Prior to the 2017 edition of the NEC, 120-volt receptacles equipped with USB charging outlets had not been addressed by the National Electrical Code.
Universal Serial Bus (USB) connections have been around since the 1990s and are widely used to charge portable devices and computer peripherals, as well as transfer data.
Relatively new on the scene is the 120-volt receptacle with a built-in USB charger, this device is now widely available and growing in popularity. With most of us charging multiple devices every day, consumers embracing a 120-volt receptacle equipped with an outlet to serve the most popular charging cord in the US is no surprise.
While these devices are designed to fit a standard duplex receptacle wall outlet box, not all of them will be equipped with a 120-volt duplex receptacle. Some include just a single 120-volt receptacle with USB outlets. While others are equipped with nothing but USB charging outlets. Whichever configuration you choose, pay attention not to fall outside of compliance with NEC Code section 210.52, for the required placement of receptacle outlets along a wall space. While this USB device is an excellent addition to a wall space, it fails to negate the requirement for a receptacle in any wall space deemed to require one when the NEC is the standard for electrical work.
The NEC Code Making Panel (CMP) has addressed the growing popularity of these receptacle/USB combination devices by adding two basic Code requirements to the NEC in this 2017 Code cycle. The inclusion of this device in this new Code sub-section 406.3(F), will help ensure the device is safe for consumer use.
Code section 406.3 (F) is a brief Code section. It simply states: A 125-volt 15- or 20-ampere receptacle that additionally provides Class 2 power shall be listed and constructed such that the Class 2 circuitry is integral with the receptacle.
So, the two requirements concern:
- Using only a listed device, and
- The way the device is constructed.
First, what do we mean when we say “listed?”
Article 100 from the NEC defines listed as:
Equipment, materials, or services included in a list
published by an organization that is acceptable to the authority
having jurisdiction and concerned with evaluation of products
or services, that maintains periodic inspection of production of
listed equipment or materials OR periodic evaluation of services,
and whose listing states that either the equipment, material, or
service meets appropriate designated standards or has been tested
and found suitable for a specified purpose.
Therefore, listed equipment must be on a list published by an approved company that conducts testing.
There are many Nationally Recognized Testing Laboratories (NRTLs) that can certify that equipment meets a given standard. The example above is listed by the Canadian Standards Organization (CSA). The small “US” mark below the emblem indicates it is approved for use in the United States. There are other listing organizations, such as Intertek, UL, and FM. OSHA maintains a list of approved NRTLs on their website https://www.osha.gov/dts/otpca/nrtl/nrtllist.html
NRTLs must be recognized by OSHA to list products sold in the US.
Listed products often meet a given standard. Standards organizations write the requirements that the product must meet during testing. UL is the most recognized NRTL and is also a standards agency. Other standards agencies include ANSI, ASTM, and FMRC.
The product standard for receptacles, ANSI/ UL 498, contains requirements that pertain to this type of 120-volt / USB combination outlet. UL 1310 is another applicable standard.
Why is it important to use a listed product? Any electrical product has the potential to cause damage or injury. Unlisted products such as USB outlets can be manufactured anywhere, sometimes with zero oversight. As demand rises, and these devices pour into the market, they have the potential to expose users to harm, including fire and shock hazards. A device built and tested by a NRTL to meet a given standard is much more likely to be safe than one that is not.
This is especially important when we consider the circuitry used in this device. We have 120-volts coming into a product that contains a transformer to produce low-voltage (class 2) DC power. If 120-volt current were to “leak” to the low-voltage USB output, the results could be disastrous. Unlisted units are prohibited and must not be allowed.
In addition to being listed, the power supply must also contain the class 2 circuitry integrally. What does that mean? We can see similar language in 406.6 (D), where receptacle faceplates with nightlights (with or without a USB charger) are required to have circuitry that is integral with the cover. In other words, the device cannot require additional physical connections to the 120-volt circuit. Previously, some face plates with USB ports required that the installer make wired connections to the existing 120-volt wiring. This is now specifically prohibited by code. They must be integral, one unit.
When installing a listed USB charging device in a wall space, care must be taken not only to ensure that the installation is not eliminating an outlet required by the NEC, but to note whether the device has 120-volt outlets. If it does, it must be tamper-resistant if it is to be installed in a dwelling or one of the other locations mentioned in NEC 406.12.
Most available devices are tamper-resistant, but it is important to make sure.
Installers must also take care to make certain devices are listed and that Class 2 components are constructed integral to the assembly.
Code section 406.3 (F) is a welcome addition to this 2017 Code cycle, as it helps the installer, AHJ, and consumer ensure a safe product is being installed.
At some point this technology may give way to widespread wireless charging, but as it stands USB charging technology is abundant, and it is bound to be with us for years to come. Proper application of the electrical code is critical in order to keep everyone safe.