Page 1 of 1

CT Sensor not working on home AC Feed

Posted: Thu Apr 11, 2019 3:26 pm
by LONGJA
Hi all,

I've been working on getting a CT sensor to work for a couple of weeks now. I've been doing my testing with a standard 13A kettle lead and have separated the live, neutral and earth - putting the clamp around the live wire. This has worked fine and I've got some accurate, calibrated readings.

However, when I put the clamp around the main incoming live wire to my house (in the consumer unit) I get readings that are 4 times what my testing has lead me to expect. Unfortunately it's not simply a case of dividing the figure by 4 as this doesn't work for readings below 250W. The return voltages from the CT sensor seem to have completed changed and the figures are useless. As far as I'm aware, the incoming cable is single phase and is a single cable therefore I shouldn't be seeing current duplication.

Has anyone had to deal with this before or could point me in the right direction?

Many thanks, James

Re: CT Sensor not working on home AC Feed

Posted: Fri Apr 12, 2019 4:07 am
by klricks
Have you installed the CT on the wire in the correct orientation?

Re: CT Sensor not working on home AC Feed

Posted: Fri Apr 12, 2019 8:34 am
by LONGJA
Nope, I put the clamp the other way around and it hasn't made a difference :(

Re: CT Sensor not working on home AC Feed

Posted: Fri Apr 12, 2019 10:09 am
by omegaman477
LONGJA wrote:
Thu Apr 11, 2019 3:26 pm
Hi all,

I've been working on getting a CT sensor to work for a couple of weeks now. I've been doing my testing with a standard 13A kettle lead and have separated the live, neutral and earth - putting the clamp around the live wire. This has worked fine and I've got some accurate, calibrated readings.

However, when I put the clamp around the main incoming live wire to my house (in the consumer unit) I get readings that are 4 times what my testing has lead me to expect. Unfortunately it's not simply a case of dividing the figure by 4 as this doesn't work for readings below 250W. The return voltages from the CT sensor seem to have completed changed and the figures are useless. As far as I'm aware, the incoming cable is single phase and is a single cable therefore I shouldn't be seeing current duplication.

Has anyone had to deal with this before or could point me in the right direction?

Many thanks, James
Just to clarify, you are still placing the CT around the single ACTIVE wire in the fuse board?

What country are you in? Local quirks like ring mains configurations in UK houses and USA 240 Two Phase supplies can cause issues.

Can you borrow a handheld clamp meter to double check the CT is reading correctly.

Re: CT Sensor not working on home AC Feed

Posted: Fri Apr 12, 2019 4:14 pm
by LONGJA
I'm based in the northwest of the UK. I'll try and get hold of a clamp meter. I've just bought an 'Owl Energy Monitor' and tried that for comparison - the readings on this are much closer to what I'd expect. Still doesn't explain the weird results I'm getting.

Re: CT Sensor not working on home AC Feed

Posted: Mon Apr 15, 2019 1:15 pm
by JohnsUPS
LONGJA wrote:
Thu Apr 11, 2019 3:26 pm
Hi all,

I've been working on getting a CT sensor to work for a couple of weeks now. I've been doing my testing with a standard 13A kettle lead and have separated the live, neutral and earth - putting the clamp around the live wire. This has worked fine and I've got some accurate, calibrated readings.

However, when I put the clamp around the main incoming live wire to my house (in the consumer unit) I get readings that are 4 times what my testing has lead me to expect. Unfortunately it's not simply a case of dividing the figure by 4 as this doesn't work for readings below 250W. The return voltages from the CT sensor seem to have completed changed and the figures are useless. As far as I'm aware, the incoming cable is single phase and is a single cable therefore I shouldn't be seeing current duplication.

Has anyone had to deal with this before or could point me in the right direction?

Many thanks, James
Have you tried looping the kettle live lead through the CT about 4,5,6 times? This would fool the subsequent circuitry and code into thinking that there is more current flowing than there actually is, as the CT would report much more current. Also try it with two loops through, or other combinations to see what happens. This may lead you to figuring it out. Without knowing the model# of the CT you're using and what you have connected to it, it is hard to diagnose what might be going on. There might be stray coupling from other mains wires to the CT when you have it on one of the house mains.