# Extended data rules net consumption calculation

Im just looking to get it half right until i can find something at the right price to do the job properly

Notwithstanding lwsmiser’s comments above, the CT clamp that you’ve installed will not be able to determine the direction of the current flow in the wire. It will only be able to read a ZERO or NON-ZERO value.

If the CT clamp shows zero value then either there is no load in the dwelling or GENERATION = CONSUMPTION.

If the CT clamp is reading a non-zero value there are two possibilities. (i) CONSUMPTION > GENERATION or (ii) GENERATION > CONSUMPTION.

You would need to relocate the existing CT in the main board to a point where it will only be able to measure current moving in a single direction. You would also need to introduce a second CT to a point in the sub-board where it too can only measure current moving in one direction.

Why do you say that the CT can’t determine the current direction? Polarity is an inherent property of CTs. Are you maybe saying that the measuring device only records the magnitude of the output of the CT and not the direction?

hi,pjschaffer, if you look at the picture above you will see the CT is round TOO wires and is therefore unable t0 function as it normally would-- jim

Actually, a CT will work just fine that way. It’s done all the time. The CT will see the net flow between the two wires that pass through it. That said, I don’t think the red and green traces in the image are actually two different wires. That’s not the way main panels and sub panels are wired. Most likely, the inverter is connected to the “sub board”, the “sub board” is connected to the “main board” which is then connected to the “meter box”. Regardless of that, the CT Clamp as shown will measure net current to/from the meter box.

1 Like

All CT clamps can be used to determine direction of current flow. They put out a positive voltage when current flows from the grid and a negative voltage when current flow into the grid if they are connected correctly. This is the nature of the current transformer. However, if the device reading the CT output is programed to ignore flow into the grid you are correct but it doesn’t make sense to have such a device if that is the way CT data is processed. A pulse counter on the other had cannot determine the direction of flow. It would require another device used in tandem to determine the current’s direction.

sorry i have been on holidays and drew the graph up quite quickly before I left.
its only 1 wire but the green colour shows generation perhaps i shouldn’t of drawn it all the way back to the meter box.

what pjschaffer said is correct

sorry I don’t follow… As far as i was aware a CT clamp can not determine current flow.
if I clamped it on the other way around are you saying it would then read a negative number?
if the clamp can indeed read direction what device would i require that can get that data from the clamp?

I have a pulse counter on my system and it can recorder pulses for import or export.

If that device could output 2 pulses and i could set it as 1 for import and 1 for output i would use that for the setup i require for my parents. but it can only record 1 pulse and its also a 3 phase unit but they only have single phase

I’ll try not to get too technical, but a current transformer (CT) in its basic form has an output current that is proportional to the current flowing in the conductor passing through the CT opening. CTs have a parameter called “Turns Ratio”. This represents the number of times the CT’s internal wiring is wrapped around the conductor being measured. For example, if internally, the CT had 100 loops of conductor, then the current output from the CT would be 1 amp for each 100 amps of current passing through the conductor being measured.

Most clamp on CTs used in consumer devices are actually modified CTs that have a known resistance placed across the output of the CT internally. The reason for this is that it is dangerous to leave a CT open circuited when is use. Since current can’t flow through an open loop, the voltage at the output of the CT will continue to rise to the point of failure. Adding an internal known resistance allows the output of the CT to be voltage that is proportional to the current flow.

You mentioned that you are using a Pi to record net power. I don’t have any experience with that, but I expect that it does have the capability to determine the polarity of the CT signal which would allow you to determine direction of power. Maybe someone else can provide more detail on that.

i use a CC ENVIR to record the net power. i use a pi to upload it to pvoutput

I haven’t used that device either but in looking at the literature for it, it appears that in an effort to make it simple for a consumer to install, the device only uses the magnitude of the measured current and does not consider the current’s polarity. Without that capability, I think it would be very difficult, if not impossible, to determine actual net power with this device.

There are many products out there that can do what you’re looking to do. I use a TED 5000 (The Energy Detective) system that I installed years ago. I works OK, but if I were to replace it now, I would likely go with Neurio system due to its public API. I’m sure that others will have different suggestions as well.

thanks.
I used to run this system and had my solar setup so it worked fine apart from the accuracy was not quite there.
i then moved into a new house and got S0 Pulse meter connected to a flukso for consumption and water from a reed switch and then years later eventually got solar.
all works great.
my parents got solar so i hooked the old envir up and it can not be setup correctly so i now have issues and looking for a way to best set it up.

Looking at the CC ENVIR website and looking through the instructions that they provide as well as viewing the short video that they display I was unable to find anything that says the clamps have to be installed in a particular orientation. They are quite specific about ensuring that the clamp is completely closed and that the clamp is to installed around a single wire. It would seem to be an odd omission if the clamps were able to detect which way the power was flowing and they do no stress the correct orientation of the clamp around the cable! This leads me to conclude that these clamps are unable to detect the direction of flow and will simply return a value proportionally to the magnitude of the flow and not the direction. i.e. a non-negative value.

http://www.currentcost.com/installation.html

I did contact the supplier nearly two weeks ago to ask this question but they’re either overwhelmed with customer question of they’ve simply not bothered to reply.

I also can’t see how in isolation a CT clamp can determine the direction of flow. The measuring device would need to be able to ascertain the phase relationship between current and voltage in the wire. This would require some other measurement.

Looking at the website https://shop.openenergymonitor.com/ac-ac-power-supply-adapter-ac-voltage-sensor-euro-plug/ they provide a ‘device’ which is used in conjunction with a clamp and:

Used to give an AC voltage sample which can be used to calculate the rms voltage, real power, power factor, frequency and to detect power flow direction.

The specification sheet shows that this is simply a step-down transformer.

they are hopeless. im guessing they hit their peak years ago and then on a downward run and now just don’t seem to get back to you… i ended up getting more help from their ebay store…

it’s quite an old device and was put there for a temp setup until i can get a proper permanent solution… just need the time to find whats going to be the correct setup for this situation

I have gone over the Envir’s site data and it appears that there are at least two versions of the device. One for monitoring the home’s energy usage without a PV system and the second one which has an additional sensor (CT) for monitoring the home with a PV system. You are required to trade in the former unit to be able to monitor your home’s NET energy usage. You will need both sensors (CT) to do so since power will flow into and out of the home at different times of the day.
AC current is directional and therefor has to be signed in order to determine whether power is flowing into or out of the home. In most homes the phase difference between voltage and current is very small unless you are operating some sort of powerful machine in your home which has large reactances.
As for the CT usage and current direction. CT’s are only used in circuits. For this reason the secondary coil produces both current and voltage. For most home the values of current and voltage are given as RMS (root mean square) values. Current doesn not have a sign but voltage does and indicates which direction power is flowing…into or out of the home. In the case of a home without a source of power such as a PV system, the polarity of the voltage in the secondary winding of the CT determines the direction of power flow. Apparently this value is ignored by the Envir intended for use consumption only with no PV system input present. If this Envir model is used with a PV present the voltage is ignored and all power is assumed to flow into the home. (You can trade in your consumption only device for this one which probably requires additional cost.) This results in the zero values when PV power exceeds the consumption by the home circuits and power begins to flow out of the home and into the grid. It appears then that the Envir model which is designed for no PV system homes cannot accurately show NET power but instead only records the power which flows into the home ignoring the PV power which flows into the grid.