Shielded Wire In Power Cords: What You Need To Know

While shopping for the best power cord for electrical appliances, factors like cable length, gauge rating, and ampacity quickly come to mind. Ideally, you want a cord that delivers three critical metrics - performance, safety, and durability.  

But if you’re looking for a high-quality power cord for industrial applications or data centers, advanced specifications like weatherproofing elements and shielding will also be necessary. You deserve a cable that’s professionally tailored to fulfill the needs of its intended use environment.  

In this blog, we shall shine the spotlight on power cord shielding and what it entails. Some of the key areas the post will address include what is shielded power cord, the perks of shielded cables, and the different shielding materials available.  

Let’s dive in for an insightful read! 

Shielding is an electrical practice that involves adding an extra layer around power cord conductors to protect the cable from electromagnetic interference (EMI).  

A shielded AC power cable typically has a conductive material covering its midsection (the layer between the outer jacket and conductor wires).  

To better grasp the concepts of power cord shielding and electromagnetic interference, it’s important to step back and familiarize ourselves with electrical noise. 

Unpacking Electrical Noise 

In electrical parlance, noise refers to fluctuations in the amount of current and voltage that flows through an electric circuit. These vibrations are typically spontaneous and occur at relatively low amplitudes.  

Electrical noises exist in nearly all electronic systems, albeit in different intensities. The fluctuations are often due to the thermal motion generated by electrons as they flow through a circuit, as well as the quantized nature of the electrical charge. Despite their intensity, electrical noises can reduce the performance of a power cord and the connected equipment.  

Common human-made sources of electrical noise include using signal cables next to power cables, frequently switching between different power loads, and alternatingly plugging and unplugging power cords. The phenomenon may also result from natural sources like solar storms, solar flares, and lightning.  

The intensity of electrical noises typically depends on a power cord’s use environment and the type of equipment it’s connected to. Industrial plants (especially heavy processing factories like steel mills) and data centers are noteworthy environments associated with high electrical noise. As for appliances, heavy motors, generators, transformers, and relay controls are major culprits.  

Electrical noise is usually conducted or radiated as electromagnetic interference. Without proper shielding, it can significantly reduce equipment operation. 

What Does A Shielded Power Cord Look Like? 

You're probably already familiar with the general anatomy of NEMA power cords. Most electrical cables have two primary components.  

First is the outer insulation that protects the enclosed conductor wires from environmental damage. The insulation is typically made from polyvinyl chloride (PVC), although fiberglass, rubber, Teflon, and silicone may also be used.  

The second part is the actual conductors (and a ground wire for grounded power cords). These wires are usually encased in wear-resistant insulation.  

Now, shielded power cords have an additional component to their anatomy - the shielding material. The shield is usually a tube-shaped layer between an outer, weatherproof jacket and the individual conductors.  

Some power cords come with a single shield whereas others are double-shielded. In the latter case, the outer shield commonly features a braided mesh while the inner one comprises a metal foil, with aluminum being the most preferable metal.

Understanding the Mechanism of Power Cord Shields 

Most shields reflect excess electrical noise away from a power cord and/or direct the vibrations to the ground. This minimizes electromagnetic interference, improving the connected appliances’ safety and efficiency.  

Shielded cables function as a Faraday cage, which refers to an earthed cage or casing surrounding equipment to protect it from electrostatic and electromagnetic forces.  

A Faraday cage is the same concept used in automobiles and airplanes. If lightning strikes a car or plane, the occupants stand protected as long as they remain inside the vessels.  

Using shielded power cords blocks EMI signals generated from inside the cable from affecting the functionality of nearby electrical devices while also ensuring external interferences do not penetrate a power cord and impact its performance. 

Benefits of Using Shielded Power Cords 

As you may have gathered by now, the primary benefit of power cord shielding is to combat electromagnetic interference. The shield redirects excess electrical noise generated by power-carrying conductors, preventing interference with nearby equipment.  

Allowing EMI to build up in electric circuits unmitigated can impede signal integrity in data centers. Note that data centers have various electromagnetic signals that compete for attention. The constant interplay between these forces can significantly decrease the quality and performance of electronic devices, resulting in costly downtimes.  

Heavy industries, such as steel mills and foundries, are other notable environments that require shielded power cords. As these factories utilize energy-intensive machinery that are often powered up and down alternately, they can generate significant electromagnetic interference. Shielding helps to reflect the EMI, keeping industrial equipment in peak condition.  

Besides guarding against electromagnetic interference, power cord shields may also prevent radio frequency interference (RFI). RFI is a high-frequency interference that mainly results from wireless devices like cell phones, radios, televisions, and radars. Like EMI, RFI can degrade the performance of electronics. 

Power Cord Shielding Versus Insulation 

Although commonly used interchangeably, power cord shielding and insulation are fundamentally different.  

Insulation protects electrical cords from mechanical and environmental factors that could impede the cables’ performance and pose hazards to users. It has minimal effects on electromagnetic and radio frequency interferences.  

Since both insulation and shield play critical but distinct functions, they’re essential power cable features to consider while shopping for these resourceful electrical devices.  

What Are Power Cord Shields Made Of? 

The table below highlights the most common cable shielding materials, along with their standout features: 

What Makes Up The Ideal Power Cord Shield? 

Each power cord shielding material has its standout features. Therefore, it’s essential to research every option extensively before determining its suitability.  

As evident from the table above, power cable shielding made from metallic foils and tubes has the highest frequency range. However, foils can be painfully difficult to terminate. Besides, their high resistance impedes their effectiveness against low-frequency EMI.  

When it comes to individual shielding materials, the choice is usually between copper and aluminum. Compared side by side, aluminum outperforms copper due to its lighter weight and superior reflectivity.  

Power strip shielding materials have varied design specs, each impacting their performance.  

Flexible options like braided wires can be instrumental in workplaces where electrical cables are frequently moved about or routed through tight spaces. But in environments that require bulk wires, shield weight would be a bigger consideration.  

Thickness is another design spec that affects the efficacy of a power cord shield. Denser shielding materials are more effective against higher-frequency electromagnetic and radiofrequency disturbances.  

As you analyze the density of a power cable shield, you also want to pay attention to the number and size of the openings. Double-shielded cables perform better than those with a single shielding layer. That’s especially true if the two layers are made from different materials. However, the first layer should have no openings to prevent signal leaks.  

Needless to mention, power cord shielding should be properly grounded and electrically continuous to safely channel EMI and RFI. Ensure the shields are properly terminated too.  

All in all, a power cord’s ideal shielding material ultimately comes down to its intended use environment. For instance, wire-based shields are more effective at low frequencies due to their low resistance. However, as the quantity of EMI increases, the focus shifts from resistance to coverage. That explains why metal foils and tubes are best suited for a larger frequency range.  

Best Practices for Power Cord Shielding 

It’s important to reiterate the significance of matching power cord shielding with the intended application. While a foil shield alone may provide sufficient protection in low-to-moderate EMI, you’ll require a foil-braid combination in high-noise environments.  

In the same vein, consider the cable’s design before adding it to your electric circuit. For instance, flex cables are better off with spirally wrapped as opposed to braided shields. The spiral design supports continuous flexing without tearing.  

Below are other best practices when using power cord shields; 

• Always check the connections to ensure all connected equipment is properly grounded. 

• Use connectors whose shielding is compatible with your power cords. 

• Ground your shielded power cord at one end to minimize the risks of the channeled EMI triggering ground loops. 

• In high-voltage circuits, break the shield into multiple sections to reduce electrical shocks and performance malfunctions. 

FAQs

1. What distinguishes shielded cables from unshielded ones?

Besides distinctions in performance, shielded and unshielded power cords also differ in physical appearance.  

Shielded cables are typically thicker and more rigid than their unshielded counterparts. The extra thickness is due to the shielding layer(s) between the wire’s insulation jacket and conductor materials.

2. Which shielding material is best?

All power cord shielding materials can be suitable depending on the intended application and use environment.  

However, all factors were constant, and metal tube shielding outperformed other shielding materials and designs. 

3. How much do shielded power cords cost?

Shielding alone doesn’t determine the price of a power cord. Other key metrics include cable length, gauge, weatherproofness, and even the brand. A regular 12-gauge, 100-foot cable goes for between $20 and $60.  

Perhaps the key to emphasize here is that shielded power cords are comparatively more expensive than unshielded cables. Obviously, they make up for the higher cost with their superior performance. 

4. How durable are shielded power cords?

Shielded power cords can last anywhere from two to five years. The actual duration will depend on the cable’s current handling abilities, frequency of use, and prevailing environmental conditions. Power cords used in heavy industrial plants may wear out much sooner than those used in, say, data centers.  

Fortunately, you can implement certain tips to extend the durability of your shielded power cord. Those include connecting the cord to an appliance rated for similar ampacity, insisting on weatherproof cables, and unplugging the cords when not in use. 

5. What should I consider more while shopping for shielded power cords - EMI or RFI? 

Most power cord shields can protect against both EMI and RFI. Since the focus is on current and voltage fluctuations within connected appliances, prioritize industrial cables rated for higher EMI. 

Wrap Up 

Shielded power cords offer certain critical benefits over their unshielded counterparts.  

Notably, shielded cables stabilize the flow of electrical current through a circuit by minimizing the disruptive and destructive effects of electromagnetic interference. This can improve the performance of connected equipment, consequently reducing workplace downtimes and costly repairs caused when the appliances malfunction or stop working altogether.  

So, while shielded power cords are typically more expensive than unshielded cables, they’re worth every penny.  

In conclusion, remember that a power cord’s shielding status isn’t the only critical aspect when shopping for industrial cables. Ultimately, the cord should be rated for similar length, current, and voltage requirements as the equipment you plan to plug it into.