What Size Wire for 50 Amps at 100 Feet?

What size wire do you need to operate an electrical appliance with a current of up to 50 amps situated 100 feet away from the main supply?

Usually, it’s required for heavy-duty appliances such as electric ovens and dryers. I will explain everything you need to know in this quick guide. You need to consider two things: ampacity and voltage drop.

In short, a 50A service at 100 feet normally requires using a 4-gauge AWG copper wire, but you can use a 6-gauge wire if the continuous current is under 40A or the appliance operates on 240V.

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

Ampacity

First, you need to know if the 50A requirement is a strict one or a theoretical maximum.

In other words, will the appliance operate close to 50A continuously, or will the current normally be under 40A? Ampacity is the maximum current a conductor can carry continuously and safely without causing excessive heat. At this stage, we’re only considering this factor, not the distance.

A Strict 50A System

If the appliance is to run close to 50A, you will need a wire with an amperage of at least 62.5A. It’s by 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:

50A current x (100 / 80) = 62.5A amperage

You might be tempted to use a 6-gauge AWG wire, rated for handling up to 60A, but the allowed amperage is no more than 50A in continuous use, which would be risky. To ensure safety by reducing fire risk, you must use the next thicker-sized wire. This 4-gauge AWG wire can handle up to 68A as a maximum or 54.4A in continuous use.

So, a strictly 50A operation will need a 4-gauge wire because a 6-gauge wire might be insufficient.

An Under-50A System

If the appliance normally operates under 40A (80% of 50A), a wire with an amperage of around 50A will be sufficient. In this case, you can use a 6-gauge AWG wire, which can handle up to 52A.

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 50A copper wire within 100 feet will be negligible (under 3%). It means that for a 100 feet distance, you will need to take voltage drop into account.

As a general rule (NEC 310-16), for a 50A ampacity, you need to raise the amperage by 20% for every 100 feet distance from the main supply. For a 50A service 100 feet away, this comes to 20%, which makes the distance a factor to consider when accounting for voltage drop.

Let’s consider both cases of 50A and 37.5A amperage:

• 50A amperage: 50A x 1.2 = 60A
• 62.5A amperage: 62.5 x 1.2 = 75A

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 6-gauge AWG wire will be inadequate for the first case, and the 4-gauge 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 50A service at 100 feet:

For a strict 50A requirement at 100 feet, you must use a 4-gauge AWG wire, which can handle up to 65A (maximum 68A, at up to 165°F). Otherwise, you can use a 6-gauge AWG wire to cover 50A if the amperage doesn’t normally exceed 40A or the appliance operates on 240V.

The voltage also affects 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.

References

Website Resources:

• 4-gauge wire. https://discountbloc.ru/archive/products/xuwv21y1x2x3.html
• 6-gauge wire. https://www.harpstarps.com/product/6-gauge-wire/