Recommendation for a (larger) AC current clamp

Good day all,

After testing my new emonPi on a sub circuit of my home, I’d like to monitor energy usage for my whole hole, but the wire coming into my panel is much too large to clamp the current sensor that came with my emonPi. Does anyone have a recommendation for a larger AC current clamp that would fit a 1.5-2.0 inch wire delivering electricity into my home? I believe one as large and configured as this would work (

Thank you!

Yes, read the page in Building Blocks about using the emonTx in N.America.

Hello Rob,

Your description sounds more like PVC or EMT conduit. Can you post a picture of it?
Which country are you in?



Thank you, Bill. Pardon the delay. Just got the pic:

It’s an AWG 2/0. I believe this AC clamp can fit around that: Mastech MS3302 AC Current Clamp Transducer (AC Current Transducer MS3302-Digital Clamp Meters - Meters - - Mastech)

Thoughts on that device serving as the CT?


Is that a single core or twin? It looks suspiciously flat to me.

That clamp transducer won’t allow you to measure real power, and it won’t interface to the emonPi without modifying both the hardware and software of the emonPi. That’s because it outputs a direct voltage (0 - 400 mV d.c.), whereas the Pi expects alternating current (0 - 50 mA a.c.).
So overall, a proper, plain, C.T. would be a better starting point.

With the exception of the two stranded grounding conductors, everything in his picture is multi-core
multi-conductor. More than likely a hot, neutral and ground.

Closer examination of the picture shows the gray jacketed conductors are 4/0 Aluminum with ground.

Not a problem, Rob. Happy to help.

It’s actually 4/0 Aluminum with ground Service Entrance Wire
That’s what the 4/0Al-G printed on the jacket means.

They’ll be split out to the individual bus bars inside the load center box. (circuit breaker panel)
A picture of the load center with the cover removed would be helpful.
You may want to seek the help of a licensed electrician if you’re not comfortable removing the cover/working inside the load center.

That said, if you have the room inside the LC, you might be able to attach your CTs to the individual legs.
4/0 wire outside diameter is typically about 5/8ths of an inch (0.625) so you’ll need CTs with an appropraite sized opening. Magnelab and Wattcore make CTs that will fit 4/0 feeders.

We call that “T&E” - twin and earth. The earth continuity conductor is sheathed but uninsulated, and reduced size compared to the live conductors. (‘Triple core’ this side of the Atlantic implies that all 3 cores are insulated.) There’s a piece of standard (but old colours) T&E but with the ECC cut off short here.

Same here.
The US Electrical trade calls it 2 conductor with ground.
Noted and recorded re: “triple core.”

Thanks, team! Good info.

When I opened the panel, I note AWG 3/0 conductor wires; L1, N, L2, Gnd.

Would you think this would work with the emonpi to wrap around the AWG 3/0

Data sheet

I’m not sure if it has the 3.5mm connector.


I see what they’ve done there, but that’s the perfect way to confuse anybody. The sales glossy rates it at 100 A, the data sheet at 125 A 400 A. So which do we believe?
Whichever, my concern is that the rated output voltage is 333 mV, and that could mean that the VA rating is inadequate to drive the 1.1 V rms that the emonPi requires for maximum input resolution. Why don’t you go with the transformers we recommend, because we have been in touch with the manufacturers and we know that those we list are suitable. Although yours might be suitable, we don’t have that certainty. So you might find that it saturates and distorts the wave shape and gives you wrong readings at higher currents (maybe above about 40 A - there is insufficient information published, only the manufacturer can tell you that).

Looking hard at the data sheet again, the situation appears even more confused as the data sheet says the input current is 5 - 400 A and the rated output is 100 mA : 100 mA. I’ve no idea what they’re trying to say there.


Here’s an example of a CT that will fit your 3/0 feeders, and has a suitable output:

Here’s another:

Both CTs cost considerably less than the unit you mentioned in your post.

Thank you, Bill.

I have some 600A Coils for sale if you want some . They are listed in the for sale. Drop me a pm if you still need coils i have clamp style ones too similar to a hand held clamp. and Rogowski coils up to 3000A. also if you need coils in bulk ie 16+ i can get them custom built for you. Also as a forum memberi can give you a discount.

On the industrial side I have used NK Technologies CTs. They are very well built. If anyone is interested.

The immediate problem with those is the output of 1 A or 5 A, or 0.333 V. The first two options necessitate a 2.5 W or 10 W resistor as the burden, which must be external to the emonPi/emonTx due to the current rating of the plug, socket & pcb tracks, and the last variant does not deliver adequate voltage for our input, using less than ⅓ of the available range.

If you can live with an external burden, then the 1 A variant with a burden resistor of 1 Ω or 1.1 Ω, or 1.6 Ω if you are using an emonTx Shield, would appear to be the best suited to our application.