I have a 20-year old house with a 200 amp main panel and it has a 125 amp subpanel that runs to a separate, 400 sqft dwelling unit on the property. The maximum load on that subpanel is minimal, except when the tankless water heater kicks on and draws 75 amps for, say, a 10-minute shower (which is only a couple of times a year when we have guests staying there). Other major loads on the main panel are:

- a double wall oven - 40 amps (though more like 20 amps as we usually only use one of the ovens)

- an electric vehicle charging receptacle - 24 amps

- an electric clothes dryer - 30 amps

- table saw - 20 amps

- shop heater - 30 amps

There is no AC, and the furnace is gas.

So the highest total of all the major loads is up to 144 amps, not counting the rarely used tankless water heater load of 75 amps. The likelihood of all of these loads drawing at the same time is about zero, and I've never had any problems with flickering lights or tripped breakers. However, I am thinking about getting a second electric vehicle and it would be nice -- though not necessary -- to add a second charging receptacle drawing at least 24 amps, and it is possible that two cars could be charging at the same time.

Before I decide to add that second charging receptacle, I would like to know if there is any electrical code limit on total major connected load. I've read that it should be limited to 160 amps for a 200 amp panel, but don't know if that is a requirement or just a recommendation. I think I would be likely to stay under the 160 amp number even with a shower running because all of those other loads just wouldn't all be happening at the same time. However, I'd like any advice on this situation, whether it's a code requirement, or simply good practice. Thanks.