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JON1980

2nd AC power supply CB / fuse

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Hi everyone 

Are there any differences between fuses and circuit breakers in the secondary AC power supply project? Why design like this?

Thanks

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On ‎2‎/‎25‎/‎2020 at 10:53 AM, JON1980 said:

Hi everyone 

Are there any differences between fuses and circuit breakers in the secondary AC power supply project? Why design like this?

Thanks

Probably need to add a picture of the schematic you are looking at so we can determine what you are actually looking to understand.  

 

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My gut feeling is the devices under load are considered more long lasting and stable and less likely to need a circuit breaker. Rare that a transformer fails, certainly at those loads. This is instrument power, 26 VAC single phase if I recall right. Never saw one fail in 26 years of fixing and flying.

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On 2/27/2020 at 3:33 AM, NATOPS1 said:

Probably need to add a picture of the schematic you are looking at so we can determine what you are actually looking to understand.  

 

Thank you for your reply.

Why not just use circuit breakers all?6466F9E1-3931-49E5-B16D-9C0C7A3091CD.thumb.jpeg.4b11f275883dd71ee5ff804fd264e31f.jpeg

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On 2/27/2020 at 7:31 AM, n1dp said:

My gut feeling is the devices under load are considered more long lasting and stable and less likely to need a circuit breaker. Rare that a transformer fails, certainly at those loads. This is instrument power, 26 VAC single phase if I recall right. Never saw one fail in 26 years of fixing and flying.

Thank you.

I see that the current used by the fuse is either 1A or 2A

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14 hours ago, JON1980 said:

Thank you for your reply.

Why not just use circuit breakers all?6466F9E1-3931-49E5-B16D-9C0C7A3091CD.thumb.jpeg.4b11f275883dd71ee5ff804fd264e31f.jpeg

While CBs and fuses essentially "do" the same thing (limit current) the way they do it and the response to overcurrent are different.  Generally, Fuses react faster than CBs to overcurrent situations. The component they (CB/Fuse) supply power to determines what type of protection they need. In this case the TQ and TIT Cbs feed 155VAC to power supplies/amplifiers while the fuses provide 26VAC to drive pressure transmitters and gauges without separate internal power supplies.  

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16 hours ago, NATOPS1 said:

While CBs and fuses essentially "do" the same thing (limit current) the way they do it and the response to overcurrent are different.  Generally, Fuses react faster than CBs to overcurrent situations. The component they (CB/Fuse) supply power to determines what type of protection they need. In this case the TQ and TIT Cbs feed 155VAC to power supplies/amplifiers while the fuses provide 26VAC to drive pressure transmitters and gauges without separate internal power supplies.  

Thank you very much for your information

Can I imagine using a circuit breaker for more loads and a fuse for less loads?

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5 hours ago, JON1980 said:

Thank you very much for your information

Can I imagine using a circuit breaker for more loads and a fuse for less loads?

Not necessarily; CBs can operate on different principals to "Open" in an over current condition whereas fuses have a heat sensitive conductor that melts. Fuses that are very high current ratings are called Current limiters. They (kinda) look like fuses only BIGGER. Instead of a small conductor they employee a very thick conductor which requires more current (heat) to melt.

Basic electricity states that as current increases more heat is generated in the conductor; so a fuse basically limits how much heat can build up in its conductor (amp rating) to control electrical power to a wire or component.

Someone that knows a lot more than I determines what a specific component needs be it a CB or fuse.    

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Many fuses are for lower amp ratings. I think 5A was the lowest for CBs, could be wrong. There were plenty of slo-blow fuses a well. And remember, Circuit breakers and fuses are there to protect the wiring, not the unit the voltage is going to.

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