100 Amp Service Ground Wire Size: Types Of Wire, How Many & More

Correct ground wire sizes are notorious for finding because they only carry current during short circuits. The AWG for ground wire can be similar to the hot and neutral wires or slightly higher. Today, we will talk about the ground wire of 100 amp service. 

While looking for the ground wire for 100 amp service, it can be as thin as 10 AWG or as thick as 2/0 AWG. The minimum ground wire size for 100 amp service is 8 AWG copper or 6 AWG aluminum wire. It can change based on several factors.

You will need to consider a few things before you decide on the exact ground wire size. To help you find it, we will help you know how you can determine the ground wire size for 100 amp service through this article. 

Knowing the correct wire size for 100 amp service

Before I share the ground wire size for 100 amp service, let’s talk about 100 amp service and its ideal wire size. 

100 amp service is a considerable service that can run an entire house with a few electrical devices. 

But it is not enough to run modern electrical, power-hungry appliances.

One of my friends used to have 100 amps to run an entire house. 

He could run 1-2 electrical appliances efficiently. Now he has upgraded to 200 amps like mine. 

The wire size for 100 amp service is 4 AWG copper wire or 2 AWG aluminum wire. 

This is what NEC says in Table 310.12. 

Isn’t it confusing because it is also the same wire for 70 amps? 

At the same time, when you see the Wire Ampacity Chart, you will see that a 4 AWG copper has 85A ampacity at 157°F, and a 2 AWG aluminum has 90A ampacity. 

I was confused, too, until I learned that NEC provides only the minimum wire gauge for different feeders. 

This discrepancy between the suggested wire size and the wire ampacity can be resolved by considering several factors like the wire material, distance, ambient temperature, wire ampacity, and voltage drop. 

The NEC allows you to use the 4 AWG for 100 amps based on the understanding that the derating factors should be considered before confirming the wire size. 

4 AWG is ideal if the distance is shorter than 50 feet.

Professionals say the precise wire gauge should be 3 AWG copper or 1 AWG aluminum wire. 

My friend used this wire size. 

You will sometimes have to use 1 AWG copper and 2/0 AWG aluminum wires. That is how the wire size gets influenced. 

Keep checking the tables, as NEC keeps changing the wire gauge. 

You need to know the actual wire size before the ground size because you must choose the correct ground conductor size for 100 amps based on this wire size. 

Demystifying 100 amp service ground wire size: A comprehensive guide 

Generally, the ideal ground wire size for 100 amp service is an 8 AWG copper wire or a 6 AWG aluminum wire. 

But examine a few things before finalizing this wire size. 

In the National Electric Code or NEC, check the NEC article 250, table 250.66, which discusses the Grounding Electrode Conductor For Alternating Current Systems. 

From this table, you must determine which hot copper wire can be grounded with which ground wire size. 

For example, if you use a 2 AWG copper wire, you must ground this with an 8 AWG copper wire. 

The same is for the aluminum wire. If you use a 1 AWG aluminum hot wire, you will use a 4 AWG aluminum wire for grounding. 

If you check the grounding table, you will find that the wire ampacity is not mentioned. 

But we can still find out with a bit of help. 

There are 3 steps to determine the correct ground wire size for 100 amp service based on NEC table 250.66:

Decide on the wire material

First, you need to decide what type of wire material you would like to use for 100 amp service: whether you will use copper or aluminum. 

Both the wires have different strengths and weaknesses. 

So, the wire sizes will be different based on the wire material. You need to find the ground size for the particular AWG. 

Find the wire ampacity

Find out the wire’s ampacity from the AWG Wire Gauge Ampacity Chart. 

Check the ampacity chart and see which hot wire can handle 100 amps from the NEC table. 

You will find that the 3 AWG copper has 100A ampacity. 

A 2/0 AWG aluminum has 108A ampacity at 157°F (average ambient temperature), but a 1 AWG aluminum wire also has an ampacity of 100 amps. 

Though you can use both, using 2/0 AWG to stay safe is better, especially for aluminum. 

The NEC table 310.12 shows that the wire gauge NEC suggests for 100 amp service is 4 AWG wire. 

While it is not incorrect, this is the minimum wire gauge for 100 amps.

Professionals will recommend using a lower AWG wire for the service that has an ampacity of 100 amps safely, thus the 3 AWG wire. 

Find the ground wire size

Once you have known the ampacity for 100 amp service, you need to ground the wire. 

You must consult the ground wire size chart mentioned in the NEC table 250.66. 

The chart shows different wire sizes with appropriate ground wire sizes for copper and aluminum. 

For 3 AWG copper wire, it is 8 AWG for the ground; for 2/0 AWG aluminum, it will be 2 AWG ground wire. 

For 1 AWG aluminum wire (since it has 100A ampacity at the ambient temperature), the ground wire size is 4 AWG aluminum. 

If you are using the minimum wire gauge suggested by NEC, then for a 4 AWG copper wire, you can still use 8 AWG copper wire for the grounding 100 amp service. 

Whereas for 2 AWG aluminum wire, you can use a 6 AWG aluminum wire for grounding. 

Choosing the correct ground wire for 100 amps: Key considerations

There are several options to choose the ground wire size for 100 amps. 

It depends on the wire size you choose for the 100 amp service in the hot and neutral connections. 

If you are a beginner, you must consider a few more things. 

I had taken the following factors into account before I decided on the wire size and grounded it:

Sub panel

In today’s technical world, 100 amp service is too insufficient. 

Most standard houses in the US will have 200 amps for conventional houses. 

My house needs a 200 amp electrical system to power my kitchen devices, laundry appliances, and heating and cooling units.

However, 100 amps is still an option; there might be chances of overloading if you use power-hungry devices. 

Installing a sub-panel can save you by providing new circuits and preventing overload. 

Sub panel’s location matters because when you install it in the same building, you will have to run the same ground wire (you use for 100 amps) for the sub-panel too. 

All the ground wires bond back in the main electrical panel together with the neutrals.

The panel’s location will affect the distance of running the ground wire. 

When the distance increases, you must use a smaller AWG with a thick diameter and high cross-section to carry enough current without increasing the resistance. 

I also have a sub panel but for a detached building. So, I had to run a separate ground wire for it.

Hot/neutral wire vs. ground wire

Choosing a ground wire based on the NEC ground wire size chart would be best. 

But you can use the same wire size for the grounding as the hot and neutral wires. 

The hot and neutral wires always carry current because one carries power from the primary power source, and the other returns it to complete the circuit. 

These wires need to be thick enough to carry enough power. 

On the contrary, the ground wire will carry current only when there is a short circuit because the excess current needs an alternate path to flow.

You can use a slightly higher AWG for the grounding wire since it carries current only during such surges.

It carries current for a fraction of a moment before the breaker trips. 

Even if the current exceeds the ground wire’s ampacity, it will not transmit for too long to overheat. 

Distance 

The distance will not change the wire’s ampacity rating. 

For example, a 3 AWG copper wire will have 100A ampacity for both 50 feet and 100 feet of distance. 

Distance influences the wire’s ability to carry the amp and doesn’t change the ampacity. 

The wire resistance and voltage drop will increase if the distance goes longer. 

According to NEC code 310-16, increase the amps by 20% for every 100 feet. 

It is essential for the hot and neutral wires as they will always stay active. 

Since the ground wire rarely carries current, you do not have to increase the wire size by 20%. 

The excess current running through the ground wire during a short circuit will transmit for a few seconds. 

So, any problem has fewer risks, despite the higher resistance. 

However, precaution is better than cure because too-thin wires are prone to overheating. 

Slightly less would be acceptable to compensate for the voltage drop. 

So, if you use a 6 AWG wire at 50 feet, use a 4 AWG wire for grounding at 100-150 feet. 

Material 

In most electrical works, copper and aluminum are preferred the most.

Copper is preferred over aluminum as it has better conductivity and resistance, which is helpful for long distances. 

Aluminum is cheaper and easy to install due to its lightweight. 

But you cannot use it for too long distances like the copper wires. 

When you use copper wire to ground 100 amp service, you can choose an 8 AWG wire. 

To use aluminum wire instead of copper, you must select a higher AWG to compensate for the copper’s superior quality. Use a 6 AWG wire. 

Another option is copper-clad aluminum. This aluminum wire can provide you with some benefits of copper through copper fittings. 

The size remains the same as aluminum: 6 AWG. 

Cable type 

Contractors have a range of cable-type options at their disposal. 

The setting and appliance can affect your decision in the location. 

In the residential, you will mostly find thermoplastic high-heat wiring nylon. 

But in the commercials, you have stranded steel armored cable. 

Before installing the ground wire, contact your local contractor to find the correct cable type. 

Some areas will have armored cable as the metal jacket works as the ground. 

The environmental conditions should also be assessed if the wire is underground. 

Use a flame retardant mechanism to keep the wires safe from outdoor elements. 

Conduit size

A conduit is a metal tubing home to the wires, protecting them from physical damage. 

Conduit works for overhead and underground wire connections, but it’s mainly used for underground services to avoid damage.

Some contractors do not like using conduits, as running the wires through the pipes is very difficult and time-consuming. 

If your ground wire is in a safe place, you can keep them bare. 

But I do not think it to be a safe choice. 

I have a bare ground wire for my house’s electrical service. 

So, I have had it run in a conduit for safety. 

If your local codes suggest mandatory conduits, you must use them. 

Such rules are good as they encourage the contractors to follow the rules and prevent them from keeping them bare. 

The conduit size depends on the number of wires. 

For 100 amps, a 1.25-inch conduit, Schedule 40 or 80 PVC gray, should be enough. 

The conduit should not be filled over 40%. 

If needed, choose a larger conduit measuring 1.5 to 2 inches. 

Rules and regulations 

Though NEC has some rules about the ground wire, you must follow the local codes and abide by them if you have any. 

When the local code suggests a different wire size for the grounding, you need to follow that and not the NEC rules. 

You can only follow the NEC rules when your area has no dedicated local code. 

Consult the rules and see what they say about the grounding wire for 100 amp service. 

Check the wire material, the distance, the wire size and ampacity, the voltage drop, and every detail. 

Some authorities specify the ground rod length, diameter, wire type, clamps, etc. 

Prioritizing electrical safety: Importance of proper ground wire sizing for 100 amps service

Prioritizing ground wire is essential for electrical safety for all electrical services, and 100 amp service is no exception. 

The ground wire is a safe path by directing electrical faults like short circuits or current leakage. 

Here are some reasons behind the importance of ground wire for 100 amps:

Fault current pathway 

Excess currents start flowing during a short circuit and require an alternate path. 

The ground wire will provide this alternate path. 

The current flows through the ground wire to the ground, thus saving you from electrocution. 

Electrical system stability 

A correctly sized and installed ground wire can maintain system stability with a proper ground reference point. 

It can further stabilize the voltage level of your 100 amps’ electrical service and reduce voltage fluctuations.

It will also reduce damage to the household equipment and prevent disruption of their operation. 

Fault detection and protection 

The ground wire is a crucial part of the grounding system for your electrical service. 

The ground wire can detect the ground faults by providing an alternate return path for the excess current to flow back to the source. 

This further signals the breakers and Ground Fault Circuit Interrupters (GFCIs) during ground faults, for which they trip off and save appliance damage and electrocution. 

The excess current flows through the ground wire just before the breaker trips off. 

Grounding solutions for 100 amp service: Installation tips

You will need a grounding electrode to install the ground wire to your 100 amp service first. 

It can be a grounding rod, a grounding ring or plate, a concrete-encased electrode, and metal pipes. 

I use a grounding rod. So, I will share the steps for the grounding rod.

To install the ground wire for 100 amp service, follow the following steps:

• Choose a grounding electrode first. It can be a grounding rod, metal pipe, grounding plate, concrete-encased electrode, grounding ring, or plate. My house has a grounding rod for my 200 amp service. 
• Find a proper location. Avoid areas with rocks, water lines, gas line pipes, etc. Make sure the grounding electrode is close to the electrical service entrance. When you do this work with a contractor’s help, he will detect and avoid all these lines. 
• Dig a 2.4-meter hole in the ground and insert the grounding electrode.
• Clamp the rod’s upper part to one end of the ground wire and the other end with your house’s main electrical panel. Try to keep the distance short and straight. 
• Tighten all the wire connections and ensure the wire is protected against any physical damage. 
• For proper grounding solutions for 100 amp service, follow the following installation tips:
• Install one or more grounding electrodes and wires by consulting the local codes in your region. I needed 2 electrodes and wires since I have a separate sub-panel for a detached building after consulting the licensed electricians. 
• Run the wire from the electrode to the main panel of your house. For the best results, make it short, tight, and straight. 
• While installing the grounding electrode, avoid rocky areas. 
• Install the Equipment Grounding Conductor on every branch circuit and connect it to the grounding bus bar of the outlets, switches, and equipment enclosure. 

You can also install the ground wire under the ground. 

That will require an expert’s help. 

My friend’s house has ground wire installed in a conduit under the ground. For this, contractors have dug a trench, run the wires inside the conduit, and then installed it. 

It cost a few dollars and was time-consuming, but the work is safer than installing it alone. 

Final Thoughts 

There is no exact wire size for the ground wires. It is based on the wire size you use for the hot and neutral connections. For 100 amps, if you use 4 AWG copper or 2 AWG aluminum wires, you can use 8 AWG copper or 6 AWG aluminum wires for grounding. If you follow the ampacity chart, you will need 3 AWG copper or 1 AWG aluminum for 100 amps. In that case, the ground wire will be 8 AWG copper and 4 AWG aluminum for grounding. 

Since the aluminum wire is inferior to copper, you can choose a slightly lower AWG with an ampacity of slightly more than 100 amps. For example, a 2/0 AWG has 108A. In that case, you can take 2 AWG aluminum for grounding. As you can see, the ground wire does not have only one but many sizes, based on the wire size you use for hot and neutral connections. Even if you use a thinner wire, there won’t be a problem because it does not always carry current except for short circuits. 

During this time, the wire carries the excess current for only a fraction of a second. So it won’t overheat the wire during the transmission. Make sure you are not using a skinny wire. Consider the factors like the distance, material, cable type, etc., before confirming the wire size. Consult with experts and licensed electricians to decide the correct gauge and the number of wires and install it for your house. 

Reference: Ground Wire Wikipedia

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