Is the circuit breaker amperage the rms amperage

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Discussion Overview

The discussion revolves around the relationship between circuit breaker amperage ratings and RMS (root mean square) amperage, particularly in the context of household circuit breakers rated at 15A. Participants explore the implications of connecting a resistor to the circuit and the behavior of circuit breakers under different current conditions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the 15A rating of circuit breakers refers to total amperage or specifically to RMS amperage, considering the peak voltage in the circuit.
  • Another participant provides a link to a datasheet that includes a graph showing the relationship between current and trip time, noting that a breaker may take a long time to trip at the rated current.
  • Some participants express uncertainty about the implications of RMS current, with one suggesting that circuit breakers are rated based on the heating effect of current.
  • There is a reiteration of the importance of understanding RMS current in the context of circuit protection devices like fuses and thermal breakers.

Areas of Agreement / Disagreement

Participants generally agree that the circuit breaker amperage is related to RMS current, but there remains uncertainty about the specifics of how this applies in practical scenarios. Multiple viewpoints exist regarding the interpretation of the datasheet and the behavior of current in the circuit.

Contextual Notes

Some participants note that the current drawn from an outlet is not constant, as it fluctuates with the AC voltage waveform, which may affect the understanding of breaker ratings.

Who May Find This Useful

This discussion may be useful for individuals interested in electrical engineering, circuit design, or those seeking to understand the operation of circuit breakers in household electrical systems.

Puglife
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The circuit breakers of my house say that they are 15a (the majority of them). The rms voltage is 120v for the outlets, and so the peak voltage is about 170v. I was wondering, if I hypthetically connected the terminals together with a 10 ohm resistor, would the breaker trip? I don't know if the amperage drawn is total amps, or amps at the rms voltage, and so that is what I am asking. I know its not safe to do, and I am not going to do it, but I would like to know if it is 15a in general or at the rms, allowing for more amperage at its peak voltages. Thank You.
 
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Grinkle said:
http://static.schneider-electric.us/docs/Circuit Protection/Molded Case Circuit Breakers/0100-400 A Frame FA-LA/FA-FC-FH/0600DB0105.pdf

Look at page 2, it has a curve of time at rated current vs trip time. A circuit breaker will take approx 1000 seconds to trip if the current is right at the rated value, according to this graph at least.
Im not exactly sure what it is saying, because no current will be consistantly be drawn out of the outlet, because many times a second, the voltage reaches zero, and thus so is the current.
 
Puglife said:
Im not exactly sure what it is saying, because no current will be consistantly be drawn out of the outlet, because many times a second, the voltage reaches zero, and thus so is the current.

Puglife said:
I don't know if the amperage drawn is total amps, or amps at the rms voltage, and so that is what I am asking.
The datasheet Grinkle linked describes RMS symetrical current.

Look up "RMS current"
then think about it - fuses amd thermal breakers work by heating an element.
Not surprising they'd be rated in terms of "heating value" of current, would you think ?
 
Thanks, Jim - yes, RMS.
 
Grinkle said:
Thanks, Jim - yes, RMS.
Thank You Both!
 

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