But your US a.c. adapter is only rated at 120 V. If you have connected it to 208 V, it will be saturating the transformer core and will most probably burn out soon. That is the reason I said connect it line-neutral.
If you have the UK or EU adapter (rated at 240 V and 230 V respectively), you’ll be OK.
More like immediately.
I’ve seen that mistake made. (120 V transformer connected to 240 V)
The magic smoke makes it’s exit post-haste.
One low-cost solution is a control transformer typical of those used in HVAC applications.
e.g. https://www.amazon.com/SXT101-Genuine-Supco-Trnsfmr-3Taps/dp/B009AX3D9I
240/208/120 Volt primary - 24/12/2.5 Volt secondary.
That will change (most likely add to) the phase errors and mean that the real power, hence also the power factor indicated by your load, will be in error.
Probably a better solution, though again we don’t know the phase error, would be a 208 : 9 V isolating transformer instead of the standard a.c. adapter.
For clarification purposes, as we’ve already covered this via PM…
The SXT101 is 240/208/120 Volts to 24/12/2.5 Volts, so the connection I was suggesting was 208 to 12 V.
(with the 2.5 Volt winding bucking the 12 Volt winding to yield 9.5 Volts.)
It had slipped my mind that you’re using an emonPi. There isn’t a 3-phase sketch available for the emonPi, and without that, the phase relationship - assuming you have a balanced 3-phase load - will be wrong if you connect your voltage sample Line-Line, so you must connect Line-Neutral at 120 V to maintain the correct phase relationship.
I apologize for my lack of knowledge in this field, but how is connecting Line-Neutral at 120 V different from how I currently have it set up?
Remind me how everything is set up at present.
Current transformer is attached to one of the three phases, and the ac power supply provided by openenergymonitor is connected.
And you have an emonPi?
But not an emonTx as well?
About the ac power supply:
Do you mean the 5 V USB d.c. power supply
or the 9 V a.c. adapter?
You must have a 5 V d.c. power supply to power your emonPi.
You can also have an a.c. adapter. If you don’t have an a.c. adapter, your emonPi assumes the mains voltage is 120 V, and estimates the apparent power (VA) from that.
If you have both, the 9 V a.c. adapter measures the true voltage, and the relationship between the voltage and current waves, and tells you the real power (watts) being measured.
I currently have an emonPi, but would not be opposed to buying an emonTx if it is necessary.
I have the 5V USB DC power supply plugged in, as well as the 9V AC adapter.
vrms is giving me a value of about 215. As you instructed I edited the configuration to work with the new ct I have connected. Should the true power I am now getting be somewhat accurate?
I may have misunderstood, but I thought that you said connecting the AC adapter would saturate the transformer core?
Which a.c. adapter do you have? And where is it connected? I get the impression that you have connected it Line - Line at 208 V. Is this correct?
The one from the OEM shop http://openenergymonitor.org/files/datasheet/USA77DA-10-09.pdf
Is only rated at 120 V a.c. I have no data for the maximum permissible voltage, and I have not had the opportunity to test this variant (only the UK one) but based on that, I can be reasonably confident that the US adapter will be seriously overloaded if it connected to a voltage significantly greater than 126 V (120 V +5%), and will not give the required faithful representation of the primary voltage.
I have the a.c.from the OEM shop, the same that you just linked. It is connected to the 9V a.c. plug on the emonPi, and plugged in to a 120V outlet via the extension cord you see in the picture.
I understand now. What worried me was your line:
from which I thought that there was a possibility that you’d connected it to the 208 V supply.
As you have it, that’s OK - what I obviously didn’t know was you’d adjusted the calibration so that the emonPi showed the Line - Line voltage of 215 V when it was actually measuring 120 V.
So, as you have it connected Line-Neutral, you need to have the c.t. on the same Line. When you do that, it will correctly read the true average power being delivered to your machine (subject obviously to getting the calibration of both voltage and current right).
If the current and voltage belong to different phases, then the phase shift between voltage and current will make the calibration both wrong and variable, because the number that you get out for power will be wrong by different proportion according to the power factor of the load.
The only adjustments I have made are the ones shown in post 15, so I am not really sure why I am getting 215 V.
This is where I get confused, as I am not even sure if the ct is connected to a line or a load. The power travels through the factory into an electric panel, and then out the electric panel to the machine. I have the ct connected to one of the phase wires traveling form the electric panel to the machine, so would that not be considered a load wire? If so how would I get the c.t. on the same line?
I’m using “Line” to mean one of the three phases, i.e. not the neutral. In that sense, it’s “line” all the way into and around inside the machine. (This is probably where you and I are divided by a common language! 
)
As you’re measuring current between the panel and the machine, you’re clearly measuring the current drawn by the machine.
Does rephrasing help: You need to connect the a.c. adapter Phase - neutral, using the same phase that the c.t. is on.
I can’t at the moment figure out where your 215 V is coming from. It’s in the direction of you not having set “USA” true in the emonPi, but the numbers aren’t really close enough for me to say with certainty that’s the problem.
In any case, for your purposes I think you need to adjust the voltage calibration so that it reads 360 V when the actual phase-neutral voltage is 120. That way, the emonPi will read the correct value for the total power across three phases (of course I assume a balanced 3φ load again).
There is no phase - neutral because there is no net neutral current.
How would I do this?
But there is still a neutral wire - you already have one side of your a.c. adapter connected to it - I know that because you tell me it is seeing 120 V - one leg is connected to one of the phases, the other leg to neutral.
All we need is the phase that you’re using for the a.c. adapter should be the same one that has the c.t. on it.
The same place where you corrected the powers, in emonHub.conf (except of course you change the scales = ... for the voltage (they’re all in order left-right).
Changing the voltage there won’t affect the power values (because the sums to calculate power from current and voltage have already been done, before the numbers get as far as emonHub).
I see what you are saying now. I am working on getting a schematic of the factory to try and determine which phase the outlet I am using for the a.c. adapter is connected to. Do you know of a simpler way to make this determination?
Yes - measure the voltage between the “hot” (your terminology) where the a.c. adapter is connected and each of the three phases where your machine is connected. You’ll measure 208 V for the ones the a.c. adapter is not on, and close to zero for the one that the a.c. adapter is on. If you measure 240 V instead of zero, it means it’s on the other leg of a centre-tapped 120 - 0 - 120 V supply.
Unfortunately I am not going to be able to connect the a.c. adapter to the same phase of the ct, so apparent power will have to do. Is it necessary to change the value of vrms to get an accurate measurement?
