I'm trying to find out information about a current transformer. Like what is the primary current and what is the secondary out. The CT is made of black plastic and is 2" round and ¾" thick and has a hole in it ½" round. It has two wires for the secondary, #18 gage, one purple and one orange. On the label is the info below.
CAT # CST-2845 100 amp FERMITER Corp. 8-85 CLASS 2, (I think the 8-85 is the date made). INSUL. CLASS 105 INDOOR TYPE 1.
Thanks
Well, it's 100 amps to something. There are a number of 'standards' for secondary current, if the secondary connections are #18, then I think 1 amp is probably a reasonable guess. I suggest you test the thing by running an approximately known AC current to it and measuring the current in the secondary. That will confirm what the ratio is, it's almost certain to be something like 100A/1A, 100A / 0.5A or something like that.
You can generate the current by simply winding a few turns around the core, and using a lamp of known wattage. The 'equivalent current' is the actual current in your primary winding times the number of turns, if you simply run the wire through the centre, that is one turn. Important: Ensure that the secondary is not allowed to go open circuit, this can generate dangerously high voltages! On the contrary, these transformers are most happy with their secondary short circuited (minimum 'burden'), so your test is best conducted with a meter set to amps straight across the ssecondary leads, with no series resistor. Alternatively, if you have a LOW VALUE resistor you can use this and measure tne voltage across it due to the secondary current.
Class 2 refers to accuracy, 2% IIRC.
For a CT of that size, you're probably talking of a maximum burden of about
3VA, that means - for example - that if the ratio turns out to be 100A / 1A, then the maximum resistance you can have across the secondary if you're expecting 100A is 3 ohms, which will give a secondary voltage of 3 volts maximum.
Once again, to stress... never let the secondary go open circuit, and ensure that the secondary load is physically solid and securely terminated. An OC secondary on a CT can generate hundreds of volts, enough to kill.