On Thu, 8 Mar 2018 07:09:40 -0800 (PST), "Dave, I can't do that"
wrote:

Thanks guys, I have just decided to stay with the single wire. I was being lazy as it is a bit of a struggle to get enough room for the clamp between them.

This morning it (correctly) measured the 11A and 9A but the combined was 19A, so obviously it is confusing the meter with a variety of probable causes as was mentioned in your replies.

I will just stop the laziness and use the single wire from the junction block to the control board. That is always accurate when checked with the pass-through meter. It just confused me a little as I was pretty sure 11+9 did not equal 14 and then this morning with the meter quite cold, it showed 19. That could have easily been confused as 11+9 is close enough to be 19 and thus assumed that measuring both was near-enough. That could have been nasty.

When combined it probably has something to do with the temps (19C at the moment) as was also mentioned. The single wire clamp and pass-through readings seem accurate despite the temp. It was about 25C yesterday when I got the 14A double-wire reading.

Lesson learned and thanks anyway.
Perhaps a "rounding error"? If the 11 was really 10.6 and the 9 was
realy 8.6, the REAL current would be 19.2, and the combined reading
would round to 19