# Time current curve graph



## kduff70 (Apr 15, 2014)

I was going through a time current curve graph from complex imaginary problem 71 afternoon section. The problem want to know the current magnitude when the instataneous override mechanism of the ICCB is activated base on the graph can anybody explain to me how to read the graph in order to better understand what the current will be? I attach the graph

SKMBT_42014041512400.pdf


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## wattersa81 (Apr 15, 2014)

The instantaneous section is the "foot" of the curve. So you will look at where that "foot" begins and that is the instantaneous amperage.


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## cupojoe PE PMP (Apr 15, 2014)

The TCC curve shows where the breaker will trip. So if you have x amps going through the breaker, it will trip in y seconds. So if you are looking at the instantaneous region, you are looking at the moment after t=0.

This TCC cuve shows two lines connected. Most software packages will shade this region with a color. Think of this as a single thick line. The front edge (left/bottom) is when the breaker might trip. By the time the time or current reaches the upper edge (upper/right), the breaker will trip. This allows you to coordinate your protection. The goal is to have the down stream breakers trip faster and/or with less current. The damage curve for the device you are protecting should always be above and to right of all protection devices. Getting these things right is an art as much as it is a science.


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## kduff70 (Apr 18, 2014)

Thank you for responding to my question it took me a minut to see what actually going on but I think i got now


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## truong (Apr 21, 2014)

Can I have the name of this book? Thanks!


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