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What Size Wire for 100 Amp Service (Wiring Guide)

When working on a project involving electrical services, picking the right wire size for those 100-amp connections is crucial. 

The most common wire size for 100 amp service is usually a #2 AWG wire, especially if the distance between the utility and breaker panel is more than 50 feet. But remember that the wire material and distance can significantly determine the appropriate wire size.

Let’s dive further into details and learn the appropriate wire sizes for a 100-amp service.

Determining Wire Size for 100 Amp Service

Copper Wire

zoom shot of a rolled copper wire

Regarding copper wires for 100 Amp service, we have a couple of options based on distance.

If your utility box is less than 50 feet from the breaker panel, I’d suggest using #4 AWG copper wire. It’s perfect for shorter distances and can handle the load without issues.

If the distance exceeds 50 feet, you’ll want to upgrade to a #2 AWG wire to ensure electrical efficiency. Trust me; you don’t want to skimp on wire size when dealing with a long run.

Aluminum Wire

rolled aluminum wire

Now, if you prefer aluminum wire, you’re still in luck! Aluminum is also a great conductor and often comes with a friendlier price tag.

For a 100 amp service, many electricians opt for wire size #2 or #1 AWG aluminum or copper-clad wiring. This is because aluminum conducts electricity slightly differently than copper.

I know it can be a bit confusing, but the main takeaway for aluminum wire size is generally to go a size up (meaning a lower number on the gauge) compared to copper.

This ensures that the wire can meet the same safety and performance standards.

There you have it! Knowing the right wire size is key whether you’re going for copper or aluminum for your 100 amp service.

When in doubt, consult a licensed electrician to ensure your project’s safe and proper installation. Good luck and happy wiring!


National Electrical Code Requirements

Let’s discuss the National Electrical Code (NEC) requirements for selecting the right wire size for a 100 amp service. These requirements are not just for making things look pretty – they play a big role in ensuring our safety.

So, here’s the deal: the NEC has some guidelines for wire size based on different factors, like voltage drop and length of wiring.

According to NEC and some licensed electricians, a 100 amp breaker panel needs either #4 copper wiring or #2 aluminum or copper-clad wiring to be safe.

Now, don’t forget about distance! For example, if you’re going for a 100 amp sub panel 100 feet away, you should opt for a #1 AWG wire with a 130 amp median capacity.

Wire Size and Distance for 100 Amp Service

Wire Size (AWG)Maximum Distance (Feet)
#435-40 Feet
#255-70 Feet
#185-100 Feet
#0 (1/0)125-150 Feet
#00 (2/0)175-200 Feet

Please note that these distances are approximate and can vary. Always consult with a professional electrician or refer to the National Electrical Code (NEC) for up-to-date information.

Remember, having the right wire size is crucial when avoiding electrical hazards and maintaining a safe environment.

The National Electrical Code is updated regularly to protect us, so always double-check the current version when planning any electrical project.


Wire Ampacities and NEC 80% Requirement

Choosing the right wire size for an electrical installation isn’t as simple as selecting a wire that can carry the required current.

Safety regulations, specifically the National Electric Code (NEC) 220-2, stipulate that the maximum loading for any branch circuit is 80% of the rating of the circuit for the ampacity of the wire for any load.

This rule is a safety measure to prevent overheating and potential fire hazards.

To illustrate, a #4 AWG wire has an ampacity of 85 Amps, but according to the NEC 80% rule, it should only be used for loads up to 68 Amps.

Similarly, a #1 AWG wire has an ampacity of 130 Amps, but it should only be used for loads up to 104 Amps.

Here’s a summary of the wire sizes, their ampacities, and the 80% value of the ampacity as per the NEC 220-2:

Wire Size (AWG)Ampacity80% of Ampacity
#485 Amps68 Amps
#3100 Amps80 Amps
#2115 Amps92 Amps
#1130 Amps104 Amps

Understanding wire ampacities and the NEC 80% requirement is crucial for safe and efficient electrical installations.

It helps ensure that electrical wires are used within safe limits, reducing the risk of electrical fires and other hazards.

When planning electrical installations, consulting with a qualified electrician or electrical engineer is important.




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About Alex Robertson

AvatarCertifications: B.M.E.
Education: University Of Denver - Mechanical Engineering
Lives In: Denver Colorado

Hi, I’m Alex! I’m a co-founder, content strategist, and writer and a close friend of our co-owner, Sam Orlovsky. I received my Bachelor of Mechanical Engineering (B.M.E.) degree from Denver, where we studied together. My passion for technical and creative writing has led me to help Sam with this project.

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