70 Amp (Breaker, Ground, Service) Wire Size Explained

70 amp wire size

If you want to upgrade your breaker to 70 amps, you are probably wondering whether the wires can stay the same. But you cannot answer that question without first identifying the correct wire size for a 70A breaker. If you know the wire size that accommodates 70 amps, you can determine whether or not your existing wiring matches that wire size. If it doesn’t, you should update the wiring in your home before you install a new breaker. Otherwise, the wrong wire size will burn your house down.

What Size Wire Is Needed For 70 Amps?

The best wire size for 70 amps is 4AWG. This wire size may change depending upon the required voltage, ambient temperature, voltage drop, distance, location and material used.

70 Amp Wire Size Chart

Volt with 70 AmpsMax DistanceAWG(Copper)Aluminum
120V95 ft4AWG2AWG
480V383 ft4AWG2AWG
Volt with 70 AmpsMax DistanceAWG(Copper)Aluminum
120V120 ft3AWG1AWG
480V483 ft3AWG1AWG
Volt with 70 AmpsMax DistanceAWG(Copper)Aluminum
120V152 ft2AWG1/0AWG
480V609 ft3AWG1/0AWG
Voltage Drop is 3%, Line=Single phase

Let’s check the wire size for 3 phase with a distance of 150 ft.

Wire size for 70 Amp 3 Phase

Volt with 70 AmpsMax DistanceAWG(Copper)Aluminum
120V150 ft2AWG1/0WG
Voltage Drop is 3%, Line=3 phase

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What Size Wire for A 70-Amp Breaker?

For a 70-amp breaker, you need a 4-gauge wire, but only if the conductors are copper. If you prefer the cheaper option, get 2AWG aluminum cables. Also, match each breaker to the correct wire size. Otherwise, the wires will melt. The breaker is supposed to protect the cables.

For instance, 6AWG is suitable for 60A breakers. If you force the wires to carry more than 60 amps, the 60A breaker will trip, preventing the wires from overheating.

But what if the wires are just 10AWG? 10-gauge cables can withstand 35 to 40 amps. They will overheat and melt long before the 60-amp breaker trips.

Therefore, you should select the breaker wire carefully. Your choice will influence the safety and security of your home.

The NEC encourages consumers to limit the load to 80 percent of the circuit’s capacity. But that is not an excuse to use thin wires. Some appliances will double or even triple their electrical draw when they start.

You need a gauge that can withstand that spike, which is why most electricians use 4AWG copper wire for 70 amps. They know that 4-gauge conductors can transmit 70 to 85 amps of current without overheating. This leaves plenty of room for error.

You can also use 6 THHN wire because it can accommodate 55 – 70 amps. But 4AWG is still better, especially for people that want a stable power supply to run welders, drills, and other heavy-duty tools.

What Size Wire For A 70-Amp Subpanel?

4AWG is the best wire size for a 70 amp subpanel (2AWG for aluminum).

I want you to consider factors like the ambient temperature, material, installation method, and more. I also want you to limit the voltage drop to 3 percent. Additionally, the soil’s thermal resistivity is just as important (if you want to bury the cable).

Those other factors only matter if you’re tempted to experiment with cables of a lower gauge.

Wire Size For 70-Amp Service

The best wire size for a 70 amp service is 4AWG. It is the safest option, especially if the conductors are copper. You need a thicker cable if you prefer aluminum.

Pay attention to the temperature. 4AWG is perfect at 140 degrees F. But you can get a thicker cable if you want to leave room for expansion down the line. 4AWG is not the highest gauge on the market. 1AWG can accommodate as much as 145 amps.

You are better off getting a thicker cable than you need, just in case the load exceeds the breaker’s capacity, and it fails to trip. Conductors with small diameters create performance problems because of the voltage drop.

Some of your devices will stop working altogether because the cable cannot transmit the minimum power they require. But that is the best-case scenario. If you have a substantial load, it could start a fire.

Keep the distance in mind. Long cables are more likely to overheat because they have a higher resistance.

Ground Wire Size For 70-Amp

The ground wire size for 70 amp is 4AWG. You can use the same gauge for the hot, neutral, and ground wires. The ground wire is a defensive component that directs the current to the earth when a malfunction occurs.

You can also use a larger ground wire than all the other wires because it has less resistance. However, you cannot use a smaller wire. It will overheat and melt.

What Does NEC Say About It?

NEC expect consumers to pair 70A breakers with 4AWG.

Wire Gauge Size60˚C

This table shows the different amp ratings for 4-gauge wire in relation to variables like material and temperature rating.

This table may confuse some laypeople. It has connected 4AWG to 70, 85, 95, 55, 65, and 75 amps. Which is it? Can you pair 4-gauge cables with all those amp ratings?

Why does the amperage change? The table answers all those questions as well.

The amp rating of a particular wire size will change in response to the temperature and material.

Copper has a greater conductivity than aluminum. Therefore, it can transmit more power without overheating. Overheating is a critical consideration.

The table shows that 4AWG is the best size for 70 amps. But technically speaking, you can also connect 6AWG, 8AWG, and even 10AWG wires to a 70A load. The conductors will transmit the current you need.

However, this practice is not safe. Small cables have higher resistance than their broader counterparts. Therefore, a 10AWG conductor with a 70A load is more likely to catch fire.

A 4-gauge cable can accommodate 70 amps, but only if the conductors are copper. Aluminum is less conductive than copper, which, in turn, means that it has a lower current carrying capacity.

A 4AWG aluminum cable can carry 55 amps at best and only at the temperature the table has stated (140 degrees F). Manufacturers make cables that can operate at higher temperature ratings, which is why the table shows 4AWG copper conductors that can carry 85A at 167 degrees F.

You cannot use the amperage alone to select the wire size. A professional will encourage you to take the material and temperature into account. Don’t be so quick to dismiss aluminum simply because copper has better conductivity.

Copper is superior to aluminum in most areas. However, copper conductors cost more money. Look at your budget. Can you afford copper? Most homeowners will use copper if the distances are short.

But if you want to cover several hundred feet, you should reconsider.

Aluminum is not a bad alternative. Ultimately, you can still achieve the same results if you get aluminum cables with a better gauge. 4AWG won’t cut it, not for 70 amps. But you can use 2AWG aluminum cabling.

How To Determine The Correct Wire Size For 70-Amps?

You don’t have to calculate the wire size for 70 amps. The NEC has already performed these calculations. You can just use their tables.

They show the wire sizes in AWG and MM and the corresponding amp ratings. The NEC tables also show the amp ratings for different materials and temperature ratings.

You can identify the appropriate wire size for your situation by visiting the NEC’s online platform. If you don’t know how to account for factors like distance and temperature, talk to an experienced electrician, especially if you want the wire to cover a long distance. An electrician can calculate the voltage drop.

What Kind Of Wire Should I Use? Does Material Matter?

Yes, the material matters. The ampacity of each wire size changes with the material. Copper has higher amp ratings than aluminum. This is because copper is more conductive. But aluminum is cheaper and lighter.

Your selection will depend on your budget. Copper can transmit more power safely, but you can achieve similar results with a higher gauge aluminum cable.

Does Distance Matter? 70-Amp VS Distance

The distance affects the gauge. A longer distance requires a higher gauge because you have to compensate for the growing resistance. You should calculate the voltage drop before you proceed. Find a gauge that doesn’t allow the voltage drop to exceed 3 percent. A 4AWG copper wire is sufficient for the distances you encounter in most domestic settings.

Does Voltage Matter For 70-Amps?

At 70 amps, the voltage doesn’t matter. If you check most tables that list wire sizes and amp ratings, you will notice that they rarely mention the voltage. This is because the voltage doesn’t influence the wire size.

The wire size matters to the current because a conductor’s diameter affects the amount of electricity it can carry without overheating. The voltage doesn’t factor into that equation.

If your retailer is asking about the voltage, they are probably concerned about the insulation. The current shape the wire size while the voltage controls the insulation.

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