Though a seemingly simple device, a power cord is responsible for providing a critical function; it is the essential conduit through which electricity flows from a power outlet to a piece of equipment.
Despite consisting of just three elements, power cords are subject to a variety of regulations and standards ── underscoring the importance of their role. Power cord specifications vary among different countries, from the color of the wiring to the plug type.
When considering the power cords that will be deployed with your IT equipment in North America, it is helpful to have a general understanding of the various components and factors, including:
1. Type ─ There are two options when it comes to power cords: detachable and non-detachable. A detachable power cord, also known as a line cord or power cord set, consists of a plug, cordage and a connector or receptacle. A non-detachable power cord, on the other hand, is hard wired to the equipment enclosure, and is generally not meant to be removed. This type of power cord consists of a plug, the cordage and a strain relief device to secure the cord to the equipment.
2. Wiring ─ Power supply cords typically have three wires: the “line,” “neutral” and “ground.” In North America, the line wire is black, the neutral wire is white, and the ground wire is green.
3. Electrical rating ─ It’s imperative that a cord’s electrical rating is higher than that of the product being powered. Most product standards require the plug to be rated at least 125 percent of the equipment’s rated current. This consideration is due to the potential for an under-rated power cord to overheat and cause an electrical fire. Power cords designed for use with IT equipment are rated 125Vac/10A, but other higher ratings are also available.
4. Plugs ─ The NEMA 5 family of plugs and receptacles (the most common type in North America) typically has a male plug featuring two flat blades and a current rating that does not exceed 20 amps. For higher-rated current needs, a power cord featuring a NEMA L14-30P plug and NEMA L6-30R receptacle is rated at 30 amps. Depending on the type of plug and its intended use, it may include a third pin, or “ground pin,” which ensures connection to protect against insulation failure of the connected device. Typically, equipment with double insulation doesn’t require a ground pin and will be sufficient with a 2-pin plug. In order to maintain correct polarization between the plug and socket, typically one of the plug pins is either larger or wider than the other. In North America, the neutral pin is larger, so the plug can only be inserted into the larger socket opening, which ensures that the live conductor and the live pole are properly connected.
5. Cordage ─ In North America, the cord’s conductor size is rated in AWG (American wire gauge). The country also uses its own unique nomenclature to identify the cord type, including SVT, SJT, SJTW, ST, SPT-1, and SOW. All flexible power cords are tested to UL 62/CSA C22-2 No 49-14 standard.
6. Certification markings ─ The markings required for each country will differ for agency labels, certificates of compliance, letters of approval, certificates of approval or registration. These marking requirements are often different for the plug, cordage and connector. In North America, NEMA is responsible for developing standards for power cords, while agencies including UL and NRTL test and certify them. Be sure to look for certification marks such as UL and c-UL.
In terms of markings, all power cord components should include the manufacturer and type. Plugs and receptacles should also display the electrical rating and NRTL file number, while cords should include additional details including voltage and temperature rating, type of cable, NRTL file number, and the number of conductors and wire gauge.
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