Noob ALERT! What is (Za x Ia ≤ Uo) ?

[shakin2011]

Doing my 17th edition and trying to comprehend a few things in the red bible, and i feel ive arrived at the right place because ive been told by wise men that this is where i will find my answers

I understand Zs is earth fault loop impedance, Ia is the current in amperes causing the automatic operation of the disconnecting device within the specified time, Uo is the nominal a.c rms etc etc.....

but can anyone expound upon this (Zs x Ia ≤ Uo) is simpliar terms?

Much thx if you can

 

[SirKit Breaker]

Having read this a time or 2, i dont understand what you trying to find out. As i see it, its back to basic's "V over I xR".
But then i am a bit of a thick **** at times.

Cheers.........Howard

 

[malcolmsanford]

Not seen a Za as of yet but are you meaning Ra x Ia ≤ 50v ?as in regulation 411.5.4

 

[shakin2011]

sorry i made a typo, i changed it from (Za x Ia ≤ Uo) to (Zs x Ia ≤ Uo). refer to reg 411.4.5

 

[Paul.M]

Edited due to question changing.

 

[malcolmsanford]

It's simply a way of confirming for your disconnection times So for a BS 60898 MCB type B 32 amp you would have 1.44*160= 230volt it's simple ohms law.

The Zs is found in table 41.3 and the Ia is found in Figure 3.4 in the appendix. Another way the C&G do this is Zs = Uo/Ia so you have 230/160 = 1.44 same as table 41.3.

Is this what you wanted to know?