Any issues adding to CTs?

[dancudds]

My PW has a non-backed up panel, which until recently only had a single breaker on it - a dual-pole EV charger. To true-up the usage, Tesla installed CTs on each phase in my main panel and all the reporting was correct...

Recently I had some work done involving a lot of drywall removal near my panel and I took the opportunity for my contractor to run conduit and cable for a future subpanel at the other side of the house. My intention would be to run another EV charger off this and any other additional loads. The contractor run the sub-panel conductors through the existing CTs in the main panel (noting the correct phases).

I don't have the subpanel breaker on but my main panel loads are now under-reporting by close to 50%. Is this a case of one CT losing its connection? Being knocked offline? Or is something going on with the CTs having some 4 AWG wire inside them, even if it's unenergized?

 

[aesculus]

Conceptually there is nothing wrong with running two conductors through one set of CT's. It should just add up the current.

I would completely remove the CTs from the conductors and make sure they actually are reporting something. Maybe one or both became disconnected. Any chance the contractor put the wrong CT on each phase?

 

[dancudds]

Any chance the contractor put the wrong CT on each phase?

I tried tracing it and it looks correct (my main panel is a rat's nest of all the thru routing Tesla did for the subpanel). I'll try your removal idea too but it really is tight back there

 

[Vines]

My PW has a non-backed up panel, which until recently only had a single breaker on it - a dual-pole EV charger. To true-up the usage, Tesla installed CTs on each phase in my main panel and all the reporting was correct...

Recently I had some work done involving a lot of drywall removal near my panel and I took the opportunity for my contractor to run conduit and cable for a future subpanel at the other side of the house. My intention would be to run another EV charger off this and any other additional loads. The contractor run the sub-panel conductors through the existing CTs in the main panel (noting the correct phases).

I don't have the subpanel breaker on but my main panel loads are now under-reporting by close to 50%. Is this a case of one CT losing its connection? Being knocked offline? Or is something going on with the CTs having some 4 AWG wire inside them, even if it's unenergized?

Almost certainly one CT is no longer connected. Either the CT magnetic ring is not fully closed, or a wire has been damaged/disconnected.

There would be no negative effects of adding an additional wire to the CT, except a tiny loss in measurement accuracy when the wire is not centered in the CT.