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30 amp Circuit Breaker...but says current interrupting rating max RMS SYM Amperes is

30 amp Circuit Breaker...but says current interrupting rating max RMS SYM Amperes is

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  #1  
Old 08-11-06, 04:11 PM
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30 amp Circuit Breaker...but says current interrupting rating max RMS SYM Amperes is

10,000.

What does this mean?
 
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  #2  
Old 08-11-06, 05:57 PM
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Root Mean Square, if no one else responds. I'm certainly not qualified to explain it... the SYM is Symetrical...
 
  #3  
Old 08-11-06, 06:04 PM
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Originally Posted by bverdon
10,000.

What does this mean?
It means that the maximum fault current that the breaker can interrupt is 10000 amps.
 
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Old 08-11-06, 06:09 PM
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Fault current being a short circuit or such. The amperage skyrockets for an instant under fault current conditions.
 
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Old 08-11-06, 08:18 PM
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AIC Ratings

Electrical distribution system components such as circuit breakers, panelboards and fuses are assigned fault amperage interrupting capacities, or AIC ratings. These are mechanical ratings that assess the device’s ability to maintain integrity if a fault condition occurs downstream of the protection device. For example, a 10 kAIC-rated circuit breaker can safely interrupt 10,000 amps of fault current without blowing apart or internally short circuiting. A 65 kAIC switchboard must mechanically sustain 65,000 amps of fault current flowing through the switchboard and remain undamaged. These fault current ratings can be determined by consulting the manufacturer’s data sheet and are most often listed on the protective device.
This is the best I could find to explain AIC which, from what I also found, is not exactly the same thing as AIR but its intent is the same and gets used more or less interchangeably.

Basically, as petey posted, the available fault (as in dead short) can be extremely high. It gets into what current is actually available to your house from the POCO. The device needs to be able to withstand whatever current the POCO can deliver (albeit for a short time) without literally blowing up. If the device is not able to trip at whatever current is available, one of two things would happen. Either the device would more or less explode or it would not be able to clear the fault causing much greater damage to devices down the line.
 
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Old 08-12-06, 12:44 AM
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guys there is no tripping involved it is a 30 amp breaker it will trip at 30 amps as designed. the other thing that you are debating is the contaiment. or shoottrugh capability. somebody explained this before but not in theses terms. Did i help?
 
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Old 08-12-06, 05:39 AM
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Originally Posted by nap
This is the best I could find to explain AIC which, from what I also found, is not exactly the same thing as AIR but its intent is the same and gets used more or less interchangeably.

Basically, as petey posted, the available fault (as in dead short) can be extremely high. It gets into what current is actually available to your house from the POCO. The device needs to be able to withstand whatever current the POCO can deliver (albeit for a short time) without literally blowing up. If the device is not able to trip at whatever current is available, one of two things would happen. Either the device would more or less explode or it would not be able to clear the fault causing much greater damage to devices down the line.

Great explaination...makes perfect sense.

Thank you everyone!
 
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Old 08-12-06, 05:46 AM
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Originally Posted by neon
guys there is no tripping involved it is a 30 amp breaker it will trip at 30 amps as designed. the other thing that you are debating is the contaiment. or shoottrugh capability. somebody explained this before but not in theses terms. Did i help?
So what you are saying is, under a fault, such as a short circuit, when the amperage gets to 30 the breaker will trip?

I eagerly await your reply.
 
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Old 08-12-06, 05:54 AM
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Originally Posted by neon
guys there is no tripping involved it is a 30 amp breaker it will trip at 30 amps as designed. the other thing that you are debating is the contaiment. or shoottrugh capability. somebody explained this before but not in theses terms. Did i help?
A 30 amp breaker does not actually trip at 30 amps. As with any thermal-magnetic breaker (which is what a typical breaker is)., the actual trip value varies upon many circumstances.

A 30 amp breaker will actually easily carry 35 or so amps for a limited time. Actually they are designed to carry over 100 amps for a very imited time without tripping. This all involves the thermal tripping feature. Temp must build over some period of time before the breaker will trip by cause of this feature.

The other trip mechanism, magnetic (and a more or less instantanuous action), actually takes much more than 30 amps to make it trip. I don't have the specs available at the moment but I can tell you this.The last time I installed a 250 amp breaker with a variable setting for the magnetic trip, the lowest setting was actually 1250 amps. Yes, that is one-thousand, two hundred, and fifty amps. That means the breaker would not trip on the magnetic (instantanouos) mechanism until it experiences at least 1250 amps. The high setting was 2250 amps. So if you transfer those numbers to a 30 amp breaker, it would trip around 150 amps utilizing the instantanuous mechanism. This can be proven by the fact that when dealing with inrush current on a motor or AC compressor, 4 or 5 times name plate run current is not uncommon as a start up current.


What was being discussed here is not actually the value that would make the breaker trip but what amount of current is available on the load side that the breaker could experience in the event of a fault. While the breaker is designed to trip at the lower current, there are many thousands of amps available from the POCO that the breaker will be subjected to.

You have to realize that just because your home is limited to the 200 amps or so allowed by the THERMAL breaker mechanism, the POCO has thousands, and in some cases 10's of thousands of amps available (for a small amount of time since their breaker systems would also be activated that would limit the time this flow is available to your home). What this AIR or AIC rating is the ability to work as designed (break the circuit) when exposed to those thousands of amps of current. If they cannot withstand all the POCO can deliver, they can, and have, simply exploded with often devastating effects. The other possibility, with even more damaging effects possible is that the contacts become instantly welded. This will cause the current to flow much longer than if the breaker actually did trip and allow the fault current to flow to the actual fault until either the POCO's overloads trip or the fault is burned into non-contact.

So neon, while we were not discussing the actual tripping of the breaker, we were speaking of it's ABILITY to trip given the current it WILL be exposed to in a fault situation.
 
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Old 08-12-06, 06:22 AM
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Now NAP, I was hoping Neon would explain "the contaiment. or shoottrugh capability." theory to us.
 
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Old 08-12-06, 06:26 AM
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Would it be accurate to say that the CB is rated for the ability to trip at loads under 10,000 amps, but over that they will not guarantee that the CB would not fuse together into a big ball of metal and plastic allowing current to flow through even though it is physically deformed?
 
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Old 08-12-06, 07:40 AM
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Originally Posted by Speedy Petey
Now NAP, I was hoping Neon would explain "the contaiment. or shoottrugh capability." theory to us.
I am glad he didn't explain it. If I want to catch a Cliff Claven answer to a question I will watch Cheers.
 
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Old 08-12-06, 08:14 AM
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.. ..
 
  #14  
Old 08-12-06, 08:19 AM
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I think nap's explanation was excellent, and mdtaylor summed it up very well. A breaker which would trip at say the 30 amp rating, more or less, but under a direct short would fuse the contacts together , would not be very useful. So, they are required to have that very high 10,000 amp interupt rating.
 
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