Worst comes to worse, just double up the wires to reduce voltage drop. 

Jase2985:

 

Worst comes to worse, just double up the wires to reduce voltage drop. 

 

That's a fundamental misunderstanding of how a CT works. The EVSE will have a large resistor across the terminals so effectively no current flows, therefore there is no voltage drop.
You need to be preventing spurious signals from getting onto the wire.

fastbike:

 

Jase2985:

 

Worst comes to worse, just double up the wires to reduce voltage drop. 

 

 

That's a fundamental misunderstanding of how a CT works. The EVSE will have a large resistor across the terminals so effectively no current flows, therefore there is no voltage drop.
You need to be preventing spurious signals from getting onto the wire.

 

maybe so, but it will need a minimum wire size for x distance. so if the 22-24AWG wire in CAT cable isn't enough, you can just double it up for the distance.

Jase2985:

 

maybe so, but it will need a minimum wire size for x distance. so if the 22-24AWG wire in CAT cable isn't enough, you can just double it up for the distance.

 

Further confusion in that answer. If the OP wants to understand how the CT works, and what the requirements are for a long cable to connect to the measuring device, then I suggest reading the linked article.
https://docs.openenergymonitor.org/electricity-monitoring/ct-sensors/extending-ct-cable.html#extending-the-current-transformer-cable

fastbike:

 

Jase2985:

 

Worst comes to worse, just double up the wires to reduce voltage drop. 

 

 

That's a fundamental misunderstanding of how a CT works. The EVSE will have a large resistor across the terminals so effectively no current flows, therefore there is no voltage drop.
You need to be preventing spurious signals from getting onto the wire.

 

To expand on the above, a CT is all about current and will try and keep the current flowing in the sensor by raising the voltage until the current flows. So if you have a 60Amp to 10 mA CT then 10 mA will flow when 60 Amps is in the primary. The easiest way to measure the current is to use a resistor (called a burden resistor because it provides a load to the CT) and measure the voltage across it.

Sometimes the burden resistor is built into the CT and therefore you can measure voltage directly and little current will flow as fastbike explained. Some other CTs will have a TVS installed to limit the open circuit voltage and for these you need to provide the burden resister. The two types are shown below and varies depending on the size of the primary current.

The version that I bought for measuring my house didn’t have the burden resister installed so I suggest you check how your CTs are internally wired.

Be very careful when working with CTs and make sure that you do not have any current in the primary while you are working on it if there is no burden resister as the high voltage that occurs is nasty.

This does depend on the type of CT; in industrial metering applications they're normally designed for 5A secondary current and therefore need large cables, especially over long distances as voltage drop reduces accuracy. This improves noise rejection.

IOT meter CTs are usually either mV output or tens of mA and will do better on thin wires, but shielding and twisting is more important.

wired:

 

To expand on the above [response to GeOrge's query about using 40m of existing CAT6 wiring to connect an Evnex E2 to a CT clamp], a CT is all about current and will try and keep the current flowing in the sensor by raising the voltage until the current flows. So if you have a 60Amp to 10 mA CT then 10 mA will flow when 60 Amps is in the primary. The easiest way to measure the current is to use a resistor (called a burden resistor because it provides a load to the CT) and measure the voltage across it.

 

Sometimes the burden resistor is built into the CT and therefore you can measure voltage directly and little current will flow as fastbike explained. Some other CTs will have a TVS installed to limit the open circuit voltage and for these you need to provide the burden resister. The two types are shown below and varies depending on the size of the primary current.

 

The version that I bought for measuring my house didn’t have the burden resister installed so I suggest you check how your CTs are internally wired.

 

 

 

 

Be very careful when working with CTs and make sure that you do not have any current in the primary while you are working on it if there is no burden resister as the high voltage that occurs is nasty.

 

If the CT clamp is labelled in amps per volt (e.g. "30A/V"), then it'll have a sampling resistor.  There'll be 4V across its outputs if there's 120A through its primary.  The voltage sensor in the EVNEX unit will surely have a very high impedance -- much much higher than 40m of CAT6 cabling (even if it is CCA rather than copper).

If the CT clamp is labelled in amps per milliamp (e.g. "100A : 50mA"), then it has a TVS.  The burden resistance will be in the Evnex unit, and it'll possibly be 22 ohms.  The series resistance of 40m of CAT6 cabling might be problematic, because it'll add to the burden -- possibly causing the CT clamp to overheat (because the current through the secondary will remain constant, but its voltage drop will increase).  Hmm... a roundtrip total 80m of (perhaps) 24AWG, if it is copper, would have a resistance of perhaps (80m)(89 ohms / 1000m) = 7.1 ohms.  That'd be a significant addition to a 22-ohm burden.   That'll increase the phase error and thus degrade the accuracy of the current measurement whenever the power factor of the household supply is not 1.0.    Worse: the CT clamp could overheat or fail, due to the (roughly) 30% increase in the wattage it dissipates in its secondary winding.

I found the following note in an installation manual for Enphase IQ Gateway-M monitor.  "The electrician may add as much as three ohms round trip resistance to the consumption CT or up to 1.5 ohms per wire. For reference, the following maximum lengths at 75° C by gauge are: 64 meters of 0.75 mm2 7-strand Cu = 1.5 ohms, 85 meters of 1 mm2 7-strand Cu = 1.5 ohms, 128 meters of 1.5 mm2 7-strand Cu = 1.5 ohms".  This monitor is specified to have a "Production / consumption metering accuracy +/- 2.5%".  The concern about the resistance of the cabling strongly suggests to me that this is a TVS CT clamp.

I can readily imagine that noise-injection could also be problematic on long cabling to a TVS CT clamp which is carrying only tens of milliamps of current.   High accuracy certainly isn't required for this application; but if the Evnex unit wildly underestimates the draw from a household that's nearing its supply limit, then ... "Don't try this at home, kids!"

My sources:

Does this split-core clamp current transformer have a built in burden resistor? : StackExchange discussion indicating how to read the label on a CT clamp.

YHDC SCT-013-000 Current Transformer : A Report on the properties of the YHDC current transformer and its suitability for use with the OpenEnergyMonitor system.

Enphase IQ Gateway-M Installation and Operation Manual : extending the cabling on the CT clamp for the Gateway-M won't invalidate its  specification, if the cabling has a low enough series resistance.

Ge0rge: For those who have had an Evnex E2 installed, what cabelling was used to connect the CT clamps?

There's a lot of speculation in previous posts about requirements, but this is the requirements from the manufacturer:

7.4kW Single Phase – Residential

 

Customer/Electrician to run a 32A 2C+E dedicated supply cable and a 1-pair or 3-pair (depending on number of phases to be monitored*), overall screened instrumentation cable, ≥0.5mm² and appropriately rated at the max. Voltage present in the switchboard (≥230/400V), between the main switchboard and the charger location. Consult with your electrician regarding supply cable size, (6mm² minimum).

 

 

 

22kW Three Phase – Residential

 

Customer/Electrician to run a 32A 4C+E dedicated supply cable and a 3-pair, overall screened instrumentation cable, ≥0.5mm² and appropriately rated at the max. Voltage present in the switchboard (≥400V), between the main switchboard and the charger location. Consult with your electrician regarding supply cable size, (6mm² minimum).

RunningMan:

 

[ Ge0rge: For those who have had an Evnex E2 installed, what cabelling was used to connect the CT clamps? ]

 

There's a lot of speculation in previous posts about requirements, but this is the requirements from the manufacturer:

 

7.4kW Single Phase – Residential

 

Customer/Electrician to run a 32A 2C+E dedicated supply cable and a 1-pair or 3-pair (depending on number of phases to be monitored*), overall screened instrumentation cable, ≥0.5mm² and appropriately rated at the max. Voltage present in the switchboard (≥230/400V), between the main switchboard and the charger location. Consult with your electrician regarding supply cable size, (6mm² minimum).

 

22kW Three Phase – Residential

 

Customer/Electrician to run a 32A 4C+E dedicated supply cable and a 3-pair, overall screened instrumentation cable, ≥0.5mm² and appropriately rated at the max. Voltage present in the switchboard (≥400V), between the main switchboard and the charger location. Consult with your electrician regarding supply cable size, (6mm² minimum).

 

AWG24 is still only 0.2mm² (0.5mm diameter). To get to the minimum spec from Evnex (≥0.5mm²), AWG20 would be needed. Online calculator here.

What cable would meet the spec?

1-pair or 3-pair (depending on number of phases to be monitored*), overall screened instrumentation cable, ≥0.5mm² and appropriately rated at the max. Voltage present in the switchboard (≥230/400V)

RunningMan:

 

AWG24 is still only 0.2mm² (0.5mm diameter). To get to the minimum spec from Evnex (≥0.5mm²), AWG20 would be needed. Online calculator here.

 

What cable would meet the spec?

 

1-pair or 3-pair (depending on number of phases to be monitored*), overall screened instrumentation cable, ≥0.5mm² and appropriately rated at the max. Voltage present in the switchboard (≥230/400V)

 

Just had the OpenEVSE installed. It's a really good unit and I will integrate it via MQTT so it throttles with the solar output.
It is so good not to be owned by some crowd that will only hold you captive via a cloud connected device. Apart from the issues of who really owns the kit, the ongoing energy consumption of cloud infrastructure, you seriously need to consider what happens when these companies eventually change ownership.  Look at the cluster that Juicebox became when their ownership changed, and services were down graded without warning.

https://www.youtube.com/watch?v=p1A6x_oyufg

fastbike:

 

Just had the OpenEVSE installed. It's a really good unit and I will integrate it via MQTT so it throttles with the solar output.
It is so good not to be owned by some crowd that will only hold you captive via a cloud connected device. Apart from the issues of who really owns the kit, the ongoing energy consumption of cloud infrastructure, you seriously need to consider what happens when these companies eventually change ownership.  Look at the cluster that Juicebox became when their ownership changed, and services were down graded without warning.

 

https://www.youtube.com/watch?v=p1A6x_oyufg

 

 

 

Where did you purchase from? Did your installer give you any grief about AS/NZS compliance?

boosacnoodle:

 

Where did you purchase from? Did your installer give you any grief about AS/NZS compliance?

 

Purchased from the web shop. Get a correctly rated switched socket (PDL 56 etc) installed/certified by sparky, with a B type RCD in the distribution board, then just plug it in.