Explaination of lr, tr& li on electronic trip unit

[milemaker13]

Hello,
I am working with a square D PowerPact breaker. Cat # JDA36250U31X. It is a 250 amp frame with an adjustable electrronic trip unit.

I am reading thru papers, booklets, websites, ect and still havn't found a good explaination of how to properly adjust this unit.

lr seems fairly self explainatory in that it is marked from 70-250 with (A) below the dial. This is the amp range of the breaker, so this would be amprage adjustment.

tr and li I don't understand. How do these relate to amperage adjustment? Sorry if this is day one stuff, but I guess I was out that day:?:dunce:

 

[jim dungar]

Your breaker has settings for
Long Time = Ir: effectively the continuous rating
Long Time delay = tr: the delay time for the transition between the continuous and instantaneous trip functions
Instantaneous = Ii: the point for tripping with no intentional delay.

 

[milemaker13]

I'm trying to post a pic, but what you've explained so far is very helpful. Can you further explain below the tr dial it has @6 lr. What does this mean ?

And below the li dial it has (x ln). What's this?

 

[jim dungar]

The tr setting is based on 6X the Longtime setting of the breaker. It is simply a reference point on the breaker tripping curve.

"In" refers to the Nominal continuous rating of the breaker (it is the end result of where you have set the Long Time pickup).

 

[zog]

I'm trying to post a pic, but what you've explained so far is very helpful. Can you further explain below the tr dial it has @6 lr. What does this mean ?

And below the li dial it has (x ln). What's this?

li is your instatenous trip setting, it is a multiplier of In which is your rating plug value. So with a 250A plug and li set to 10x the breaker will trip without any delay at 2500A. The @6 Ir is the time in seconds the breaker will trip at a 600% overload (Actually the middle of the trip band but close enough).

Now in your first post you said you are trying to figure out how to adjust this unit?? These settings should be determined by a coordination study, do you mean you are trying to set these up per the study or are you asking where they should be set?