current transformer multipliers

If I understand this correctly, it sounds like your source is a 240 v delta with a center tapped phase to provide 120/240. I don't completely understand your CT setup, could you provide a little more detail? Does the watt-hour meter read energy for the load from the transformer, or the line into the transformer?

But maybe that is getting too complicated, or at least more than it has to be. A typical CT has a 5A secondary. If the max line current is 400A, then a 400:5 CT, instrumentation grade. There should be some kind of adjustment or scaling factor on the watt-hour meter to set it for the proper CT ratio. Lastly, watch out for the polarity of the wiring off the CT's, or you'll get some strange watt-hour readings.

lendog The 240/120 volt have parallel conductors, the split core 200/5 c.t.'s will fit over only 1 conductors of L1, L3, thus reading 1/2 the current in lines L1, L3, the CT in L2 will read the full current.the ratio being times ?, how would you figure the muiltplier? if I had 400/5 split cores that would fit over the parallel conductors the ratio would be 80/1 the rule is N-1 where N is the number of phases thanks

Perry, the set-up just sound so unusual to me. If the CT only measures one of two parallel conductors, then I wonder what steps where taken to insure that the current would divide equally between the two conductors. Making sure the conductors are the same length is standard practice, but I am fairly certain that is not enough to insure an equal flow between the two conductors to the point of obtaining an accurate measure by just measuring the current flow through only one conductor. I would not consider the readings from your meter as accurate, and hope that it is not being used for a monetary basis.

None the less, it seems to me that if you have CT's measuring half the current should have twice the ratio as the CT measuring the whole current, and the watt-hour meter should be set to the ratio of your L2 (whole current) CT. If L1 and L3 are 200:5, then L2 should be 400:5.

What about changing out your CT's to 3 equal 400:5 CT's large enough to fit?

The 240/120 volt have parallel conductors, the 200/5 split core will only fit around one conductor, thus I'm reading 1/2 current in L1 & L3, the high leg L2 is reading 200/5, or 40 times The rule is N-1 N being the number of phases