What Size Wire Do I Need?

Electrical wires come in different sizes. The thicker the wire size, the more amperage it can handle. But to determine the wire you need, you must know its gauge. For example, a 30 amp wire size requires a different wire gauge than a 10 amp or 40 amp (A) wire size. Expressed as American Wire Gauge (AWG), 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.

Why Does Wire Size Matter?

Circuit breakers are sized according to the wire gauge of the circuit. Since a breaker is designed to interrupt current flow before the conductor is damaged, using too small a wire gauge can result in an overload. The breaker will allow too much current to flow and won’t trip even if the wire is compromised. Using too large a wire gauge, with a higher rated amperage than the circuit breaker, can lead to a tripped circuit even if the load doesn’t exceed the wire’s rating.

Common Wire Sizes

There are a few common wire sizes used in homes. Here is a look at these and what applications each is best suited for:

10 Amp Wire Size: Use a #16 AWG wire for appliances such as toasters, dishwashers, 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, a 50 amp wire size is needed. A #6 AWG wire supports a maximum of 50 amps.

How to Identify Wire Size

When you buy wire or cable, the product label will indicate the wire size in AWG. Oftentimes, just the number is listed. For example, a 10 gauge wire will be labeled “10”. If the format is something like 10/2, 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.

Other Factors that Affect Required Wire Size

When selecting wire size, the amperage requirement isn’t the only consideration. One important factor is 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. For a 30 amp wire, increase amps by 10% for wire extending 50 feet from the sub panel, 20% for wire up to 100 feet away, and 30% for wire up to 150 feet away. For a 200-foot wire, boost amps by 40%, which requires a wire that handles 52.5 amps (for this, you’ll need a #6 AWG wire with a 65 A capacity).

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

You also need to follow the requirements of the National Electric Code (NEC). It stipulates that a 30 A wire size can’t be used strictly for 30 A service. That’s because a branch circuit’s maximum load is 80% of its rating for ampacity of wire (any load). Applying some math, 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 V, 220 V, or 240 V circuit.

The NEC requirement is in place to prevent heat build-up and a breaker trip when turning on appliances. The number of outlets on a circuit is calculated based on it as well.

Contact Express Electrical Services for Wiring/Re-Wiring Help

When installing or replacing electrical wiring, one must consider capacity requirements and other factors to ensure the right sized wire is used. Our electricians are trained, licensed, and insured. They fully understand the wire gauges suited for each home application and when different variations may factor in. Whether you need electrical repair or help with installation, a home remodel, or new outlets, request service on the web or call 323-727-7799.