CT "extender"

Z

zbang

Senior Member
Location
Roughly 5346 miles from Earls Court
In a couple of months, I'll want to hang some snap-on CTs on the incoming conductors* to a panel and already know the CTs I have won't fit. In theory, I could take a couple loops of 12g THHN around each hot conductor and through the CT and get an accurate-enough reading..... OTOH something is also telling me that it won't work the way I want. Yes/No?

*Aluminum and oversized for voltage drop

Getting larger CTs is probably off the plate ($$), it's kind of a charity job and will only be in for a week.

(Yes, I will open the upstream breaker before installing anything.)
 
CT's get connected to some piece of equipment that can read their output. The reading is done based on the current ratio of the CT so I'm not seeing how you could rig something up and get an accurate reading.
 
Theory and practice are not always the same.
The wraps of copper will not provide the magnetic coupling you get with the 'iron' core of a transformer.
 
zbang said:
In a couple of months, I'll want to hang some snap-on CTs on the incoming conductors* to a panel and already know the CTs I have won't fit. In theory, I could take a couple loops of 12g THHN around each hot conductor and through the CT and get an accurate-enough reading..... OTOH something is also telling me that it won't work the way I want. Yes/No?

*Aluminum and oversized for voltage drop

Getting larger CTs is probably off the plate ($$), it's kind of a charity job and will only be in for a week.

(Yes, I will open the upstream breaker before installing anything.)
Click to expand...
Rogowski coils?
(Rope CT)
 
1) If you have a 20A circuit feeding fat conductors for voltage drop, you could certainly extend the circuit a bit with 12ga wire and run that through the CT. If you run multiple loops of 12ga through the ct you will simply scale up the reading, possibly with lower accuracy.

2) If you are installing a consumer grade energy monitor (eg. 'sense', 'emporia vue', etc) then you can get large cheap snap on CTs for lots less money then you might think.

eg https://www.homedepot.com/pep/Sieme...-3-Phase-Sensor-Kit-Add-On-INHEM010/336199492

-Jonathan
 
Um, I already have the meter and the CTs, they just won't fit around a 3/0(?) cable (that's in the original question). And I can get other CTs, I don't want to spend the money if I don't have to.

It looks like Jim actually answered the question.
 
Apologies, I misunderstood your original question. I thought you wanted to extend the 3/0ga circuit conductors with 12ga wire, not that you wanted to use the 12ga to couple the existing CTs magnetically to the circuit conductors.

As Jim says, you need a magnetic core to get sufficient coupling. If you did have such a core then you're essentially creating a current transformer. With a suitable magnet core the current in the 12ga would be proportional to the current tn the 3/0.

You absolutely can take the output of a CT and run it through a second CT, but I don't think that lets you avoid buying ( or building) a new CT. :)
 
With some CT's you can extend the leads and with others it's best not to. Some are current sources (extending is OK) and some are voltage sources (best not to).
 
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