Rick,
The Comparitive Tracking Index (CTI), ASTM D3638 and UL746A, is a test intended
to show the susceptibility to surface tracking of solid electrical insulating
materials when exposed under electrical stress, to a contaminant solution.This
test applies to relatively low voltages under 600 volts.
The CTI test attempts to cause a permanent electrically conductive carbon path
along the surface of a material using an aluminum chloride electrolyte applied
at the rate of 1 drop every 30 seconds to the test specimen. The surface of the
specimen is subjected to an AC voltage, s.c. current limited to one amp. The
current flow must exceed 100 mA for at least a half second to register as an
established path.
ANSWER TO 1) The CTI level (205 in your note) is the voltage level that
corresponds to 50 drops on the tracking-voltage curve that is plotted as a
result of testing multiple 3.0mm thick samples at various voltage levels, up
to600 V.
ANSWER to 2) UL has CTI index levels, while international standards call out
the actual voltage levels. Either way 200 volts is an probably an OK level for
the material and what you will be using it for. I believe levels anywhere from
100 to 250 volts are typically called out for that use. Just my humble opinion,
though.
Any other questions, I have a bit of experience on this subject, please do not
hesitate to e-mail me.
Regards,
Bob Tims
Standards and Compliance
[email protected]
