Zs too high at distribution boards

[pennywise]

Is that 0.80 or 0.08

 

[knasher]

pennywise, Ze is 0.08.

 

[pennywise]

sorry just picked up all other responses to my query. Ze at origin is 0.08,(should be 0.35 shouldnt it for TN-C-S?

Sorry mate just got a bit confused with the wording.

 

[Deleted member 26818]

Not certain if the Ze of 0.08 is the measured value, or reference to the given value of 0.8 for TN-S systems?

 

[knasher]

thanks for all your input guys, this site is a great help to someone who is not ashamed to admit that I have only recently got my City & Guilds (In response to Tonys question, "am I an electrician?", no I feel as though I've still got a lifetimes learning ahead of me still, but find this whole subject fascinating. Cheers

 

[knasher]

Not certain if the Ze of 0.08 is the measured value, or reference to the given value of 0.8 for TN-S systems?

I'ts not clear from the PIR if this figure was measured or got through enquiring

 

[Deleted member 26818]

From looking at your post No. 14 re. the Zs at individual boards, I would imagine that it was measured.

 

[knasher]

thanks for that

 

[IQ Electrical]

Yes, you would never get 0.08 Ohms by enquiry.

The earthing conductor size is not an issue as regards Ze/Zs.

What is the type of the BS 3871 devices?

 

[knasher]

Hi, its 3871 MCB, type 2, 60A. Hope that helps

 

[IQ Electrical]

So you have 2 DB's with exceeded maximum Zs values.

Are these DB's much more remote or supplied by smaller CSA distribution circuits?

I'm really asking if this is down to poor design or cpc continuity faults on the distribution circuits in question...

 

[Deleted member 26818]

It may be possible to reduce the Zs by the installation of supplementary bonding.

 

[IQ Electrical]

I want to know the reason for the high Zs before he starts stringing green/yellow to the nearest sink!

 

[Deleted member 26818]

I want to know the reason for the high Zs before he starts stringing green/yellow to the nearest sink!

I wasn't thinking about the sinks, more along the lines of crittle windows.

 

[IQ Electrical]

Spin, have you ever used a 'smiley' ?