kA ratings

[SeanM]

Good Evening

I would like to confirm when testing three phase PSCC, you test each phase and multiply the reading by 1.73

[AndyD]

Yep, for 3 phase if would be the highest phase to neutral reading multiplied by 1.732 (square root 3) unless you have a tester that's rated to test phase to phase. Generally for rule of thumb I usually just work on double the single phase reading to err on the side of caution.

[ConcernedHomeowner]

Just checked with the product manager at CBi and the old RCD was manufactured in 1974, and it does have overload protection built in. Had it tested today and it is in good working order. It trips at 20mA which is at its spec. PSC also done, and highest reading was 0.88 (so multiplied by 1.732 gives me 1.52416). Seems all the breakers are well within spec, with the lowest at 2.5 kA. Thanks for all the input.

[AndyD]

Thanks for the follow-up info, it's always nice to know the outcome and I'm glad to hear you got some reliable info from the manufacturers. It's also good to hear your RCD is still functioning within its I∆n spec even after 44 years.

[ians]

Generally white lever CBI breakers have overload protection...but can be used as an isolator if the correct number of poles are used.

green ones dont have overload protection...nomally used to ISOLATE a circuit only.

just to put a spanner in the works...an orange lever cbi is a curve 1 breaker also has overload protection...but can withstand startup currents and can be used where big magnetic tables are used ( a curve 2 breaker can also be used for magnetic tables as per manufacturers specs) ...you need to understand these breakers before installing.

then of course you get D curve breakers...etc...etc we wont confuse the matter.

A note with regards to KA rating...if your equipment is installed close to the supply transformer 500 kva and bigger...make sure you know what you a re doing...you dont want to get caught out using under sized cables...no mater how much you reduce the KA using buss bars...cable length etc to reduce the fault level.

[ians]

Thanks for the follow-up info, it's always nice to know the outcome and I'm glad to hear you got some reliable info from the manufacturers. It's also good to hear your RCD is still functioning within its I∆n spec even after 44 years.

we have more problem with brand new "expensive" cbi earth leakage units than we do with the good old stuff.

another good example is the good old lumex plug and light switches...the stuff last forever...replace it with an produc and it is all plastic junk.

same applies to geysers...once you replace it...you are lucky to get 5 years...some old geysers are still working 25 + years later...the old geysers had a copper drum.

[12mathaba]

Hello everyone, I would like to know, I am using new psc tester TOP TRONICof which I am not familiar with, know when I measured the psc it gives me a value 758 amps, the main circuit breaker is 63 amps 3ka rating. My quation is this valve acceptable?

[SeanM]

Morning Mathaba

Provided your tests were carried out correctly i.e: with the load off and at the main breaker then your value is acceptable.

758 amps reading breaker can handle 3000 amps fault current even at three phase (758 x 1. 73)