What is the wire size for a 40 amp switch

Content

Wire size for 40 amp circuit breaker
- Wire length
- Building material wire
Is 6 AWG copper wire suitable for a 40 amp circuit breaker?
How many amps can a 40 amp circuit breaker handle?
- The 80% NEC rule
- Why should I follow the NEC 80% rule?
How many watts can a 40 amp switch handle?
How do you determine wire size?
- Does the wire diameter include insulation?
- What if I don't see a rating on the insulation of a wire?
Summing up

For many high powered appliances such as hobs, electric dryers and electric stoves, you will need a 40 amp circuit breaker.

Having a 40 amp circuit breaker helps protect your electrical appliances. But if you don't choose the right size wire, you risk the safety of circuits and components. So, if you're having trouble choosing the wire size for your 40 amp circuit breaker, I'm here to give you some advice.

Typically, 8 AWG copper wire is the minimum wire size for a 40 amp circuit breaker. However, 8 AWG wire is only suitable for lengths less than 100 feet. Alternatively, you can also use 6 AWG wire.

I'll go into more detail below.

Wire size for 40 amp circuit breaker

8 AWG copper wire is the most suitable option for a 40 amp circuit breaker. We can label this wire as the minimum wire size for 40 amps. However, you should check the following two factors.

Wire length

If you are using 8 AWG wire for a 40 amp circuit breaker, the wire length must be less than 100 feet. In electrical circuits, resistance increases as the length of the wire increases.

According to Ohm's law,

V=Voltage
I = flow
R = resistance

Therefore, the voltage drop varies with the resistance.

In other words, if you run 240 volts through the 8 AWG wire for 50 feet, you won't get the full 50 volts at the 240 foot mark. Instead, you'll get a lower value. We called this voltage drop. There is a recommended value for this voltage drop. You must keep the voltage drop below 3% for lighting and 5% for other appliances.

When you run 8 AWG wire 100 feet or more, the voltage drops below the recommended level. When this happens, the electrical appliance will not receive the required voltage. This may damage electrical appliances.

Building material wire

Aside from length, the main factor to consider when choosing 8 AWG wire is the material the wire is made from. For example, when you request 8 AWG wire from your local hardware store, the salesperson might ask what type of wire you need, aluminum or copper.

There is a good reason for this question. While both copper and aluminum are excellent electrical conductors, copper is a much better choice than aluminum. Copper is the best conductor.

So for a 40A and 240V circuit, 8 AWG copper wire is an excellent choice. However, if you are going to use aluminum, you will need 6 AWG wire for the same circuit.

Is 6 AWG copper wire suitable for a 40 amp circuit breaker?

In truth, 6 AWG wire is best for 65 amp circuit breakers. But that doesn't mean you can't use it with a 40 amp switch. Using 6 AWG wire will give you room to expand. If necessary, you can replace the 40 amp switch with 50 or 60 amps.

Tip: Using 6 AWG wire on a 40 amp circuit breaker does not violate NEC regulations.

How many amps can a 40 amp circuit breaker handle?

Each circuit breaker will start tripping when it reaches maximum power. For a 40 amp circuit breaker, the maximum current is 40 amps. Thus, the switch will withstand 40 amps without any problems. But when the load exceeds 40 amps, the switch will trip.

Although the circuit breakers can carry the corresponding maximum load, according to NEC, the maximum power must be 80%. Here is some information about this rule.

The 80% NEC rule

Only 80% of the circuit breaker's full capacity should be used. The circuit must be able to maintain this limit for 3 hours or longer.

So if we consider a 40 amp switch,

So, keep the load at the 32 amp limit for 40 amp breakers. Use a larger circuit breaker if your circuit regularly draws more than 32 amps. For example, a 50 amp circuit breaker would be a good choice.

Tip: Some circuit breakers are rated at 100%.

Why should I follow the NEC 80% rule?

If a circuit is constantly drawing too much load, it will heat up over time. The same will happen with circuit breakers. Thus, the circuit breakers will start to trip. Or overheating may cause electrical fire. (1)

How many watts can a 40 amp switch handle?

Whenever we calculate power, we use Joule's law.

When we consider a 40 amp, 240 V power supply:

Theoretically power = 40 × 240 = 9600 watts.

But you cannot use the maximum power of the circuit breaker. You should only use 80%.

Consequently, the

Power (taking into account the power of 80%) \u40d 80 × 240% × 7680 \uXNUMXd XNUMX watts.

For example, a 40 amp (80% rated) switch can handle up to 7680 watts. If the circuit breaker is rated at 100%, it can handle 9600W.

Keep in mind: Whether you are using an 80% or 100% rated circuit breaker, 8 AWG wire is a good choice for the above circuits.

How do you determine wire size?

American Wire Gauge, also known as AWG, is the North American standard for wire sizes. This will give us an estimate depending on the diameter of the wire and the load that a particular wire can carry.

The corresponding number will be printed on the wire insulation. The marking will indicate 4 AWG, 6 AWG, 8 AWG, 10 AWG, etc. From these figures, you can calculate the diameter of the wire and the current that the wire can pass.

For example, 12 AWG wire is 0.0808 inches in diameter and 6 AWG wire is 0.162 inches in diameter.

As you can see, with a higher gauge number, the thickness of the wire increases.

Does the wire diameter include insulation?

AWG wire manufacturers do not include wire insulation in the wire size. So, the diameter of the wire is the diameter of the conductor.

What if I don't see a rating on the insulation of a wire?

If you can't see the rating on the wire insulation, use a digital caliper to measure the thickness of the wire. Here is a simple guide on how to do it.

First strip the wire you want to measure.
Then place the bare conductor on the fixed jaw of the digital caliper.
Next, bring the movable jaw to the wire.
After that, get the readings on the digital display.
Finally, use the AWG wire size reference chart to get the appropriate rating for that wire.

Use this link for AWG wire sizes.

Tip: Some calipers may show the scale in millimeters. And some will show in inches.

Here are some common copper wires with their diameters and amperage ratings.

wire gauge	Diameter (inches)	Rated current
12 AWG	0.0808	20 amplifiers
10 AWG	0.1019	30 amplifiers
8 AWG	0.1285	40 amplifiers
6 AWG	0.1620	65 amplifiers

Summing up

For modern kitchens, having a reliable electrical circuit is critical. You won't get a good quality electrical circuit without proper wire sizes. So, when you use a 40 amp circuit breaker at home, be sure to use 8 AWG or 6 AWG wire. It will definitely protect you and your household appliances. (2)

Take a look at some of our articles below.