# What Size Wire for a 30 Amps Service at 300 Feet?

Contents

In my article below I’ll cover what size wire you need to operate an electrical appliance that requires a current of up to 30 amps and is situated 300 feet away from the main supply.

I hate to say “it depends” but you do need to consider ampacity and voltage drop.

In general, though, a 30A service at 300 feet requires using a #6 AWG wire, but if the actual continuous current is under 24A, then you can use a #8 AWG wire.

This article explains how I worked this out with calculations. It assumes you will be using copper wiring and normal ambient conditions.

## Ampacity

The first thing you need to know is if the 30A requirement is a strict one or a theoretical maximum.

In other words, will the appliance be operating close to 30A continuously, or will the current normally be under 25A? Ampacity is the maximum current that a conductor can carry continuously and safely without causing excessive heat. At this stage, we are only considering this factor and not the distance.

### A Strict 30A System

If the appliance is to run close to 30A, you will need a wire with an amperage of at least 37.5A. This is in accordance with the rule (NEC 220-2) that the maximum load must not exceed 80% of the ampacity rating of the wire. I calculated this as follows:

30A current x (100 / 80) = 37.5A amperage

You might be tempted to use a #10 AWG wire, which is rated for handling up to 35A, but this is a little under the required amperage. To ensure safety by reducing the risk of fire, you must use the next thicker-sized wire. This is the #8 AWG wire, which can handle up to 50A.

So, a strictly 30A operation will need a #8 gauge wire because a #10 gauge wire will be insufficient. This requirement is the same regardless of whether the mains supply voltage is 110-120V or 220-240V.

The voltage does make a difference, however, to how much power the wire can deliver. The 110-120V system will be limited to 3.3-3.6kW, whereas a 220-240V system can deliver 6.6-7.2kW.

### An Under-24A System

If the appliance is going to run at no more than 24A (which is 80% of 30A), a wire with an amperage of 30A will be sufficient. In this case, you can use a #10 AWG wire, which can handle up to 35A.

## Distance and Voltage Drop

After considering ampacity, the next thing to consider is voltage drop, which is the fall in voltage due to distance. The voltage drop for a 30A copper wire within a distance of 10 feet will be negligible (under 3%). This means that for a 300 feet distance, you will definitely need to take voltage drop into account.

As a general rule (NEC 310-16), for a 30A ampacity, you need to raise the amperage by 20% for every 100 feet distance from the main supply. For a 30A service 300 feet away, this comes to 60%, which makes the distance a significant factor when accounting for voltage drop.

Letâ€™s consider both cases of 30A and 37.5A amperage:

• 30A amperage: 30A x 1.6 = 48A
• 37.5A amperage: 37.5 x 1.6 = 60A

After taking voltage drop into account, the above calculations show we will have to make a drastic change in selecting the right size wire. The #10 AWG wire will be inadequate for the first case, and the #8 AWG will also be inadequate for the second case.

## The Right Size Wire

Having considered both ampacity and voltage drop, we can now answer the question of which size wire will be appropriate for a 30A service at 300 feet:

For a strict 30A requirement at 300 feet, you must use a #6 AWG wire which can handle up to 65A. Otherwise, to cover 48A amperage, you can use a #8 AWG wire which is good for 50A.

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