Current Transformer or CT wires

[jim dungar]

And from page 12 is the true recommendation:

Consumption meter lead wires can be extended to be installed in panels away from where the lQ Gateway is located. These wires may be extended to a maximum of 1.5 Ohms per wire and 3 Ohms for both wires end to end. Appropriately rated, 0.75 mm2 to 1.5 mm2, twisted-pair wire cable is recommended. Install in accordance with all applicable electrical codes and standards.


Table 1: Cable manufacturer and description

Manufacturer	Cable description	Recommended length extension
Elcon Cables	Elcon/LAPP instrumentation cable 1.5 mm2 (1 or 3 core)	100 m (328 ft)
Clipsal CBus	Cat. 5e rated 4 pair unshielded twisted pair (UTP) cable	50 m (164 ft)
Belden	Belden 8471NH unshielded twisted pair cable (1.33 mm2)	75 m (246 ft)

I too have been searching for an economical solution to this issue.

I called Enphase because I need to do a 50 ft extension. They were very adamant that the wires needed to be twisted for that length to minimize noise.

To throw another wrench in the mix, the Cat5e cable they recommend in the table is 24awg and doesn't even follow their own sizing guidelines in the paragraph above.

Also, as a tangent response to a point that was brought up in the thread, twisting a pair of wire neutralizes the magnetic fields generated by each conductor in the pair itself, not external fields.

I have never seen this product line, but it looks like they are using some type of current transducer rather than a typical current transformer. I have never seen 'instrumentation cable" used for CT's with 0-5A AC outputs, while it is common on transducer outputs.

This may be another case where a marketing team has used language differently than our 'power' industry does.

 

[Solar_ice_caps]

I have never seen this product line, but it looks like they are using some type of current transducer rather than a typical current transformer. I have never seen 'instrumentation cable" used for CT's with 0-5A AC outputs, while it is common on transducer outputs.

This may be another case where a marketing team has used language differently than our 'power' industry does.

That may be true, but every mention, including language in all of their technical briefs and installation guides also refer to them as Current Transformers https://enphase.com/store/communicatie/consumption-ct

 

[SKSolar]

Thanks for sharing.
The costs of those CT wires are beyond imagination consider the size of them. In the end I bought the Southwire 600V #18 AWG wires @$18 per 100 feet (4 x100 wires) and twisted them together. So I have two pairs and I haven't installed them yet . Mt extension is about 80 feet from Combiner to the MSP. My MSP main breaker has 2 poles and therefore, I have 2L1 and 2L2 need to be hooked up with 4 CTs but the combiner only came with 2 Consumption CTs.
These extended twisted pairs are to be connected in the Combiner box and 2 pairs of L1 CT wires & 2 pairs of L2 wires connect to the other end of the extension CT wires in parallel in the MSP.
I hope that works. These are my twisted wires.

 

[jaggedben]

In my opinion twisted pair is not required for Enphase consumption CTs. The doc cited above still calls it 'recommended'. Previous instructions didn't mention twisted pair at all. I've extended CTs with a variety of methods depending on the situation and it makes no difference that's discernable to a homeowner. They are not certified for revenue grade measurement in the first place.

 

[SKSolar]

And from page 12 is the true recommendation:

Consumption meter lead wires can be extended to be installed in panels away from where the lQ Gateway is located. These wires may be extended to a maximum of 1.5 Ohms per wire and 3 Ohms for both wires end to end. Appropriately rated, 0.75 mm2 to 1.5 mm2, twisted-pair wire cable is recommended. Install in accordance with all applicable electrical codes and standards.


Table 1: Cable manufacturer and description

Manufacturer	Cable description	Recommended length extension
Elcon Cables	Elcon/LAPP instrumentation cable 1.5 mm2 (1 or 3 core)	100 m (328 ft)
Clipsal CBus	Cat. 5e rated 4 pair unshielded twisted pair (UTP) cable	50 m (164 ft)
Belden	Belden 8471NH unshielded twisted pair cable (1.33 mm2)	75 m (246 ft)

I too have been searching for an economical solution to this issue.

I called Enphase because I need to do a 50 ft extension. They were very adamant that the wires needed to be twisted for that length to minimize noise.

To throw another wrench in the mix, the Cat5e cable they recommend in the table is 24awg and doesn't even follow their own sizing guidelines in the paragraph above.

Also, as a tangent response to a point that was brought up in the thread, twisting a pair of wire neutralizes the magnetic fields generated by each conductor in the pair itself, not external fields.

Are you installing the 3rd Gen Enphase ESS. with Combiner 5C and Battery 5P?

 

[PaulMmn]

I don't know if this is an issue, but I believe that in factory twisted wiring the individual strands are twisted in the opposite direction from the pair twisting so that there is no net twist putting strain on the insulation.

Run the drill in reverse to nullify the net twist...

 

[PaulMmn]

A note about cat 5 or 6 four-pair wire-- although each pair is twisted, each pair has a different twists per foot-- this has 2 benefits-- the twists don't line up perfectly, which would increase cross-talk between the pairs. Second, if you're talking about a round cable vs a flat (silver-satin) cable, the round cable doesn't have lumps every so often as the twists line up.

 

[Todd0x1]

Twisting wires induces noise equally into each conductor and cancels the external noise. That is why cat 5, 5e data wire is twisted

Thats a differential signal though.

 

[SKSolar]

Run the drill in reverse to nullify the net twist...

If the direction of the twist matters, the two ends of a twisted wires should be in reverse direction then. Shouldn't you just reverse the wire connection? So, did a purchased twisted wire says you need to connect the CT on this side?

 

[Solar_ice_caps]

Are you installing the 3rd Gen Enphase ESS. with Combiner 5C and Battery 5P?

We do in general but not in this case and have not needed to extend CTs on an ESS system yet.

 

[Carultch]

If the direction of the twist matters, the two ends of a twisted wires should be in reverse direction then. Shouldn't you just reverse the wire connection? So, did a purchased twisted wire says you need to connect the CT on this side?

Direction of twist doesn't matter. Due to both leads carrying current in opposite directions and having the same direction of twist, the magnetic fields will add up to zero. Regardless of whether the twist is right-handed or left-handed, it will still cancel the magnetic fields and any interference. Twisting each lead with opposite handedness would make the problem worse, but I cannot fathom how make that to happen practically.

There is a convention for which wire of the CT connects to which input terminal of the meter, and the device itself is marked with a direction for which current flow direction will count as positive. This is a situation where two wrongs make a right when they are the right two wrongs, in the event that the CT is installed backwards. Swapping the two leads

 

[SKSolar]

The guidelines on CT wiring states:
Make sure the main load center wires are de-energized until you have secured the CT wires in the terminal blocks.
Questions:
1.) Shouldn't you connect the CT wires to the terminal blocks first before you hook/clamp the CT to L1 & L2 later? With that , does it matter whether the load center is energized or not?
2.) I have a Murray 200A Man Service panel (MSP) . 2L1 (red) & 2L2 (black) feed the 2-pole 200A breaker. See Pictures When the main breaker is turn off, power is only cut off (de-enegize) to all the load breakers, but the 2L1 and 2L2 are still live and there is no switch to turn them off ! Do you still call that de-energize, simply because the other breakers have no power and they are not drawing power from the 2L1 and 2L2?

 

[Carultch]

The guidelines on CT wiring states:
Make sure the main load center wires are de-energized until you have secured the CT wires in the terminal blocks.
Questions:
1.) Shouldn't you connect the CT wires to the terminal blocks first before you hook/clamp the CT to L1 & L2 later? With that , does it matter whether the load center is energized or not?
2.) I have a Murray 200A Man Service panel (MSP) . 2L1 (red) & 2L2 (black) feed the 2-pole 200A breaker. See Pictures When the main breaker is turn off, power is only cut off (de-enegize) to all the load breakers, but the 2L1 and 2L2 are still live and there is no switch to turn them off ! Do you still call that de-energize, simply because the other breakers have no power and they are not drawing power from the 2L1 and 2L2?

Answer for Q1:
Yes, you should connect the output leads of a CT to either the metering equipment or a shorting block, before you connect it around a current-carrying circuit.

The reason: since a CT scales the current down, it will scale the voltage up. Unless it has built-in voltage limiting components (See Elkor for examples) to limit the maximum voltage, the voltage drop across that single inch of wire will get amplified to dangerous levels. CT output leads should never lead to an open circuit, when there is current through their core.

Answer for Q2:
There are two kinds of energization that matter here: voltage-energized and current-energized. What you are describing for these service conductors is a circuit that is voltage-energized, but not current-energized. This means there is still a danger for your hand or tools to touch or get near the exposed live terminals, but the circuit itself is a dead-end for current, and won't let current flow when the breaker is open.

There is no electrical contact between the circuit being measured, and the CT, since it is installed on an insulated conductor. The fact that the line circuit is voltage-energized, doesn't make a difference to whether it will energize the CT. Current, rather than voltage, is what ultimately matters to whether the CT will energize its windings & output leads. It is current rather than voltage, that generates the magnetic fields that the CT picks up.

It makes a difference for installer safety, since you are working on an energized circuit with exposed live parts. Hopefully, you have split-core CT's, and don't need to disconnect the wire.

 

[SKSolar]

Answer for Q1:
Yes, you should connect the output leads of a CT to either the metering equipment or a shorting block, before you connect it around a current-carrying circuit.

The reason: since a CT scales the current down, it will scale the voltage up. Unless it has built-in voltage limiting components (See Elkor for examples) to limit the maximum voltage, the voltage drop across that single inch of wire will get amplified to dangerous levels. CT output leads should never lead to an open circuit, when there is current through their core.

Answer for Q2:
There are two kinds of energization that matter here: voltage-energized and current-energized. What you are describing for these service conductors is a circuit that is voltage-energized, but not current-energized. This means there is still a danger for your hand or tools to touch or get near the exposed live terminals, but the circuit itself is a dead-end for current, and won't let current flow when the breaker is open.

There is no electrical contact between the circuit being measured, and the CT, since it is installed on an insulated conductor. The fact that the line circuit is voltage-energized, doesn't make a difference to whether it will energize the CT. Current, rather than voltage, is what ultimately matters to whether the CT will energize its windings & output leads. It is current rather than voltage, that generates the magnetic fields that the CT picks up.

It makes a difference for installer safety, since you are working on an energized circuit with exposed live parts. Hopefully, you have split-core CT's, and don't need to disconnect the wire.

Thank you very much for the detail explanation. Appreciate that.

 

[jaggedben]

The guidelines on CT wiring states:
Make sure the main load center wires are de-energized until you have secured the CT wires in the terminal blocks.
Questions:
1.) Shouldn't you connect the CT wires to the terminal blocks first before you hook/clamp the CT to L1 & L2 later? With that , does it matter whether the load center is energized or not?

You are correct. They should have written something like: "Do not clamp the CTs arouns conductors, and/or do not energize the conductors, until you have secured the CT wires in the terminal blocks."

There is a slight danger of shock or arc from the CT leads if they are not landed. Also, the CTs will likely vibrate, loudly enough for a homeowner to ask you what's wrong. Don't ask me how I know.

2.) I have a Murray 200A Man Service panel (MSP) . 2L1 (red) & 2L2 (black) feed the 2-pole 200A breaker. See Pictures When the main breaker is turn off, power is only cut off (de-enegize) to all the load breakers, but the 2L1 and 2L2 are still live and there is no switch to turn them off ! Do you still call that de-energize, simply because the other breakers have no power and they are not drawing power from the 2L1 and 2L2?
View attachment 2569060

With that particular panel you're not likely to be able to fit CTs around those middle two factory conductors to the main breaker, because there's just not enough space. So you'll end up putting them on the load wires anyway.

 

[SKSolar]

You are correct. They should have written something like: "Do not clamp the CTs arouns conductors, and/or do not energize the conductors, until you have secured the CT wires in the terminal blocks."

There is a slight danger of shock or arc from the CT leads if they are not landed. Also, the CTs will likely vibrate, loudly enough for a homeowner to ask you what's wrong. Don't ask me how I know.



With that particular panel you're not likely to be able to fit CTs around those middle two factory conductors to the main breaker, because there's just not enough space. So you'll end up putting them on the load wires anyway.

Thanks for your inputs.
I am currently installing the 3rd Gen Enphase ESS Solar plus battery without backup to see how that work against NEM 3.0. The CTs are the latest CT clamps which are round shape not the old square shape CTs. One Enphase employee said I may be able to get around the 4 l4ads which is 1" apart- not to sure at this point. I may want to make a fake one to see how it will fit in .

Isn't clamping on the 4 factory installed leads consider on the load side as they feed the loads?

BTW, how is that possible to putting CTs on the load wires as there are many individual load breakers (circuit branches)? If I have 15 circuit branches, how can I do that?

The installation of consumption CTs on the Murray MSP can be complex and installing entry conduit for my PV power leads can be quite challenging as I may need to rearrange the other conduit entry points. My MSP and my AC Disconnect are at the corner at 90 degree angle. I am looking for a PV installer near Los Angeles who can help me making the entry from AC Disconnect and installing the CTs on the MSP.
Anyone?

 

[jaggedben]

....

Isn't clamping on the 4 factory installed leads consider on the load side as they feed the loads?

Those factory installed wires are on the supply side of the service disconnecting means, is what I was referring to.

BTW, how is that possible to putting CTs on the load wires as there are many individual load breakers (circuit branches)? If I have 15 circuit branches, how can I do that?

You have split them up carefully by L1 and L2 and run them all the the appropriate CT in the same direction. You can put through as many as fit, 15 12awg will not be a problem.

 

[SKSolar]

Those factory installed wires are on the supply side of the service disconnecting means, is what I was referring to.




You have split them up carefully by L1 and L2 and run them all the the appropriate CT in the same direction. You can put through as many as fit, 15 12awg will not be a problem.

I guess you said I can sort them out into L1 wires and L2 wires to install the CTs - from those wires at the bottom shown in the picture below.
Make sense ! Thanks

 

[Carultch]

I guess you said I can sort them out into L1 wires and L2 wires to install the CTs - from those wires at the bottom shown in the picture below.
Make sense ! Thanks

Alternatively, some CT's allow you to parallel the output leads.

You could use a group of 4 CT's, and parallel the output leads on those of corresponding phases, so that the current of both CT's on the same phase will add up to measure the combined power on wiring that isn't practical to combine into a single CT. You'd need to make sure to use identical CT's and that the sum total of both CT outputs at full load is within the limits of the metering equipment. This could be an easier solution to implement, than needing to disassemble all load circuits, and re-route the wiring through the same CT.

 

[SKSolar]

Alternatively, some CT's allow you to parallel the output leads.

You could use a group of 4 CT's, and parallel the output leads on those of corresponding phases, so that the current of both CT's on the same phase will add up to measure the combined power on wiring that isn't practical to combine into a single CT. You'd need to make sure to use identical CT's and that the sum total of both CT outputs at full load is within the limits of the metering equipment. This could be an easier solution to implement, than needing to disassemble all load circuits, and re-route the wiring through the same CT.

Thank you Carultch & Jaggedben.

All the while, I have been thinking about how I can do that by picking the wires just before they connect to the breakers and never thought that I could pick the wires at the bottom where they group together. Also thanks for suggesting using 4 CTs is another way when 2 CTs cannot capture all the wires by 2 CTs. Thanks again.