NEC Article 220 load-calculation for entire house

Question

My house was built 32 years ago, with 200 amp electrical service. Since then I have added a number of large electrical loads, and decided I should do a load calculation for the entire house using NEC Article 220.

Here is what I have so far:

Items I'm unsure about:

Lines 7, 8, 9: Are these square-footages part of my dwelling unit, and thus part of the 3VA/sq-ft calculation? Do they not count at all, because they're not habitable living space? (Lines 7 and 9 are un-heated, and line 8 does not have code-compliant access, an uncompliantly-steep spiral staircase). Does line 9 require a calculation outside the 3VA/sq-ft, since it's served by its own subpanel? It does not, however, have hardwired loads.

Am I counting the EV charger correctly? It is a Clipper Creek HCS-50, rated at 40amps, calls for 50amp breaker & wiring.

Am I counting the water-heaters correctly, do they need to be uprated 125%?

Does 220.53 reduce my total at all?

Anything else that seems wrong (in either direction)?

Part 2 of the question:

If, after corrections given here, I come in over 200 amperes, how worried should I be?

If I decide to upgrade my service to 225 amperes, what is required other than a 225 ampere main load center?

• Obviously, and cheaply, the THW cables from the meter to the main breaker (currently 2/0 for hots and 1/0 for neutral).
• What about the transformer (I have my own private one in this rural area), the lengthy buried cables from the transformer to the meter base, and the meter itself?
• Are these questions only the POCO can answer?
  • Call to them said surely the transformer/cables/meter can handle 225 amps; pinned down, they said cables were 4/0 aluminum (3/0 neutral) which ampacity charts seem to say are only good for 180 amperes; so something doesn't jibe.

Answer 1

The calculated load valve is for new services, for existing services you can measure the load on the service. Do you want to put in a new service? Did you just win the lottery?

Putting in a new service in many states requires you to update everything to code and in the last 32 years there are a huge number of changes that will be required. Would I even consider a upgrade from 200 to 225? Not a chance, I would not really think about it until 250, and at 300 sure it makes sense.

I have measured many homes and have never found one at 80% in fact most residential homes even in all electric are 80 amps or less on average.

Now to help you feel better about your home, have you changed from all incandescent lights to CFL or LED? CFL cuts the lighting load in 1/2, while LED gives close to an 85% reduction. Has the furnace been upgraded to a newer heat pump? Have the refrigerator, dishwasher, and oven been updated to energy star devices?

All these upgrades relieve the actual demand and the code panels are looking to change the load calculations for this reason.

What would an electrician do to evaluate the demand? They would pull the dead face off your main service panel and clip a clamp meter on one leg then the other, then tell you to turn on the oven and heater or air conditioner and all the lights and repeat the test heavily loaded. As I just described it, I would bet that your home probably will not be drawing over 125 amps.

If you want to get really crazy add the washing machine and dryer, and turn the hot water on. Unless you have an electric on demand water heater, you will probably still be below 180 with just about everything on at the same time.

You can do this same test yourself with a amp clamp meter costing under 100$

If you see an imbalance from 1 leg to the other this may need to be balanced, but don’t balance with crazy loads; balancing should be done with normal loads that you have running.

Just FYI car chargers are calculated at 125%.

The feeder to the house only has to be 83% not 125 because of the diversity of the load, even turning so much equipment on I would be surprised to see 80% and there are additional safety factors built in.

For example a 14AWG wire is limited to 15 amps by Code, but in a equipment panel from memory it is over 75 amps. There is a huge safety factor.

Answer 2

Am I counting the EV charger correctly? It is a Clipper Creek HCS-50, rated at 40amps, calls for 50amp breaker & wiring.

Not quite. The EV must be accounted for at 125%, hence 50A breaker. 50A x 240V = 12,000 VA.

I'm sure we've had the conversation about how 50A charging isn't actually necessary for 99% of people (even though their vanity definitely prefers it, their vanity probably doesn't want to write the check for a service upgrade). So turning down EV charge rate is a great answer here - unfortunately CrippleCreek units don't allow that feature.

However, the other conversation that should be added to this topic is about modern energy management systems. Technology Connections has a video for that too and a part 2 on the way.

We're not supposed to do product recommendations here, but the video mentions the SPAN panel which does energy management for breakfast (at about $7000 with mandatory installation)... So let me mention a much more practical alternative. Emporia makes one of the cheapest EVSE's (car "chargers") on the market - but amazingly, they added the software for it to sync up with the Emporia VUE home energy monitor. The latter is just another energy monitor like Sense or Curb, but the VUE will handshake with the Emporia EVSE, and slow down your car charging when your house's loads are near limits. Here's the cool part: Doing this removes the EV from the Load Calculation. (or rather, it calculates as the lowest setting it will automatically reduce to, and if that's zero, then it's zero on the Load Calc.)

As Alec discusses, most of our electrical loads are actually storage loads - the EV obviously; the water storage tank; the dryer (if you realize it can be interrupted for short times without harm). And the A/C or heater is also a storage load since the storage is your house - a 5-30 kWH storage battery you didn't even know you had :) As such, it's pretty easy to exploit time to shift these loads around (without significantly impacting their function), and get more stuff on a panel than would otherwise be possible if they were not coordinating.

So "watch this space" for emerging developments, aside from EV charging which is already here.