Special systems over 600 volts

Yes. Above-ground conductors for systems over 600 volts may be installed in rigid metal conduit, intermediate metal conduit, cable trays, cablebus, other suitable raceways, or as open runs of metal-clad cable designed for that purpose, but open runs of non-metallic-sheathed cable or bare conductors are only permitted where the location is accessible only to qualified persons. See 1926.408(a)(1)(i).

• Metallic shielding components (tape, wire, braid) must be grounded when used. See 1926.408(a)(1)(i).

Conductors emerging from the ground must be enclosed in raceways, and raceways on poles must be rigid metal conduit, intermediate metal conduit, or PVC schedule 80 (or equivalent) from the ground line up to 8 feet above finished grade; conductors entering a building must be protected by a grounded metallic enclosure from ground to the point of entrance. See 1926.408(a)(1)(ii).

• Metallic enclosures must be grounded as required in the same paragraph.

They must be supported to prevent physical damage to the braid or sheath. See 1926.408(a)(1).

• Proper support prevents abrasion and exposure of underlying conductors or shield; follow manufacturer and industry good practice in spacing supports.

Indoor circuit breakers for systems over 600 volts must be metal-enclosed or fire-resistant, cell-mounted units; open mounting is only permitted where locations are accessible only to qualified personnel. Also, a means of indicating open or closed positions must be provided. See 1926.408(a)(2)(i).

• Ensure visible or mechanical indicators are reliable so workers know breaker status before working on equipment.

Fused cutouts installed in buildings or transformer vaults must be of a type identified for that purpose and must be readily accessible for fuse replacement. See 1926.408(a)(2)(ii).

• "Identified for the purpose" means using equipment rated and listed for the application; maintain access clearances for safe fuse changeouts.

Employers must provide a means to completely isolate equipment for inspection and repairs. See 1926.408(a)(2)(iii).

• Isolation means should fully disconnect energy sources and be lockable or otherwise secured to prevent re-energization during work.

A metallic enclosure must be provided on the mobile machine to enclose the power cable terminals, and that enclosure must provide a solid ground connection to the machine frame, prevent strain on cable terminations, be lockable for access by authorized qualified persons, and be marked to warn of energized parts. See 1926.408(a)(3)(i).

• The grounding terminal must reliably bond the frame; strain relief reduces the risk of loose connections and arcing.

All energized switching and control parts must be enclosed in effectively grounded metal cabinets or enclosures; operating means (such as breaker handles) may project through the enclosure so units can be reset without opening locked doors, and enclosures must be locked and labeled to restrict access to authorized qualified persons. See 1926.408(a)(3)(ii).

• Grounding the enclosure reduces shock risk; locks and labels help ensure only trained workers access energized parts.

Yes. Circuit breakers and protective equipment must have their operating means project through the grounded metal cabinet or enclosure so breakers can be reset without opening locked doors; however, doors must remain locked to prevent unauthorized access to energized parts. See 1926.408(a)(3)(ii).

• Only authorized qualified personnel should have keys or means to open locked enclosures for internal access.

Conductors in tunnels must be installed in metal conduit or other metal raceway, Type MC cable, or other suitable multiconductor cable; they must be located or guarded to protect from physical damage, and an equipment grounding conductor must run with the circuit conductors inside the metal raceway or cable jacket. See 1926.408(a)(4)(ii).

• The equipment grounding conductor may be insulated or bare; portable multiconductor cable may supply mobile equipment if it provides equivalent protection.

A disconnecting means that simultaneously opens all ungrounded conductors must be installed at each transformer or motor location in tunnels. See 1926.408(a)(4)(iv).

• This ensures complete de-energization of the equipment before maintenance and reduces the risk of backfeed.

All nonenergized metal parts of electric equipment, metal raceways, and cable sheaths must be grounded and bonded to all metal pipes and rails at the portal and at intervals not exceeding 1,000 feet throughout the tunnel. See 1926.408(a)(4)(v).

• Regular bonding intervals maintain an effective equipotential grounding system along the tunnel for worker safety.

Bare terminals of transformers, switches, motor controllers, and other equipment in tunnels must be enclosed to prevent accidental contact with energized parts. See 1926.408(a)(4)(iii).

• Enclosures should be grounded and labeled to warn personnel of energized components.

The tunnel-installation provisions apply to portable and/or mobile high-voltage power distribution and utilization equipment associated with tunnels, including substations, trailers, cars, mobile shovels, draglines, hoists, drills, compressors, pumps, conveyors, and underground excavators. See 1926.408(a)(4)(i).

• If equipment is used in tunnels and is portable or mobile, the tunnel-specific wiring, protection, grounding, and guarding rules apply.

A Class 1 power-limited circuit is supplied from a source having a rated output of not more than 30 volts and 1,000 volt-amperes. A Class 1 remote control or signaling circuit may have voltage up to 600 volts (power need not be limited). See 1926.408(b)(1)(i).

• Understand the distinction between voltage and power (volt-amperes) when classifying circuits.

Class 2 and Class 3 circuits have voltage and power limitations that depend on whether the source is inherently limited or limited by overcurrent protection: for inherently limited sources, Class 2 max is 150 V and Class 3 max is 100 V; for sources limited by overcurrent protection, Class 2 max is 30 V AC / 60 V DC and Class 3 max is 150 V AC or DC. See 1926.408(b)(1)(ii).

• Apply the limits to sinusoidal AC or continuous DC sources where wet contact is not likely, per 1926.408(b)(1)(iii).

Yes. A Class 2 or Class 3 power supply unit must be durably marked where plainly visible to indicate the class of supply and its electrical rating before it is used. See 1926.408(b)(2).

• Durable, visible markings help users and maintenance personnel recognize the circuit classification and avoid improper connections or servicing.

Each communication circuit so exposed must be provided with an approved protector. See 1926.408(c)(2)(i).

• Protective devices should be grounded as required by 1926.408(c)(5).

Each conductor of a lead-in from an outdoor antenna must have an antenna discharge unit or other means to drain static charges from the antenna system. See 1926.408(c)(2)(ii).

• Proper lightning and static discharge protection reduces risk of fire or equipment damage and improves worker safety.

Receiving distribution lead-in or aerial-drop cables attached to buildings and lead-ins to radio transmitters must be installed to avoid accidental contact with electric light or power conductors, and the clearance between lead-in conductors and any lightning protection conductors must be at least 6 feet. See 1926.408(c)(3)(i)(A) and 1926.408(c)(3)(i)(B).

• Adequate separation prevents arcing or interaction during storms or failures.

Indoor antennas, lead-ins, and other communication conductors attached as open conductors inside buildings must be located at least 2 inches from conductors of any light, power, or Class 1 circuits unless an equally protective special method of separation is used. See 1926.408(c)(3)(iii).

• If using a special separation method, document and verify equivalent protection to prevent accidental contact or induction.

Where practicable, communication conductors on poles should be located below light or power conductors to reduce the chance of accidental contact. See 1926.408(c)(3)(ii).

• Pole installations should follow utility practice and local codes to maintain safe separation and accessibility.

No. Communications conductors shall not be attached to a crossarm that carries light or power conductors. See 1926.408(c)(3)(i)(A).

• This prevents mixed conductor configurations that increase risk of accidental contact or damage.

Masts and metal structures supporting antennas must be permanently and effectively grounded without splice or connection in the grounding conductor. See 1926.408(c)(5)(ii).

• Avoiding splices helps maintain a low-resistance continuous grounding path for lightning and fault currents.

If aerial cable sheaths entering buildings are exposed to contact with electric light or power conductors, the metal sheath must be grounded or interrupted near the entrance by an insulating joint or equivalent device. Transmitters must be enclosed in a metal frame/grill or separated by a barrier and all metallic parts must be effectively grounded; external metal handles and controls accessible to operators must also be grounded. See 1926.408(c)(5)(i) and 1926.408(c)(5)(iii).

• When equipment is unpowered but connected to a coaxial cable with an effectively grounded shield, it is considered grounded under the provision.

Not entirely. Communication system installations covered by 1926.408(c) need not comply with 1926.403 through 1926.408(b) except they must comply with 1926.404(c)(1)(ii) and 1926.407. See 1926.408(c).

• Confirm applicability and follow the referenced provisions for wiring methods and protective equipment where required; see 1926.404(c)(1)(ii) and 1926.407.