Electronics in breakers

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mbrooke said:
And adjustment dials such as this automatically indicate electronics, correct?

Forgive the basic questions- I've never taken on of these larger frames to pieces.
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Neither have I; I just know electronics.


See if the potentiometer on the lower right in this pic looks familiar:

515deb26ce395f3959000000.jpg
 
a voltage divider shunt and a comparator is all that is needed to accurately calculate current in the wire.

I am more curious to know how these items survive glitches in the power, like spikes/dips, harmonics, and noise. Years ago I made some electronics for automotive use, the most tricky part was power regulation and filtering because alternators are noisy as heck. The regulation and filtering had 1.5x as many discrete components as the ckt itself, and I made it using minimal amount of parts.
 
mbrooke said:
Ok, last question- but how do these dials work? What are they attached too? I can't see semiconductors in a 1970s FPE breaker.
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They are not potentiometers. They are dials on the ends of screws that move the parts that make up the magnetic trip assembly. They increase the air gap which means the breaker can tolerate more current before it trips.
 
jim dungar said:
They are not potentiometers. They are dials on the ends of screws that move the parts that make up the magnetic trip assembly. They increase the air gap which means the breaker can tolerate more current before it trips.
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But aren't two of those thermal?
 
Looking at the Square D catalog, you can spec. thermal magnetic for up to 400 amp breakers with the Q4 and LA breakers;

https://download.schneider-electric...CT1901_SEC-07.pdf&p_Doc_Ref=0100CT1901_SEC-07




With that said- can fixed trip standard thermal magnetic breakers coordinate with fused switchboards?
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I assume you mean upstream fuse, and downstream CB. You can probably coordinate them if you keep a big enough ratio between the two. If the fault current available at the breaker is to the left of the fuse curve, or the instantaneous trip setting of the breaker is to the left, there is a chance they will coordinate.

Unfortunately, it's obviously much easier to coordinate fuses with electronic trip breakers since you have more control over the breaker curve. :(
 
steve66 said:
Looking at the Square D catalog, you can spec. thermal magnetic for up to 400 amp breakers with the Q4 and LA breakers;

https://download.schneider-electric...CT1901_SEC-07.pdf&p_Doc_Ref=0100CT1901_SEC-07






I assume you mean upstream fuse, and downstream CB. You can probably coordinate them if you keep a big enough ratio between the two. If the fault current available at the breaker is to the left of the fuse curve, or the instantaneous trip setting of the breaker is to the left, there is a chance they will coordinate.

Unfortunately, it's obviously much easier to coordinate fuses with electronic trip breakers since you have more control over the breaker curve. :(
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Yes, main gear being fused switches, breakers after that.


But any general tips or recommendations I'm open.


From what I'm seeing, its a bit of a challenge since you have fused branch circuit panel-boards where coordination is necessary.
 
steve66 said:
No, probably a separate magnetic trip for each phase.
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Why would each phase need its own? Assume its easier to eliminate a common linkage then there being a technical reason for one pole having a higher mag trip and another a lower mag trip?
 
mbrooke said:
Why would each phase need its own? Assume its easier to eliminate a common linkage then there being a technical reason for one pole having a higher mag trip and another a lower mag trip?
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Some manufacturers use a common linkage, but many do not. It depends on the internal mechanism and the layout of the breaker inside. Sometimes there is no physical room for a common linkage.
All of the adjustments should be be set the same.

Personally I have seen more switches >800A mechanically failing to open, than I have breakers. Often services do not have enough available fault current to cause large fuses to enter their current limiting region, particularly when the fuses have been sized to handle transformer inrush currents.

There is no single right answer. A good design considers all of the pros as well as the cons.
 
jim dungar said:
Some manufacturers use a common linkage, but many do not. It depends on the internal mechanism and the layout of the breaker inside. Sometimes there is no physical room for a common linkage.
All of the adjustments should be be set the same.

Personally I have seen more switches >800A mechanically failing to open, than I have breakers. Often services do not have enough available fault current to cause large fuses to enter their current limiting region, particularly when the fuses have been sized to handle transformer inrush currents.

There is no single right answer. A good design considers all of the pros as well as the cons.
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But all fuses will clear faster (in general) then a comparable breaker, correct?
 
mbrooke said:
But all fuses will clear faster (in general) then a comparable breaker, correct?
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Not necessarily.
Fuses are often only faster in their current limiting region. Current limiting often only occurs at fault currents in excess of 10 times the fuse rating. Thermal magnetic breaker often begin to open at 5-10x their frame rating.
Nowadays, many circuit breakers are current limiting to a degree. True current limiting requires the maximum current to be limited as well as the clearing time and can be obtain with 'special' breakers.
 
jim dungar said:
Not necessarily.
Fuses are often only faster in their current limiting region. Current limiting often only occurs at fault currents in excess of 10 times the fuse rating. Thermal magnetic breaker often begin to open at 5-10x their frame rating.
Nowadays, many circuit breakers are current limiting to a degree. True current limiting requires the maximum current to be limited as well as the clearing time and can be obtain with 'special' breakers.
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What do you think of this?


https://www.youtube.com/watch?v=3dckmSgp1nw


My understanding is that once a fuse "blows" current limiting immediately starts and current goes to zero before the zero crossing where as circuit breaker must in the least relay on the zero crossing to break the arc.
 
mbrooke said:
My understanding is that once a fuse "blows" current limiting immediately starts and current goes to zero before the zero crossing where as circuit breaker must in the least relay on the zero crossing to break the arc.
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You are mistaken.

Fuse performance is all about the amount of current flowing in the fault. Not all fuse openings result in true current limiting.
Circuit breaker also exhibit current limiting to some degree, the industry often calls it dynamic impedance, it is the reason that series rated fuse-breaker combinations must be done by actual testing.
True UL Listed current limiting thermal magnetic circuit breaker have been in existence for many decades. Part of their performance is due to how fast and long they can stretch out an arc, thereby reducing the need to wait for a zero crossing. You might want to research breaker 'arc chute'.
 
jim dungar said:
You are mistaken.

Fuse performance is all about the amount of current flowing in the fault. Not all fuse openings result in true current limiting.
Circuit breaker also exhibit current limiting to some degree, the industry often calls it dynamic impedance, it is the reason that series rated fuse-breaker combinations must be done by actual testing.
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How does this work? Is it the same as the series rating ie you can have a 20amp 10AIC breaker at 22,000amps provided the main is 22kaic series rated?

True UL Listed current limiting thermal magnetic circuit breaker have been in existence for many decades. Part of their performance is due to how fast and long they can stretch out an arc, thereby reducing the need to wait for a zero crossing. You might want to research breaker 'arc chute'.
Click to expand...


But while you are stretching that arc, sand has already turned into glass within the fuse.
 
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