Electrical Systems Design-Wiring Methods

Can we run the equipment bonding jumper as a separate conductor on the exterior of a raceway?

We may under some conditions.

Generally, do we run all conductors of the same circuit in the same place?

Unless specifically permitted by another code provision, all conductors of the same circuit, including the grounded conductor, the bonding conductor, and the EGCs, shall be run together in the same raceway, cable tray, auxiliary gutter, cablebus assembly, trench, cable, or cord.

What section contains the conditions outlining when the requirement that all conductors of the same circuit be run together need not apply?

Section 300.3(B)

When can conductors of different system occupy the same raceway?

When they’re 1000V or less. They can be AC or DC. 

When we run conductors of different systems in the same raceway, how do we determine the required insulation rating?

All conductors shall have an insulation rating equal to the highest circuit voltage applied to any conductor within that raceway or wiring enclosure

What does 300.3(C)(1) do?

300.3(C)(1) permits the use of power and control wires from two different systems to be installed in a single raceway to supply a motor load. This section also allows the secondary wiring of electric discharge lamps rated 1000 V or less to occupy the same luminaire, sign, or outline lighting enclosure as the branch circuit conductors where the secondary conductors are rated for the voltage involved.

What protection do the conductors in raceways and cable assemblies require?

The conductors inside raceways and cable assemblies require protection against penetration by nails and screws.

How far do holes drilled into framing members to allow raceways or cables need to be from the nearest edge of the wood member?

1 1/4”

What does Table 300.5 do?

Table 300.5 establishes the minimum cover requirements that cables and raceways shall have when installed in the ground.

What is cover?

Cover is the shortest distance measured between a point on the top surface of any direct-buried conductor, cable, conduit, or other raceway and the top surface of a finished grade, concrete, or similar cover.

How far below finished grade should cables an conductors emerging from the ground be protected from physical damage?

All cables and conductors emerging from the ground shall be protected from physical damage to a maximum depth of 18″ below finished grade.

How high above finished grade do cables and conductors installed on the side of a pole or building need physical protection?

8’ above finished grade

How can we provide this physical protection?

We can use EMT, RMC, IMC, Schedule 80 PVC, RTRC-XW, or equivalent as determined by the AHJ.

What do we need to do with service laterals buried 18” or more that aren’t encased in concrete?

They need to be identified with a warning ribbon placed in the trench at least 12” above the installation.

How much airspace is required in wet locations?

In wet locations, there shall be at least 1/4” airspace between the electrical system and the wall or supporting surface. 

What problems do installed raceways that are exposed to different temperatures present?

Condensation may build up in the raceway system. The temperatures can cause the raceway system to expand and contract.

How shall we bond together all non-current-carrying metallic parts of an electrical system?

They shall be bonded together with a permanent and continuous bonding method. If the raceway system is nonmetallic, these non-current-carrying metal parts must be bonded to the EGC.

What section governs how raceways, cable assemblies, boxes, cabinets, and fittings are fastened?

Generally, all raceways, cable assemblies, boxes, cabinets, and fittings must be securely fastened in place according to Section 300.11(A).

What does Section 300.11(B) require?

Section 300.11(B) requires wiring systems installed within the cavity of a fire-rated floor-ceiling or roof-ceiling assembly to be secured and supported by identifiable independent means.

What does the exception to Section 300.11(B)(1) say?

Section 300.11(B)(1), Exception, allows the ceiling assembly to support the wiring system if the ceiling assembly and support of the wiring system were both tested together as part of the fire-rated assembly.

Can the grounded conductor of a multiwire branch circuit be dependent on device connection?

No. 

What is the only circumstance where we can open the grounded conductor of a multiwire branch circuit?

The grounded conductor of a multiwire branch circuit shall never be opened unless power has been disconnected from all of the ungrounded conductors that make up the multiwire circuit.

What do we do when we run multiwire branch circuits from outlet box to outlet box?

When a multiwire branch circuit is run from outlet box to outlet box, the terminal screws of a device, such as a duplex receptacle, shall not be used to make the grounded conductor continuous. Additionally, the grounded conductor shall not be spliced by using the back-stab connections of the receptacle. All the grounded conductors of a multiwire branch circuit within an outlet box shall be spliced together with a tail provided for connection to the device. If this device were replaced while the circuit was energized, the grounded conductor would not become open.

What do we need to put at each connection, splice point, outlet, switch point, junction point, or pull point?

A box, conduit body, or fitting shall be installed at every splice point, outlet, switch point, junction point, or pull point unless permitted in 300.15(A) to (L).

What does Section 300.15(A) say?

Per Section 300.15(A), a box or conduit body shall not be required where the conductors are contained in wiring methods with removable covers, such as wireways, multioutlet assemblies, auxiliary gutters, and surface raceways. The cover must be accessible to provide access to the splice(s) after the wiring method is installed.

Do we need a box or conduit body where cables enter or exit conduit/tubing used for support or protection of the cable?

No.

What does Section 300.15(C) say?

Section 300.15(C) requires a fitting to be installed on each end of the conduit or tubing being used to provide support or protection in order to protect the cable from abrasion.

What does Section 300.15(F) say?

Section 300.15(F) allows identified fittings to be used instead of boxes or conduit bodies in the connection of conduit and cables. Splices and terminations are not permitted in the fitting, and the fitting must be accessible after installation unless it is listed

for concealed installation.

How shall we arrange AC conductors installed in metal raceways and enclosures?

AC conductors installed in metal raceways or enclosures shall be arranged so as not to cause induction heating of the metal raceways or enclosures. To accomplish this, all phase conductors, grounded conductors (if used), and EGCs shall be grouped together.

Why does arranging circuit conductors together in metal raceways eliminate inductive heating?

Since all the circuit conductors are grouped together, the magnetic fields around each individual conductor cancel out. This eliminates the inductive heating effect on the ferrous metal.

What do we need to do when we have single conductors carrying AC current that have to pass through metal?

Single conductors carrying AC current must not pass through metal with magnetic properties unless the inductive heating effect is minimized by cutting slots in the metal between the individual holes through which the individual conductors pass.

How should conductors carrying ac current enter a metal enclosure?

Through the same hole

What do we need to do whenever an electrical system penetrates a fire-resistant wall, floor, or ceiling?

. Whenever an electrical system penetrates a fire-resistant-rated wall, floor, or ceiling, the opening around the penetration shall be fire-stopped using approved methods to restore the fire resistance rating. Installers should request detailed drawings that show the approved methods for sealing fire penetrations for a project. All penetrations must be executed exactly as detailed in the drawings. The manufacturer of the approved fire penetration compound can be contacted for additional information if help is needed.

What can we run in ducts or plenums used for environmental air?

MI, MC, EMT, FMT, IMC, or RMC may be run in ducts or plenums used for environmental air. Flexible metal conduit is permitted in these ducts and plenums provided the length does not exceed 4′ and it is used to connect physically adjustable equipment and devices. The connectors used with this flexible conduit shall effectively close any openings in the connection.

What is an other space?

An other space is the space over a hung ceiling used for environmental air.

What does the exception to Section 300.22(C) do?

Section 300.22(C), Exception permits NM cable, for example, to pass through a closed-in stud or joist space used as a return in a forced-air heating/air conditioning system. This exception applies only to dwelling units.

When can we run wiring in air-handling areas beneath raised floors of computer/data processing equipment?

When the six conditions required by 645.4 are met.