300 Amp service is a type of service that is more common for commercial and industrial environments rather than residential ones. For 300 Amp service, you may need 350 kcmil copper wire or 500 kmil or 600 kcmil aluminum wire. 

• The amp rating of 350 kcmil copper wire is 310 at 75˚C (THW/THWN, SE, USE, XHHW ) and 350 at 90˚C (THWN-2, XHHW-2). 
• The amp rating of 500 kmil aluminum wire is 310 at 75˚C and 350 at 90˚C. A 600 kmil aluminum wire has 340 amp at 75˚C, and 385 amp at 90˚C. 
• If your run is over 1000 feet, consider using 400 kcmil copper wire or 600 kmil aluminum wire.

Where is 300 Amp Service Used?

A 300 Amp service is used in residential, commercial, and industrial settings. In residential settings, 300 Amp service is common for multi-family units, such as upscale apartment buildings, condominium complexes, mixed-use developments with commercial and residential spaces, and senior living communities. 

For a single-family unit, a 300-Amp Service is most often an overkill. If it is used, the house has to have a large electrical load, including extensive outdoor lighting, extra-large HVAC systems, multiple electric vehicle charging stations, saunas, and pools. In any case, if you are planning to install a 300 Amp service in a residential building, it is recommended to consult an electrical service and perform a load calculation. In many cases when 300 Amp service is considered for residential settings, 300 Amp service proves to be more than enough. 

  300 A services are not popular with utility companies in the United States. Most companies install 100A, 200A, and 400 A three-phase service. However, in some areas and states, 320 A service is offered by utility companies. If you are considering upgrading to 300 A service, many utilities will go straight to 400 Amp service, so you should consider this possibility. Read more on the 400 Amp service here.

All things concerned, 300A services are more common in commercial and industrial settings. Some of the common applications of these services include:

• Office buildings
• Large retail stores and supermarkets
• Large restaurants
• Hotels
• Hospital buildings
• Data centers
• Manufacturing facilities
• Processing, power, and water treatment plants
• Paper, steel, and textile mills.

Which Types of Cables are Used for 300 Amp Service?

When it comes to choosing cables for a specific service, the most important factor is size. However, it is also essential to overview the types of cables for this type of service. Please note that UF-B and NM-B cables are not used as they are not made to sustain large electrical loads. Common cables for 300 Amp service are:

• THHN/THWN Wire: Available in 350 MCM copper and 500 MCM aluminum. Often used in conduit or trays.
• 350 MCM XHHW-2 Copper Building Wire with XLPE insulation for services feeders and branch circuits. Just like THHN/THWN, it is often used in conduit or tray.
• Service Entrance SER Cable: Service entrance cables for 300 AMP panels are available in copper and aluminum. These cables transmit power from the service drop to the meter base but are suitable for general service applications.
• 500 MCM Aluminum RHH/RHW-2/USE-2 and 350 MCM XLP USE-2 RHH RHW-2 Copper Building Wire for underground applications and when extra sturdiness and abrasion resistance are preferred. Suitable for direct burial and used in most demanding environments.
• 500-500-350 Rider Triplex Aluminum and 500-500-500-350 Wofford Quadruplex Aluminum are an excellent aluminum cable option for direct burial installations.

• In industrial conditions, Type W and DLO cables may be used in 300 Amp circuits.