I have been involved in the contracting business for many years and have done just about all there is to do in new construction.
It doesn’t matter if it is residential or commercial when I do the bid I also do a load calculation of the service in order to establish the size of the service disconnect and the service entrance conductors even if an engineer has done a calculation. I will also do this calculation when doing renovation work in order to give the customer what they are paying for.
When called to evaluate an electrical system by a homeowner or realtor I also do a load calculation to ensure that the service is up to par. It is very rare that I find a service that is too small for the building being served. In most cases the ones that are too small will be a fuse panel where the appliances were changed from gas to electric or an old oil furnace was changed out for an electric.
A 2000 square foot home with a three ton heat pump and a 10kw air handler will only need a 150 amp service unless it has more than the average home such as but not limited to pool, hot tub, work shop with heavy equipment such as large air compressors and the like. Use gas appliances such as heat, water heater, and cooking appliances and this home would only require a 100 amp service.
My home has 1980 square feet all electric with two heat pumps and also supplies two out buildings one 2400 square feet brood mare barn and the other a 960 square foot work shop for my farm equipment that has air compressor, welder, drill press, grinders and the like and the calculated load is just 227 amps.
I agree that it is good for everyone to know how to do a service calculation when doing a home inspection but I don’t think it is necessary in every case. What we need to realize is that when doing a load calculation we don’t add everything that a homeowner might plug into a receptacle we only use 3 watts per square foot. It doesn’t matter if the home owner is going to plug in a blow dryer, big screen TV or even portable electric heaters we still figure the load at 3 watts per square foot.
This will equate to an 1800 square foot home having 3- 15 amp circuits for the lights and receptacles 2- 20 amp for the kitchen and dining room 1- 20 amp for the laundry and 1- 20 amp for the bathrooms. This is code compliant no matter what they buy and plug into those receptacles.
As far as the other thread is concerned even if the service is too small there is not much can be done except to spend the monies to upgrade the service and bring the two wire circuits up to par with a complete rewire. The question is which one will pay for this high dollar fix, the buyer or the seller or will it remain as it is. It is obvious that the seller is not going to spring for the fix or it would have already been done so I suppose if the buyer wants it done it will be on their dime.
What we have to keep in mind is that if it was compliant at the time of installation it is compliant today no matter what we think people is going to plug into those receptacles be it two wire or not.