Max zs values

[Farmelectrics]

I like the 35 way. I've always done it this way but its longer . b type 5 times, c type 10 times, d type 20 times. so if its a c type 32amp it would be 230 divided by 320=0.71. 0.71x 80%= 0.56. 0.56 x 0.95 c mim =0.55, long winded so in future might youse the magic 35.

 

[pc1966]

What bothers me about "quick calculations" like 35/In is they end up being used and not understood. Yes, that works fine for a B-curve MCB but not for other cases!

So Farmelectrics method is better as it shows the key point - the 0.4s disconnection is achieved by ensuring the magnetic trip is reached under worst-case conditions (0.95 supply volts and 0.8 for cable temperature on R1+R2).

 

[Mark Wright]

Can't say I'm a huge fan of this guy, seems a bit harsh after posting his video but I get the impression he doesn't know why it's 35 - also on his site he uses little r1 for a reading on a Radial and few other things that a tutor should know better.