What would a current transformer's wiring be classified as? Is it a communication circuit? I have to run ct wires for long distances, longer than the factory wiring. I'm trying to find a cable to run through existing conduit, I.e. a 2" conduit with 3/0 copper, that is rated for use with the 240 volt conductors, thus avoiding making another penetration in the home. I found a 22 gauge FPLP/760, CMP/800, CL3P, CL2P/725 rated for 300 volts. Would this be legal to run with 240 volt circuits?
CT wiring classification
- Thread starter sketchy
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- Wisconsin
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- PE (Retired) - Power Systems
It is extremely unlikely that any wire size smaller than #14AWG will provide reasonable performance at distances >50'.
This is basically a voltage drop problem, you need to determine if your CT's can handle the resistance of your leads + the metering equipment. The math is relatively easy, getting the proper equipment parameters can be much more of a problem.
Your CT supplier should be able to help you.
If the distances are really great, you could consider a CT transducer, where the 5A output is converted to a 0-20mA signal. This would allow you to follow Class 2 'communication' wiring practices.
This is basically a voltage drop problem, you need to determine if your CT's can handle the resistance of your leads + the metering equipment. The math is relatively easy, getting the proper equipment parameters can be much more of a problem.
Your CT supplier should be able to help you.
If the distances are really great, you could consider a CT transducer, where the 5A output is converted to a 0-20mA signal. This would allow you to follow Class 2 'communication' wiring practices.
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- Wisconsin
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- PE (Retired) - Power Systems
The issue is the output power of the CT.
You mention 3/0 copper, so I could guess you are using a 200:5 CT. A typical burden capacity for an inexpensive metering CT will be at most 5VA, which equates to a load of roughly .2 ohms.
If you use #14AWG you might be able to get to 40' as long as you are using a low impedance meter or electronic load, before your CT is overloaded and its output becomes 'inaccurate'.
iceworm
Curmudgeon still using printed IEEE Color Books
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Slow poster - following jim's comment
Sketchy -
I can't help, but I am kind of curious:
22 gauge is ~ 16ohms/1000ft. For 400 feet, 800 feet round trip, that's 12.8ohms. For a 5A CT, that's a 64V drop - about 320VA. And you would have to add the burden of your end device. Are your CT rated for that kind of a burden?
Most CT I've seen are usually rated 2VA - 10VA, a few rated up to 35VA.
What kind of accuracy do you see with 400 feet of cat 5?
Just curious
ice
Sketchy -
I can't help, but I am kind of curious:
22 gauge is ~ 16ohms/1000ft. For 400 feet, 800 feet round trip, that's 12.8ohms. For a 5A CT, that's a 64V drop - about 320VA. And you would have to add the burden of your end device. Are your CT rated for that kind of a burden?
Most CT I've seen are usually rated 2VA - 10VA, a few rated up to 35VA.
What kind of accuracy do you see with 400 feet of cat 5?
Just curious
ice
- Location
- Illinois
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- retired electrician
It would be my opinion that the CT wiring would be an Article 725 Class 1 circuit.
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A question that seems to have been bypassed is what the voltage on the CT output leads will be if they are left open-circuited. That may have a bearing on the choice of wiring method, even with limited power.
The open circuited CT is just a voltage step up transformer with a weak core which will saturate at some point. You are counting on that core saturation to limit the Voc under load.
A standard commercial CT will likely not have an open circuit voltage above 25V or so, but it is worth confirming for the CT you are specifying.
Ditto
kingpb
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Out of curiosity, what is the application the CT is being used for?
As far as accuracy, I can't answer that. It was for a company I used to work for. We would run a cat 5 accross an entire target store from the service to a monitoring panel. 400' might be an exageration, 300' for sure. This particular application is for monitoring solar production. I ended up using a pair of TFFN wires.
iceworm
Curmudgeon still using printed IEEE Color Books
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- North of the 65 parallel
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- EE (Field - as little design as possible)
just curious.
The cat 5 across an entire target store really sounds line a transducer output - not a 5A CT output. do you recall?
This TFFN pair you used - How far was that?
ice
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