NETA Circuit Breaker Maintenance 4

Question 1

According to NETA MTS, what is the recommended maximum contact resistance for a 15 kV vacuum circuit breaker measured across each pole?

Accepted Answer

100 microhms

Answer

NETA MTS specifies that contact resistance for medium-voltage vacuum circuit breakers should not exceed 100 microhms per pole unless the manufacturer specifies otherwise.

Question 2

Which dielectric test method is used to verify the vacuum integrity of a vacuum interrupter bottle?

Accepted Answer

DC hi-pot test across open contacts

Answer

A DC hi-pot test applied across the open contacts of a vacuum interrupter checks the vacuum integrity; a degraded vacuum will allow current to flow at lower voltages than expected.

Question 3

When performing a trip timing test on a low-voltage power circuit breaker, what parameter is being verified?

Accepted Answer

Time from trip signal initiation to contact separation

Answer

Trip timing tests measure the elapsed time from when the trip signal is applied to when the main contacts physically separate, verifying the breaker responds within manufacturer specifications.

Question 4

A power circuit breaker's charging spring fails to charge after the close-open operation. The MOST likely cause is:

Accepted Answer

Failed spring charging motor or limit switch

Answer

The spring charging motor or its associated limit switch is the most common cause of failure to recharge the closing spring after an operation.

Question 5

NETA recommends that circuit breaker insulation resistance tests be performed at what minimum test voltage for 600 V class breakers?

Accepted Answer

500 V DC

Answer

For 600 V class equipment, NETA MTS recommends a 500 V DC megohmmeter test voltage to measure insulation resistance.

(NETA) InterNational Electrical Testing Association Certified Technicians Practice Test

(NETA) InterNational Electrical Testing Association Certified Technicians Practice Test

NETA Circuit Breaker Maintenance 4