Are 333mV current transformers safer to use?


#1

I know the risks of shock associated with using 1A and 5A current transformers, and I am wondering whether 333mV current transformers offer a safer alternative?


#2

Current transformers are used to measure AC current. They can reduce current levels from thousands of amperes down to a ratio of a standard output, typically 5A or 1A, allowing measurement of the primary current by any powermeter configured with the CT conversion ratio. A popular alternative is to add a “burden” resistor to the secondary winding of the CT to create voltage, producing a standard output of 333mV.

Current transformers with a 1A or 5A output should not be left open-circuited when current flows on the primary conductor. Instead, one should short-circuit the secondary terminals to avoid the risk of shock. A device called a ‘shorting block’ exists for this very purpose, and is recommended for energy projects when metering systems must be retrofitted on live circuits.

333mV current transformers do not require shorting blocks because the current output flowing through their terminals is extremely low. It permits safe opening of the secondary and the output voltage always remains safe.