The Electrical Service

How Much Power do I need?

   Now that you've input your information in my service load calculator and had a number spit back at you, let's discuss what that number means.

    What size service you install to your house is decided by figuring your calculated load. The term calculated load is used because we don't just simply add up every electrical load in the house and use the end result. Why not? Consider this... when was the last time you had something plugged in to every outlet in your house and turned on at full power, had all your lights on and all of your appliances running on high? The point is that it just doesn't happen! For an example, why would your air conditioner and heat be on at the same time?

    When we calculate the potential load on a house electrical service, we add up all of the legally required circuits, add in the optional circuits, and then apply some demand factors that have been found to work well and so have been set into the NEC as electrical code. What we end up with is a number, in amps, that we then base the service size off of. If you are interested in seeing the actual tables and numbers used in this calculation, you can look in article 220 of the NEC.

    Our next step is to decide, based on our calculated load, what standard service size to install. Legally, house services can be as small as 100 amps, and are essentially limitless from there, but there are some pretty easy standard sizes and those are the ones we'll discuss here.

    Except for very specific and rare instances, I would never recommend installing less than a 200 amp service on your house. The cost, even from the minimum 100 amp to the 200 amp, is actually pretty minimal. Part of this being due to supply and demand, the fact that the 200 amp service is the most commonly installed size, and partly because some of the parts are actually the same. So even if your calculation came out at 50 amps, I would install a 200 amp service on your house, even though it's not required by code.

    The next step up, realistically, for a house service is 320 amps. For the 320 amp service we use what is called a "continuous" rated meter and two 200 amp panels. This service is normally only required on fairly large houses with all electric appliances. If your house calculation came out over 180 amps, I would consider this service size, and if it came out over 200 amps, this size would be required.

    Anything larger than a 320 amp service on a house requires some pretty hefty equipment and more than a basic knowledge of wiring practices and electric codes. I would recommend that if you need a larger service than the 320 amp you hire a licensed electrician, at least to complete your service for you.

    Now that you have decided which size service you will install, on the next page I'll discuss the different types and styles available.