Limits of Error / Terminal Markings

Limits of Error for Measurement for Special Purpose Applicable to Transformers having a Rated Secondary Current of 5 A

Limits of Error for Protection

Extended Current Rating

(Standard values 120%, 150%, 200%)
Current transformers with for instance 200% can be operated continuously
with 2 x lN and remain within the limits of error of their accuracy.


The secondary circuit of a current transformer may not be operated with an open circuit as due to the high crest voltage at the terminals of the secondary circuit the operating personnel as well as other connected devices can be exposed to danger. Especially in case of a high primary current, a high number of secondary turns (sec. 1 A), and a (protection) core with a high rating, a dangerous high voltage can occur.

* The markings set in brackets can be used alternatively or additionally.