Sorry I haven't responded in a while. I had a job that had to get done and I was working late every day to get it done so I didn't have time to do anything with this.Sounds like you have a 3 phase motor and they monitor a single phase current which is not unusual at all. For some reason I want to believe your original CT is a 50/5? Meaning with 50 Amps through the primary (the single wire through the hole) you would get 5 Amps out of the secondary when properly terminated into a burden resistance. Your analog meter serves as a burden resistance. You never want to run a CT into an open circuit. The CT needs to see a load on the secondary which we call the burden resistance. Think of it this way. A CT with a 50/5 is a transformer with a 10 to 1 ratio correct? The primary line through the doughnut hole is current but also a voltage. So if the voltage is let's say 200 volts then the CT secondary, open circuit, would have 2,000 volts without a burden resistance. My guess (and only a guess) is with the system shut down if you measure the input resistance to the current meter it will be about 0.200 Ohms. That is with nothing connected to the terminals, only your ohmmeter. So with 50 amps primary and 5 amps secondary through 0.2 Ohms the voltage will be 1.0 volt. The meter is likely a 0 to 1 volt meter scaled to read 0 to 50 Amps. The meter has an internal "shunt" which serves as a burden resistor.
The problem with extending the leads of a CT are multiple. Most CTs like what you have are designed to work into a very low burden resistance. It doesn't take much lead length to upset the balance of the burden resistance and cause large errors. Additionally there is a matter of lead length contributing to causing the transformer to go into saturation. Something I have not mentioned is if you were to terminate the CT secondary at the source (in the panel or at the CT location) you may be able to run a light gauge twisted pair to a meter but the meter now would need a high input impedance.
Here are your options with the current transducer. You are looking at a 0 to 40 Amp AC transducer. The output will be 4 to 20 mA on that model. So 0 to 40 Amps = 4 to 20 mA. You place a resistor (a good 1% resistor) in the current loop. Using a 500 Ohm resistor the voltage drop across the resistor will be 4 to 20 mA = 2 to 10 Volts and you get a scalable panel meter to read 2 to 10 volts = 0 to 40 Amps. That is how it is done.
Ron
Yes you are right about the 50/5 CT. But the wire running through the primary is wrapped around so it basically goes through 3 times. From the research I did, that means it now becomes 25/5 correct? Which is what it was setup from the factory. So would adding more turns to the primary help out my situation? I also read adding turns to the secondary can also change the ratio. Is there any way that this might work? Or is there just no way to get these 2 wires at 50 foot which means a 100 ft loop to work with my CT and panel meter? Would adding a second CT in my control panel (which is the one 50 ft away) be worth trying?
Running new wires would be possible its just a matter of buying more wire. If this would 100% work, it might be the best way to go. Vs buying a Current Transducer and another meter to use the wires I have now. If I were to buy more wire, what AWG would be the best to go with. I know a few were mentioned above, but I don't want to buy a bunch of wire to find out I should of went a tad bigger. If you were in my situation, what would you do?
I looked on eBay for the 10$ version but there are hundreds of them. Is there a specific one you have used? I don't even know if it will work so I dont want to get into this to much. Plus its not something that needs to be dead nuts accurate.In N.A. there is Red Lion Controls or the $10.00 version on ebay.
Max.
Yes, inside the main cable that carries the 36 wires to and from the control panel, there are 6 groups of 6 wires and each group of 6 is all twisted together. So I am using 2 of the 6 on one of the 6 twisted wires. If that makes sense. Why do you ask? Does it make a difference?Your CT cable is a twisted pair, right?