Lifetime/Duration of Circuit Breaker After Short Circuit

I think this is variable for each breaker as all the faults are not equal...I generally go by nuisance tripping as the time to replace...

https://www.mikeholt.com/mojonewsarchive/EES-HTML/HTML/ElectricalCircuitBreakers~20030621.htm

This is from the BEAMA guidance notes for EN60947...

<< Icu is tested by a cycle...

Open on fault Icu.

Wait 3 minutes.

Close onto fault at Icu & open.

Carry out overcurrent and dielectric tests to find condition.

......Where 2 or more faults occur between Ics and Icu in service, condition of breaker must be verified suitable for further service.>>

I know that on oil rigs, where fault levels are high everywhere, a breaker is replaced immediately if it has cleared a short circuit.

En60947 defines ratios of Ics - service breaking S/C capacity - to Icu; of 25% to 100%; which should be stated in maker's spec.

In short, Icu really can be an Ultimate maximum and should not be relied upon more than two times. Closing breaker onto fault more than once after initial trip could be dangerous, especially with < 3 min between events.

If the installation has Icu fault level at origin, you should consult the breaker manufacturer about how many shorts are tolerable and set operating rules on site.

If you really must use the Icu of the breaker, you should consider if you should have monitoring equipment which tells you if a breaker opened on S/C or overcurrent and written safety rules based on a safety risk review. If that breaker, only 100 amp, is hand operated; a fail to break could injure or kill .

Remote operation, deliberately at a safe difference, will reduce the risks - always supposing the back-up (HV?) protection will clear fault without major damage to switchboard or starting a fire which destroys the installation.

If you're really concerned about continuity of service and/or protecting the equipment fed by the equipment, then treat the breaker as if it were a fuse and replace it after it opens under a 40kA fault. Of course you'll need to verify that it actually saw that I_cu, and then choose what is an acceptable level that avoids replacement; i.e., 38, 35, 30kA??

That's why some circuits use a "belt and suspenders" approach and place High Interrupting Capacity fuses in series with the breaker. The other alternative is to choose a breaker that has an I_cu higher than than can be reached by the circuitry.

How about discussing it with the manufacturer, the name of which has been withheld from the forum, over the telephone?

I agree with most of the above - the standard does not define it beyond O-C-O.

Many years ago one of our partners was asked the same question and used our board as a test bed. They equipped it with a range of MCCBs (mostly small up to about 50A) and carried out conditional tests at 50kA (Icu) - repeatedly on the same device. After 10 shots they took them away for investigation and at that point they were all still working. So they could them claim (and prove) they were good for several short circuit events without replacement. Good to know.

On another test (different manufacturer), we did an 80kA short circuit test on an MCCB (100A) which was it's Icu value and it blew up first time - test failed.

So the bottom line is ask the manufacturer and choose with care.