KVa and ka and overload.

[Joe9876543210]

Hi,
I'm an apprentice electrican. Please could someone give me some guidance on this as I am confused? Thanks.

What is the difference between overload rating ie 6amp on a circuit breaker and breaking capacity on a circuit breaker ie 10ka?
I'm confused.

Thanks

 

[Simonslimline]

The 6 amp circuit breaker is designed to carry a continuous load of 6 amps without operating. If the device is subjected to a greater load than its rated current it will operate. How fast the device operates is dependent on how much it is being overloaded. Information regarding this can be found in BS7671 under the Time Current graphs. In regards to the 10KA this is the maximum amount of fault current the device can safely break. Although the device will not be good for continued use after this occurs.

I would advise if you do not already own BS7671 and the On Site Guide to purchase these.

Well worth joining the trainee section of the forum as well mate as there is lots of helpful people in this section

 

[Darkwood]

Under short circuit the mcb may be subject to a current of many thousands of amps... the Ka rating is what then device can cope with without failing - If you have a 6Ka mcb and a fault current under short circuit is higher than this the its possible the device could fail closed thus not breaking the fault.

As above the overload is the continuous current value that your circuit design should not exceed.

 

[Pete999]

As above get the relevant documents and look for yourself it will be money well spent

 

[Joe9876543210]

Cheers for the help guys brill x

 

[NickD]

In regards to the 10KA this is the maximum amount of fault current the device can safely break. Although the device will not be good for continued use after this occurs.

Breakers can potentially have two separate fault current ratings, Ics and Icn - I remember them as Ics(erviceable) and Icn(ackered). Ics is the fault current rating up to which the breaker can break and still be good for continued service. Icn will be a higher figure and is the fault current rating up to which the breaker can break but then be considered ruined. So for example you might get a breaker with an Ics of 6kA and Icn of 10kA.

 

[Darkwood]

Icn - F.U.B.A.R.

 

[Simonslimline]

Think I read this in one of your posts the other day, what does it stand for?

Icn - F.U.B.A.R.

 

[Darkwood]

Think I read this in one of your posts the other day, what does it stand for?

I cant reply all of it but '-Fed-up beyond all recognition' well the first word is wrong!

 

[NickD]

Life gets difficult when you have breakers with separate Ics and Icn ratings cos if maximum prospective fault current is large enough to lie somewhere in the range between Ics and Icn (say Ics 6kA, Icn 10kA, max PFC 8kA) then for any given fault that tripped the breaker you can't be sure how big the fault current was and so have to chuck and replace the breaker as a precaution. Isn't life complicated?

 

[D Skelton]

Life gets difficult when you have breakers with separate Ics and Icn ratings cos if maximum prospective fault current is large enough to lie somewhere in the range between Ics and Icn (say Ics 6kA, Icn 10kA, max PFC 8kA) then for any given fault that tripped the breaker you can't be sure how big the fault current was and so have to chuck and replace the breaker as a precaution. Isn't life complicated?

Any decent designer would have specced the breakers to have an Ics higher than the PFC though.

 

[trev]

I cant reply all of it but '-Fed-up beyond all recognition' well the first word is wrong!

I thought it was "fed up beyond all repair" (first word wrong of course)

 

[Brightspark2]

I thought it was "fed up beyond all repair" (first word wrong of course)

Quote off saving private Ryan "****ed up beyond all recognition"

Again first word changed but we're getting closer to the actual word lol...

 

[trev]

I stand, well actually sit, corrected

 

[telectrix]

the word was "repair" before private ryan was out of nappies. but either will do to describe a committee.