Article 400 of the 2020 National Electrical Code (NEC) provides the requirements for flexible cords and flexible cables. OSHA also has requirements for them [29CFR1926.405(g)]. Think of cords as being designed for temporary wiring and cables as being designed for permanent wiring. This is how manufacturers of cords and cables refer to them. Article 400 makes a similar distinction (something apparent in Table 400.4).
OSHA requirements
Most NEC Chapter 3 Articles have a pattern of X.10 and X.12, where X is the Article number, 10 is the Section with “Permitted Uses” and 12 is the Section with “Uses Not Permitted”. OSHA does something similar with flexible cords and cables.
OSHA states the permitted uses in 29CFR1926.450(g)(1)(i)(A) through (H):
A. Pendants. For example, the pushbutton controller for a hoist. These are usually manufacturer-attached.
B. Wiring of luminaires. For example, high-bay luminaires might be wired with flexible cords.
C. Connection of portable lamps or appliances. For example, portable fans or heaters. These are manufacturer-attached.
D. Elevator cables. These are approved by the manufacturer and attached by a manufacturer-certified installer.
E. Wiring of cranes and hoists. These are manufacturer-attached.
F. Connection of stationary equipment to facilitate their frequent interchange. This is regarding equipment that is moved about, but not in the same sense that portable equipment is moved about. For example, a small parts washer sits at the end of a production line for a particular order. After that run, it might be moved to another line or just disconnected because there is only an occasional need to wash the finished parts.
G. Prevention of the transmission of noise or vibration. This is often done with high-vibration operations, such as stamping or mixing.
H. Appliances where the fastening means and mechanical connections are designed to permit removal for maintenance and repair. Kitchen refrigerators typically connect with flexible cord because you are supposed to roll them out and clean their coils.
OSHA does “Sec. 12” with 29CFR1926.450(g)(1)(iii)(A) through (E), except they call these “Prohibited Uses”:
A. As a substitute for the fixed wiring of a structure. For example, you can’t run SO cord from the panel to the receptacle in the wall.
B. Where run through holes in walls, ceilings, or floors. It’s easy to run an extension cord. To “be safe,” some DIY types drill a hole in a wall to get power from a receptacle on the other side (and of course, there’s no grommet!). This makes a cord act like permanent wiring, although it’s not designed for that purpose.
C. Where run through doorways, windows, or similar openings. Running a cord through a doorway is another “easy fix” that reduces safety. Flexible cords are soft-jacketed (that’s why they are flexible) rather than being encased in rigid conduit (that would make them useless as cords). What happens to such a cord when a door is shut on it? Or, because it’s in a doorway, it gets stepped on a dozen times with a door sill edge acting as a blade?
D. Where attached to building surfaces. It almost makes sense that saddle stapling a cord out of the way is a safety improvement. The problem is you are using the wrong wiring method. Remember, cords are meant to be temporary wiring. If you’re going to attach a wiring method to a building surface, use a wiring method designed for that purpose. A surface raceway is a good choice; it works well and looks better than an SO cord saddle-stapled to a wall.
E. Where concealed behind building walls, ceilings, or floors. Among other things, this leaves them vulnerable to undetected damage by rodents.
Using portable cords safely
It may be tempting for companies with a large investment in battery-powered hand tools to de-emphasize portable cords in their safety program — but that would be a mistake. Large stationary tools and many kinds of test equipment/hand tools are cord-connected. Plus, judicious use of cords can reduce battery management problems.
Cords are important enough that OSHA puts separate emphasis on them. For example, it refers to “flexible cords and cables” [1926.405(g)] and states a requirement for how “Type SJ, SJO, SJT, SJTO, S,SO, ST, STO cords” must be marked [1926.405(g)(2)(ii)]. Following that, it provides splicing [1926.405(g)(2)(iii)] and strain relief requirements [1926.405(g)(2)(iv)] for cords.
Thermo what?
Most cord jackets are composed of one or more of these three compounds: thermoset, thermoplastic, and thermoplastic elastomer.
- Thermoset jackets are heavy-duty grade or specification-grade rubber. Cords made from thermoset are flexible, even in extreme cold. These cords also have much higher melting temperatures than their plastic counterparts. They are noticeably heavier than the other types of cords.
- Thermoplastic is a light-duty plastic compound. Cords made from thermoplastic are suitable for light-duty use.
- Thermoplastic elastomer is a medium-duty plastic that is lighter than thermoset. For most jobs, thermoplastic is a good choice because it gives high performance with a relatively low weight. However, it can’t withstand the extremes that thermoset can.
Select the right cord
- Select a cord suitable to the working conditions. Wet conditions, oily conditions, and extreme cold merit a condition-specific cord. Using a cord not suited to the conditions of use puts the cord at high risk of insulation damage, followed by electrocution or an arcing fault.
- Always use an industrial-grade or construction-grade portable cord. One thing you will notice is these (being 3-wire cords) always have a ground plug. Don’t use an adapter with a 2-wire cord, use a 3-wire cord.
- Choose a cord long enough not just to reach the utilization equipment but to be safely routed to there.
Jacket designations
You’ll see these markings on a cord jacket.
- S: 600V service cord.
- J: junior service – 300V service cord.
- T: thermoplastic.
- E: thermoplastic elastomer.
- O: oil-resistant outer jacket.
- OO: oil-resistant outer jacket and oil-resistant insulation.
- W-A: approved (in the United States) for indoor/outdoor use (weather resistant).
- W: CSA approved (in Canada) for indoor/outdoor use (weather/water resistant)
Cord cautions
- Inspect the cord jacket for damage before use. Look for sharp bends or breaks.
- If a cord has tape on it, determine if it is there as a repair attempt. If so, destroy the cord and dispose of it.
- Inspect cord ends for damage, such as fraying or a broken ground plug.
- Route cords so they are not tripping hazards or exposed to damage. Where practical, use a cord protection device; there are many designs to choose from, and they are not expensive.
- If your firm relies on an assured grounding program, a GFCI is not a requirement. Otherwise, use a GFCI with any portable cord.
- If you must run a cord on a stairway, don’t route it across steps (this creates a tripping hazard). Run the cord lengthwise on the stairway and tape it to one side. If you really must run it horizontally, push it all the way to the back and tape it down.
- If a cord must cross a pedestrian pathway, run it in a cord guard and tape the cord guard in place. If the path is also a lift truck path, forget about the cord guard; run the cord overhead using a cord tree system or similar.
- If using an overhead system such as a cord tree, ensure you have sufficient vertical and horizontal clearances for people and vehicles.
- You may solve cord routing problems by finding a different power source or moving your tools and equipment. Even if this means connecting two long cords, it may be the best solution.
- Even if a cord is rated for oil or water, avoid running it into oil or water. While there is almost no chance that doing so will result in an electric shock, the operative word is “almost.” And almost is not good enough. You don’t know the history of that cord and what it’s been through. It may have insulation damage that you cannot see. Always give the cord the best chance of protecting you instead of making “optimum condition” your default assumption.
Cancel cord and cable confusion
To avoid confusing cords with cables, think of temporary versus permanent. An elevator cable is permanently installed, and a lamp cord is not. Cables are terminated via splice, bolted connection, or similar while cords are plugged in.
To select the correct type of cord or cable for the intended use, start with NEC Table 400.4. Other Art. 400 tables, such as the various ampacity tables, can help you refine your selection.
If you’re using a portable cord, think about how to route it from the receptacle (a GFCI unless you have an assured grounding system) to the utilization equipment. You want to protect it from damage and ensure it’s not a tripping hazard.
Mark Lamendola is an electrical consultant based in Merriam, Kan. He can be reached at [email protected].
