• We will be performing upgrades on the forums and server over the weekend. The forums may be unavailable multiple times for up to an hour each. Thank you for your patience and understanding as we work to make the forums even better.

Current Transformer or CT wires

Merry Christmas

SKSolar

Member
Location
Los Angeles
Occupation
Engineer
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
1691098618465.png
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
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

Senior Member
Location
Bend, OR
Occupation
Electrical engineer (retired)
Yea that's expensive. You can get 2 conductor #18 SEOOW—600V cable for less than half of that
 

SKSolar

Member
Location
Los Angeles
Occupation
Engineer
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 .
 

Joethemechanic

Senior Member
Location
Hazleton Pa
Occupation
Electro-Mechanical Technician. Industrial machinery

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.

 

Todd0x1

Senior Member
Location
CA
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

Senior Member
Location
CA
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

Senior Member
Location
Massachusetts
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.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
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

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Consulting Electrical Engineer - Photovoltaic Systems
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

Member
Location
Los Angeles
Occupation
Engineer
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.
 
Top