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Digitrip OPTIM Long Time Setting

Digitrip OPTIM Long Time Setting

Digitrip OPTIM Long Time Setting

(OP)
I am working on a coordination study, and I am having trouble understanding the TCC for Digitrip OPTIM 510 with 480V, 2000A frame and plug. The issue is that the TCC's X-axis is in multiples of long time pickup setting, but the curve starts at a value greater than 1—shouldn't be at 1. Note 7 in the TCC documents states that the longtime delay nominally occurs at 116% of the Long time pick setting. I am concern that if I have a 2000A plug, I cannot protect it with a long time setting of 1 because it will actually pick up 2320A. Is this the correct setting, or should I choose a lesser setting? I have attached the Manufacture's TCC curve  

RE: Digitrip OPTIM Long Time Setting

The plug doesn't really need protecting, but if you want to make sure it always picks up at exactly 2000 A, you'll need a lower pickup setting.  

This will depend on what you are trying to protect and what codes you have to comply with.   

David Castor
www.cvoes.com

RE: Digitrip OPTIM Long Time Setting

2000A trip unit rated for 100% duty is not supposed to trip at 2000A if set at 1.0.

Breaker trip units have wide tolerances as seen in their curve width. It can trip at any current within that tolerance. If you want precise tripping you will need to use relays, not LV breaker trip units. "Why" is a different story.

Rafiq Bulsara
http://www.srengineersct.com

RE: Digitrip OPTIM Long Time Setting

(OP)
I meant to say I was protecting a 2000A bus. What is common-practice long time setting to protect a 2000A bus?

RE: Digitrip OPTIM Long Time Setting

Common practice is to set LTPU at 2000A, or pick up of 1.0 x P in your case.  

Rafiq Bulsara
http://www.srengineersct.com

RE: Digitrip OPTIM Long Time Setting

(OP)
Will a LTPU setting of 1 protect a 2000A bus, even though it will pick up at 2320(2000*1.16)?  

RE: Digitrip OPTIM Long Time Setting

Yes. Plus it is permitted by Code, at least NEC.

The tolerance is true for any other type of protective device using or emulating thermal overload, which a digital trip unit for breaker does.

A 2000A bus will not start to melt at 2300A. Thermal protection is not an exact science. But history of acceptable practices is the proof.

You may also want to compare your TCC with that of a 2000A Class L fuse and draw conclusions.
 

Rafiq Bulsara
http://www.srengineersct.com

RE: Digitrip OPTIM Long Time Setting

By the way, I presume that the actual field conditions are "typical" building type ventilated environment. No extreme conditions.

 

Rafiq Bulsara
http://www.srengineersct.com

RE: Digitrip OPTIM Long Time Setting

(OP)
Thanks for the input.  

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