CT Wire Size...


First of all congratulations on this excellent project. I'm new to this and just starting to install a array of solar panels to my house.

I was considering using the PV Monitor Kit, but my main problem is, I have a two floors house, the panels are on the roof, and the main switch board is on the ground floor, so I'm not sure how I'm going to measure the CT on the switch board and the GTI on the top floor without having to drill holes in my house :P

The first idea was to pass the 220V gti input cable all the way down but then I've tought of expanding the CT cable, which cames with a 1m long, how much long can I expand this CT cable?

Or there are other ideas?


Thanks for the help.




Robert Wall's picture

Re: CT Wire Size...

First question: How and where will the Inverter connect in to the house wiring?

If it is under the roof, then my first thought is add a second emonTx to your PV kit. Mount one emonTx close to the feed-in point measuring just  the PV current, have a second emonTx close to the consumer unit / switchboard, measuring mains supply current and voltage. Both send their measurements by radio to the nanode and hence to the display.

You could extend the CT secondary using a good quality screened twin microphone cable (connected not the obvious way, but using the two cores for the current connections and earthing the screen at the emonTx end), but it's probably easier to use wireless and a second emonTx.

rechena's picture

Re: CT Wire Size...

Thanks for the quick answer, after browsing the forums for some more time, I came to the same conclusion that I will definitely need two emonTX... 

The inverter will be connected to a normal plug in the top floor.

Thanks once again :)

calypso_rae's picture

Re: CT Wire Size...

"Or there are other ideas?"

I wonder what you're intending to achieve?  If, like me, you simply want to control your spare PV power so that it's consumed on site rather than being exported, then I reckon you only need to measure power at one place - at the grid-supply cable - hence only one CT. 

Robert Wall's picture

Re: CT Wire Size...


I just realised that you could read my reply as meaning you don't need to monitor the voltage at the emonTx that measures the PV output power. Of course you do, in order to calculate the power and determine the direction of power flow. Bear in mind most PV inverters consume a small amount of power all the time. This is supplied by the PV array when it is generating, but when dark, it comes from the mains.

What I meant was, you don't need to display separately the voltage at the PV (because notwithstanding voltage drops, it's the same all over the house).


(To answer calypso_rae's point, if you are only interested in nett power, then yes, you only need to monitor the mains incoming supply. If you want to know how much you are generating, then you need to monitor both - and then what you are consuming is the sum. There may be economic advantages in consuming as much of your own generated power as possible in preference to selling it back to the grid).


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