TCC chart questions

[Grouch]

Hey all,
I have 2 questions of the TCC curve that you'll find on page 5 of the PDF in this link: (i have yet to master attaching a pic! the file sizes are too large)

http://www.eaton.com/ecm/idcplg?Idc...eleased&Rendition=Primary&dDocName=TD012019EN

#1) If you look at note 8 on the right (it's not labeled with an '8', but you'll see the paragraph start right below the number 7.. looks like a typo), it says "When rated amps (Ir) is set to the maximum position (position H), then both the SDPU and the Instantaneous Override pickup are equivalent. Therefore, the breaker will trip on Instantaneous Override." Does this mean that for a 600 amp breaker, even though my Short time pickup is set at 6, for a value of 600 x 6 = 3600 amps for the pick up, that pick up is nonexistent? so there is no short time pick up, but rather only instantaneous pickup at 600 x 12 = 7200 amps?

#2) There are 3 settings for short time delay: instantaneous, 120ms, and 300ms (shown on the graph)... is this truly considered 'instantaneous"?... it starts at around .04 seconds. If you go further down the chart, the actual instantaneous region picks up at .01 seconds.

Thanks!

 

[templdl]

Hey all,
I have 2 questions of the TCC curve that you'll find on page 5 of the PDF in this link: (i have yet to master attaching a pic! the file sizes are too large)

http://www.eaton.com/ecm/idcplg?Idc...eleased&Rendition=Primary&dDocName=TD012019EN

#1) If you look at note 8 on the right (it's not labeled with an '8', but you'll see the paragraph start right below the number 7.. looks like a typo), it says "When rated amps (Ir) is set to the maximum position (position H), then both the SDPU and the Instantaneous Override pickup are equivalent. Therefore, the breaker will trip on Instantaneous Override." Does this mean that for a 600 amp breaker, even though my Short time pickup is set at 6, for a value of 600 x 6 = 3600 amps for the pick up, that pick up is nonexistent? so there is no short time pick up, but rather only instantaneous pickup at 600 x 12 = 7200 amps?

#2) There are 3 settings for short time delay: instantaneous, 120ms, and 300ms (shown on the graph)... is this truly considered 'instantaneous"?... it starts at around .04 seconds. If you go further down the chart, the actual instantaneous region picks up at .01 seconds.

Thanks!

Think of it this way, a molded case breaker has a specific withstand, that is the magnetude of fauld current that it can interupt without being destroyed. The short time adjustments with respond appropriately where you select it. But, should the current magnetude exceed that adjustment the breaker ignores the time delay you have selected and responds by tripping/interupting instantaneously in order to protect its butt.
With a molded case breaker the priority is to trip instantaneously in relationship with its withstand rating.
If you look at air, insulated case,, and power breakers you will find that the short time adjustments are longer because t he makeup of these breskers provided a greater withstand before a trip is required.
All this stuff is really only relevant for coordinating with other devices. Otherwise by itself there is not much to be gained by having these adjustments.

 

[jeremy.zinkofsky]

Hey all,
I have 2 questions of the TCC curve that you'll find on page 5 of the PDF in this link: (i have yet to master attaching a pic! the file sizes are too large)

http://www.eaton.com/ecm/idcplg?Idc...eleased&Rendition=Primary&dDocName=TD012019EN

#1) If you look at note 8 on the right (it's not labeled with an '8', but you'll see the paragraph start right below the number 7.. looks like a typo), it says "When rated amps (Ir) is set to the maximum position (position H), then both the SDPU and the Instantaneous Override pickup are equivalent. Therefore, the breaker will trip on Instantaneous Override." Does this mean that for a 600 amp breaker, even though my Short time pickup is set at 6, for a value of 600 x 6 = 3600 amps for the pick up, that pick up is nonexistent? so there is no short time pick up, but rather only instantaneous pickup at 600 x 12 = 7200 amps?

#2) There are 3 settings for short time delay: instantaneous, 120ms, and 300ms (shown on the graph)... is this truly considered 'instantaneous"?... it starts at around .04 seconds. If you go further down the chart, the actual instantaneous region picks up at .01 seconds.

Thanks!

#1) When in position H you are setting the breaker sensing rating (In) to be the same as the rating of the breaker (Ir). SDPU is a multiple of the sensor rating (In) and not the actual rating of the breaker (Ir). When they are both equal, the SDPU multiple becomes 1 which makes it equal to the instantaneous setting. You have basically pushed the SDPU curve as far right as it can go which creates a straight vertical line from the Instantaneous region (0.01 seconds) to just before LTPU region (0.9 seconds). The setting is still there, it just "senses" fault current of the same magnitude as the Inst. setting does (12 x breaker rating). If you look at the TCC on the left, the curve of SPDU setting 12 directly lines up with the curve of the Inst. Override setting on the TCC to the right.

#2) The Inst. setting actually starts around 10 x the breaker sensing rating. Fault current of that magnitude will be cleared faster than a fault current that is 8 x the breaker sensing rating. So, a fault of 10 x the breaker sensing rating will cause the breaker to trip after 0.01 seconds where a fault of 8 x the breaker sensing rating will cause the breaker to trip after 0.03 seconds. Its all about what is considered acceptable exposure to current. The breaker manufacturer has determined the amount of current that this breaker can withstand over a given duration. A larger current will need to be cleared faster than a smaller one to prevent damage to the breaker. So the Inst. region for this breaker is can be anywhere from 0.01 to 0.9 seconds depending on it's magnitude.