Originally Posted by fumbles
I'm in an apartment using a range outlet
fumbles: if you are on 40A and want to run two kettles at the same time, you are going to have to keep total power at 9000W or less, and you can't really power anything else except the elements unless you drop down further.
9000W will pull 37.5A when both elements are running ... IF you actually have 240V available.
240V is not a guarantee. It could be higher or lower than this, which is going to affect the amount of current you pull.
If you are only getting 220V instead of 240V, then a "4500W/240V" element (for example) is really only acting as a 3780W element and will pull 17.2A... so two of those will pull 34.4A and your 40A breaker would handle things fine.