yes its called planetary twist which wraps the wires around eachother without twisting to putting any tension on the conductors. Drill has the potential to damage the wire.
Current Transformer or CT wires
- Thread starter SKSolar
- Start date
gadfly56
Senior Member
- Location
- New Jersey
- Occupation
- Professional Engineer, Fire & Life Safety
If the requirement is part of the spec package or drawing, you don't have a choice. That's what you bid, that's what you install. Otherwise, you owe the customer the difference in cost between the two, or the customer can require you pull out the homebrew cable and install what the spec/drawing requires.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Specs need to be followed, however if they don't included more details, like a suggested part number, then simply saying a 'twisted pair' doesn't excluded a wrap your own solution.
I'll argue that a 'twisted pair' is a factory made assembly and not a couple wires twisted together in a drill. (the two are rather different). Now if you happen to own a planetary wire twisting machine then maybe you could assemble your own as it would be identical to the factory made product, but there's still the issue of UL.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Does UL get involved in the twist or are they just interested in the insulation rating?
The stress from being non-planetary might be a concern for a 1000' spool, but wont be a problem on a 30' run. If it was there would be problems in many pulls through conduit, where conductors regularly twist.
At least one manufacturer, New England Wire Technologies, does not mention less insulation stress as one of the reasons for planetary twisting.
I am not against following specs, I am just saying don't read more into them than what they say.
I believe so. The stuff I have made has a UL sticker for processed wire, in addition to the UL listing of the wire itself. I think UL wants to make sure the wire isn't being damaged during processing.
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
In this case Enphase has not called that out.
I think whoever called it out is probably overthinking things.
probably.....
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I agree. We have extended CT wiring by both field twisting and by not twisting and it never made any difference.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Yep.
If it did, there would be readily available specs and recommendations from the manufacturers of monitoring equipment that can capture waveforms and utilities that care about accuracy.
Enphase says to not extend leads on revenue CTs because it will kill the required accuracy.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
If it's the kind that generates a voltage across a resistor internal to the CT, then yes, since the resistance of the wiring is part of a voltage divider network and a change in length will change the reading. If it is the type without an internal resistor, then no; the only resistance that contributes to the calculation is the one in the sensing equipment.
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
That's not what it says here on pg 11.
gadfly56
Senior Member
- Location
- New Jersey
- Occupation
- Professional Engineer, Fire & Life Safety
If there is a spec, and it's written by a half-competent engineer, it will include a section on approved manufacturers with an "or equal." Don't get cute and try to think a roll your own solution is "or equal." You'll need to prove that to the engineer.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
But what if they do not provide any example, but simply say 'twisted conductors'.
They either need to clearly tell you what is expected, provide an example, or live with what you think is appropriate.
As it appears in the OP, many so called specs are really nothing more than recommendations from manufacturers.
That's for consumption CTs. I said revenue CTs. From pg 11 here: https://enphase.com/download/guidelines-current-transformer-ct-installation
"Production CT lead wires must not be extended, if revenue grade production metering is required. These
CTs are certified for revenue-grade production metering. Extending lead wires voids the certification."
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
Right, 'revenue CTs' is not a term they use, so your post was somewhat ambiguous.
We frequently refer to revenue grade CTs, I was lazy in typing leaving out 'grade'. Guess I should have said production to keep in the context of solar.
Solar_ice_caps
Member
- Location
- Florida
- Occupation
- Solar EPC
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.
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Twisting wires induces noise equally into each conductor and cancels the external noise. That is why cat 5, 5e data wire is twisted