Need a bit of guidance

Hi folks,

First time poster - we recently renovated our house, complete with Air-2-Water Heating System and am looking to fit a EmonPi monitoring both the house electricity usage, and the Air-2-Water System usage. Our energy company meter box is fitted externally - this is pretty standard in Ireland, in a location with no power.

Is there any wireless battery powered sensor the EmonPi can hook that I can fit in this location?
The other option is to fit something at the trip board - where there are plenty of socket, but I believe to measure you need the live, neutral and earth to be split out.


Ray K

Welcome, Ray, to the OEM forum.

Unfortunately, yours is a fairly common problem. As you don’t mention PV, I assume you don’t have any, so there is a possible solution. It depends on your supplier’s meter having a flashing LED that indicates energy. If you have that (and this won’t work if you have on-site generation and you export energy, because the LED either won’t flash when exporting or you can’t tell the difference between export and import), then you can in fact add our optical pulse sensor to the emonTH temperature and humidity sensing node, which is battery powered, and that will feed the pulse count into the emonPi and hence into emonCMS.

As you say, the alternative is to install a c.t. inside your trip board, and that might be difficult if (a) it’s sealed or (b) there’s not enough space inside.

Hi Robert,

So no PV at this stage, unlikely to change as Ireland doesn’t subsidize micro-generation much.

Also so believe it or not, I still have a ye olde 1970’s supply meter. So there are no lights just, an old spinning disk with a notch on it, remember those? The energy company is upgrading it to a Smart Meter in the next year or two, I could call em and as them to do it early, if I thought it would help?

In my last home - I had an Efergy energy meter, it’s (CT?) sensor was wireless and ran off a couple of AA cells. Can EmonPi do something similar, or does it lack accuracy?

The trip box is not sealed, so installing something there is definitely an option and would probably be the best solution. My only obstacle is getting the sometimes grumpy electrician who wired our house to fit it, is there a howto for that documented anywhere?


Ray K

But presumably the consumer unit (fuse box / breaker box) is inside? Therefore can you access the cable from the meter to that box? Photos help with this.

Exactly - accuracy is the problem. One of those will sample current and pass that to the base unit. That might or might not measure the mains voltage, and it will certainly only give you apparent power. So at best, a good guess - OK for comparing against past usage, but less good for accurate measurement.

No - only for the normal mainland UK installation, where the connection between the supplier’s fuse and meter, and between meter and consumer unit, are single core “meter tails”.
You’d need to take the front off the switchboard – keep your fingers out unless you know exactly what you’re doing – and supply a photograph, and I can point out where it should be fitted. You shouldn’t come to any harm just doing that, but actually fitting the c.t. could be a different matter.

Alternatively, can you get a fairly thin wire (~5mm diameter) from where you have sockets into the meter box, and extend the c.t. cable?

Hi Brian,

So yes the consumer unit is inside my study/workshop, I am not 100% sure which cable runs from there to the supply meter - but it’s probably a safe bet, its the biggest thickest cable.

I have added some photo of the consumer unit and the supply meter here.


Ray K

Do you have a friendly electrician or feel competent to open up the face of the consumer unit? You might find you can access the supply cable in there.

OK - understood, guessed the efergy was probably trading battery life for accuracy.

Can’t imagine the Irish specification will deviate too much from the UK, so the UK should be interesting. Where can I find it?

OK - I will do this.

Impossible, I am afraid. :worried:

I can open the face of the consumer unit - but think I would need the electrician (involved in the house
construction) to do anything beyond that. He does need to come back at some point to fix a motorized ceiling window, so if I had exact instructions on what he needed to do, I could make it happen.

If he is willing to, you need to clip one of these around the supply cable (either live or neutral - right terminology @Bill.Thomson?) .

Could probably feed the CT cable out the top of the consumer unit. You will then need a double socket nearby as well for the emonPi.

If not, your only option is the battery powered emonTX I’d suggest.

I think it depends where you live. Active+Neutral in Australia. Phase+Neutral in NZ.

Thanks Brian,

I think the CT cable out of the Consumer Unit, there is already a double sockets nearby .
Is there a diagram or photo anywhere?

Ray K

Of what?

Of wiring the CT into Consumer Unit, would be only nice to have.

You just clip it over in the incoming supply cable (but either the live or neutral not both as I said).

the usual view can be seen here — Solar divert showing as export - #6 by nisirob

Robert will remind you that both conductors are considered live.
(which is also the case here in the US)

We call them “hot” and neutral.
However, Robert also told me that in the UK, “hot” refers to an overheated conductor.

The correct terms are line and neutral.

If the neutral becomes disconnected on the supply side, then the neutral on the load side of the break may be live at line voltage. That’s why both line and neutral are regarded as live conductors.

If you can do that and supply a picture, one of us can mark it up with where to fit the c.t.

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Ok - so look before I do anything else, let me at least order a CT cable, so I am ready to go in case the builder’s electrician happens to materialize.

This one looks pretty bulky, is the a neater one for putting inside the Consumer Unit?

Unfortunately not on the main incoming cables. That is a “split-core” one, which you need to get onto the cable without disconnecting anything - and you can’t do that safely unless you have your own isolator between the meter and consumer unit, which most people don’t have, or without taking the supplier’s fuse out, which means breaking their seals (and they don’t like that).
The approximate overall dimensions of the SCT-013-000 are 22 × 36 × 57 mm. If you do get one fitted, it can go on the line (which way round according to the arrow on the case) or neutral (the other way round) and really you should short the plug tip to sleeve until you get whatever it plug in to. It ought to be OK without the short, but you’re relying on the protection device inside, so it’s best to be careful.

Actually, I think he might. I remember thinking how useful that was when I saw the photo. I know you don’t like following links to off-site photos, so here it is: