How to Calculate Electrical Service Size

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Determining the electrical service size for a home is important to understanding how much electricity can be used at one time. Modern lifestyles filled with electronic devices to make our lives easier, is very electrically demanding. The minimum acceptable service size a residential home is 100 amps. There are many methods for determining the service size. The most accurate method is using the gauge and type of the service entrance wires. This information is printed on the insulated cover of the wires. Never touch service entrance wires because the power they contain are capable of killing or severely injuring you.

  • Look at the service entrance wires where they fasten to the utility wires, if your power is delivered above the ground. The wires are connected at the drip loop where they fasten to the home. You are looking for the wire type (aluminum or copper) and the gauge that is printed on the insulated cover. Only attempt this if you can safely get close enough to the wires with zero chance of touching them.

  • Look at the service entrance conductors at the main disconnect if your electricity is delivered underground. Read the type and size off the insulated cover. Do not remove the cover for the main disconnect if you can't read the wires. Only a certified electrician should work around wires of this amperage.

  • Look at the size of the main breaker for the electrical system. The amount of amps is printed on the breaker switch. This is the safest way to determine the electrical service size for the house. But if the wrong-sized breaker is installed, it will be inaccurate.

  • Compare wire gauge to these common copper sizes (copper wire only): Copper 6-gauge -- up to 70 amps; copper 4-gauge -- 100 amp; copper 2-gauge -- 125 amp; copper 1-gauge -- 150 amp and copper 2/0-gauge -- 200 amp. The electrical service size is determined by the size and type of wire used, then comparing this information to government regulated wire sizes for these applications.

  • Compare wire gauge to the common aluminum sizes (aluminum wire only): Aluminum 4-gauge -- 70 amp; aluminum 2-gauge --100 amp; aluminum 1/0-gauge --125 amp; aluminum 2/0-gauge -- 150 amp and aluminum 4/0 gauge -- 200 amp.

Tips & Warnings

  • Service entrance wires contain enough electricity to stop the human heart instantly. Never touch them. Even your home's distribution wiring can kill or harm you. Be extremely careful when working around live wires.
  • Photo Credit Jupiterimages/Creatas/Getty Images
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