[volt-nuts] current-nut question .. total waste of ones time type question

Pete Lancashire pete at petelancashire.com
Tue Apr 29 16:48:50 EDT 2014

Getting 2 % is pretty easy, many commercial CT's at 0.3% at the
transformer, resistance of the wire from the CT to the load (burden in the
electrical world), and all the things that effect voltage measurements come
into play. A well designed setup can get to 0.5%.

Thanks to surplus a classic 5A CT can be found for a few $'s. More modern
instrument grade CTs are expensive unless you can grab one off the usual
auction places.

A "classic" 100A or 200A:5A is a good 4-5" square and can be as much as
2-3" thick.

Today you don't need the 5 Amps, heck 10-50 mA is good enough, so the size
can be smaller.

I've been trying to shoot for say 0.1% to 0.2%. Again for 'fun'.

Where some more fun comes in is when you get below 10%, that would be
10Amps using a 100A CT. The industry specs stop at 10%. A 0.3% transformer
is only 0.3% at full rating (and above).

Was just looking to see if anyone has come up with something new / low cost
/ etc.

On Tue, Apr 29, 2014 at 12:06 PM, Brent Gordon <volt-nuts at adobe-labs.com>wrote:

> Years ago I installed a TED-1000 (now obsolete) system from <http://www.
> theenergydetective.com/>.  Their software is terrible but the system
> works.  This system uses two current transformers and a single voltage
> measurement system that all go inside your circuit breaker box.  I don't
> recall the sampling rate (1 KHz maybe).  The instantaneous voltage and
> current measurements are multiplied, summed, and transmitted once per
> second.  The data is transmitted to a receiver using the house wiring
> (similar to X-10).  People have hacked the system to use their own receiver.
> I haven't directly measured accuracy; monthly totals are usually about 5%
> low when compared to my electric bill.  The software compensates for
> missing readings.  Resolution seems to be around 10 watts.
> Brent
> On 4/29/2014 11:25 AM, Pete Lancashire wrote:
>> Next spring I'm going be rewiring my house. And for 'fun' I want to drop a
>> couple current sensors on the input side of the main panel.
>> Being a beginner 'nut', I'm looking for more accuracy then needed.
>> Voltage, Frequency, waveform will be taken care of later, but accurate
>> current has be a bit flustered.
>> I've been reading up on CT's Iron core and Ferrite, and on Rogowski coils.
>> And the many new IC's on the market that take care of a lot of things.
>> Has someone done this before ? And if so any experiences to share ?
>> -pete
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