Current Transformer or CT wires

[SKSolar]

I have to extend the Consumption CT wires for an Enphase Solar System. The call out is to use a 18-20 AWG twisted pair. I checked that it costs $200 for a 100-foot 600V coil. That is incredibly expensive than a #12 awg wires.
I found that in a local hardware store, they sell #18 AWG doorbell wires for $0.39 per foot.

Can I use that? Thanks

 

[Joethemechanic]

I don't think the hardware store doorbell wire is going to be rated 600v

 

[SKSolar]

I don't think the hardware store doorbell wire is going to be rated 600v

I thought wire sizes are based on amperage not on voltage and I don't understand why the voltage was listed on the above sample.

Any thoughts?

 

[Joethemechanic]

The voltage rating is for the insulation. Current transformers can produce very high voltages if the circuit becomes open

 

[jim dungar]

The only reason to twist CT wires is to keep them together as one circuit. Imagine a switchboard panel with 36 sets of CT leads all with the same color coding.

Unless the designer specifies the number of twists per foot you could make your own.

This is another case of someone not wanting to change the way grandad did it.

 

[BarryO]

Yea that's expensive. You can get 2 conductor #18 SEOOW—600V cable for less than half of that

 

[SKSolar]

The only reason to twist CT wires is to keep them together as one circuit. Imagine a switchboard panel with 36 sets of CT leads all with the same color coding.

Unless the designer specifies the number of twists per foot you could make your own.

This is another case of someone not wanting to change the way grandad did it.

It requires twisted pair and I found the doorbell wires but that according to my research, it is for low voltage. I guess I have to buy those capable to handle 240V and twist them myself .

 

[SKSolar]

Yea that's expensive. You can get 2 conductor #18 SEOOW—600V cable for less than half of that

It has to be twisted - as called out.

 

[infinity]

We just buy TFFN and when needed we put the white and black in a drill and twist them.

 

[Joethemechanic]

handle 240V

Those current transformers will produce much greater than 240 volts if the circuit is opened

 

[Joethemechanic]

OPEN CIRCUIT CURRENT TRANSFORMER CHARACTERISTIC​

March 24, 2019adminPower Engineering

Open circuit condition in a current transformer (CT) can result in dangerous over voltage condition at the secondary terminals of the CT. An open circuit CT especially of high ratio and carrying high currents can produce secondary open circuit voltage in the range of few kilo volts. This voltage is usually sufficient to sustain steady state arcing between CT shorting blocks and is a potential fire risk.

Open Circuit Current Transformer Characteristics – Voltage Disturbance

 

[Todd0x1]

I have CT wire. I have it made for inhouse use here and I sell it to some solar contractors who need it. 2C 18ga UL1015 / MTW tinned copper,l 1 twist per inch. I'm in LA too ill DM you.

 

[Todd0x1]

The only reason to twist CT wires is to keep them together as one circuit. Imagine a switchboard panel with 36 sets of CT leads all with the same color coding.

Unless the designer specifies the number of twists per foot you could make your own.

This is another case of someone not wanting to change the way grandad did it.

It has to be twisted. This is per the CT manufacturers as well as those who make the stuff the CT lands on. Its a tight twist, 1 per inch usually. Necessary for measurement accuracy.

 

[Carultch]

The only reason to twist CT wires is to keep them together as one circuit. Imagine a switchboard panel with 36 sets of CT leads all with the same color coding.

Unless the designer specifies the number of twists per foot you could make your own.

This is another case of someone not wanting to change the way grandad did it.

It has to be twisted to minimize the influence of external magnetic fields.

 

[SKSolar]

We just buy TFFN and when needed we put the white and black in a drill and twist them.

Thanks. That should be it! UL listed 600V & 7A rating. 500 Ft coil - $35 to $45.

 

[jim dungar]

It has to be twisted to minimize the influence of external magnetic fields.

External magnetic fields would have little affect on the CT signal in the wire, unless your field was large like in an MRI.

I have never seen specs from any major CT manufacturer nor power monitoring equipment manufacturer requiring twisted CT leads. If have seen many installations of non-twisted CT leads employed in utility substations and control rooms.

Twist your own if you need to meet job specifications.

 

[ggunn]

We just buy TFFN and when needed we put the white and black in a drill and twist them.

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.

 

[SKSolar]

External magnetic fields would have little affect on the CT signal in the wire, unless your field was large like in an MRI.

I have never seen specs from any major CT manufacturer nor power monitoring equipment manufacturer requiring twisted CT leads. If have seen many installations of non-twisted CT leads employed in utility substations and control rooms.

Twist your own if you need to meet job specifications.

Thanks for sharing the info. I need two sets in a raceway, therefore, the first function is to keep each set separate by twisting them together.

 

[jim dungar]

Thanks for sharing the info. I need two sets in a raceway, therefore, the first function is to keep each set separate by twisting them together.

If they are installed in metallic grounded raceways, there is even less fear of being affected by stray magnetic fields.

 

[curt swartz]

We just buy TFFN and when needed we put the white and black in a drill and twist them.

That is exactly what I have done.