# What is the meaning of KA(kilo amps) of a miniature circuit breaker?



## micromind (Mar 9, 2008)

The kA (kilo amps) rating of any circuit breaker is the absolute maximum amount of current it can safely interrupt at its rated voltage. 

This is also known as AIC (Amps Interrupting Current). For almost all residential breakers this rating is 10,000 amps. I believe the largest industrial breaker I've ever seen was 100,000 amps. 

All power distribution systems have a source of some sort, usually a utility transformer. This source, whatever it is, has a full-load current rating, and a short-circuit rating. 

Finding the full-load current rating is easy, simply divide the VA (volt-amps) by the voltage, and you get amps. 

Finding the short-circuit rating is a bit more difficult. It involves the impedance (resistance) of the primary (high voltage) source, the impedance across the transformer itself, and the impedance of the secondary (low voltage) conductors. 

A typical residential service will have a short circuit rating (also known as 'available fault current') of about 2,000 to 8,000 amps. A large industrial service might be 80,000 amps. The breaker must be able to interrupt the available fault current in the event it is shorted out. If there's more current available than it can handle, it will likely explode, sending bits of hot plastic and an electrical arc into the hand of the operator. Not pretty! 

This is why, when turning on a large breaker, an experienced electrician will always stand to the side, never directly in front of the breaker. 

Rob


----------



## frenchelectrican (Apr 12, 2006)

Typically the KA stand for Kiloamps { X,000. The X is the number you put in there }

And all the breaker and _fuses_ are rated AIC in KA not only they will list in the KA but sometime will list like 10K AIC which it means 10,000 amp fault amp inturpeting capicity but also the breaker and fuses will list the max voltage as well so it can change the performace on them.

Typically majotry of resdential breaker are rated for 120/240 which it mean 120 volt line to netural or 240 volt line to line and if it run on 208Y120 system the 120/240 volt breaker will work just fine on this system but for other system like 240 v 3 Ø delta system that diffrent story normally it will not useally covered in this section unless you got one of oddball service system comming in your house then you have to pay attetion where you land the breaker { ditto with fuses }

However.,, in commercal and industrail sisuation that is a whole diffrent ball of game to deal it more compatied there due the system voltage is useally much higher than resdentail system or small commercal system { 120/240 or 208Y120 or 240 D }

If you see some low voltage breaker they used in 12 or 24 volts system you will noted it will list the max voltage with the X of amp AIC 

Merci,Marc


----------

