SNAP-AIPM with Current transformer reading 0 ARMS

Hello, first post here. I am thus far unable to get my AIPM power monitor to read the current transformer (OPTOEMU-ACT-0750-050, 0.333VAC secondary) to monitor a 110VAC power supply, following the wiring diagram on page 11 of form 1453. Point 0 reads line voltage just fine, point 1 reads 0 (points 2 and 3 read 0 as well, of course).

Using my trusty DMM I can measure AC voltage coming out of the CT as it should, but as soon as it’s connected to the AIPM field connector the output drops to 0 in PAC manager, control, and on the DMM, regardless of CT lead polarity.

The data sheet is a little murky about exactly which CT to use; the diagrams mention a ‘typical 5A CT’ in a couple places and ‘0.333 secondary CT’ in others (e.g. 3 phase). Do I simply need a CT with current secondary to measure line current with this module?

Thanks in advance,

Hi Neutral.Tom,

Welcome to the forums.

Sorry that you found the power module manual a bit ‘murky’… We try really hard to make them clear.
If you have any input on how to make it clearer, lets know.

On page 1 of doc 1453, we show in the text under ‘Description’ the three types of power modules we offer and what CT’s each requires.
Same again at the bottom right of page 1 in the table.
AIPM is single phase 1-10 amp input
AIPM-3 is three phase 0 to 5 amp input
AIPM-3V is three phase .333VAC CT input.

This is then broken out in the wiring diagrams for each of the modules.
Page 11 has the heading ‘Wiring Diagrams - SNAP-AIPM’. If you are going to be measuring less than 10 amps current, you can skip the CT altogether as shown on the top left of the page.
If you need to measure more than 10 amps, then you can use a 5A CT as shown on the diagram at the bottom right of that page.

Page 14 is for the AIPM-3 and the diagrams mention using 5A CT’s.

Page 16 is for the SNAP-AIPM-3V and shows using .333VAC CT’s.

So, to answer your question, yes, you need a CT with a current secondary, not voltage, to measure current with the SNAP-AIPM module.


Thank you for the reply, Ben. Page 1 of doc 1453 reads “The SNAP-AIPM module is designed for 85–250 volts and 0–10 amps, but it can also [B]monitor AC line currents greater than 10 amps using a standard current transformer (CT) of suitable ratio.[/B]” Perhaps I do not know enough about current transformers to know what a “standard” one is, but this table gives me no clear indication of what I need to order to use the module. In addition, I see only split core CTs with VAC secondaries on your website, so I hope you understand my confusion.

Can you please direct me to a suitable CT that will handle no less than 30 amps? Thanks!

Tom, let me take your comments to the doc team and see what they think…

In the mean time, you need to pick a CT that gives a ratio of your measured current to 0 to 5 amps on the secondary.
You say no less than 30 amps, but I wonder what your max amps is. Also what cable size you need fit around. Lastly, if you can disconnect one end of the circuit and fit the CT or if you need a split core CT so it snaps around the cable.

Here is one page that a quick Google showed up;
Looking at the table you can see the first number is the max amps the circuit will see, the second number is all 5amps, this is the ratio of the CT, so if you pick the first one, you see 50 amps in will give 5 amps out.
Put this 5 amps in to the SNAP-AIPM module, set the scaling as per the manual and you will see 50 amps in the software when there are 50 amps flowing. It will be pretty liner until you get to the edges, but that’s the nature of CT’s the magnetic field coupling the cable to the CT is the way it is.
In other words, pick a ratio that is in the range you need and you will have all the accuracy you need.

And yes, your right, we only sell the .333vac CT’s for the new EMU and SNAP-AIPM-3V module. We found them to be the most popular and most requested. The 5amp CT’s seem to be not as popular as they once were.


tom, if you have a AIPM module (not AIPM-3V) then the CT you mentioned above will not work (correct me if i’m wrong here people…).
that CT is like a current transducer, not a transformer. it produces a voltage proportional to current not current proportional to current. you will have to get an AIMP-3V module to use with these CT’s.

note AIPM-3 is different to AIPM-3V. the AIPM-3 will measure 3ph power with 0-5A (0-10A for old modules) current input, where the AIPM-3V will measure 0-0.333VAC (at whatever scaling you have) current input. as with your trusty DMM, you can’t put a potential across your current input or else you’ll break it.

for your install it sounds like you’ll probably want a 75:5 ratio CT (or 50:5 or whatever you can get closer to your max current). this will give you a range of 75A max for 5A max input to the aipm. IME make some good CT’s ( TAIBB series are pretty good. i’m using them now on some AIPM-3’s and they’re cheap and should be readily available from any electrical wholesalers.