Zs values

[electech]

I am a little confused about the Zs values.
Example:
A TN-S system supplies a 32A type B 60898 c/b. The Zs for this must be no more then 1.44 Ohms. However my book also states that the maximum earth fault loop impedance for a TN-S system should not exceed 0.8 Ohms.
Can some one help me with this?

 

[RF Lighting]

0.8Ω is the maximum permitted Ze for a TN-S type of earthing system.

1.44Ω is the maximum permitted Zs for that particular type of protective device.

 

[davelx]

be no more then 1.44 Ohms. ?

No more THAN! Sorry, but I am seeing this more and more all over the place - including newspapers, journals and especially online and it drives me nuts .

Is it just a typo, or do people really think that "then" is the correct word?

 

[ricicle]

I am a little confused about the Zs values.
Example:
A TN-S system supplies a 32A type B 60898 c/b. The Zs for this must be no more then 1.44 Ohms. However my book also states that the maximum earth fault loop impedance for a TN-S system should not exceed 0.8 Ohms.
Can some one help me with this?

Assuming Ze was exactly 0.8 then in this example, you would therefore have to ensure that R1+R2 did not exceed ( 1.44 - 0.8 ) = 0.64 ohms.
This ignores any correction factors which would make the R1+R2 requirement even lower.