Cordsets have come a
long way. Because cordsets do not consist of continuous conductors, the
National Fire Protection Agency (NFPA) considered them "splices" and therefore
unusable for power distribution in many industrial applications. This ruling
changed in 2002 when NFPA 79 was revised to allow the use of molded-on cordsets
featuring quick-disconnect connectors and rugged cable for exposed-run installations.
These connectors could now be used to
power motors, pumps and other
When "installed to closely follow the surface and structural
members of the machinery" (NFPA, 2006, 79-6), cordsets can now be used in place
of conduit and raceways - allowing engineers to design and install a system
more efficiently than prior methods.
Before this revision to NFPA 79, hard wiring was the primary
option for power distribution and all wires were required to be run through
protective conduit to prevent wire damage. Junction and pull boxes were
frequently used for protection of the conductors and terminations, and users
needed to install, support and run raceways from one part of the equipment to
the next to power multiple sections at once. In some cases, gutter boxes and
other approved wire methods were also used.
These requirements resulted in excess equipment costs, while the
lack of flexibility and the significant time required for installation led to
expensive downtime for many users. In addition, when large projects were commissioned at one site and
installed at another, teams of electricians were often required to re-assemble
the equipment once it was moved to the site of installation. These issues were
also a factor when relocating or reusing equipment.
To alleviate many of these concerns, molded-on cordsets
were introduced with a modular, quick-disconnect design for more efficient
installation. In a cordset, all wires are bundled into a single cable clad with
a jacket material designed to withstand diverse environmental conditions,
including water, oil and temperature fluctuations. By eliminating the need for
conduit and individual terminations for each wire, cordsets deliver
Environmentally protected cable was developed to provide the same
crush and impact resistance as conduit to withstand the toughest industrial
conditions. It can be used for distributing 15 to 40 amps of power from one
machine to another, including on conveyor lines and other large-scale systems.
When used for loads such as motors or pumps, cordsets can lead to a decrease in
the equipment replacement time due to ease of installation. So long as the
equipment load and other parameters do not change, molded-on cordsets do not
require recommissioning, making relocating, rerouting or servicing of equipment
- particularly in areas requiring certification - more convenient and,
therefore, cost-effective. Additionally, cordsets do not require the high cost
of engineering and labor associated with the installation of conduit and
raceways. As a result, labor can be reduced by up to 40 percent using molded-on
cordsets, depending on the scope of the project.
Once a type of cordset
has been selected to meet unique environment requirements (such as water
resistance or high temperatures), designers should consult tables provided
within the NFPA 79 code to determine the appropriate ampacity of the cordset.
Ampacity is dependent upon the number and size of the conductors. It is
recommended to use one conductor for a protective earth ground, and it should
be positioned as close as practical to the load conductors to minimize
impedance in the protective earth circuit in case of a fault. Some cordsets are
manufactured to include a protective earth ground within the cord itself, which
ensures that a protective ground is immediately adjacent, or as close as
practical to the power conductors.
Though the NFPA 79 code allows cordsets to be exposed on the
surface of the system, they must be protected from damage that could occur if
the cordsets hang loose, droop or are obstructing doors or moving parts during
normal everyday use. To prevent movement, as well as maintain support to the
equipment, cables are to be supported and fastened "every 305 mm (12 inch) in a
non-vertical run; every 914 mm (36 inch) in a vertical run; when suspended in
air spanning a distance up to 457 mm (18 inch)" (2006, NFPA 79-36). Additional
protection measures such as guard railings or walk/drive overprotective devices
may be used to prevent damage. An alternative method is to install the cordset
in a wireway or deck cover. Sections of individual exposed lengths of cable are
allowed in these applications up to 15m (50 ft).
Installation Design Considerations
While terminal blocks and enclosures are not required in
cordset installations, cordsets still must be supported at all terminations. This design reduces pressure caused by the
cable pulling downward on the terminations and receptacles, thus increasing
reliability and minimizing failures at these connections. Cable ties, supports
or clamps can be used to support both the cable and terminations. Cable ties
should be snug, but not over-tightened, and cut flush to protect workers as
well as to prevent a possible snag point for other cables. Throughout the
system design process, design engineers need to ensure that neither the cable
nor the insulation in the selected cordset could be damaged during installation
or during operation due to system design.
By adding service loops or extra length to the cables, designers
can make it easier for users to more easily connect or disconnect the cordset
to and from a load or device. For example, a loop may be used to connect a
small motor, so that it may be disconnected and removed without requiring the
cable to be detached. Loops should be kept as small as possible to minimize
Quick-disconnect connectors are not intended for disconnection
under a load. Therefore, no power should be delivered via any connectors with
exposed male pins, as this would pose a shock hazard. The power should always
end on the female connector. To prevent damage or dirt from entering the
devices while unplugged, cover any externally mounted receptacles with closure
caps - protecting the cable until it is reconnected.Jay Bartsias is product manager-connectivity at TURCK.