Power strips are widely used in households and offices. Much of the time they are used because there are not enough outlets to meet the electrical demand. The proper use of a power strip usually does not cause a hazard. Improper use can cause safety issues such as electrical failure, possible fire hazard, equipment failure, or electrical shock. An example of using power strips unsafely is when they are “daisy chained” together.
The circuit breaker has an amp rating, the wire from the breaker to the outlet has an amp rating, the outlet has an amp rating, and each power strip has an amp rating.If you exceed that rating you will hopefully just cause the breaker/fuse to trip, but could also start a massive fire. When you draw more amps (aka current) than a wire is rated for then it gets hot, draw too much more and it will catch the plastic of the wire on fire.
All electric heating devices (stove tops, hair dryers, curling irons, etc) use this principle to create heat.Daisy chaining power supplies can allow you to easily exceed any of those amp ratings if you plug in high amp draw devices (vacuums, microwaves, power tools, or other small appliances/electrical motors).
Even worse is if you connect a small low amp strip to the wall, and then daisy chain a large high amp strip off of that. When you plug 12 amps of devices into the second daisy-chained power strip it will overload the 1st one; if you are lucky it has a built in a fuse and will trip, if not it will overload the power supply, burn the wiring, and possibly damage the devices plugged into it.
This is even more compounded if you use use an extension cord that is not rated high enough (12AWG is good for anything you would plug into a normal wall socket. 14 AWG can handle up to 15 for short run, 10–12 for long cord). Daisy chaining extension cords together can cause internal heating of cords, damage the insulation, and could damage the integrity of the cord. This prolonged activity could increase the chance of fire and electrical shock to the end user. Other hazards associated with this activity is overloading the main circuit breaker.
Daisy chaining goes against codes from the Occupational Safety and Health Administration (OSHA), National Fire Protection Association (NFPA), and Underwriters Laboratories (UL). These regulations and codes are listed as:
OSHA 29 CFR 1910.303(b)(2): Installation and use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.
OSHA Standard Interpretation: The Letter of Interpretation regarding power strips, an OSHA Director, Richard Fairfax (Fairfax, 2002), included this statement: “Manufacturers and national recognized testing laboratories determine the proper uses for power strips. For example, the UL directory contains instructions that require UL-listed RPT’s to be directly connected to a permanently installed branch circuit receptacle; they are not to be series-connected to other RPT’s or connected to extension cords.”
NFPA 1 Standard 11.1.4 (Bigda, 2016):
11.1.4.1-Relocatable power taps (RPTs) shall be of the polarized or grounded type with overcurrent protection and shall be listed.
11.1.4.2-The relocatable power taps shall be directly connected to a permanently installed receptacle.
11.1.4.3-Relocatable power tap cords shall not extend through walls, ceilings, or floors; under doors of floor coverings; or be subject to environmental or physical damage.
UL 1363 1.7 (Laboratories, 2015-2016):
A cord-connected RPT is not intended to be connected to another cord-connected RPT.
UL White book (2015-2016): The UL White Book states: “Relocatable power taps are intended to be directly connected to a permanently installed branch-circuit receptacle outlet. Relocatable power taps are not intended to be series connected (daisy chained) to other relocatable power taps or to extension cords.”
References
Bigda, K. (2016). NFPA 1: Electrical Fire Safety and Relocatable Power Taps (power strips). #FireCodeFridays, 1.
Fairfax, R. E. (2002, November 18). OSHA Director. Letter of Interpertation, p. 1.
Laboratories, U. (2015-2016). UL. Northbrook: Underwriters Laboratories, Inc.
Lavato, Mary. (2020, September). Construction News Sense: Electrical Safety Power Strips & Daisy Chaining p.1-2.