# Re: status report, questions, etc.

• To: tesla
• Subject: Re: status report, questions, etc.
• From: chip (Chip Atkinson)
• Date: Wed, 15 Nov 1995 16:55:17 +0700

```
>>>

Most (not all) CT's I've seen have the ratio somewhere on the unit.  If
that's the case, you really shouldn't have to "calibrate" anything.  The
transformation ratio is simply the current in to current out ratio (ex. - a
200:1 CT that you're running 50A through would give you 50A/200 =
250mA short-circuit current between the CT output terminals).  In this
example, you would use a 250mA full-scale AC ammeter to monitor up
to 50A.  You would then "calibrate" your ammeter by simply multiplying
the values on the faceplate by 200.  I imagine that you could put a
known resistive load across the CT terminals to monitor the current
indirectly from the voltage (V=IR),  but just using an ammeter would be
simpler and more direct (COMMENTS from anyone welcome?).
<<<
I'm not trying to argue, just to understand...
The CT has 400 turns, which would, I assume, give a 400:1 ratio.
Why don't I just get a run away current if I use an ammeter?  What's limiting
the current?  Mark Barton suggests a burden load, which makes sense as an
answer to me.  I'll try things out, but I hope to understand things a little
better, so the I can keep the smoke inside the meter. :-)

Chip

```