What Size Wire For 32 Amps Single & 3 Phase 240V Circuit?

what size cable for 32 amps cooker, breaker, ring main, single & 3 phase, hot tub

You won’t find 32A devices in conventional homes. Most houses feature 15 and 20A circuits because the average household appliance uses 20 amps or less. A 32A item will exceed the capacity of a 15 or 20A circuit. But these products are more common than you think. For instance, Johnson’s Hot Tub offers 32-amp hot tubs. 32A is a lot of power, so you can’t afford to get the wire size wrong.

Wire Size for 32 Amps

The best wire size for 32 Amps is 8AWG.


But finding the correct wire size is tricky. Consider the following factors:

1). Ampacity Chart Suggests Using 8AWG

Most online ampacity charts and tables associate 12AWG with 20 amps, 10AWG with 30 amps, and 8AWG with 40 amps.

The table doesn’t mention 32amps. What does this mean? Should you select 10AWG, which supports 30 amps, or 8AWG, which can withstand 40 amps? A layperson may ask a more obvious question.

Why not use the wire size between 8AWG and 10AWG? First of all, most NEC tables increase by two wire sizes. For instance, they jump from 20AWG to 18AWG, 16AWG, 14AWG, and so on.

You don’t see any mention of 19AWG, 17AWG, or 15AWG.

What does this mean? Rationally, you are better off using 8AWG because it can withstand 40 amps. The 10-gauge wire will carry 32 amps, especially if you secure a cable with a higher temperature rating.

However, this wire size is not safe. What if a malfunction occurs? What if the hot tub’s electrical requirements spike to 40 amps? You will burn your house down. 8AWG gives you more room to breathe.

2). Remember The NEC’s 80% Rule For Breaker

You can pair 32A machines with 10-gauge wiring in emergencies. The wire size is not recommended, but it can serve your needs in the short term. The same cannot be said for a 32A breaker.

Remember the NEC’s 80 percent rule. Your home’s load should only use 80 percent of the breaker’s capacity. Again, the objective is to give your circuit room to breathe in case of malfunctions.

You cannot pair a 32A breaker with a wire that withstands 32 amps. Your wire’s ampacity should exceed 32 amps. Therefore, 8AWG is still your best option. Even if 10AWG can transmit 32 amps safely, a contractor wouldn’t pair it with a 32-amp breaker.

10AWG will work for a while, depending on the load size. But it leaves you vulnerable to various challenges, including:

  • The conductors will melt if a defect manifests and the load exceeds the capacity of the wire. If you’re lucky, you will only lose the wire. But a melting wire can also start a fire.
  • Small wires are less likely to deliver the current a device requires. They have higher resistance, which translates into a significant voltage drop. As such, some devices won’t start until you replace the 10AWG cable with a thicker alternative.
  • Even if the machine starts, it may not perform as effectively as you want. The voltage drop can destroy the device. If the appliance has a motor, it may burn out because the machine is working harder to compensate for the voltage drop.

The threat of fires rarely attracts the concern contractors expect because consumers trust the breaker to keep them safe. They expect the breaker to respond to an overload by tripping. Therefore, they don’t think the 10AWG wire will melt.

Even if it fails to transmit the 32 amps your equipment uses, the breaker will cut the power before the worst comes to pass. But breakers are not immune to defects. Some of them will fail outright. Others will respond slowly, allowing the 10-gauge wires to melt before tripping.

The only way to prevent this eventuality is to prioritize 8AWG wires. 10AWG is tempting because lower gauges are cheaper. However, the cost of an 8-gauge line is worth it for the security and peace of mind it offers.

5 Things To Consider Before Choosing Wire Size For 32 Amps

On the surface, selecting a wire size for 32 amps seems easy. Find an amp chart, look for 32A in the ampacity column, and identify the corresponding gauge.

However, it is never that easy. You will select the wrong wire size if you forget to consider the following factors:

1). Increase The Gauge With Increasing Distance

For Copper Wire,

Single Phase

VoltageAmpVoltage DropMax Distance
120V32A3%77 ft
240V32A3%155 ft
480V32A3%311 ft

Three Phase

VoltageAmpVoltage DropMax Distance
120V32A3%89 ft
240V32A3%179 ft
480V32A3%359 ft

Gauge and ampacity increase with the distance. That is not a coincidence. The distance affects the length of the cable, and the length influences resistance.

The longest lines have the highest resistance. This makes them dangerous because the higher the resistance, the more heat you get in a live conductor. You overcome this threat by increasing the wire size.

Compare this situation to a water pipe. Water in a large pipe can flow more freely than water in a small pipe. 10AWG will only tolerate 32 amps over a short distance. You can’t trust the size to transmit 32 amps at 100 feet without melting.

Even though 8AWG is the safer option, a contractor may encourage you to opt for 6AWG if the distance continues to increase.  Some people think that a wire’s amp rating changes with the length.

They make this assumption because they have seen tables where the gauge grows with the length. However, the amp rating won’t change. Instead, the contractors in those situations will abandon smaller cables for their thicker counterparts. 8AWG seems thick, especially for a 32A load. After all, it can withstand 40 amps. But 8AWG conductors can overheat if they are too long.

2). Use Copper Wire

Aluminum was once the material of choice for contractors but they abandoned the material in favor of copper because aluminum’s expansion profile (under load) was a problem.

Today, most contractors will use copper if they have a choice in the matter because it has superior durability, stability, and conductivity. A 10AWG copper wire will carry more electricity than 10AWG aluminum.

Therefore, if 10AWG is the only option available to you, use copper. You cannot trust 10AWG aluminum to transmit 32 amps without overheating or introducing detrimental voltage drops.

Aluminum is only viable if you find it in a higher gauge such as 8AWG or 6AWG. But people only use aluminum when they want to save money. Some contractors gravitate towards the material because it is lighter and easier to install.

But for consumers, the cost is the most significant consideration. With that in mind, there is little point in buying 6AWG aluminum if 8AWG copper is an option. As you now know, higher gauges are more expensive. If you can afford a higher aluminum gauge, use a lower copper gauge like 8AWG.

3). Single Phase VS Three Phase Matters

The phase matters more than you think. Single-phase systems appear in residential settings. They operate common household appliances like refrigerators. You cannot rely on them to withstand the electrical demands of industrial machinery.

Three-phase systems are superior because you get more power. For that reason, you typically find them in industrial settings with heavy electrical requirements. Therefore, a contractor is more likely to pair a three-phase system with thicker wires.

4). Stranded/Solid Wire Matters

What kind of wire do you want? Some cables have one solid conductor. Others have strands. Stranded wires are more flexible. You can maneuver them around twists and bends in a conduit with greater ease. 

Solid wire is the opposite. Pulling it through conduits is not easy because of the thickness of the conductor. But it is also durable and more likely to survive extreme conditions. If you’re trying to select a wire type for 32A loads, solid wires have a higher current carrying capacity. Surprisingly, solid conductors are also cheaper.

5). Check The Rules

The rules in your area will determine the wire size. Contractors use the NEC’s tables to identify the wire size of any given load. But the NEC’s regulations are not mandatory. Local authorities can create and enforce their own rules.

Check your local authority’s information to identify the wire size recommended for 32 amps. If they don’t have anything to say about this subject, use the NEC’s recommendations.

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Stellar is an engineer. He has an unconventional approach to problem-solving, and is adept at devising original solutions to complex issues. He is an imaginative thinker and regularly comes up with resourceful answers to challenging problems.

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