NETA Circuit Breaker Maintenance 5

Question 1

A sulfur hexafluoride (SF6) circuit breaker shows a low gas density alarm. According to NETA procedures, the FIRST action the technician should take is:

Accepted Answer

Lock out the breaker and verify gas pressure with a calibrated gauge

Answer

A low SF6 density alarm is a safety-critical condition; the breaker must be locked out and the gas pressure verified with a calibrated gauge before any further action.

Question 2

What does the 'close-open' (CO) operation rating on a circuit breaker signify?

Accepted Answer

The breaker can close and immediately reopen on a fault without damage

Answer

A CO rating certifies that the breaker can close onto a fault and immediately reopen (trip), completing a full duty cycle without sustaining damage that impairs its ratings.

Question 3

When testing a molded-case circuit breaker's long-time delay element with a 300% rated current injection, approximately how long should the breaker trip for a properly functioning thermal-magnetic breaker?

Accepted Answer

2 to 30 seconds

Answer

At 300% of rated current, a properly calibrated thermal-magnetic MCCB typically trips in 2 to 30 seconds through the thermal bimetal element, per NETA MTS acceptance criteria.

Question 4

Primary injection testing differs from secondary injection testing of a protective relay-circuit breaker system in that primary injection:

Accepted Answer

Injects current through the actual primary conductors and CTs

Answer

Primary injection passes test current through the actual primary conductors and current transformers, verifying the entire protection scheme including CTs, wiring, relay, and breaker trip coil.

Question 5

According to NETA MTS, what minimum insulation resistance value (in megohms) is generally acceptable for a 480 V switchgear bus section at ambient temperature?

Accepted Answer

100 MΩ

Answer

NETA MTS Table 100.1 specifies a minimum acceptable insulation resistance of 100 MΩ for 480 V class equipment tested with a 1000 V DC megohmmeter.

(NETA) InterNational Electrical Testing Association Certified Technicians Practice Test

(NETA) InterNational Electrical Testing Association Certified Technicians Practice Test

NETA Circuit Breaker Maintenance 5