OpenEnergyMonitor Community

Still Confused about alternate CT's

yeah, I already looked at that page and found that I was lost. I just wanted a like for like alternative, like you suggested and I got the feeling I was just being brought to the edge of a cliff to then be told to jump and flap. I’m not there yet. “me? a baby eagle… no flappin, just feed me”.

I ordered two of those SCT023R through amazon and I’ll get them … whenever they turn up.

I was nervous to post questions because on a lot of other forums the smart people are helpful but generally rude to the new guys and learners testing the waters. After reading through a few posts I found that the people here are not jerks and wanting to look smart at the expense of noobs like me so I’m glad I asked.

Thank you for being fast, willing and informative.

I wonder if the OEM shop would stock those CTs for future US purchasers who have a 200 amp service? that was what i was looking for and I loved the fact that with this open project there was a store to help me get going really fast. now, once I get connected back up, I can start to learn again and get comfortable playing around. I’ve tried to follow some of the discussions on here but I’m just not that clever.

@Duncan_Cunningham if you had to guess, what proportion of US homes have 200A? Is it some general upgrade being carried out across the US?

It would have to be a guess but it would seem that all new homes would get a 200amp service. When I had my solar installed the power company told me to upgrade my service, from the incoming lines to the house, to 200amps as though it was a new home. I didn’t have to upgrade the link from the service panel to my breaker box in the cellar but a new home would probably have 200amps taken that far too. I do not know if this was just a requirement of my local power company or a national trend in the US to bring all new homes, or those having any work done, brought up to 200amps. so I’m guessing. Lots of older homes have much smaller service. usually 100amps and I’ve seen some at 125amps. but I don’t get into the habit of nosing about the outside of people’s homes i don’t know but I have been a active buyer of a home and that is what a saw of older homes.

Either way, a choice of CTs from the shop to fit over those 200amp wires would be helpful for noobs like me. I went with the 100amp version of the larger CTs (so they would fit over the 4AWG) as I don’t think I’ll be getting over that anytime soon and if I do I’ll upgrade them at that time.

Thanks again for a great forum and engagement guys and gals.

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No - provided that it’s protected from damage. It might just be possible to get the resistor inside the body of the plug, but the best way is to take your Pi apart and add the parallel resistor to the PCB - there are holes provided just behind the jack socket.

Thanks for those comments. We do try to be helpful, mostly we think we get there. But of course a query has us stumped on occasions.

You actually asked the right way - honestly. You said exactly what your problem was. And that allowed me to answer you clearly. The only way you could have done better would have been to say you’d looked at the N.America page, but didn’t know which to choose.

Bill Thomson has reminded me that he posted a full explanation some time ago. For those who weren’t around at the time, didn’t search or didn’t remember it, here’s a link

Finally, a brief update on my installation of Wattcore CT’s, WC3-100-MA100 for use in conjunction with my emonPi. They seem to be working fine. Using these CT’s on the service lines generates a complex output that requires some interpretation. My basis for concluding that they are working properly is a comparison with the output of the original CT’s while they were monitoring my water heater circuit. The heater consumed 1780 watts, give or take, on each of the service lines. With the new CT’s, it is easy enough to identify when the power consumption increases due to the water heater. Again there is an increase of 1780 watts, give or take, and the sign is the same.

As these CT’s have a 100mA output for 100 Amps input, I used an additional 22-ohm resistor across the input leads to provide the final burden resistance of 11-ohms required for 100mA output.The following picture shows how I implemented this:

I could not fit the resistor in the jack, as I used a moulded jack with lead wires. I prefer this methodology as the original CT’s are still usable without modification of the emonPi.

If any further information is wanted, I will be happy to supply, but at the moment I am experiencing difficulties with the web interface to the emonPi. This is gist for another post

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Some 100a CTs that will fit around my 200AMP copper service lines arrived today from China. that took a while. The CT have no plugs on them, just soldered ends, but I have a cable I can use, both ends will fit in the CT sockets on the EmonPI box and match the other CTs.

Does it matter which way around the wires go? Black or white to ??

I’ve not done soldering for quite some years, so this will be fun. Glad i finally gave in and bought some reading glasses to help me see little things again.

Hopefully, your CTs will obey the same convention as the USA, so look at the “Use in North America” page for details:
“For consistency with the standard YHDC CT supplied by the shop, connect the white wire to the plug tip and the black wire to the sleeve. There should be no connection to the ring.”
Elsewhere in ‘Learn’, you should find enough information to determine whether you need to change the burden resistor inside the emonPi, and calculate the calibration coefficient.

did some pretty nasty soldering and got them connected with the white to the tip and black to the rim or sleeve.

I get outside, and by this time is cold and dark. I manage to open up the panel but the two copper wires that feed in from the meter side are too close together for the CT to slip around the lines and clip together. I’m going to come back to this when I have day light and less risk of blowing myself up. So the main issue I’m having is the lines are closer together than the thickness of the CTs that I got in from YHDC.

Wish me luck

Those of us who are engineers would have looked inside the panel first, before buying anything. (He says - too late!)

You might be able to split the cables apart with some gentle persuasion, but this is where experience is necessary to know when to stop - before you do damage. A photo might help.

i am familar with my panel and I’m not an engineer. What I didn’t know was the size of the CTs they are very chunky and no dimensions were on the webpage and, anyway, I had no choice of what I was to get and I see others stating that they sometimes have to make changes to the hardware to allow them to fit. I’ll take a picture when it’s not dark and attach to this post. I was able to move, safely, the wires to allow the CT to wrap around the lines coming into the service panel.

I’m now trying to figure out how I set this up a few months ago and get it going again. US setups are not as straight forward as the UK and I do miss that simplicity but I don’t miss small homes and gardens and the lack of sunshine… a list of what I miss or don’t for another book.

I think I’ve got it going and I’ll post my findings.

That would depend on which web page you looked at. On the “Use in North America” page of ours, there are dimensions for some and links to the manufacturers or distributors’ websites for the remainder. We can’t speak for c.t’s that we haven’t looked at and checked.
If we were to reproduce the manufacturer’s data, there might be copyright issues but more likely, there is a risk that we would not know when there was a change and we’d be offering out of date information.

Robert, I’m not attacking or criticizing anyone, I’m stating that when I ordered from the company I didn’t look for dimensions because I’m not smart enough to realise that maybe the CT would be larger thickness from the inside to the outside and more difficult to fit into place. If I’ve offended anyone by asking questions and reporting back what I’m doing wrong then I apologise, this is not my intention. I’m just trying to use OEM in a different situation to most of you. I envy the UK typical power to a home, 240V or 220V or whatever it is now is much better than 2 lines of 120v and having different loads on them means that i have twice any many CTs to get accurate readings so the steps a little bit different and it takes me a long time to figure out and the page you keep referring to “use in North America” that I’ve look at many times isn’t helping me all the areas I’m dealing with. I’m not ready to start tearing apart my emonpi and putting on resistors to the CTs, i’m just not that confident at this kind of stuff yet but I’m not afraid to ask.

I think I have put one of my CTs on backwards over one of the legs coming in from the array inverters and I will not be able to fix than until I get home tonight, by which time I’ll have less than 40 mins of light to test.

I might be able to get a picture of the service panel then too.

So let me know in what areas it isn’t helping, and maybe it can be improved. There seems to be a lot more interest now from that continent than when the page was created, therefore we’ll try to respond to that interest by filling in the gaps.

If it’s not connected to another c.t hardware-wise (i.e. it’s physically wired in parallel), then you don’t need daylight. You can put a minus sign in front of its scale factor in the “scales = …” line in emonHub. That’s equivalent to turning the c.t. round on its cable, or swapping the connections to the plug. (Be warned - don’t disconnect the c.t. from its burden while it’s on a current-carrying cable. Yes, I know there’s supposed to be protection inside most c.t’s, but don’t bank on it and don’t rely on it.)

the service panel I have is the type that most new homes in America might have. so maybe it would be a good example to work from. anything else should have smaller gauge cabling. Maybe I’m not doing this right but my setup for EmonPi is a little different because I read both hots coming in because it’s not uncommon, since outlets are 120v there there is a imbalance going on. using this tool I’m managed to balance equipment in the house, washer, fridge, microwave on to circuits that don’t put the load on just one leg or line. I so miss UK power… kettles take ages to boil here running on 120v.

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"If it’s not connected to another c.t hardware-wise (i.e. it’s physically wired in parallel), then you don’t need daylight. You can put a minus sign in front of its scale factor in the “scales = …”

I’m sorry, I don’t know what that means yet. Scale Factor? I’ve been going through the inputs and I don’t see where I would add this. is it a line in the process list?

I’ve managed to get this thing working using the steps but I feel very lucky so far in getting out the results that I do. I’m not as smart as you guys so bear with me.

Oh but you are doing it right. Even though you’ve tried to balance the loads, which in itself is the correct thing to do, you’ll never achieve perfect balance all of the time. There will inevitably be an imbalance most of the time. You must measure the current in both legs. If you -
and your neighbours who are supplied by the same transformer - could always guarantee a balance, your electricity company would be most grateful because they could do away with the neutral conductor and save money! [It won’t happen - ever.] And then you could guarantee both voltages would be the same too, so you wouldn’t have any error from assuming they’re the same when they aren’t. But experience shows there’s little error in that assumption.

There’s nothing technically against a 240 V kettle connected line-line, but I’m prepared to bet there’s a regulation forbidding it.

You have an emonPi? If you go in via your web browser, you’ll find listed under “Setup”, and entry for Emonhub, and there “Edit config”. That takes you into the configuration file for emonhub - emonhub.conf, which you’ll find mentioned very frequently here. It’s in sections, the one you want is


and your emonPi is Node 5

    nodename = emonpi
        names = power1,power2,power1pluspower2,vrms,t1,t2,t3,t4,t5,t6,pulsecount
        datacodes = h, h, h, h, h, h, h, h, h, h, L
        scales = 1,1,1,0.01,0.1,0.1,0.1,0.1,0.1,0.1,1
        units = W,W,W,V,C,C,C,C,C,C,p

Your scale multipliers are there.

If you want to do it in the process list, you can. Just add “x” with a value “-1” fairly early on in the list. But as I wrote here only minutes ago in another thread, there’s a danger of needing to do it more than once if you re-read the input to process it for another purpose.

I’m not that smart - I’ve just been doing it a long time.

i thought it was config file so I edited it. I looked for the lines related to power2 on the TX, which is the one my Solar lines are connected to. my emonpi only has two CTs and those read the service lines only.
anyway, I changed it from 1 to -1 for the 2nd digit on the line called “scales” under node 6. Saved, rebooted the emonPi and it didn’t change the input feeds readings, is that ok or should i see the reading flip the other way in the inputs page?

edit: whoops… Emontx3 is node 8… wrong place. see, I’m learning but only through my mistakes.

If you change the config file, you should see the input and the feed change. If you change the process list, only the feed will change.

You’ve only mentioned the emonPi, so though I realised the might be others, that’s why I wrote “Node 5”. But all follow the same pattern.

If you edit emonhub.conf, you don’t need to reboot the PI. In fact, I’m not sure that you even need to restart emonHub, but restarting it won’t hurt.