Electrical Panel Size Considerations

What size should the Main Electric Service Panel be for all the Electrical Circuits? How to Determine What Size an Electrical Panel Should Be, Factors that must be considered when sizing an electrical panel. © By: Dave Rongey

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Electrical Service Panel
Electrical Project: What size should the Main Panel Electric Service be for all the Electrical Circuits?

• Do I need a 100amp 150amp or 200amp electric service for our electrical circuits?
• I had a 24′ x 36′ building erected and I would like to install an electrical service panel. The back part is residence and the size is 24′ x 16′
• The only 220v item will be the stove.
• It will have baseboard heating and the usual outlets. no washer, no dryer, but it will have a hot water tank.
• Do I need a 200 amp service, or will 150, or even 100 amp service be adequate?

This electrical wiring question came from: Mick, a Homeowner from Yuma, AZ, Arizona.

Additional Question: I’m working on a remodel project where we will be adding a laundry room with a sink and the following circuits:

• Tank less water heater rated for 240 volt 40 amp 9600 watt.
• Clothes dryer rated 240 volt 30 amp 7200 watts.
• Lighting 120 volt 20 amp.

Is the sub-panel power adequate at 60 amp with 6 wire?

This electrical wiring question came from Mike, in phoenix, Arizona.

Dave’s Reply:
Thanks for your electrical wiring question Mick and Mike.

Electrical Panel Size Considerations

• Application: Main Electric Service Panel.
• Skill Level: Advanced – Best Installed by a Licensed Electrical Contractor – Not Recommended for Homeowners.
• Tools Required: Electricians pouch of hand tools and the various power tools necessary for the specific method of electrical service installation.
• Estimated Time: Depends on the type of panel, the location, and available access to the project area.
• Precaution: This is an extensive project. Working in an electric panel has possible arc flash hazards and should be performed by a Licensed Electrical Contractor.
• Notice: Installing an Electrical Service Panel should be done according to local and national electrical codes with a permit and be inspected.

Key Factors for Electrical Panel Size

• Type of Building and Size
  • There are several factors that must be considered when sizing an electrical panel, and some building departments may have size requirements as well, depending on the type of building and what it will be used for.
• Equipment Voltage and Amperage
  • All of the electrical loads must be determined stating the voltage and the amperage or watts.
• Calculations Base on Occupied Space
  • Some of the calculations may be made according to the size of the dwelling and actual occupied or living space.
  • Areas such as a garage are typically not a part of this calculation, however circuits for equipment in the garage will be a factor, such as a water heater, whole house vacuum system etc.
• Project Layout Design
  • Most all of these items are identified when a design engineer or architect creates the layout for the project and inserting all the devices as required by the local building codes.
• Building Department Approval
  • Submitting the plan or layout to the local building department is essential.
  • This is the all important planning step of the project that must be taken, otherwise the project will most likely not contain some of the essential circuits and equipment.
  • For Example: Required devices which are required for a home include:
    • Smoke Detectors.
    • GFCI Ground Fault Circuit Interrupters for protected outlets and devices.
    • AFCI – Arc Fault Circuit Interrupter.
    • Appliance circuits in specific locations.

When all of these required items have been identified then the panel size can be properly determined. It would be a shame to invest your resources to construct this building and then fall short where it really matters.

• Sizing a Sub Panel for a Laundry Room
  • Question #2 from Mike provides enough information to show that a 60 amp panel will easily become over loaded, especially when the dryer and tank less water heater turn on at the same time.
  • Keep in mind that ideally an electric panel should be loaded no moire than 80% of the load capacity.

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