Already have a Pi3

I already have a Pi 3. I live in the US. I would like to build a emonPi with the case and everything for solar.

What all do I need to buy?

My solar already has its own monitor system, so I just need to monitor my home usage inside the house. Coming into my breaker box in the basement is a single large cable. See attached picture.

There are 4 cables coming out of the main cable. One looks like earth ground because it is bare wire.

The other 3 are black, black / red and black / white. The black and black / red both go into the center area of the breaker box. The black / white one only goes to one side of the panel where all the white wires from all the plugs in the house connect to.

With that information what can you tell me about hooking up the whole thing.

You should need:

See the getting started guide. Specifically, the notes about use in the USA:

@Bill.Thomson will be able to advise you on placing your CTs, but it’s likely that the CT included WON’T fit on your cables. There’s a lot more in the “N.America” page and lists of suitable CTs.

Good eyeball calibration, Robert. His feeders look to be AWG 2/0 i.e. too large for the shop-sold CT.


Other OEM users in the US have used Magnelab and Byram Labs CTs with good results.
One CT which we’re familiar with, and is known to work well with OEM is the Magnelab SCT-0750-000.

See the section titled EmonTx - Use in North America on this page for more info.

Correct. The bare wire is a grounding conductor.

The black and black/red wire are the hot legs. The black/white wire is the neutral leg.

Use care while working inside your load center (breaker box) as the black and black/red wire are always live unless there is a disconnect upstream from the load center.

You are all awesome. This is why I posted here.

Now I just need to bring it all together and make it work.

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Is there a standard connector on that larger CT? It seems like it will only come with a twisted pair of wire.

Would it be safe to just chop off the connector that comes on the CT that will come in the package from you OpenEnergyMonitor when I buy the kit or do I need something larger?

Which cable in my breaker box should I connect the large CT to? Obviously it would be easiest to connect to one of those black cables going into either side of the breakers, but I want whole home usage and those look like they go to one side or the other…

Correct. It ships without a conector.
The connector you need is a standard 3.5mm (1/8th inch) stereo plug. Tip and sleeve are used, the ring is not conected. Here’s an example sans insulating shell:

Thank you for the answer. The package I will buy comes with the smaller CT. Can I just cut that connector off and solder the wires to the new one? Are they polarized or does it not matter which wire to which?

Correct. The large black wires are where you’ll attach your CTs.

You’ll need two CTs. There are a couple of ways you can arrange them on your feeders.

See the section titled “Measuring Whole-house Power” on this page for details.

You could do that. But 1/8th inch stereo plugs are inexpensive, and one similar to that in the picture would make a “cleaner” installation.

They aren’t polarized in a DC sense, but you need to keep the phase relationship between the two correct. It’s explained on the “Use in North America” page I linked to above.

Thank you.

The latest YHDC CTs come with a moulded-on plug. If yours comes like that, cutting it off won’t help you. It’s a case of 2 new 3.5 mm plugs. If you do get the phase relationship wrong, it’s simply a case of flipping the CT on its cable, or if that’s hard, multiplying by -1 in the software somewhere.

I took it to mean "could the plug be cut off the YHDC CT along with some of the cable so it could be spliced onto the wires from the substitute CT.

And he’ll need to replace the burden resistor in the emonPi, too.

Tony, correct me if I’m wrong.

That is what I was asking and you bring up another point about replacing the resister. This seems to be getting complicated.

Replacing the resistor does involve a bit of soldering, and a calculation. (for the new burden resistor value) We can help you with the calculation.

Do you have any idea what your peak load is? (in Amps)

I appreciate the help. I really don’t know. What is the best way to figure that out?

Make a list of the electrical loads (appliances) you have. The large loads, like air conditioner, water heater, stove, oven, etc. If you have gas fired water/space heating, etc, you simply ignore the item.

Look at the nameplate on each item for the current draw. Add them up and you’ll have a rough estimate.