dstutz
March 28, 2025, 6:58pm
4
morphus:
So if I do 2 cables, reverse direction, that are both connected to the same 40 AMP, I need to use a 100 AMP CT?
I haven’t personally done any of the splitting/merging/combining, but the way I understand it is that if they are separate phases, they need to go through different directions or usage on one will cancel the other out, you can combine the same phase the same direction. And yes, 2 40s would be 80, so a 100A CT.
I know I’ve read stuff on here about pushing more current through a CT then it’s rated for but I can’t remember, so I’ll wait for others that are sure to comment.
Some info here:
Either should work provided you orient the CTs appropriately for phase. I recommend before combining that you plug each CT sans the splitter and insure you are getting positive power.
As far as the capacity issue, the CTs should be fine, even in your worst case scenario. The reason for oversizing is to insure the combined input doesn’t exceed the ADC capacity. The unit is conservatively rated at 50mA. There is about a 15% overcurrent tolerance so the IoTaWatt can actually handle about 57A bef…
As far as I know, of the many thousands of units worldwide, nobody has cooked the ADCs. The TVS diodes in the CTs are there to protect the CTs. Without them, if disconnected from the IoTaWatt while clamped to a current source, they can develop very high voltages internally and damage themselves.
The IoTaWatt has its own protection. First in line are the burden resistors. They are 20 ohm 1/8 Watt. 1/8 Watt would be 158mA input - about three times the 50mA design limit. Somewhere above tha…
and
The SCT019 CTs are rated at 200A. They have a ratio of 6000:1 which means they would be at full scale at 250A when used with an IoTaWatt. That’s what I have had in my main panel for more than a year and my accuracy is better than .5% when compared to the meter.
The ECS24-200 (and ECS25200-C2) are 4000:1 ratio. They are full scale in IoTaWatt at 167A. By all accounts that’s more than enough and in the unlikely event the current were to exceed that, the grace leeway would get you to 175, and the protection diodes on the input would prevent any damage after that.