100 amp service

I am a newer inspector and have a question regarding electrical service. I inspected a home with a 100 amp service; however similar sized homes in the area have 200 amp service. The home is approximately 6,000 ft square. My question is, how will a home owner know if their electrical service is undersized?

I’m going to guess and say that a 6000 square foot home cannot be run in a code compliant manner off of a 100 amp service. The HO would need to find someone to do a load calculation to know for sure.

It is no question asked! I lost the program when my hard drive was damaged but I think you can still get it at InspectorPro website.

If you would like to play around you can find a free residential load calculator here:


I talked to a local Electrical contractor who was just at a manufactures meeting .
They said that they expect to see more 100 amp installations and less 200 .
It seems more efficient equipment and a lots less loads in the homes could be in the near future .
You can see this with Lighting more insulation and better TVs, computers ect .
Time will tell

The only real way to know is to do the calculations. Obviously an electrician with years of experience can estimate the size fairly close but the only true way of determining the proper size of a service is through Article 220 calculations.

Great responses, thanks everybody.

Paul always likes to think we know all these Articles. :wink:

I think this is what he is talking about. http://www.ecmag.com/?fa=article&articleID=5737

If not, he can interject and correct. :slight_smile:

How old is the house? Salt Lake City may have an addendum to the NEC that states that all new homes must have a 200 amp service.


3 watts per square foot and 2 small appliances and 1 laundry is all that is required. Using the optional calculation this house would only require a 62.5 amp service.

If everything is gas such as the cooking heating and hot water it is very possible that this house could get by with a 100 amp service.

Around here a 6000 sq ft home with natural gas would need 100 amps just for the kitchen. :smiley:

Around here there would be two 200 amp panels side by side.:Dsee it all the time.

As a HI I do thermal imaging on every electrical panel in the home with every electrical item operating that I can find. My # 1 problm I find is homes that were added onto and remodeled kitchens going from gas to electric stoves and not updating the electrical panel old 100 amp panels just don’t cut it with all the modern toys we can stick in a home

Well…thats a large statement saying that i " like to think we already know this". If those making electrical recommendations to people do not know it…possibly a change in profession or CEU’s are in order. But again lol…you said i assume it…i dis not assume it;)…i expect it my friend.

Since not doing calculations nor about to start my rule of thumb is pretty basic.
Around here if they use electric instead of gas in the kitchen it is normal to expect 200 amp service.

Any other easy tips for us regular humans ?

Around here the AHJ will require 200 A minimum and 400 for larger homes, even if heavy gas use is anticipated. Reasoning is that gas appliances are often later replaced with electric.

My house is small, about 1400 sf, and I have a 100 amp panel and it is way to small.
Most circuits are overloaded and no more room in the panel.
Any house built around here now has a 200 amp panel minimum.


Mr. Cyr, I can understand the size (# of circuits available) being a problem, I am having some difficulty understanding (most circuits are over loaded) unless you have 1 with very few circuits and have all electric appliances. what year was your home built. Really just making conversation, as having wired many homes over 30 years 1 thing that is a certainty is most contractors will ultimately install the least they can unless someone tells the they want more than the minimums. If I am not wrong and Mr. Pope may be able to assist with the NEC on this but believe there is is a requirement for designing for future expansion of the electrical system and this may be a commercial requirement rather than a residential requirement. Enjoy reading the posts thanks to all for their input.


Well this is yet another case of an AHJ playing fortune teller on someone else’s dime. Calculations don’t lie and municipal inspectors should inspect for what they see…not what the predict they will see.

Terry, this is common and not new to this area.

My house was built in 1967, and I bought it in 1987.

It is a Tri-plex meaning you have a single car garage and a family room on a slab with six steps down to the basement from the family room.

The electrical panel is in the garage exterior wall and ceiling in the garage and family room.
The panel is totally inaccessible.
Most of the wiring is 14/2/ground #18 cut off in most outlets.

The house was not wired originally for micro-wave, dishwasher, computers, additional TV’s, portable heaters, exterior lights for Christmas and so forth.

I had an electrician sort out and clean up a few circuits when I bought the house, but did what he could with what he had to work with.

With no access to the panel, gutting out all the ceilings is the only option.

Circuits get overloaded in certain areas when too many things operate at the same time.

I need to look into it more when I get time. :slight_smile:

I definitely agree, but that is the case here. For example, I have a house with all gas appliances except A/C and I was required to install a 400 A service. The interesting thing is that outside the city limits there has been no building inspection for many years, yet the houses I inspect there generally adhere to the same rules. Go figure! All that said, as a H.I. I try not to pass judgement on the size of the service unless it is obviously way out of line. If they want me to provide engineering services, I will do that but not at home inspection rates!