Maximum Zs values for BS3871

[gazdkw82]

Where can I find the max Z's value for a BS3871, type 3, 32A MCB?

Iv had a look through BS7671 and done some searching online but I cannot find it. IV found some tables with listed Zs values for a 3871 but I have no idea where they originate from or how old

 

[The Ghost]

This is from the Unite guide, a great little pocket book. Much the same as OSG except it is £7.

 

[Deleted member 26818]

I believe the NICEIC/Electrical Safety Council published a chart showing the values back in 2008.
Here’s a link to the 2011 version:
https://www.----------------------------/media/1627/master_earthfaultlooptable.pdf

 

[gazdkw82]

Those 2 references contradict each other? The unite guide says it's 0.719 and the other chart says 0.58??

 

[Deleted member 26818]

The one I posted a link to, shows the 80% values.

 

[Taylortwocities]

Those 2 references contradict each other? The unite guide says it's 0.719 and the other chart says 0.58??

My guess is that the NICEIC figures include the 80% rule of thumb malarky.

0.719 x 80% = 0.57

 

[Taylortwocities]

The one I posted a link to, shows the 80% values.

Snap!

 

[gazdkw82]

Ah... Lovely.

Thankyou

 

[Strima]

Don't forget to adjust for Cmin... (0.95)

 

[The Ghost]

And bear in mind they are adjusted values for 230v instead of 240v.

 

[gazdkw82]

It's just for a minor works cert so no need for Cmin

 

[Strima]

It's just for a minor works cert so no need for Cmin

Why not?

 

[westward10]

Type 3 was on the same Table as a type C.

 

[gazdkw82]

Why not?

It's not required. It asks for the max Zs values listed in BS7671.

 

[westward10]

You would need to look in a 16th Ed to find them as I said they were the same Table as a type C.