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I'm pretty sure all that information has been published before. A dedicated page or few is on my "to do" list.

You're right about the burden resistor, that is the correct value. If your load is going to be less than 190 A, then go for the higher value resistor. Otherwise, choose the 36 Ω. (Or 39 Ω and 1 kΩ in parallel if you want to get really close).
The resistor to replace is the 22 Ω (marked "22R0") for inputs 1 - 3, or 120 Ω (marked "1200") for input 4, right behind the jack socket. There are holes for wire-ended resistors which are easier to obtain and fit. 1/10 W should be good enough (the actual dissipation is approx 0.04 W at max current).

Because the CT has a fixed VA rating, by taking the output voltage up by a factor of 3, we need to derate the current by the same factor, so your 600 A CT is now only good to 200 A.

You'll need a programmer because the current calibration factor needs changing, and that means reloading the sketch. When you know the resistor value, you can calculate:

  current constant = (primary current ÷ secondary current) ÷ resistor value
    = 200 ÷ 0.0266 ÷ 37.5 = 200
(That's a starting value - it will need adjusting to cater for CT, resistor and reference voltage tolerances.)

Robert, Thank you for your response. Do you have any guidance/advice on how many resistors I need to replace? 

Thank you, Patrick

There is one for each CT (or current input). Obviously, you don't bother with unused inputs.

If I changed the resistors to all 4 of the inputs would all 4 inputs still be able to be used?  Asked a different way, is modifying the emonTx to work in the US going to diminish the number of usable inputs?

Thank you

No. All you are doing is configuring (in hardware, with the resistor change) that input for that CT.

Thank you very much for your help. Once I get it up and running I will post an update.

Robert, do you think would these resistors work for me?

1/10 watt 37.4 ohm thick film resistor: http://www.amazon.com/Thick-Film-Resistors-10watt-37-4ohms/dp/B00LWKGO2K/ref=sr_1_45?s=industrial&ie=UTF8&qid=1424663325&sr=1-45&keywords=37.5

I have also been able to find  a 1/8 w 37.4 ohm wire ended resistor: http://www.amazon.com/Metal-Film-Resistors-Through-37-4ohms/dp/B00LWOEHSO/ref=sr_1_19?s=industrial&ie=UTF8&qid=1424663596&sr=1-19&keywords=1%2F10+watt+37.4+ohms

EDIT - Fixed links, BT

Those would be OK, but there is no real need to get the exact value, a much more readily obtainable E24 series value (36 Ω or 39 Ω) would be fine. You just tweak the calibration in the software.

Hi Patrick,

I'm also in the US and very interested in using this for monitoring my residential heat pump installation.  I don't have any hardware yet, looking to order soon.  I'd definitely be interested to hear your progress with this.  Also Robert I would be very appreciative of any how-to guides or pages on running this in the US. 

Thanks,

Eric

Robert,

For a 200 Amp circuit, I am replacing resistors 1-3 with a 36 ohm resistor, would resistor 4 (the 1200 ohm resistor) also need a 36 ohm resistor, or a different value?

Thank you,

Patrick 

Progress so far:

Eric,
Your guide is being written, I've done some diagrams, and there are some words, so progress is being made.

Patrick,
Please yourself! If you want that input to be the same rating as the other 3, then 36 Ω is what you want. If you need a higher sensitivity (which is the idea of the higher value) then you can derate the input accordingly.

Robert,

Thank you for your quick response!

-Patrick

Update: CT 1-4 resistors swapped out with 36 ohm resistors