Author Topic: Question on setting up CT's on a Spyder  (Read 1611 times)


  • Newbie
  • *
  • Posts: 1
  • Karma: +0/-0
Question on setting up CT's on a Spyder
« on: November 15, 2016, 11:30:10 AM »
  I've set up my TED Pro system and the main circuit seems to report correctly.  However, I set up a Spyder on several smaller circuits in the panel, including 2 30 Amp 240V circuits.  I used a single 60 amp CT on each of those circuits and put the CT around the red wire on each.  I also configured the circuits in the Sypder to report 2x the usage, assuming that I was only measuring one leg of a 2-pole breaker.  What I am seeing is both circuits reporting exactly the same usage (one is on a pump for our water and one is on the dryer), and that usage is higher, by a factor of 2 or 3, than the usage reported by the main feed to the panel.  The other smaller circuits reporting through the Spyder seem to report correctly, and I've verified the main feed and it appears to report the usage correctly (e.g. 600-900 watts normal load, goes to 6 kW's if I turn on dryer).  Any ideas on what I did wrong?  Should the CT's be around the black wire?  Do I need 2 CT's on each circuit?



  • Sr. Member
  • ****
  • Posts: 427
  • Karma: +0/-0
    • My home page
Re: Question on setting up CT's on a Spyder
« Reply #1 on: November 15, 2016, 05:21:30 PM »
What you describe sounds right, and is the way I set up the Spyder CTs for my electric wall ovens and HVAC system. Is it possible that your higher voltage circuit feeds are actually two legs of a three-phase mains, rather than the normal domestic balanced split supply? This could certainly cause confusing readings on '240V' circuits with normal readings on the 120V ones. It shouldn't (otherwise) matter which live feed you monitor, you shouldn't need to monitor both, and you should need to double the measured usage on one live feed (as you have) to get a correct total.
Peter R. Fletcher
TED Pro Home - main MTUs monitoring utility and PV Solar feeds; 2 Spyders monitoring selected individual circuits