Factory Default Breaker Settings

[mayanees]

Below is a snip from a picture of a trip unit on a 2000-amp, 480 Volt, Square D SE type breaker in a gov-owned facility that was constructed in 1999. This is what's known as factory-default settings. The longtime pickup LTPU is set for 1.0, and all the other settings are set to minimum. This gives indication that there was never a Power Study performed (Fault, Coordination and now Arc Flash which wasn't really around in 1999), or at least that the breakers were never adjusted.

If you see these types of settings, I advise letting someone know because reliability can be greatly improved with a coordinated system.

 

[augie47]

I am surprised they have not had nuisance tripping of the main.

 

[ron]

Often the LTP is set at minimum too

 

[Barney B]

If the engineer who specified that breaker did not specify the desired settings, that's an engineering failure. Either way it's a failure on the part of the installing electrician, who either failed to use the settings given or failed to ask for the settings if they were not given.

 

[jim dungar]

Often the LTP is set at minimum too

No. From the factory it is set at the nominal specified rating, which is often its maximum setting.

 

[jim dungar]

I am surprised they have not had nuisance tripping of the main.

If they haven't had tripping issues it would appear the coordination is acceptable. This would not be surprising if most of the branch devices are less than 25% of the main device size.