Frequently Asked

Why is the CT not showing zero's when the CT is not connected

Reading values with the CT unconnected will output a small value. This is normal.

The CT sensor is an analog sensor and has noise. i.e. It will always measure an approximate value. Hence zero + noise when not connected.

Even if nothing is connected there will be always a tiny current running in the burden resistor inducing a small voltage. In turn this will convert into a small power. For a board setup for the SCT-013-000 with 100A fitted burden resistor one might find a background noise under 100W.

If the admitted noise value appears too high then one might have to opt for lower range burden resistor.

Why is voltage sometimes zero then? Voltage will show zero when unplugged because the sketch is programmed to give zero if it times out finding enough sign changes. No sensor -> no ac signal -> no sign changes. Note that voltage sensors are also analog and same applies concerning noise. The zero in that case would only mean "timeout" rather than "value is 0".

I can not read anything once the CT is clamped

Make sure the SCT is clamped around A SINGLE PHASE.

Clamping the SCT on the whole cable will never read anything as it measures two currents. One positive minus plus one negative which sums to 0 (or 0 + noise).

The easiest for a quick test is to connect the SCT at the meter level on a single phase. Otherwise if you wish to measure the power used by a single application then one should make a special cable that split phases.