Wolf said:
ajw22 said:
It's for sensing L1-N(120v) and L2-N(120v) of a split phase 240V system, and feeding back on the combined L1-L2(240v), right?
That wiring seems all wrong to me. Does it work well for you under all conditions?
I use 2 sensors wired in parallel (no resistor), feeding back just on L1-Neutral(120v). Obviously unbalanced, but no issue since the meter combines L1+L2 anyways.
When I used just 1 GTIL hooked to L1 and L2 that is the CT comboI used as it was on sale on ebay claiming to solve the Split phase problem.
Unfortunately as my panel was seriously unbalanced I was back feeding the grid even with those sensors like that.
Whetherthey are right wrong or just plain stupid I don't know :huh:I just know that they did not work properly for me.
Since then I got another GTIL and now feed L1 with one and L2 with one. No backfeed whatsoever but that is to be expected as I am no longer supplying an uneven panel with 1 GTIL
Here is the graph of one GTIL hooked to both L1 and L2 with the CTs as shown above.
You can see that the output of the GTIL LI and L2 are a mirror image of each other so whatever L1 was demanding was also supplied to L2. If L2 was not using anything it would backfeed it to the grid. If L2 was using something the difference was still backfeeding.
This was occuring till 4/12 when I installed the other GTIL and started to feed the legs separately.
This is what the chart looks like now absolutely no backfeed.
Neutral hookup I have no idea. I mean neutral has no potential (Voltage) as it is basically"earth"?.
Can you measure the current in a neutral wire? I suppose you can. As electron flow is electron flow no matter where in the circuit.
So we know that electron flow represents current which is measured in amps.
I have some spare CTs and will put one on the neutral on my panel and see if it correlates with the other legs. It will be an interesting experiment.
Wolf
Wolf,
First off thanks alot for the pictures! I will make my comments on the cable later.
I think your dual CT clamp set up didn't work because it seems to me you we're using a 120V GTI??? Ajw22 and myself use a 240v GTI. As ajw22 said your after the sum of the amperage draw. The CT clamps essentially take a sample of this back to the GTI to determine your power consumption.
I need to clarify a few things about the 240v split phase first before I continue with my understanding of CT clamp operation.
1. Neutral and Earth are NOT the same. The power company's neutral comes from the center tap. That's the 0v reference. You can essentially complete a 120v circuit using ground, from L1 and / or L2 but highly not recommended or safe.
2. If you turn on a hair dryer which draws 10 amps say from L1 and you put an ammeter on the neutral leg without anything drawing power from L2 You WILL get a 10A reading on the neutral leg. I'm sure of this. L1 will complete the 120v circuit through neutral. More on this in a second.
3. There should be no potential voltage difference between neutral and ground, unless you have something backfeeding voltage on the neutral but rest assured there will be a current shooting through the neutral wire to complete the 120v L2 or L1 circuit. After having said that that statement is not completely true because if you draw 10A off L1 and 10A of L2 then you'd actually not have any amperage through the neutral leg when L1 and L2 loads are balanced and this is where we run into problems with 1 CT clamp on the split phase electrical.service. Which is why a CT clamp on the neutral leg alone to report back an reading of your power usage can't be accurate but itself.
I am pretty sure that all these statements are true and accurate.
The CT = Current Transformer that came with my GTI is a 100A /50ma and interestingly enough the ohm reading is 125 ohms... 2 of these in series would be 250 ohms I would imagine. To be accurate we really aren't measuring resistance it's the impedance of the windings in the coil but I can't see why the resistor in your cable would be of any help. You are after the sum of the current readings. I do have one question which is unclear to me. If the GTI just takes the sample of the current reading and uses this alone to calculate the power usage you have from.the grid or if voltage is considered at all?
These CT clamps I do believe have a voltage range as well and this is something very important to consider. If anything to stay within design range. Especially in your case Wolf. If the voltage is considered ( which I doubt ) but not sure- then you would have perhaps provided a somewhat correct sum of the current to your GTI but your voltage since clamps are in series would be the sum of your voltages. I believe the voltage of my CT clamp which my GTI is expecting me to connexct to 240v would be 3.3v , your 120v GTI would be seeing the SUM of the voltages. If your clamps where in parallel then you would NOT add the voltages. Your voltage from CT clamp to GTI is always constant- what changes with power consumption is the sample of the current draw.
Can you tell me what your CT clamps have stamped on them or take a picture? I think we are gonna get to the bottom of this soon.
ajw22 said:
This is what I use at the moment, and it's working 100% as intended. Senses the currents on L1 and L2, and feeds the sum back on L1. No resistors used, except for the one inside the GTI (I assume there is one).
I actually have 2 GTILs (with 4 sensors)set up in the same way. They don't share the work equally, but L1 feedback is always equal to or less than L2 consumption.
I'm thinking of rewiring myGTIL1000s to L1/L2 (240V) to hopefully increase efficiency, but then I will need to halve the sensed current. I think this could be achived by adding another burden resistor (same value as the GTIL internal one) into the sensor cable.