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Those instructions apply to the standard British installation. You give not hint in your profile where you are in the world, so I can't help you. If you look at Building Blocks - 3 Phase Power, you will see pictures of European installations where the Line, Neutral and Earth are separate cables. I suggest you need to ask a local qualified electrician how you should install the c.t.

i am in australia and i have watched the video online regard about the emontx shield to measure the power consumption of a coffee machine. but in the video i cannot see clearly where the CT is clipped on?

"The primary winding of the CT is a wire that carries the current you want to measure. If you clip your CT around a two- or three-core cable that has wires carrying the same current but in opposite directions, then the magnetic fields created by the two wires are equal and opposite and will cancel. Your CT will have no output."

in Australia, the power plug cable comprises three wires, line, neutral and ground. According to above, therefore i should clip the CT on either line or neutral only. my question is that do i have to peel of the insulator rubber and find the line or neutral wire then clip on it, is that  right(isnt too dangerous)? i watched the video regard about the power monitor of a coffee machine, i cannot see clearly where the CT is clipped on which wire. in the video, demonstrator did not peel off any insulator rubber from the cable.

so in australia, if i want to use this clip CT to measure the current of some electrical appliances, how should i connect it 

thanks

Rather than butchering the cable for every appliance you want to measure, consider hacking an extension lead to expose the neutral, and clamp that (see attached photo).   Take great care not to damage the inner insulation (blue in my photo) when you slice through the outer layer (white).  If you see any exposed copper, throw it away and start again.

@dBC  Where did you get that small white CT from?  It looks smaller than the normal blue one in the openenergymonitor shop.  I am looking for a small CT that I could put in my fuse box so that I could monitor the power usage of a couple of circuits.

I've got a bunch of different CTs I'm testing for someone, but I'm afraid I don't know where you can buy them commercially in small volumes.  For what it's worth, that one in the photo is one of these:

http://www.yuanxing.net/5-2.asp

That particular one is not really suitable for an emonTx setup though, as it has a built in burden and only produces a swing of 0.333V at full scale.  On the plus side, it does have a relatively flat phase error (Vs current) compared to some I've seen.

Thanks anyway. If anyone is aware of a small CT that is compatible with an emonTx I would be grateful for the info.

You could probably use a c.t. designed for 0.333 V output provided you can remove the internal burden resistor, if it's fitted. You need to choose one rated for a current at least three times the current you are measuring, and set the value of the new burden resistor to give you 1.1 V rms (for the emonTx) across the burden at your maximum current (i.e. the product of secondary voltage and secondary current should be the same before and after the modification).

If you don't need a split-core c.t. (meaning it is legal and safe to disconnect a wire to thread it through the c.t.), you are much more likely to find a small ring type.

Thank you for the suggestion. A non split-core CT would do fine.