AC Power Cords Explained
Choosing the right power cord for any application
The humble power cord, a power cable with a plug or receptacle on each end, sounds like a simple product. But there's more to a power cord than meets the eye. In this article, we delve into the various types of power cord available and the features you should consider when buying a power cord.
Types of Power Cord
Replacement Power Cords – these products replace the original cord that came with a powered device, such as a laptop, game console or TV. This might be because the original was damaged or lost, the device will be used in another country, or a cord of a different length is needed.
Extension Cords – an extension cord is a perfect solution when you need the flexibility to place a device further from a power outlet. Extension cords extend an existing power cord so it can reach an outlet. Extension cords can be up to 100-feet (30 meters) in length.
Power Cord Splitter – a power cord splitter allows two or more devices to share an AC wall outlet, saving space and reducing cable clutter. Depending on the number of outlets you need, a splitter might be more cost-effective than a power strip too.
Adapters – power adapters convert from one plug type to another. For example, a NEMA 5-15R to C14 adapter would allow you to connect a server with a NEMA 5-15P plug to a UPS or PDU with a C13 outlet.
Hospital-Grade Power Cords – also known as "green dot" power cords, these products are specifically designed for use in medical facilities and meet stringent ANSI/UL and CAN/CSA standards that help protect patients and staff from shock hazards.
PDU Power Cords – these power cords connect servers and networking equipment to the power outlets on rack mounted or vertical PDU. They come with a variety of connectors, including C14 to C13, C20 to C19 and NEMA 5-15P to C13. To make the most of space in a crowded rack, these cords are often different lengths, depending on how far the device is from the PDU outlet.
How to Choose the Right Power Cord
Thinking of buying a power cord? Here are the main factors to consider:
Cord Length: Determine the distance between the device and the outlet and choose a cord with the appropriate length to minimize the risk of tripping over a cord that's too long or not being able to reach the outlet with a cord that's too short.
Voltage & Current: Make sure the cord's voltage and current rating match the requirements of the device you're using it with.
Plug Type: Ensure the plug type of the cord matches the receptacle or outlet that you'll be using it with. Different countries have different plug types, so make sure to choose a cord with the right type of plug for your region.
Equipment Class: For certain equipment, such as medical devices, the power cord must meet specific safety standards and certifications. Make sure to choose a cord that meets the appropriate standards for your device.
American Wire Gauge (AWG)
In the United States and Canada, wire size or thickness is expressed as an AWG value. The smaller the number, the thicker the wire. The largest wire size in the AWG system is 0000 AWG and the smallest is 40 AWG. Note that 12-gauge and 12 AWG are the same thing.
Most other countries, notably European countries, measure the cross-section of the wire in square millimeters. IEC 60228 defines a set of standard metric gauges.
When you know the length and current rating you need, you can select a power cord with the right gauge.
Current Rating
The current or amperage rating for a power cord depends on the device it will power. The amperage rating is the maximum amount of current it can safely carry. The device's specifications should state the required amperage, and the cord should be rated for at least that amount.
To determine the amount of current required by a device, you can use one of the following methods:
- Check the device's specifications or manual for the rated current (in Amps)
- Use an ammeter to measure the current drawn by the device while it is in use
- Your device's nameplate or manual may specify wattage instead of current. Calculate the current using the formula Watts/Volts = Amps (e.g. 3600W / 240V = 15 Amps)
Gauge
Gauge refers to the thickness of the wires inside the cord, which determines its electrical conductivity and maximum current carrying capacity. A lower gauge number indicates a thicker wire, and a higher gauge number indicates a thinner wire. Common gauges for power cords range from 18 to 10 gauge. As a rule, higher current and longer lengths will require a cord with a lower gauge number.
| Usage | Cord Length (ft.) | Cord Length (m) | Max. Current (amps) | AWG | OD (mm2) |
|---|---|---|---|---|---|
| Light Duty | 50 | 15 | 13A | 16 - 18 | 0.82 - 1.31 |
| 100 | 30 | 10A | 16 - 18 | 0.82 - 1.31 | |
| Medium Duty | 50 | 15 | 15A | 14 | 2.08 |
| 100 | 30 | 13A | 14 | 2.08 | |
| Heavy Duty | 100 | 30 | 15A | 12 | 3.31 |
| Extra Heavy Duty | 100 | 30 | 20A | 10 | 5.26 |
Voltage Rating
The voltage used in a country depends on the electrical grid and infrastructure in that region. In the United States, the standard voltage is 110-120V. In most European countries, the standard voltage is 220-240V. In some countries, such as Japan, Australia, and parts of South America, the standard voltage is 100-127V.
The voltage rating of a power cord is the maximum voltage it can safely handle. The device's specifications should state the required voltage, and the cord should be rated for at least that voltage.
It is important not to exceed the voltage rating of the cord, as this can cause it to overheat, become damaged, or pose a fire risk. If the device requires a higher voltage than the cord can safely handle, it may be necessary to upgrade to a cord with a higher voltage rating.
Plug Type
There are 15 plug types in common use around the world. The International Electrotechnical Commission (IEC) has assigned a letter to each, ranging from Type A to Type O, and created a handy tool to help travelers select the right power adapter or exporters to know if a device can be powered in a particular country.
The United States, Canada and Mexico use the two-prong, ungrounded Type A (also known as NEMA 1-15P) and the three-prong, grounded Type B (NEMA 5-15P).
In Europe, Britain uses a three prong Type G plug, also referred to by the British Standard BS 1363. In mainland Europe, most countries use the ungrounded Type C and grounded Type F.
Two-prong plugs (NEMA 1-15P) come in two varieties: polarized and non-polarized. A polarized plug is easy to recognize because the prongs are different widths, ensuring that they can only be plugged in one way. The wider prong/slot is the "neutral". The other is "hot".
Non-Polarized Replacement Power Cord, NEMA 1-15P to IEC-320-C7
Three-prong plugs (NEMA 5-15P) have an extra ground pin in addition to hot and neutral wires.
Typical Desktop Computer Power Cord, NEMA 5-15P to IEC-320-C13
Special Features
Coiled Power Cords
A coiled power cord can stretch and contract like a spring. When in use, the cord can be extended to its full length, and when not in use, it can be contracted to a smaller size for easy storage. The spiral design of the cord provides a convenient and compact solution for users who need to bring power to different locations, as the cord can be easily carried and stored when not in use.
Locking or Gripping Plugs
Locking or gripping plugs are a type of electrical plug that have a locking mechanism to secure the plug in the receptacle. The locking mechanism usually consists of a sleeve or collar that rotates around the plug and locks it in place, preventing it from being accidentally disconnected. This type of plug is commonly used in industrial, commercial, and outdoor applications where a secure connection is important, such as in power generation, construction sites, and temporary power setups.
Locking plugs come in a variety of shapes and sizes, with some of the most common types being NEMA L5-15, NEMA L6-20, and NEMA L14-30. These plugs are designed to be used with matching receptacles, which have the corresponding locking mechanism to secure the plug in place.
Locking or gripping plugs provide a safe and secure connection for electrical power, which is particularly important in applications where vibration, movement, or exposure to the elements can cause a non-locking plug to become loose or disconnected.
Right-Angled (90-degree) Plugs
Right-angled plugs have a 90-degree bend in the cord leading to the plug body, allowing the plug to be plugged into a wall outlet at a right angle. This design allows the plug to fit in tight spaces, such as behind furniture or other equipment, where a traditional straight plug might not fit. The right-angle design also reduces the strain on the cord and plug, which can help to prevent damage to the cord and plug over time.
Piggyback Plugs
A piggyback plug allows two devices to be plugged into a single electrical outlet. It typically consists of a plug with prongs on one side and a socket on the other, so another device can be connected to the same outlet simultaneously. This type of adapter can be useful in situations where there are limited outlets available or when it is necessary to conserve electrical power.
Power Cable Jackets
If you look closely at a power cord jacket, you'll see an alphabetic code. A common example is "SJTW". The combination of letters defines the specific type and properties of the cable jacket.
Each of these letters designates a usage rating derived from the National Electrical Code. The most common power cord jacket ratings in North America are:
- SJT (Service Junior Thermoplastic)
- SJTW (Outdoor-Rated Service Junior Thermoplastic)
- STOW (Service Oil Resistant Thermoplastic Overall Wiring)
Color-Coding
In a recent study by the Uptime Institute, 42% of data center outages were caused by human error. One way to reduce this number is to color-code power cords. For example, red cords cannot be disconnected under any circumstances, but green cords can be disconnected without causing downtime.
Colored power cords are often more attractive than the standard black. For instance, if you have a white kitchen or white desk in your office, a white cord might blend better than another color.
Questions & Answers
What is the maximum length of a power cord?
The maximum length of a power cord is determined by safety and performance standards, as well as the specifications of the device it is connected to. As a rule, the maximum length for an indoor power cord is around 100-150 feet, and 50-75 feet for outdoor use. However, this can vary based on the cord's gauge and amperage rating.
What kind of power cord should I use with a portable generator?
There are three main considerations:
- Plug: Choose a plug that matches the outlet on your generator.
- Current (Amperage) Rating: Choose a cord capable of safely carrying the maximum current generated by a portable generator.
- Cable Jacket: The cable jacket should be rated for outdoor use (e.g. SJTW).
Can you plug a power strip into an extension cord?
Never plug a power strip or surge protector into an extension code. Power strips and surge protectors should be plugged directly into a wall outlet.
Can you plug an extension cord into a power strip?
Yes, you can plug an extension cord into a power strip. However, it's important to consider the combined amperage rating of the devices being used with the power strip, to ensure that the power strip is able to handle the total current load and prevent overloading and potential fire hazards.
What kind of extension cord should I use outdoors?
For outdoor use, choose an extension cord rated for outdoor use. These cords are made from durable materials that can resists UV rays and stays flexible in sub-zero temperatures. It is also important to select a cord that is rated for the amount of electrical power you will be using, in order to prevent overloading and fire hazards. Look for cords with a "SJTW" or "STOW" rating, which indicate that they are suitable for outdoor use. Additionally, be sure to use an extension cord with a proper grounding plug if you will be using electrical devices that require a grounded connection.
Is there a fire rating for power cords?
Yes, there is a fire rating for power cords. The rating indicates the cord's resistance to fire, heat and/or smoke. The most common fire ratings for power cords are:
- VW-1: Vertical Wire Flame Test
- FT1: Flame Test
Additional ratings cover use in riser and plenum spaces, but these should not apply to a pre-terminated power cord.
What is the difference between grounded and ungrounded power cords?
A grounded power cord has three prongs: a neutral wire, a hot wire, and a ground wire. The ground wire provides a safe path for electricity to follow in case of an electrical fault, reducing the risk of electrical shock or fire. An ungrounded power cord has only two prongs - a neutral wire and a hot wire. It does not have a ground wire, so it does not provide the safety benefits of a grounded cord.
Can I extend the length of a power cord?
Yes, you can extend the length of a power cord by using an extension cord. An extension cord is a cable with a plug on one end and a receptacle on the other end that allows you to connect a device to a power source from a greater distance. However, it's important to note that using an extension cord can also decrease the safety and performance of the device, as the cord's gauge (thickness) and length may not be able to handle the full power demands of the device. It's recommended to use the shortest cord possible and choose an extension cord with a gauge that is appropriate for the power needs of the device.
What is the maximum wattage a power cord can handle?
The maximum wattage a power cord can handle is determined by the wire gauge (thickness) and length of the cord. Generally, the thicker the wire gauge and shorter the cord, the more power it can safely handle. As a rule of thumb, a standard 16 gauge power cord can handle up to 13 amps, which is equivalent to about 1625 watts for a 120V circuit (13A x 125V = 1,625W). However, it's important to check the specifications of the specific power cord you are using to confirm its maximum wattage handling capacity. Overloading a power cord can pose a fire hazard and potentially damage the cord or the connected device.
Why is a power cord rated 125V when the input voltage is only 120V?
In the US, a power cord rated for 125V can handle voltages higher than the standard 120V to account for voltage fluctuations that may occur in the electrical grid. The standard voltage range in the US is between 110V and 120V, but in practice, the voltage may vary slightly due to factors such as changes in demand on the grid, power outages, or other conditions. By rating the power cord for 125V, the cord is designed to handle these voltage fluctuations without failing or posing a safety hazard. This allows for a margin of safety and helps ensure reliable and safe operation of the connected device.
What is a polarized power cord?
A polarized power cord has one blade that is wider than the other. The wider blade is the neutral prong, and the narrow blade is the hot prong. The idea behind polarization is to ensure that the electrical device is always connected to the power source in the same way, reducing the risk of electrical shock or fire. Polarization also helps to reduce electrical interference from other devices connected to the same power source. In general, lamps, appliances, and other devices that use a polarized plug must be used with a polarized outlet for safety.
What is the difference between a power cord and a power cable?
A power cord is a cable that connects an electrical device to a power source. It typically has a plug on one end that goes into an electrical outlet, and a connector on the other end that goes into the device. A power cable, on the other hand, is a more general term that encompasses any cable used to transmit electrical power, including power cords. So, a power cord is a specific type of power cable. The term "power cable" can also refer to heavier-duty cables used for industrial or commercial power applications, such as high-voltage electrical transmission cables.
Can I use my 120V laptop in a country with a 230V power supply?
Typically, no. Most laptops are designed to work with a specific voltage range and cannot safely handle voltage that is different from their design specification. If a laptop is designed for 120V, it may not work properly or can be damaged when connected to a 230V power source. However, if your laptop is equipped with a dual-voltage AC adapter, you can safely connect it to any voltage in the supported range.
- On the AC adapter label, look for "Input" or "Input Voltage".
- If it says "100-240V 50-60Hz" or similar, your 120V laptop can be safely connected to a 230V power source and vice versa.
Another challenge is the input plug on your laptop's AC adapter. If you are traveling, you may need to purchase a power cord with a plug that matches the outlets in your destination country.
Typical power cord for a 120V laptop sold in the US, Canada and Mexico
Power cord for a 230V laptop sold in the UK
How many amps are supplied by standard electrical outlets?
The number of amps supplied by outlets in a home or office varies depending on the country and the type of electrical system in use. In the US, standard electrical outlets typically supply between 15 and 20 amps. Power-hungry devices like air conditioners and large laser printer may require a dedicated circuit with a higher current.
What is a C39 outlet?
When you purchase a PDU, you need to plan for the number of C13 and C19 outlets you will need. This can be problematic when you later need to add or upgrade equipment (for example, newer, more powerful servers have adopted the C19 power cord rather than the lighter gauge C13). Designed by Eaton, the C39 outlet accepts both C14 and C20 plugs, providing future flexibility and avoiding the cost and inconvenience of ordering a new PDU when outlet requirements change.
What are harmonized power cords?
Harmonized power cords refer to electrical cables that have been standardized according to the specifications of international safety and performance standards. These standards ensure that power cords can be used safely and reliably in different countries and regions, and reduce the risk of compatibility issues and potential damage to electronic equipment. Harmonized cords are often marked with a harmonized code such as H05VV-F or H03VVH2-F to indicate that they meet the required standards.
How can I hide a power cord?
There are several ways to hide power cords:
- Use cord covers: Cord covers can be placed along the floor or mounted on the wall to conceal cords.
- Use cable ties or clips: Bundle cords together and secure them to the wall or baseboard using cable ties or clips.
- Install cord channels: Cord channels can be mounted on the wall or baseboard to hide cords while still allowing easy access to them.
- Use furniture: Place furniture like bookshelves, desks, or entertainment centers in front of cords to conceal them.
- Colored cords: Choosing a cord that is similar in color to the wall or carpet will help it to blend into the background.
Regardless of the method used, always ensure that cords are not a tripping hazard or impede safe movement in the space.
Do extension cords reduce power?
Using an extension cord can reduce the amount of power that is delivered to the device connected to it. This occurs because an extension cord adds resistance to the circuit, causing a drop in voltage. The length of the extension cord and the gauge (thickness) of the wire both play a role in how much the voltage and power are reduced. Using a shorter and/or thicker gauge extension cord will result in less reduction of power.
It's also important to note that overloading an extension cord can cause it to heat up and potentially start a fire. It's always best to use an extension cord that is rated for the amperage required by the device you are connecting to it.
Why Buy from Eaton?
We know you have many brands to choose from. On the surface, they may all seem alike. It's what you don't see that makes the difference. With Eaton, you get solid engineering, proven reliability and exceptional customer service. All our products undergo rigorous quality control before they are offered for sale, and independent testing agencies verify our products meet or exceed the latest safety and performance standards. Our commitment to quality allows us to back our products with industry-leading warranties and responsive customer service. It's the Eaton difference.
