Impedance of short circuit path??

[Lazlo]

Hi,

Probably fairly simple but I'm learning.

Have an example for working out fault current/disconnection times.

"A 10mm PVC sheathed MI copper cable is short circuited when connected to a 400V supply. The impedance of the short circuit path is 0.1 ohms. Calculate the permissable disconnection time and show that a 50A Type B MCB (EN-60898) will meet this requirement."

My question relates to the 0.1ohms short circuit path impedance, how do we/I know the impedance is 0.1 ohms? How is this calculated? I don't get it! :ninja:

We have covered Z[SUP]s[/SUP]/earth fault loop impedance and I think I understand that...

 

[telectrix]

same reason you know the voltage. it's given in the question.

 

[Lazlo]

OK I get that but how is it or would it be measured?

 

[telectrix]

with a low resistance ohm meter or the continuity range on your MFT. .

 

[JamesBrownLive]

Hi,


My question relates to the 0.1ohms short circuit path impedance, how do we/I know the impedance is 0.1 ohms? How is this calculated? I don't get it! :ninja:

We have covered Z[SUP]s[/SUP]/earth fault loop impedance and I think I understand that...

It's not calculated, it's measured. Just as Tel has said.