Current Transformers

   I've been catching up on the last three months of mail I missed while
I was overseas and came across a discussion of current transformers.  I 
believe Chip had purchased a flex-core 400 amp CT and had a few questions
about it.
    If there is a 400 stamped on it is a 400:5 CT meaning if 400 amps
flows in the primary 5 will flow in the secondary. A CT such as this
would be hooked to a 5 amp ammeter with the dial calibrated 0-400 amps.
    All CT's are rated xxx:5 amps.  This CT probably wouldn't be all that
accurate for the current levels you intend to measure.  A 50:5 would 
probably be a better choice giving you a good needle swing on a five amp
ammeter.  Your 400 is probably awful large compared to the smaller units
that are typically around a 3x3x1 inch block with about a 1 inch hole in
the center.  Our local electronics surplus has piles of the smaller ones
(100:5 and lower) for about five bucks a piece.
   One last warning, don't open the secondary of these with the primary
energized, some have voltage limiting, most don't. It will destroy the
CT and possibly try to take you with it.
    Hope this helps!