5,000A Magnum SB Ground Fault verification

[MrBolt]

Does anyone have experience doing a Ground Fault verification through a neutral CT on a 5,000A Magnum SB main Breaker with a Digitrip 520 trip unit?

[SecondGen]

Does anyone have experience doing a Ground Fault verification through a neutral CT on a 5,000A Magnum SB main Breaker with a Digitrip 520 trip unit?

Fairly standard breaker and test, what is the issue?

[MrBolt]

Fairly standard breaker and test, what is the issue?

ground fault setting is 1200A max.
I dialed it down to 0.25, and Delay @ 0.5 - but it kept tripping at 700A. I just don't understand why.

[SecondGen]

ground fault setting is 1200A max.
I dialed it down to 0.25, and Delay @ 0.5 - but it kept tripping at 700A. I just don't understand why.

What size sensors and plug? Assuming 5000/5000, a GF setting of 0.25x should still be 1200A like you stated. What is the test setup, are you pushing current straight across the neutral CT in a switchboard? What are your phase LTPU values when ground fault is disabled?

[SecondGen]

ground fault setting is 1200A max.
I dialed it down to 0.25, and Delay @ 0.5 - but it kept tripping at 700A. I just don't understand why.

Depending on your test setup, you may be getting a half trip if your polarities are backwards. The 0.5 time delay would allow for a little extra current over the expected 600A half trip.

[MrBolt]

What size sensors and plug? Assuming 5000/5000, a GF setting of 0.25x should still be 1200A like you stated. What is the test setup, are you pushing current straight across the neutral CT in a switchboard? What are your phase LTPU values when ground fault is disabled?

yes 5,000A plug. pushing current from Line side of A phase, Jumper From load side of A phase to Neutral CT, and other side of CT - back to test set.
my question is, Shouldn't 1200*0.25=300A?
and shouldn't it trip @ 50% its current setting?

[SecondGen]

yes 5,000A plug. pushing current from Line side of A phase, Jumper From load side of A phase to Neutral CT, and other side of CT - back to test set.
my question is, Shouldn't 1200*0.25=300A?
and shouldn't it trip @ 50% its current setting?

Typically ground fault settings are based off the sensor, in this case assuming 5000A would be 5000 * 0.25 = 1250A. Since 1200A is max, the trip unit will default to 1200A. My guess is that you are getting a half trip, try reversing the direction of current through the neutral CT. If that fixes the problem, verify that the CT is facing the proper direction per design drawings.

[Kalbi_Rob]

Below is the link to the Digitrip 520 manual.

https://docs.natlswgr.com/docs/W1000028.pdf

If you notice the table on page 12, for a 5000A breaker, all ground fault settings place the trip at 1200A maximum per NEC. Thus the GF trip setting is not adjustable on such a large breaker. As described above, it sounds like your CT is reversed. No trip test is placing test set leads on the line side of the breaker phase, and Neutral Ct, and the jumper across the load side phase of the breaker and Neutral CT. 50% trip test would be reversing the leads across the neutral CT. For visual reference see the below link.

https://testguy.net/content/279-Grou...Testing-Basics

[MrBolt]

Below is the link to the Digitrip 520 manual.

https://docs.natlswgr.com/docs/W1000028.pdf

If you notice the table on page 12, for a 5000A breaker, all ground fault settings place the trip at 1200A maximum per NEC. Thus the GF trip setting is not adjustable on such a large breaker. As described above, it sounds like your CT is reversed. No trip test is placing test set leads on the line side of the breaker phase, and Neutral Ct, and the jumper across the load side phase of the breaker and Neutral CT. 50% trip test would be reversing the leads across the neutral CT. For visual reference see the below link.

https://testguy.net/content/279-Grou...Testing-Basics

Thanks for the information, I didn't understand why the breaker was tripping around 600A. now it makes sense if the GF is not adjustable.