Electrical Panel

[Alan R. Glabe]

I have never seen this item before. It is a blue rubberized collar surrounding an electrical conductor (from a 30 amp breaker) inside the main electrical panel. The rubberized collar has a thin black wire and a thin white wire protruding (into the wall). Anyone know what this is?

[Michael Larson]

Current transformer/metering device

[Alan R. Glabe]

Thanks Michael.

[Joe Funderburk, CMI]

Originally Posted by mlarson

Current transformer/metering device

Used for what?

[Jim Port]

Ct's measure a portion of the current kind of like a scale ruler.

[Robert Meier]

A quick caution about CT's. They work by reducing the output current to a lower level so that it can be read by metering equipment. Small CT's may work on a 100:5 ratio. Meaning that for every 100 amps of current passing through the CT 5 amps of current will be imposed on the secondary leads which would go to the metering equipment. You should never disconnect the secondary conductors when the circuit being monitored is energized. Although the current is reduce by the 100:5 amp ratio the voltage on the secondary can ramp up and be increased by the same ratio. Most CT's secondaries are shunted to prevent this from happening before they're connected to the metering equipment.