70 Amp Wire Size: Charts, Gauge, Breakers (120,240 & 480 V)

You should know the correct wire gauge to install 70 amps. Knowing the proper wire size that accommodates 70 amps will let you know whether to keep the same wiring or change it. Today’s article is about the wire size for 70 amps. 

Professionals suggest 4 AWG wires as the most recommended wire size for 70 amps. According to the NEC or National Electric Code, a 4 AWG wire can handle up to 85 amps. So, it is the best one for 70 amps. The AWG will reduce based on factors like wire material and distance. 

It is the right place if you have 70 amps and want guidance about the wire size. Please read this article till the end to learn in detail about the wire size for 70 amps and how several factors can change the wire size for it. 

Decoding 70 amps wire size: A comprehensive guide

Earlier, 50 amps were considered the standard service for most houses as they did not have many electrical appliances. 

With 1-2 appliances that draw a minimum power of 5 to 10 amps, 70 amps service will be able to run an entire house. 

Earlier, my house used to run on 70-80 amps service because we did not have many electrical appliances back then. 

Then I had 150 amps and then again upgraded it to 200 amp service as I added a few modern appliances that draw power between 10 amps to 45 amps. 

The correct wire size for 70 amps service is a 4 AWG copper wire. 

According to the NEC, a 4 AWG wire is the minimum range for 85 amps.

So, it can be a perfect fit for 70 amps. 

Since today’s modern electronics are pretty advanced than the older ones, 70 amps service may not be enough to run a whole house. 

Some appliances draw power between 15 to 50 amps. Using 70 amps service for the entire house can be dangerous for both house and the appliances. 

Wire size for 70 amps service 

With time, the use of electrical devices has increased. 

In the world of technology, these devices are improving day by day. 

As a result, the amount of power they draw is relatively high. 

Since I have some of them, my house runs on 200 amp service. 

70 amps are now used as circuit breakers to run only a few power-hungry appliances. 

But if you do not own any such high-power drawing appliances, 70 amps service is still an option. 

The wire size stays the same, 4 AWG copper wire and 2 AWG aluminum wire. The same is for the main breaker panel. 

The panels are designed to handle the maximum amperage. 

So, a 200 amp breaker box will be appropriately sized for 200 amp electrical service. 

If the distance is too long, go for 2 to 3 AWG copper or 1 to 1/0 AWG aluminum wires.

Also, pay attention to the temperature and distance. 

A 4 AWG wire is fine for 70 amps at 140°F, but use a thicker cable to leave space for expansion down the line. 

If the distance is too long, you will need a lower AWG wire, like 1 or 2 AWG wires.

4 AWG is not the highest one. 

So, you can always choose a lower AWG if the load exceeds the breaker’s capacity and the distance gets longer than 100 feet. 

Ground wire size for 70 amps

The ground wire for 70 amps is also 4 AWG. 

You can use the same gauge for both hot and neutral connections or a smaller gauge. 

But reducing the AWG for grounding won’t be necessary. 

The hot wire carries the current for the primary power source and the neutral return it to complete the electrical circuit. 

These wires are always positive. 

So, there may be a reduction of the AWG for safety. 

While the ground wire only carries current when there is a short circuit. 

The excess current needs an alternate path to flow, and that is when the grounding comes to the rescue. 

Since this wire is inactive except for the short circuits, 4 AWG should be enough. 

Wire gauge for a 70 amps circuit

Circuit breakers are the breakers that run individual appliances like refrigerators, microwaves, and vacuum cleaners. 

I have one 70 amp circuit breaker to run 2-3 appliances like a refrigerator, heat pump, and water heater. 

There are other breakers too for other appliances.

For a 70 amps circuit breaker, I use the same wire size: 4 AWG copper or 2 AWG aluminum wire. 

How many amps can a 70 amp breaker handle?

Here, you should follow the 80% breaker rule. 

In this rule, out of 70 amps, you can use only 80% of the load, i.e., 56 amps. 

Based on that, I run a refrigerator drawing 10 amps, an electric water heater drawing 18 amps, and a heat pump drawing 12 amps. 

So, in total, it will be 40 amps. I did not want to use up all the 56 amps in case I needed to add appliances drawing fewer amps.

A 2 or 4 AWG wire is enough for 70 amps. 

Wire size for a 70-amp subpanel

The wire size is no different from the breaker and service for a 70 amp sub panel. 

A 2 AWG or a 4 AWG wire is the ideal choice for a 70 amps sub panel. 

Several rules and factors are needed to select the precise wire size for 70 amps to avoid electrical accidents. 

Common factors include the 80% rule, material, distance, and ambient temperature. I recommend keeping the voltage drop to 3% only. 

Unveiling the mystery of 70 amps wire size: A complete overview, including factors to consider

Generally, the correct wire size for 70 amps is 4 AWG. But the gauge size will reduce based on a few things. 

There are some rules and factors to consider before selecting the gauge size of 70 amps. 

Let’s have a look at them in detail. 

NEC 80% ampacity rule

To ensure safe wire sizing for 70 amps, following the 80% rule is essential.

According to the 80% rule, 70 amps should be able to represent at most 80% of the wire ampacity. 

The wire size should be based on the maximum allowable current. 

This rule is called the 80% NEC ampacity requirement. 

For that, divide 70 amps by 80%. So, 70A ÷ 0.8(80%) = 87.5 amps. 

So, the wire size you choose for 70 amps should have at least 87.5A ampacity. 

In that case, the wire gauge will reduce to 3 AWG as it will contain an ampacity of around 100 amps, and you will have rare to zero chances of electrical accidents. 

Voltage drop rule 

The following rule is the voltage drop. 

This rule is considered when running the wire for 70 amps longer distances. 

The voltage drop is the voltage loss during the current flow through the resistance. 

The rule is that for every 100 feet of wire, the voltage drops by 20%.

So, for every 100 feet, increase amps by 20% to receive a similar power output according to the power equation Power (Watts) = Current (Amps) x Voltage (Volts). 

Let’s say I need to run the wire for a 70 amps sub panel 150 feet away. 

Using the 80% rule, I must use a wire that handles at least 87.5 amps. 

For 150 feet, there will be 30% of voltage loss. 

Thus, I should increase the amps by 30% by the formula = 87.5A x 1.3 = 113.75 amps. 

So, the wire for 70 amps 150 feet away should handle 113 amps. 

The wire size should be 1/0 AWG because it can handle 125 amps. 

These are just estimations through manual calculations. Ask a professional for the actual wire size. 

Distance and voltage

Voltage drop and distance are related. The ideal voltage drop allowed should be 3% to 5%. 

At longer distances, the voltage drop and resistance will increase. 

The wire will overheat. 

Use a thicker gauge that handles the current flow and resistance and does not allow the voltage to drop over 3% or 5%. 

Speaking of the voltage, it does not affect the wire size much. 

While going through the charts in the NEC, you will rarely find any mention of the voltage because it doesn’t influence the wire size like the other aspects.

For 70 amps, you can use a 4 AWG or a smaller AWG, based on how long you are running them. 

You can always use smaller AWGs for 70 amps.

If you use a wire gauge smaller than 4 AWG, for example, 2 AWG or 1/0 AWG, you can run it for longer distances. 

Below are three tables that show the maximum distance of the recommended wire sizes for 70 amps at different voltages:

Single line phase

4 AWG copper or 2 AWG aluminum wire

Volt with 70 amps	Maximum distance in feet
120V	95 feet
240V	191 feet
480V	383 feet

3 AWG copper or 1 AWG aluminum 

Volt with 70 amps	Maximum distance
120V	120 feet
240V	241 feet
480V	483 feet

2 AWG copper or 1/0 AWG aluminum

Volt with 70 amps	Maximum distance
120V	152 feet
240V	302 feet
480V	609 feet

3-phase line

If the maximum distance to run the wire for 70 amps is 150 feet, follow the following table for precise wire sizes:

Volt with 70 amps	Copper wire	Aluminum wire
120V	2 AWG	1/0 AWG
240V	4 AWG	2 AWG
480V	4 AWG	2 AWG

Use a thicker wire with a smaller AWG at longer distances and phase lines. Only then you can run the wires safely for 70 amps without any risks of electrical accidents.

Wire material 

You might have noticed the difference in wire sizes based on copper and aluminum. 

Wire material matters because the ampacity will change with the material.

Of all the materials, copper wire is considered the best after silver. 

Copper has better conductivity, higher amp ratings, and good resistance than aluminum wires. 

Since copper has better conductivity and resistance, it can carry enough current for longer distances without overheating. 

These wires are also malleable. 

You can mold and bend them without worrying about breakage risk.

Aluminum wires are not better than copper; they are still helpful. The wire is cheaper and lighter than the copper wires. 

You can easily handle aluminum wires, use them for shorter distances, and save money. 

While choosing the aluminum wire, select the size double the copper’s size. 

For example, if you need 4 AWG copper, take 2 AWG aluminum. 

Try copper-clad aluminum wires to get a wire that performs better than aluminum but is cheaper than copper. 

It is costlier than aluminum but more affordable than copper. 

These aluminum wires have copper fittings that provide some copper benefits. 

The size stays the same as aluminum. 

For example, if you use 4 AWG wires for copper, you should use 2 AWG aluminum or copper-clad aluminum wires. 

Since copper wires are costly, I use both aluminum and copper wires. 

Since 4 AWG wire is hefty, I use them not only for 70 amps but for 50 and 65 amps as well sometimes. 

I have used aluminum wires for short distances and copper wires for longer distances. 

Temperature rating 

When selecting the wire size, check the temperature rating of the wire and its ampacity. 

Different wire sizes will have different ampacities at different temperatures. 

Also, check the insulation. If the insulation is good, the wires will only stay fine when the current flows. 

If you select a 4 AWG wire, its ampacity is 70 amps at 140°F, 85 amps at 157°F, and 95 amps at 194°F.

A 4 AWG aluminum has an ampacity of 55 amps at 140°F, 65 amps at 157°F, and 75 amps at 194°F. 

That is why you need a 2 AWG wire for 70 amps. 

The importance of proper wire sizing

Using the proper wire gauge for every amperage is of utmost importance. 

While using a smaller AWG will be safe and won’t cause a problem, a larger AWG can be dangerous. 

For any amperage, 70 amps in this case, the wire you choose should be able to handle the current flowing through the service or breaker. 

When the wire size fails to handle enough current, the appliances work inefficiently; the wires overheat, melt, and start a fire. 

In worse scenarios, the appliance can bust and start a fire.

Since the breaker protects the wire, it can trip off before electrical accidents. 

With a wrong wire size, the breaker will trip multiple times immediately after you reset it. 

I had this tripping problem once. 

But luckily, one of my expert friends suggested using a thicker gauge. 

I immediately hired a professional and got the wires upgraded. 

Most people do not understand that their wire choices can have an impact. 

To save money, house owners and contractors use thinner wires. 

That only brings danger to the electrical system and appliances. 

The amperage level and wire length help determine the correct wire gauge. 

The narrower the diameter, the more excellent the resistance during the current flow. The wire will overheat and start a fire. 

The wire’s cross-sectional area lets you know the proper gauge for 70 amps. 

The diameter of the 4 AWG wire is 0.2043 inches or 5.189 mm. 

The cross-section of the 4 AWG wire is 21.2 mm2. 

With such a cross-section and 4.89 turns per inch, this wire can easily handle 70 amps. 

Empowering decision-making: Charts and gauges in 70 amp wire sizing

This section shares tables about copper and aluminum wire sizes for 70 amps at different distances and voltages. 

These values are calculated online. There are multiple online calculators present. 

When you choose the wire size, check the NEC charts and tables and consider calculating them once. 

In the chart, I have considered the voltage drop as 3%. 

Single phase

120V

Distance in feet	Copper wire	Aluminum wire
50 feet	4 AWG	2 AWG
75 feet	4 AWG	2 AWG
100 feet	3 AWG	1 AWG
200 feet	1/0 AWG	3/0 AWG
250 feet	2/0 AWG	4/0 AWG
300 feet	2/0 AWG	4/0 AWG

240V

Distance in feet	Copper wire	Aluminum wire
50 feet	4 AWG	2 AWG
75 feet	4 AWG	2 AWG
100 feet	4 AWG	2 AWG
200 feet	3 AWG	1 AWG
250 feet	2 AWG	1/0 AWG
300 feet	2 AWG	1/0 AWG

480V

Distance in feet	Copper wire	Aluminum wire
50 feet	4 AWG	2 AWG
75 feet	4 AWG	2 AWG
100 feet	4 AWG	2 AWG
200 feet	4 AWG	2 AWG
250 feet	4 AWG	2 AWG
300 feet	4 AWG	2 AWG

3-phase

120V

Distance in feet	Copper wire	Aluminum wire
50 feet	4 AWG	2 AWG
75 feet	4 AWG	2 AWG
100 feet	4 AWG	2 AWG
200 feet	1 AWG	2/0 AWG
250 feet	1/0 AWG	3/0 AWG
300 feet	2/0 AWG	4/0 AWG

240V

Distance in feet	Copper wire	Aluminum wire
50 feet	4 AWG	2 AWG
75 feet	4 AWG	2 AWG
100 feet	4 AWG	2 AWG
200 feet	4 AWG	2 AWG
250 feet	3 AWG	1 AWG
300 feet	2 AWG	1/0 AWG

480V

Distance in feet	Copper wire	Aluminum wire
50 feet	4 AWG	2 AWG
75 feet	4 AWG	2 AWG
100 feet	4 AWG	2 AWG
200 feet	4 AWG	2 AWG
250 feet	4 AWG	2 AWG
300 feet	4 AWG	2 AWG

You can reduce the AWG number as per your concern and safety. 

Final thoughts 

70 amps are rarely used to run an entire house due to the increased electrical appliances and their hunger for power. Nowadays, it is used as a circuit breaker to run appliances individually. But you can run if you do not use such appliances. A 4 AWG wire is ideal for 70 amps because it can handle up to 85 amps. But a lot of factors and rules can change the wire size. 

For example, if you follow the 80% ampacity rule, you will need a wire gauge with 87.5A ampacity. The voltage drop increases by 20% for every 100 feet when the distance increases. In that case, you will need a 1/0 AWG wire to run it for 70 amps 150 feet away. 

Like these, several other factors can influence the wire size, for example, the wire material, the ambient temperature rating, and the distance. The wire size for 70 amps service, circuit breaker, and sub panel is the same. Consider the rules and factors before choosing the wire. 

Reference: Wire Sizes Wikipedia 

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