SO Wire Applications


Below is a list of the permitted and prohibited applications of flexible (portable) cables and an explanation of the applications of SO wire.

Need to know how to select conductor sizes? See our selection guide for more information on flexible cable and a general overview of how to select conductors.

For information on what the letter designations mean, please see SO wire letter designations.

Flexible Cable Applications

The 2011 National Electric Code (NEC) specifies the following uses and prohibitions for flexible cable in article 400.7 and 400.8.

Permitted Uses for Flexible Cable(400.7)

• Pendants (i.e. suspension cable)
• Wiring for light fixtures • Connection of portable lights, portable and mobile signs, or appliances
• Elevators
• Cranes and hoists
• Connections of utilization equipment to facilitate frequent interchange*
• To reduce or prevent transmission of vibrations between parts (e.g. in automotives)
• Appliances that are readily removable to allow for maintenance or repair
• Connection of moving parts

*The wording may be confusing for #6, so we've included some definitions from the U.S. OSHA (Occupational Health and Safety Administration) to clarify the terms.

Equipment - A general term for any device, appliance, fixture (e.g. indicator lights), etc.

Utilization equipment - Any equipment that uses electric energy (e.g. for lighting, heating, transmission of signals, etc.)

Putting it all together, #6 simply means you can use flexible cords and cables for anything that uses electricity (equipment, device, appliance, fixture, etc.) and needs to be moved around.

Prohibited Uses for Flexible Cable(400.8)

Do NOT use flexible wiring:

• As a substitute for fixed wiring in a building or structure (though not all wiring in a structure will be fastened in place)
• For wiring that will run through holes in walls, ceilings, or floors
• for wiring that will run through doorways, windows, and similar openings
• for wiring attached to surfaces of buildings
• ** for wiring that will be concealed behind a building surface (i.e. wall, floor, or ceiling) or located above suspended or dropped ceilings. Please see the section on Defining "Accessible," "Concealed," and "Exposed" below for an explanation.
• if the cable will be installed in raceways unless allowed elsewhere in the NEC
• *** if the cable will be subject to physical damage

** Flexible cables are allowed for use under raised floors with removable panels because such wiring is not considered "concealed."

***Welding cable is a special type of flexible cable with its own set of codes covered in NEC chapter 6. This kind of cable is designed with physical damage resistance and durability in mind.

Exceptions to 400.8

Flexible cable IS permitted to be attached to surfaces of buildings if all the provisions in article 368.56(B) are met.


1) Cable is attached by an approved method.
2) The length of the cable from the plug-in device to a suitable tension support device does not exceed 1.8 m (6 ft). (Tension supports are like strain relief except supports are installed along the length of a cable and do not necessarily protect terminal joints).
Exception: Only in industrial environments where conditions ensure that only qualified persons service and maintain wiring installations, lengths greater than 1.8 m (6 ft) are allowed between the plug-in and a suitable cable support device as long as supports are provided at intervals no longer than 2.5 m (8 ft).
3) If the cable will be installed vertically between a tension support and the equipment.
4) Strain relief cable grips are installed at both the plug-in device and equipment terminals.

Defining "Accessible," "Concealed," and "Exposed"

To understand prohibition #5 and its exception, it is important to understand the NEC definitions for accessible, concealed, and exposed. The following definitions come from NEC article 100 in application to wiring methods.

Flexible cable is not permitted for use when attached to a building surface, but is allowed as wiring behind removable panels.


1) the wiring can be removed or exposed without damage to the building structure or finish, OR
2) the wiring is not permanently closed in by the building structure or finish (e.g. drywall is a type of building finish).


The wire is made inaccessible due to a building’ structure or finish. Flexible cables are not allowed for use as concealed wiring.


1) the wiring is on or attached to a building surface, OR
2) behind panels specifically designed to allow access (i.e. removable panels)

SO Wire Applications

SO wire has been largely replaced by SOOW cable, which has both an oil resistant outer jacket and conductor insulation and is rated for indoor and outdoor use. The -W suffix in SOOW means the cable is weather, water, and sunlight resistant and can be used in wet locations (see 2011 NEC table 400.4 note 15).

Our SO wire can be used as pendant cable, in damp and wet locations, and as connections for portable equipment. SO wire can also be used on theater stages, in control booths, and garages.

You may not use SO wire for any of the applications listed under the prohibited uses for flexible cable listed above.