Much like snowflakes, every copper wire is unique.

Well, maybe not every copper wire, but you can get granular specifying what product you need for a specific application.

Depending on the need, your wire could be bare copper or insulated, and made using solid or stranded conductors. It may be shielded with Mylar or insulated and jacketed with a plastic polymer. Your requirements will always dictate the wire you need, so know how your cable will stand up to the conditions around it.

But based on those same applications, you might end up with something you didn’t expect… “fat” wire.

What Makes Wire Fat?

The size of your wire and cable is dependent on a lot of factors, but the three main ones include:

  • Wire gauge – This is the physical size of the copper conductor. The smaller the number, the larger the wire diameter. Wires larger than #4/0 AWG are measured in MCM (thousands of circular mils), and the size increases alongside the number.
  • Insulation – The compound material surrounding the conductor is its insulation. “Typically, insulation thickness is related to the electrical performance of your wire,” Brian Prusinski, Regional Sales Leader for Kris-Tech, said. “That means the wire needs to have durability, flexibility, and other characteristics to maximize system performance and maintain budget.”
  • Accessories – Your PV wire isn’t as useful without the additives making it sunlight resistant and suitable for wet locations. Other accessories may include jacketing material, shields, and additives that give the insulation its unique properties.

Together, these attributes determine the wire’s “fatness” or overall diameter, sometimes referred to as NOM OD (nominal OD). The nominal OD is a cross-section of the wire. Although some parts of the construction process are non-negotiable (wire gauge and insulation), other pieces are added based on what the project calls for.

Exploring Gauges

When someone talks about a wire’s gauge, they’re discussing the conductor’s size.

In the United States and Canada, we measure wire in American Wire Gauge (AWG), with #36 AWG being the smallest and #4/0 AWG being the largest. Wire larger than #4/0 is measured in MCM, ranging from a low of 250 MCM to a high of 2,000 MCM.

It’s also important to know not every wire will work for every situation. You wouldn’t use your home stereo’s speaker wire to power a generator because it doesn’t have the carrying capacity needed to power it. It would burn out quickly, creating a safety hazard for anyone nearby.

This isn’t to say every project needs #4/0 cable. An oversized wire may seem smart, but it would quickly cause issues across the entire installation footprint. The large wire is not only pricier, but workers also need to create bigger pathways and terminals and deal with bulkier installations because the wire is too thick.

Of course, cutting corners, being cheap, and using a thinner wire doesn’t work, either. For example, using a 600v PV wire on a 2kv installation could result in high temperatures generated by the current melting the protective insulation around the conductors, leading to failures, fire, and other damage.

Wire Gauge Also Determines Safe Carrying Loads

When we talk about wire gauge, ampacity – how much current the conductor can safely carry without compromising the wire, insulation, or jacketing – matters.

Ampacity depends on a few things, including insulation rating, conductor material, ambient temperatures, and whether other wires or materials are nearby. “Fatter” wires have higher ampacity because they have larger gauge sizes and thicker insulation/jacketing, allowing more current to safely flow through the conductor.

When an installation needs a lot of electricity, larger conductors and thicker insulation keep everything running safely. Knowing how much power you need to complete the circuit is critical to finding a wire capable of dissipating heat without losing performance.

Insulation: More Than Just Compounds

If a conductor is the highway, cable insulation and jacketing are the guardrails.

There are many insulation and cable jacket types available today, and each one offers different protections.

Some protections offered include:

  • heat resistance
  • crush and abrasion resistance
  • gas, and oil resistance
  • flame retardance
  • sunlight resistance
  • chemical resistance
  • improved effectiveness in hot or cold temperatures
  • flexibility
  • low-smoke, zero halogen (LSZH)
  • direct burial
  • plenum rated – this is the space above a drop ceiling, but below the construction ceiling. It’s used as a general ducting system and is widely used in commercial and public buildings

Insulation and jacketing are made from non-conductive materials. This means they protect the cable from electrical leakage that may occur while in use.

With so many options and materials available for your copper conductors, it’s worth knowing where and how the wire will be installed. For example, if the wire will be buried in rocky soil, consider insulation that offers increased crush and abrasion resistance.

What Happens If the Insulation Is Wrong?

Insulation might look like plastic at first glance, but choosing the wrong one can have severe consequences.

Everything may seem fine at first – and it could be – but eventually, the wire will show signs of distress. The insulation will start to crack and fade, all while normal wear and tear take its toll.

Eventually, the insulation won’t provide ample protection, putting your conductors at risk of shorts, faults, arcs, fires, corrosion, and even breakage. On top of all the issues that could develop, if you try to skirt around requirements for a specific insulation rating, you could find yourself in hot water with inspectors.

If the installation isn’t compliant, you’re responsible for pulling and replacing every foot of the installed wire. It’s an expensive delay, costing time, money, and effort to buy and replace all the previously installed wires.

Wire Thickness Matters More Than You Think

As we mentioned, insulation does everything from regulating heat dissipation and preventing electrical leakage to stopping fires and electrocutions from occurring, as well as maintain system performance.

“If the wire used for a project isn’t up to spec and you’re lucky, an inspector will catch your mistakes and force you to change out the wire because it doesn’t comply,” Prusinski said. “If you aren’t lucky, the system will not perform correctly and damage could occur, opening the door to liability issues, injuries, or even death.”

Let’s go back for a second to the PV wire example we used earlier. Using a 600v PV wire in a 2kv installation is a bad idea, but is it an issue to use a 2kv PV wire in a 600v application? In this case, using a wire with a higher capacity is compliant because it can handle the ampacity the solar energy system will put it through.

“Sometimes you might actually see 2kv wire encouraged on certain installation projects, especially if the owner wants to upgrade or future-proof their system later on,” Prusinski explained.

Terminations, Conduits, Burials, and Other Considerations

A loose fit might be great for your jeans, but it can be a disaster for wire termination.

“If you’re terminating wires to connectors, the thickness of the wire, known as its nominal outer diameter (OD), or cross-section, has to match the nominal inner diameter (ID) of the connector,” Prusinski explained. “If the connection isn’t tight, it won’t meet IP68 waterproof standards and could underperform.”

Long story short – make sure your connections are snug!

Underground installations require the wire jacket and insulation to pass crush tests and survive in the harsh environment. This means the wire’s insulation must be direct burial rated. It should also have other protections like abrasion, moisture, oil, and gas resistance.

Finally, if the wire is going to be pulled through conduits, follow the fill capacity regulations laid out by the National Electrical Code (NEC). The conduit fill capacity is only 40% to allow for heat dissipation from the wires, so insulation thickness is critical to staying within the rules.

Insulation Always Matches Installation

When in doubt, consider the environment the wire will live in and choose insulation designed to meet those needs effectively.

If the temperature fluctuates, ensure the wire’s temperature ratings can adjust accordingly. Don’t leave anything to chance.

Although it might seem like the wire you buy from Kris-Tech or any other manufacturer is too thick, it’s like that for a reason. The correct wire will save you time, money, and maximize performance while keeping you, other workers, and everyone else safe.

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