AIC RATING

[mrcheese]

If a breaker has an AIC rating of 100KA ( for example) and it is exposed to a 30KA fault.

should the breaker still operate correctly after the fault 100% of the time OR does the 100KA rating insure that the breaker will operate for the said fault but there is no guarantee that the breaker will not be damaged?


Ohm's it not just a good idea, Its the law.

 

[dpc]

That will depend on the type of breaker and what standards it was designed and built to.

For a typical molded case circuit breaker, the UL standards require only a very limited number of successful operations at the maximum fault current - I believe the number is six, but I'm not sure and I'm too lazy to look it up.

If the fault current is lower, presumably it is more likely to survive more fault interruptions, but there is no guarantee of anything.

As a minimum, I'd want to verify that breaker is still operating properly manually, with no obvious signs of damage. In an ideal world, the breaker would be tested after a fault interruption. In the real world, 99% of the time, if the breaker is still in one piece with no obvious damage, it will be closed back in and everyone hopes for the best.

David Castor

http://www.cvoes.com

 

[mrcheese]

"the UL standards require only a very limited number of successful operations at the maximum fault current - I believe the number is six, but I'm not sure and I'm too lazy to look it up.
"

what is the UL standard for this. the breaker in question is a SQD master pack NWH

Ohm's it not just a good idea, Its the law.

 

[jimbofitz]

I believe UL 489 is for circuit breakers.

 

[Zogzog]

From NW(H) manual:

2. If a short-circuit has occurred, inspect the circuit breaker. Make sure all power is disconnected prior to inspection.
— Check the condition of the arc chambers (see page 90)
— Check the condition of the contacts (see page 90)
— Check the torque of the connections (see the connector installation instructions)
— Check the condition of the clusters (see page 90)
3. After eliminating the cause of the trip, reset the device.

 

[mrcheese]

Sounds like a bunch of CYA to me. If I really have to take the breaker out of service and test it after any fault trip I might as well use fuses.

thanks to all that responded.


Ohm's it not just a good idea, Its the law.

 

[Zogzog]

Maybe there is some CYA there but we see the end result of these in our breaker shops everyday, there can be a lot of damage done from a fault interuption.

Keep in mind no actions are required following an overload (LT trip), just a fault.

Masterpacts have had a few issues and safety notices released, you may want to check out those also.

 

[mrcheese]

still not convinced.

according to the lit. new masterpact breakers are designed to meet IEC 947-2

this is taken from page 10 of the attached document
______________________________________________________
IEC 947-2 & BS EN 60947-2
This standard replaces IEC 157-1,
applicable since 1973.
The circuit breaker selection criteria remain
unchanged, but the new standard provides
the user with a better guarantee concerning
quality and performance.
Circuit breakers are now subjected to tests
that are more representative of real
operating conditions.

Icu : the ultimate breaking capacity,
which must be greater than or equal to
the 3-phase short-circuit current at the
point of installation of the circuit breaker,
a value unlikely to be reached under real
conditions;

Ics : the service breaking capacity,
generally expressed as a percentage of
the ultimate breaking capacity (25, 50, 75
or 100 % of Icu). It corresponds to a
short-circuit current that is more likely to
be reached under real conditions. The
circuit breaker must continue to operate
normally after having interrupted a
current equal to Ics three times;
All Masterpact circuit breakers have a Ics
value equal to 100% of Icu.

_______________________________________________

so that tells me that a masterpact should be able to handle a fault of (100Kaic in this case) 3 times

Ohm's it not just a good idea, Its the law.

 

[Zogzog]

Yes it should , but they still recommend the inspections.

 

[rbulsara]

Why not speak to SQ D directly? The official line will always be "check" the breaker before re-closing. Although what dpc said is true in practice.

Rafiq Bulsara

http://www.srengineersct.com

 

[mrcheese]

Talking to SQD now. but they want me to replace the breaker on my dine. This was a brand new breaker. that saw a 40KA fault.

My point for posting was to find out more info on just what the "expectations" are for the end user. I think that i have convinced myself that this is a SQD issue and not a end user issue based on the expectation of the breaker being able to meet the stated testing requirements.

can i get an amen?

Ohm's it not just a good idea, Its the law.

 

[dpc]

If it is still covered by the original warranty, I would expect Square D to repair or replace. Interrupting faults is what breakers are supposed to do.

It should certainly be good for numerous 40 kA interruptions, at least that would be my position.

There are two UL standards for breakers - molded case and power circuit breaker - I believe the MasterPact can built to either one, depending on how it was specified.





David Castor

http://www.cvoes.com

 

[Zogzog]

So yours failed? What failed? Waranty should cover that.

One thing to keep in mind is that new breakers are not tested by the OEM, they only "batch test". That is why acceptance testing is always recommended.

 

[rbulsara]

It depends on whether if the breaker is needs to be replaced or you want to it to be replaced. A warranty normally would not cover damage due to a fault, but you need to read what is in your warranty.

Other than that, this is no different than anything else you own, with or without warranty. You will have hard time having mfr paying for the replacement, unless a manufacturing defect is proven. It is easier said than done. So, you need to weigh your options and costs.







Rafiq Bulsara

http://www.srengineersct.com

 

[IRstuff]

Speaking of fuses, there is an time-integration of power limit for fuse time lifetime for surges below the fuse spec.

While breakers are obviously different, they have their own physics and one could envision time-integrated power behavior similar to fuses.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[magoo2]

NWH verus NW. I'm not sure of the differences but be aware that Square D has had problems with the clusters pulling loose from the stabs in the back of their NW breakers. I found one installation where just cranking out the breaker and then cranking it back in caused one of the clusters to become dislodged. This was a 480 V installation and the cluster being loose caused an arcing ground fault when the breaker was closed back in.

I think that is why Square D says as the 4th step to inspect the clusters after a fault operation. I think what they should have said is to inspect the clusters whenever the breaker has been racked out.

You can read their notification letter (attached).