Splitting a two way cable for solar PV monitoring

Electrical question - after trying, it seems the cable that runs from my inverter to the circuit breaker has the positive and negative wires in the same cable.

FYI, it seems like I have a ‘type 2’ setup (edited, I initially wrote type 1).

What’s the best way of monitoring the current in the cable? Is there an easy/safe/approved way to ‘split’ the wire so I can put the clamp around just the positive?

There is a big red isolator switch between the circuit breaker and the inverter, and between the invert and panels.


Can you monitor the grid supply? In the Type 1 diagram, it is anywhere under the Junction block.

G for grid (to be measured)
C for Fuse box consumer Unit (you’ve already got)
S for solar (unknown)

G = S - C
So: S = G + C

Hi - sorry, just looking again at the diagram - I should have said type 2…

Do you really mean that? Are you looking at the Solar Panel side of the inverter, because that’s where the d.c. is with positive and negative wires, and you must not touch that for two reasons - (1) they’re always live until it goes dark outside, and (2) no current transformer - nor any transformer - works on d.c.

If you’re looking at the supply side of the inverter, the wires are line and neutral, and they are probably in a 3-core cable along with a protective earth conductor.

I would look at inserting a c.t. in one of two ways:
1. If it’s easy and there’s room, put the c.t. either inside the inverter or inside the consumer unit. I doubt that there’s room inside the isolator.
2. Cut the cable and put the two ends into a plastic box (using the correct grommets etc for the cable entry, inside put a screw terminal block to join the two neutrals and the two earths, take the two line conductors into separate terminals and link them with a loop of wire passing through the c.t. Obviously, the loop has to be the same capacity as the conductors you cut.

Either way, you maintain the integrity of the wiring and there are no wires exposed without mechanical protection against damage to the insulation. (Remember, the insulation is the blue or brown plastic, the outer sheath is not insulation, it’s mechanical protection.)

Hi Robert. To be honest, I’m probably getting the terminology wrong!

The system was installed last year, and I’m just getting to a stage were I’m trying to monitor it using the EmonTX. I attached the CT clamp of the EmonTX (and owl monitor) to the cable coming out of the inverter, and it just reads zero no matter what is being generated. It sounds like putting the wiring through a box and removing the protection layer, and clamping just the one of the wires may be required. I’m not sure there is room in the consumer unit, I’m not an electrician so i’m either gonna need help or make sure it’s very easy!

I see this article (monitoring an AC installation) about 1/3 the way down, recommends carefully cutting the cable… hmmm

I wouldn’t do that. I doesn’t meet BS 7657, which is invoked in the UK by Building Regs, and that’s law.


It was probably written by someone who isn’t a Chartered Electrical Engineer, who doesn’t appreciate all of the risks.