STC Rating: 25kA, 16kA, or 18.4 kA - Advantages & Clarification

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Discussion Overview

The discussion centers on the STC (Short Time Current) rating of circuit breakers, specifically comparing ratings of 25kA, 16kA, and 18.4kA. Participants seek clarity on the implications of changing the specification of a 12kV indoor breaker from 16kA to 25kA, including potential advantages and supporting arguments for such a change.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant requests clarity on the advantages of changing the STC rating from 16kA to 25kA for a 12kV indoor breaker.
  • Another participant inquires about additional information or findings related to the topic, suggesting a lack of responses.
  • A participant reiterates the request for clarity on STC ratings and asks for supporting arguments for the proposed change.
  • A welcome message includes questions about the participant's location, licensing status, and understanding of STC ratings.
  • One participant explains that the STC rating refers to the short-circuit current a circuit breaker can handle, detailing the consequences of exceeding this rating, including potential damage to the breaker.

Areas of Agreement / Disagreement

The discussion does not show clear agreement or consensus among participants. There are multiple inquiries and explanations, but no definitive conclusions or shared viewpoints have emerged regarding the advantages of different STC ratings.

Contextual Notes

Participants have not provided specific assumptions or definitions regarding STC ratings, and the discussion lacks detailed technical specifications or mathematical analysis related to the ratings.

Who May Find This Useful

Individuals interested in circuit breaker specifications, electrical engineering, and those considering changes to electrical system components may find this discussion relevant.

kranth
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I want clarity on STC rating that is 25kA or 16kA or 18.4 kA.
If I want to change my Specification of 12kV Indoor Breaker from 16kA to 25kA STC rating then how can I support my self.
What are advantageous points.

Please clarify me.
 
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I'm sorry you are not generating any responses at the moment. Is there any additional information you can share with us? Any new findings?
 
kranth said:
I want clarity on STC rating that is 25kA or 16kA or 18.4 kA.
If I want to change my Specification of 12kV Indoor Breaker from 16kA to 25kA STC rating then how can I support my self.
What are advantageous points.

Please clarify me.

Welcome to the PF.

What country are you in? Are you a licensed electrician in that country? What's an STC rating?
 
Welcome to PF.
Circuit breaker STC = Short Time Current = Short-circuit current.
Once a circuit breaker operates, due to a short circuit of the load, the CB must turn off the flowing high current quickly. The CB contacts open but draw an arc that will continue until the next change in AC load current polarity.

The STC is the extreme current that can flow in the arc while waiting for the current to reverse and the arc to extinguish. If the current is greater than the STC rating then the contact material may be sputtered against the insulator, creating a permanent conductor and an arc that reignites every cycle and destroys the CB.

http://ewh.ieee.org/r6/san_francisc...g_Capacity_and_Short_Time_Current_Ratings.pdf
http://en.wikipedia.org/wiki/Circuit_breaker#Short-circuit_current
 

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