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When you write "multicore cable", do you mean a normal 3-core (line, neutral, protective earth)? Or is there anything else in there?

I've had a quick look at that link. It's not a suitable replacement for the CT as it stands - the problem is the "peak detector". The CT feeds the actual current waveform and the maths to get the true rms value (which gives the heating effect of the current) is done inside the emonTx. The output of that sensor is clearly (though it doesn't actually say so) a d.c voltage that relates to the peak voltage. You'd need to rewrite the sketch, and modify the front-end signal conditioning circuit - or use the 2 normally unused analogue inputs - to accept the output of that sensor.

The obvious warning is that sensor needs to be precisely and immovably positioned in relation to the cable, or calibration will suffer.

Hello Robert,

Yes, a normal 3 core conductor. I am basically looking for an alternative to breaking the outer insulation of my existing wiring to isolate one of the conductor and be able to take a measurement. I don't know if you would have any other suggestions?

I am just tapped in my breaker box right now with the lid left open for the testing. I don't think there's enough room in there to fit all the CTs i would require to get the measurements I would like for individual circuits. The way the house is wired, I can have multiple "zones" (zones close to each other but that I want to monitor separately) of the house on the same circuit breaker to make the most out of each breaker/wire combination.

I think the circuitry modification you are referring to is a bit too much for the amount of knowledge I have right now. When I saw this device on MD's website, I thought there would be an alternative to measuring single core value discussed somewhere on the forums, but I can't find anything.

Thanks for your quick answer,

LM

@imagnan,

I'm afraid without separating out the conductors, your options are very limited - basically passing them all through the same C.T. aperture has a net magnetic flux of zero since the IN current balances the OUT.

The Modern Device method uses a second order effect that when very close to the conductors, the fluxes don't exactly balance out. The sensor output voltage is an *estimate* of the current flowing, but is really intended as a non-intrusive presence/absence detector.  Since I imagine those heaters are simply full on/full off isn't this close enough to say that the nameplate power is consumed or not?  This will vary somewhat with line voltage and temperature but is enough if you wanted to create a display of active/inactive heaters or even totalise up the energy dumped into each room each day.

emjay,

Heaters are indeed full on or full off.

However, with the price of the device, it makes a pretty expensive "on or off" indicator if the precision is not really there when you think you can get a regular CT for a lot less...

I came across a few other posts talking about Hall Effect devices during my forum search, but they were a solid core device that looked like a non-split core CT. I don't know if these would do the trick? I want to try to avoid splitting the wires as much as possible!

As you probably noticed, I am not super knowledgeable about electronics. I have a pretty sound electricity background but its my first time getting into that type of stuff.

Cheers,

LM

Assuming each individual zone/heater current is small (compared to 100 A), do you have room in your distribution board for rather smaller, lower current ring-core CTs? I believe Robin Emley uses either the 20 A version here: http://www.yhdc.com/en/product/425/ or this 20A:10mA one http://eppep.com/?action-viewnews-itemid-140364 from http://www.ebay.co.uk/itm/281436762683?_trksid=p2059210.m2749.l2649&ssPa... in his diverter to measure the immersion heater current. The wire would need to be dropped out of the outgoing side of the MCB to install the CT, but that's easy enough.

You'd need to change the burden resistor in your V2 for either of these, but that's not a major issue.

Hi Louis,

Here's another example of a solid core CT that might fit in your breaker box:
www.brultech.com/store/product.php?id_product=45.
Dimensions are at the bottom of the page. These CTs produce 26.23mA @ 40A primary current.
There are 50, 80 and 100 Amp versions available as well. Output specs for them are on their respective web pages.

Regards,

Bill

Hey guys,

Thanks for all your suggestions.

I thought about my heater thing again and I just remembered the other side of the other (the side not used for the actual heater connection) can be used as a junction box and has leads coming off the element, therefore giving me a lot of room for one of the CT you have suggested.

Most of my circuits are rated for either 20 amps or 30 amps (but never go over 80% of their max rating anyway), so I think most of the smaller CTs you suggested will work fine and will be way cheaper than other options.

Last thing I have to figure out to have a functional system is the best CT to monitor the mains. There is a lot of documentation about this, I just have to find the best CT for the best price, unless somebody running a North-American system has a good suggestion?

LM

Last thing I have to figure out to have a functional system is the best CT to monitor the mains. There is a lot of documentation about this, I just have to find the best CT for the best price, unless somebody running a North-American system has a good suggestion?

The wire size of your feeders will play big part in determining your choice of CT. See this for more info on CTs usable on North American domestic electrical systems. The FAQ page has three links to CT seller sites.

I use CTs from Magnelab and Byram Labs. Prices tend to be in the $35-$50 range. (per CT)

Could you not monitor the heaters at the actual heater itself - tap into the thermostat locally and monitor the on/off cycles ?

Hey Stuart,

I would prefer to stay on the "non-invasive" side of things... Easier to explain to the insurance company if the house catches on fire, even if its not related to the modifications I did ;)

Like I mentioned, the other side of the heater has lots of room for a CT and has wires coming off the element to go back to the connection side of the heater. Its a perfect place to take a reading, especially with the smaller CTs.

Cheers,

Louis