I have a two 5Kw DEYE Hybrid inverters setup which are connected to a sub-DB (located in my garage), and the main DB is located outside (at the swimming pool - about 50m away), and to which my heatpump and pump is connected to. The installers installed a CT to allow export from the inverters back to the main db to include the swimming pool and heatpump under my solar system. This seemingly worked fine, until I found that the CT reading goes into the negative when the pumps are not running resulting in the system pushing (selling) electricity back into the grid. When the pumps are switched on again the CT shows a (+) load and no electricity are exported back into the grid. After many phone calls it was suggested that the type of cable (1.5mm Surfix) used is not right for extending CTs that far, it was suggested that a CAT6 / paired data cable be used - which I've done, but the result (albeit that CT readings are less wrong) is still incorrect. i.e. it will indicate a -400W CT reading , but the load for the entire building (main & sub DBs) are roughly 1700W. 

I've tried the following suggestions with no obvious improvements:

Replaced 1.5 Surfix CT cable with CAT6 cable (using a pair for negative, and a pair for the postive)
Moved CT cables from slot 3&4 to 5&6 on inverter
Swapped the direction of the CT 
Swapped the cables (positive & negative) around on the inverter
Set export power to 0 on inverter settings
Set selling power to 0 on inverter settings
Replaced CT (same make & model)

My thoughts are that the CT reading on the inverter is wrong.

Any suggestions would be greatly appreciated!

NB

43 minutes ago, Newb said:

CAT6 cable (using a pair for negative, and a pair for the postive)

This is wrong. You should use one pair for both poles (we are talking about AC here, so there is no positive and negative). The function of the twisted pair is the same here as in data transmission.

Ahhh.. OK

 

Edited January 26, 20223 yr by Newb

37 minutes ago, P1000 said:

This is wrong. You should use one pair for both poles (we are talking about AC here, so there is no positive and negative). The function of the twisted pair is the same here as in data transmission.

Thank you P1000! So just to confirm , I should only use the one pair , splitting it for (-) & (+) ?

1 hour ago, Newb said:

The installers installed a CT to allow export from the inverters back to the main db to include the swimming pool and heatpump under my solar system.

Sounds like your installer, like so many others, dont get it.  You dont need a CT for this - the inverter will automatically pushc back excess solar to other (non-essential) loads if you permit it.  Where yiou need a CT coil is on the grid side of the main DB.  That is the only pace it should be. 

In the diagram below your main DB is On-Grid Home Load.  The CT coil should be between the main incommer and main DB.

Edited January 26, 20223 yr by Scubadude

24 minutes ago, Scubadude said:

Sounds like your installer, like so many others, dont get it.  You dont need a CT for this - the inverter will automatically pushc back excess solar to other (non-essential) loads if you permit it.  Where yiou need a CT coil is on the grid side of the main DB.  That is the only pace it should be. 

In the diagram below your main DB is On-Grid Home Load.  The CT coil should be between the main incommer and main DB.

This is my current setup

39 minutes ago, Newb said:

Thank you P1000! So just to confirm , I should only use the one pair , splitting it for (-) & (+) ?

Yes.

Did you tick "Zero Export to CT"?

36 minutes ago, Scubadude said:

Did you tick "Zero Export to CT"?

Yes - its when Zero Export to CT is selected when things go wrong (unless the load is high enough), then it "works" (does not export to grid / sell to grid)

22 hours ago, P1000 said:

Yes.

@P1000 - a huge thank you for your recommendation! It is finally working as expected (albeit that the CT reading is not 100%, the export / sell to grid has stopped)

🥳

On 2022/01/27 at 11:05 AM, Newb said:

@P1000 - a huge thank you for your recommendation! It is finally working as expected (albeit that the CT reading is not 100%, the export / sell to grid has stopped)

🥳

Good that you got it sorted out. It makes no sense to have the CT between the main DB and inverters. Even without it power will go from the sub DB to the main DB to feed the heat pump and pump. 

Normally to prevent export it is fitted to the supply from the grid to prevent export to the grid as was indicated by @Scubadude