

The system neutral must be grounded through an impedance; if a delta high‑voltage system is used, a neutral must be derived. Under 1926.404(f)(11)(ii)(A), portable and mobile high‑voltage equipment shall be supplied from a system having its neutral grounded through an impedance. If the supply is a delta connection, a system neutral must be derived so it can be grounded through that impedance.

• Why this matters: grounding the neutral through an impedance limits fault currents and helps protective devices detect ground faults while reducing the energy available during a fault.
• Practical note: work with a qualified electrical engineer to select the correct impedance grounding method and to document the derived neutral for a delta system.

(See 1926.404(f)(11)(ii) for the broader grounding requirements for systems supplying portable or mobile equipment.)

Exposed noncurrent‑carrying metal parts must be connected by an equipment grounding conductor to the point where the system neutral impedance is grounded. 1926.404(f)(11)(ii)(B) requires that exposed noncurrent‑carrying metal parts of portable and mobile equipment be tied via an equipment grounding conductor to the same grounding point used for the system neutral impedance.

• Practical steps: ensure the equipment grounding conductor is continuous, sized appropriately, and routed to the neutral‑impedance grounding point (not to unrelated ground electrodes).
• Coordination: this connection must match the system grounding scheme required by 1926.404(f)(11)(ii)(A).

(Refer to 1926.404(f)(11)(ii) for related grounding provisions.)

You must provide automatic ground‑fault detection/relaying and continuous monitoring of the equipment grounding conductor so the high‑voltage feeder is de‑energized if a ground fault occurs or the grounding conductor loses continuity. 1926.404(f)(11)(ii)(C) mandates ground‑fault detection and relaying to automatically de‑energize any high‑voltage system component that develops a ground fault, and continuous monitoring of the equipment grounding conductor to automatically de‑energize the high‑voltage feeder if continuity is lost.

• Key actions employers should take:
  • Install and test ground‑fault detection/relay systems that will trip feeders on ground faults.
  • Use a supervised continuity monitoring system for the equipment grounding conductor (alarm or trip if continuity is broken).
  • Periodically verify monitoring systems through testing and maintenance procedures.

(See 1926.404(f)(11)(ii) for full context of grounding and protection requirements.)

The portable system grounding electrode must be isolated and at least 20 feet away from any other grounding electrode with no direct connections; most noncurrent‑carrying metal parts must be grounded, except equipment that is guarded by location or pole‑mounted distribution apparatus more than 8 feet above ground. 1926.404(f)(11)(ii)(D) requires that the grounding electrode for the portable/mobile equipment neutral impedance be isolated and separated by at least 20 feet from any other system or equipment grounding electrode and have no direct connections (for example, buried pipe or fence). Separately, 1926.404(f)(11)(iii) states that all noncurrent‑carrying metal parts of portable and fixed equipment (and associated fences, housings, enclosures, supports) shall be grounded, except that equipment which is guarded by location and isolated from ground need not be grounded, and pole‑mounted distribution apparatus located more than 8 feet above ground need not be grounded.

• Practical implications:
  • Do not tie the portable system grounding electrode into nearby grounding systems (keep it 20 ft away and avoid buried conductive links).
  • Still ground exposed metal parts unless the equipment is effectively isolated by location or is a pole‑mounted distribution device more than 8 ft above ground.

(See 1926.404(f)(11)(ii)(D) and 1926.404(f)(11)(iii) for the complete requirements.)