Electrical conduit

Electrical conduit provides very good protection to enclosed conductors from impact, moisture, and chemical vapors.

When installed with proper sealing fittings, a conduit will not permit the flow of flammable gases and vapors, which provides protection from fire and explosion hazard in areas handling volatile substances.

This is commonly used in commercial buildings to allow electrical and communication outlets to be installed in the middle of large open areas.

For example, retail display cases and open-office areas use floor-mounted conduit boxes to connect power and communications cables.

Both metal and plastic conduit can be bent at the job site to allow a neat installation without excessive numbers of manufactured fittings.

In applications such as residential construction, the high degree of physical damage protection may not be required, so the expense of conduit is not warranted.

For example, a long run of conduit as grounding conductor may have too high an electrical resistance, and not allow proper operation of overcurrent devices on a fault.

Wiring regulations for electrical equipment in hazardous areas may require particular types of conduit to be used to provide an approved installation.

Such locations would include food processing plants, where large amounts of water and cleaning chemicals would make galvanized conduit unsuitable.

The plastic material resists moisture[5] and many corrosive substances, but since the tubing is non-conductive an extra bonding (grounding) conductor must be pulled into each conduit.

Joints to fittings are made with slip-on solvent-welded connections, which set up rapidly after assembly and attain full strength in about one day.

Since slip-fit sections do not need to be rotated during assembly, the special union fittings used with threaded conduit (such as Ericson) are not required.

[3] Fiberglass conduit is available in multiple wall thicknesses to suit various applications and has a support distance very similar to steel.

High temperature, low smoke, no flame, classified area (Class I Division 2), and zero halogen versions are also manufactured for specialty applications such as subway tunnels and stations and in the US can meet National Fire Protection Association (NFPA) 130 requirements.

Flexible metallic conduit (FMC, informally called greenfield or flex) is made by the helical coiling of a self-interlocked ribbed strip of aluminum or steel, forming a hollow tube through which wires can be pulled.

FMC is used primarily in dry areas where it would be impractical to install EMT or other non-flexible conduit, yet where metallic strength to protect conductors is still required.

An assembly of these conduits, often called a duct bank, may either be directly buried in earth, or encased in concrete (sometimes with reinforcing rebar to aid against shear forces).

A duct bank will allow replacement of damaged cables between buildings or additional power and communications circuits to be added, without the expense of re-excavation of a trench.

While metal conduit is occasionally used for burial, usually PVC, polyethylene or polystyrene plastics are now used due to lower cost, easier installation, and better resistance to corrosion.

Conduit bodies differ from junction boxes in that they are not required to be individually supported, which can make them very useful in certain practical applications.

This type of "decorative" conduit is designed to provide an aesthetically acceptable passageway for wiring without hiding it inside or behind a wall.

Plastic raceway is often used for telecommunication wiring, such as network cables in an older structure, where it is not practical to drill through concrete block.

The term trunking is used in the United Kingdom for electrical wireways, generally rectangular in cross section with removable lids.

In North American practice, wire trough and lay-in wireways are terms used to designate similar products.

Innerducts are subducts that can be installed in existing underground conduit systems to provide clean, continuous, low-friction paths for placing optical cables, which have relatively low pulling tension limits.

Multiduct may be either a composite unit consisting of up to four or six individual innerducts that are held together by some mechanical means, or a single extruded product having multiple channels through which to pull several cables.

Conduit is of relevance to both firestopping, where they become penetrants, and fireproofing, where circuit integrity measures can be applied on the outside to keep the internal cables operational during an accidental fire.