High Current Injection LTD Test Value

[alexlounsbury]

I disagree that my answer was wrong. The question:

7. To test the long time delay function of a breaker which is set for 1000 amps ___________ test current is needed.
From memory answers were:
a. 1000A
b. 1500A
c. 3000A
d. Need more information

I chose D, because both B and C could be correct. I also wondered if it was a trick question with the wording. LTD is set in time, they don't specify that 1000 amps is the LT pickup. My answer was marked wrong. If LTD was always to be tested at 3x, then we wouldn't need TCC's, just a standard range. I've tested a 4000a breaker at 8000 to keep a test set from overheating. It would take a lot of time, but I could test the long time function of a 1000a pickup at 1500 amps.

I dislike that in some questions, tricks are tricks, yet in others, the generic standard seems to be the right answer.

Anyone else stumble on this?

[Mcfly89]

You could test the pickup value at 1000, but the question ask for time delay which would be 3x the rated current which would be the answer C, 3000.

[alexlounsbury]

You could test the pickup value at 1000, but the question ask for time delay which would be 3x the rated current which would be the answer C, 3000.

You could test the time delay at 3x. You could also test it at 1.5x, 6x, 10x... We have TCC's to chart every level of current flow, 3x is just a standard that's been used for convenience. NETA doesn't require 3x, nor does any other governing body that I've seen.

Just because a practice is common doesn't mean it's a rule.

[Larry5443]

You could test the time delay at 3x. You could also test it at 1.5x, 6x, 10x... We have TCC's to chart every level of current flow, 3x is just a standard that's been used for convenience. NETA doesn't require 3x, nor does any other governing body that I've seen.

Just because a practice is common doesn't mean it's a rule.

This was talked about at the Neta conference and it was agreed that there is no standard for this type of question.

[Skyehaven40]

I disagree that my answer was wrong. The question:

7. To test the long time delay function of a breaker which is set for 1000 amps ___________ test current is needed.
From memory answers were:
a. 1000A
b. 1500A
c. 3000A
d. Need more information

I chose D, because both B and C could be correct. I also wondered if it was a trick question with the wording. LTD is set in time, they don't specify that 1000 amps is the LT pickup. My answer was marked wrong. If LTD was always to be tested at 3x, then we wouldn't need TCC's, just a standard range. I've tested a 4000a breaker at 8000 to keep a test set from overheating. It would take a lot of time, but I could test the long time function of a 1000a pickup at 1500 amps.

I dislike that in some questions, tricks are tricks, yet in others, the generic standard seems to be the right answer.

Anyone else stumble on this?

Since you are taking the NETA exam you need to follow as per NETA table 100.7 Inverse Time Trip Test
at 300% of Rated Continuous Current of Circuit Breakers

[Skyehaven40]

I disagree that my answer was wrong. The question:

7. To test the long time delay function of a breaker which is set for 1000 amps ___________ test current is needed.
From memory answers were:
a. 1000A
b. 1500A
c. 3000A
d. Need more information

I chose D, because both B and C could be correct. I also wondered if it was a trick question with the wording. LTD is set in time, they don't specify that 1000 amps is the LT pickup. My answer was marked wrong. If LTD was always to be tested at 3x, then we wouldn't need TCC's, just a standard range. I've tested a 4000a breaker at 8000 to keep a test set from overheating. It would take a lot of time, but I could test the long time function of a 1000a pickup at 1500 amps.

I dislike that in some questions, tricks are tricks, yet in others, the generic standard seems to be the right answer.

Anyone else stumble on this?

As per NETA it should be 300%, testing at 150% or 200% will overheat and damage a circuit breaker, especially on a molded case circuit breaker.