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Posted By Topic: Clause in AS/NZS 3000:2018

Mar 20 2020 13:56

Hi, I wonder if anyone would mind advising –

I’ve been looking at clause in AS/NZS 3000:2018+A1 and am not sure the reference there to current “I2” makes a lot of sense

To start off it is called “the current ensuring effective operation …” but what does that mean? It appears to explain what “I2” means by saying it is equal to the operating current in conventional time for circuit breakers (1.45 IN). I’m not sure what is meant by “in conventional time” however it appears to say that with respect to circuit breakers I2 = 1.45 x IN

Now equation 2.2 above requires that I2<= 1.45 x IZ. So if my understanding above is correct it appears to say (substituting for I2) that 1.45 x IN <= 1.45 x IZ. If that is true why not just say IN <= IZ?

I find this all confusing and would be grateful for any enlightenment.


Mar 20 2020 13:59

I believe the 2018 standards haven’t come into effect as yet.

Mar 20 2020 16:51

In order to fully understand all the principles involved you need to be able to fully understand the operating points of fuses and MCDs, heating of cable conductors when current flows and how this affects the permanent damage of the cable insulation and heating of the cable conductors by short circuit currents.

The treatment in AS/NZS 3000 is a bit brief and you may find the treatment of these matters better in pages G1 to G6 of the Electrical Installation Guide 2018 available at the reference below