# Long CT extension leads and transformer type

I previously raised a thread about using Emporia CTs but as this is specific to extension leads I raised a new one. I have read a few other comments from you on here about extension leads but this is a bit different.

I have an external meter box and internal sub panel. I want to measure the mains from the external box because the HWS is taken from there. Also room in the internal sub panel is tight. The problem is the metre box is 27 metres (cable length) from the internal one.

I have run Cat6 cable (22AWG solid copper) and am getting consistent reasonable results. It is only run near other cables for a short distance.

BUT … the Emporia CTs I am using are voltage type and I am wondering if voltage drop across that distance will give me inconsistent results. Which would give better consistency with high vs low consumption … current types or voltage types? I doubt any CT will see 50 amps.

From the Emporia thread I am still experimenting with Cal values. Fortunately I temporarily have CTs on the mains at both internal and external panels so can compare the effect of that long extension. With the CTs at the internal panel set at Cal 750 I get an almost identical reading from the external CTs if I set them to about 900.

1. I have not changed the Phase lead (all set at 2). Should that be increased for those on the extension?
2. Should I swap these external CTs for current type? The local Iotowatt supplier is out of stock so I was thinking of these:
SCT-013-000 CT: 100A = 50ma
3. Should I use the 2 wires in each of the 4 twisted pairs as one conductor, thus doubling the copper? i.e. The Cat6 cable then has 4 conductors and I would run a second cable so I could have 4 CTs there - 3 for the 3 phase plus the HWS.

You have a lot of variables to this equation. Most of you question can be informed by Ohms law (I = E / R). Pretty simple math, but I don’t have the numbers for Emporia CTs, so you are on your own here. Let us know if you find a solution.

I purchased the set of YHDC SCT013 CTs as in my link above (100A/50ma). However when they arrived they were the YHDQ clones.
SCT013 useless clones
At least the supplier is doing the right thing and a set of the real ones is on the way.

Can you please help with some pointers when using a long extension cable. As there will be cable resistance, does this mean I should increase the burden resistor setting? By the amount of that resistance? What about phase? Should that be changed as well? As I don’t understand the relationship between the values in the settings, and the impacts of changing them, some pointers would be helpful.

In the dropdown list of known CTs there is one for the SCT013. It has several parameters which I have no information on. If the solution is to create a custom version, how to do so without it being overwritten?

That’s covered here.

As the CT produces a proportional current, resistance does not affect the voltage drop across the burden until it increases to the point where the CT cannot produce enough power to drive the required current across the total resistance. Unlikely if you are using Catn wire.

While there is an academic argument that increased overall resistance can increase phase-shift, IMO it is not a concern here.