What Size Wire Do I Need for Home Wiring?

What Size Wire Do I Need for Home Wiring?

Not sure what size wire your new circuit needs? Electricity is the flow of electrical charge used to provide homes with energy. When supplying power to your Southern California home, the electrical grid transforms electric energy into a lower voltage, which is then transmitted using wires. These wires come in different sizes — the thicker the wire size, the more amperage it can handle. Choose the wrong wire size, and you may be looking at energy efficiency and safety hazards.

If you’re not sure what size wire you need, request a certified electrician from Express Electrical, and we’ll send out a licensed pro who understands electrical installation and can help guide you on any upgrades or repairs your home needs. Below, learn below about why wire size matters and how to optimize your home’s circuits with correct wire sizes.

Why Does Wire Size Matter?

Different gauges or sizes of wire can handle different amounts of power, with larger wires/smaller gauges providing less current resistance compared to thinner wires/large gauges.  Whether for new, extended, or rewired circuits, understanding the proper amperage and choosing the right wire size is important for safety and proper electrical functioning.

Circuit breakers and wiring fuses, which protect against overloading and overheating wires, can detect current overloads and trip to avoid conductor damage. The correct wire size should correspond to the circuit and conductor, such as a small appliance. For example, plugging a vacuum cleaner rated for 20 amps into a 15-amp circuit with a 12-gauge wire can cause the vacuum to draw too much current and overload the circuit. 

Circuit breaker sizes correspond to the wire gauge of the circuit, and since circuit breakers interrupt current flow to avoid conductor damage, using too large wire gauges can result in an overload. The breaker may allow too much current to flow and won’t trip even if the wire is compromised. In some cases, overloaded wires may overheat to the point of melting the wire insulation or even igniting the surrounding materials, resulting in the danger of a house fire from something as simple as a small appliance.

Common Wire Sizes

Your local hardware stores likely offer a wide variety of types and sizes of electrical wires. Lighting and everyday electrical sockets typically use some of the most common wire sizes, such as 14-gauge and 12-gauge. Large or higher amperage-demand appliances such as washing machines or ovens require more power and therefore larger wires.

The following are some common wire sizes in homes and the applications that each size is best suited for:

• 10-amp wire size: A #16 AWG is a good dishwasher wire size, which works well with other appliances like toasters, refrigerators, vacuum cleaners, or hair dryers.
• 30-amp wire size: A #10 AWG wire is suited for a circuit powering an air conditioner or all appliances used in an RV.
• 40-amp wire size: To power electric cooktops and most other electric cooking appliances, you’ll need a #8 AWG wire.

For breakers on an electrical panel that serve numerous appliances, such as in a kitchen or an electric dryer, you’ll need a 50-amp wire size. A #6 AWG wire supports a maximum of 50 amps. 

How To Identify Wire Size

When wiring a home, you need to determine the amount of current the wire will be conducting, which is measured in amperage (amps). For example, a 30-amp (A) wire size requires a different wire gauge than a 10-amp or 40-amp wire size. Expressed as American Wire Gauge (AWG), which is a standardized way for users to identify and select wiring, this value ranges from 0 to 40 AWG. The lower the number, the thicker the diameter of the wire and the more power it can safely manage.

When you buy wire or cable, the product label will indicate the wire size in AWG, sometimes with just a number; a “10” will label a 10-gauge wire, and a “20” may label a 20-gauge wire, and so on. Sometimes the format offers an alternative expression — a label that lists 10/2, for example, means there are two wires or conductors within the cable. The label may also have a “G” or “w/G,” meaning the cable has a ground wire not included in the total wire count.

If you don’t have the wire packaging and can’t see the AWG printed on the wire insulation, you can still find the wire size. Turn off the electricity at the circuit box, and use wire cutters to cut the cable and strip the wire. Measure the cross-section of the cut in inches. Once you get this measurement, use the following steps to identify the gauge:

1. Divide the diameter of the wire by 0.46.
2. Use the “log” (logarithm) button on your calculator to divide the answer by -0.050305.
3. Subtract 3 from the answer to find your cable’s AWG.

Alternatively, you can use online calculators to find the AWG of a wire.

Other Factors That Affect Required Wire Size

Several other factors can also affect the recommended wire size. 

Length

When selecting wire size, the amperage requirement isn’t the only consideration. For example, consider wire length — if you’re running a wire over 100 feet long or it’s inside a conduit or combined with other wires (reducing heat dissipation), choose the next largest wire size to offset the resistance increase. 

• For a 30-amp wire, increase amps by 10 percent for wire extending 50 feet from the sub panel, 20 percent for wire up to 100 feet away, and 30 percent for wire up to 150 feet away. 
• For a 200-foot wire, you should boost the amps by 40 percent, which requires a wire that handles 52.5 amps (for this, you’ll need a #6 AWG wire with a 65 A capacity).

Composition

The material of the wire matters too. Electrical wire is typically made of brass, copper, or silver. If you’re using aluminum wire, which is less common, the AWG requirement may differ as aluminum has 61 percent less conductivity than copper and weighs 30 percent less.

Regulations

In Southern California, you also need to follow the requirements of the National Electric Code (NEC), which stipulates that a 30-amp wire size can’t be used strictly for 30-amp service. A branch circuit’s maximum load is 80 percent of its rating for the ampacity of wire (any load). This NEC requirement is in place to prevent heat build-up and a breaker trip when turning on appliances. The number of outlets allowed on a circuit is also calculated based on this code. 

This means you’d need a wire that can handle at least 37.5 amps or a #8 AWG wire. This is the same for a 110/120 volt (V), 220 V, or 240 V circuit. Understanding more about the NEC and the electrical circuit you’re working with can help determine whether you should use a 10, 12, or 14-gauge wire. For example, if you want to know what wire gauge works for 220 V circuits if it draws up to 20 amps of current, it’ll need a #12. The wire size for 220 V needs to be larger if the circuit draws more than 20 amps.

Contact Express Electrical Services for Wiring and Rewiring Help

When installing or replacing electrical wiring, consider capacity requirements and other factors to determine the correct wire size to use. At Express Electrical Services, our electricians are trained, licensed, and insured. They also possess expert understanding of wire gauges suited for each home application and when variations may factor in. 

For all of your home electrical needs in the Los Angeles area and other parts of Southern California, you can count on Express Electrical Services and our team of qualified professionals. We have live operators available 24 hours a day, 7 days a week to take your call — and we offer reliable same-day service. Contact us or book online today.

Frequently Asked Questions

What is voltage drop?

Voltage drop refers to the decrease of electrical potential, AKA voltage, in response to the inherent resistance of a current flow. Excessive voltage drop can result in poor electrical performance, such as flickering lights and poor appliance function.

How does weather affect wiring needs?

Environmental conditions, such as temperature, precipitation, and more, can result in damage to your electrical system. These conditions can cause issues such as corrosion and degradation, hurting the lifespan of your wiring.

In addition to selecting the appropriate wire size, consider the material of the conduit. Material compatibility between conduits and wires can provide protection from damage, wiring longevity, and proper electrical function.

How do potential future expansions or additions to the electrical system influence wire size?

It’s best to anticipate your future electrical system and wiring needs. A flexible wiring system can allow you to revisit your wiring in the future to swap out the appropriate components. Additional or room-specific circuits can also help you avoid circuit overloads and power supply issues. Your electrician can recommend strategies for flexible wiring.