The words “listed” and “labeled” are repeated often in the National Electrical Code (NEC), and refer to devices or appliances that are designed and manufactured in accordance with the requirements of a “listing agency,” also called a Nationally Recognized Testing Laboratory or NRTL.
There are approximately fifteen certified listing agencies and, while they all follow the same standards when testing products, Underwriters Laboratory is the best known. When a product obtains UL approval, it is published in a list of ones that meet UL standards—which is what “listed” means.
Once the product has been listed, the manufacturer is allowed to put a label on it with the logo of the listing agency, like the UL mark shown above, and specify the use for which it was manufactured, which makes it “listed and labeled.” The product shown above is labeled as a “current tap,” a technical name for a plug-in multiple outlet power strip. Other examples would be “domestic range” or “heat pump.”
Because of the sterling reputation of nationally recognized listing agencies, any appliance or device that is listed and labeled will usually be quickly approved by the Authority Having Jurisdiction (AHJ), which is another name for the local building department. This is why manufacturers obtain listing and labeling for their electrical products.
An important fact to remember is that the NEC code requires that a listed and labeled product be installed according the instructions in the product packaging, and the product is only approved for the use specified by the manufacturer (per NEC 110.3(B)). This means that the instructions on the box or in the enclosed installation manual effectively become part of the code.
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Here’s links to a collection of our other blog posts about ELECTRICAL WIRING:
• Which house appliances need a dedicated electrical circuit?
• Can a short circuit cause a high electric bill?
• Can you use a light switch for a water heater disconnect?
• When did the requirement for two 20-amp kitchen counter appliance circuits begin?
• What is the maximum spacing requirement for securing NM-cable (nonmetallic-sheathed cable)?
• Is it alright to just put wire nuts on the end of unused or abandoned NM-cable or wiring?
• What causes copper wires to turn green or black in an electric panel?
• Is the latest edition of the National Electrical Code (NEC) the standard used for the electrical system of new homes?
• What are typical aluminum service entrance wire/cable sizes for the electrical service to a house?
• Why is it unsafe to bond neutral and ground wiring at subpanels?
• When was it first required that neutrals and grounds be separated (not bonded) on any panel past the main service panel?
• Should I get a lightning rod system to protect my house?
• Why is a strain relief clamp necessary for the cord connection to some electric appliances?
• Does a wire nut connection need to be wrapped with electrical tape?
• What is the minimum clearance of overhead electric service drop wires above a house roof?
• What is the difference between a UL rating for dry, damp, and wet locations?
• What is three phase electric service?
• What is a reliable way to tell if the electrical service is 3 phase or single phase?
• Can NM-cable (Romex®) be used to make a cord and plug to connect an appliance?
• What are the requirements for NM-cables entering an electric panel box?
• What is the color code for NM cable (Romex®) sheathing?
• Can I remove a 240-volt range receptacle and hard-wire the range?
• Why do some wires in an electric panel have tape wrapped around them near their connections?
• Why is undersize electric wiring in a house dangerous?
• Why is bundled wiring in an electric panel a defect?
• What causes flickering or blinking lights in a house?
• What is the voltage rating of a house electrical system?
• Why are old electrical components not always "grandfathered" as acceptable by home inspectors?
• What is tinned copper wiring?
• What is a conduit body or condulet?
• How can I find out the size of the electric service to a house?
• What could cause an extremely high electric bill?
• Can old electrical wiring go bad inside a wall?
• What are the code requirements for NM-cable (nonmetallic-sheathed cable or Romex®) in an attic?
• What is the difference between "grounded" and "grounding" electrical conductors?
• What does it mean when a wire is "overstripped" at a circuit breaker?
• What is an open electrical splice?
• What are the most common electrical defects found in a home inspection?
• What is the life expectancy of electrical wiring in a house?
• Do any pre-1960 houses have aluminum wiring?
• What is the gooey stuff on some of the wire connections in the electric panel?
• How much does it cost to rewire a house?
• What is an "open junction box"?
• What are the clearance requirements for an overhead electric service drop that is directly over or near a swimming pool?
• How dangerous is old electrical wiring?
• What is a ground wire?
• What are the most common homeowner electrical wiring mistakes?
• I heard that aluminum wiring is bad. How do you check for aluminum wiring?
• What is "knob and tube" wiring?
Visit our ELECTRICAL page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.