As you’re dealing with current, not voltage, the effect is only a second-order one, i.e. you might need larger c.t’s than our standard 100 A one (which generally won’t fit on your service entrance wires), and consequently your burden resistor might be wrong for two reasons. Have you checked ‘Learn’ and the article about using the emonTx in N.America? Pretty much all of that is applicable to the Arduino too, but as well as changing the value of the burden resistor because of the different c.t.'s different output current, you might want to increase it also to suit the higher 5 V input of your Arduino. (The aim is to get 1.6 V rms developed across the burden resistor at the maximum current you expect.)
The sums are dead simple: Take the rated c.t secondary current, scale it proportionately in the ratio of your max. current to the c.t’s rated current, then calculate the resistor to give 1.6 V at that current, and choose the nearest available value below.
The rest of the input circuit won’t change.
If you’re looking at monitoring the main incoming supply, then just because you have a (say) 200 A service, don’t assume you will take that. Go round and add up all the appliances you can reasonably expect to have on at the same time, then add (say) 20% for safety. You’ll find it will still be significantly less. See here for the details.