Zs for cert Filling!

[sixfingers]

Hi guys just want to double check this one,lighting circuit 6a bs 60898 mcb fitted, with max earth fault loop impedance of 7.67 and 80% value of 6.13,im correct in saying 7.67 value would be noted on bs7671 cert and 6.13 would be value that it would be required to be under?
Would there be any orther reason to put lower value on certificate?

 

[eddielarge]

No you must put the max zs as stated in 7671 ,,, i.e 7.67

 

[sixfingers]

No you must put the max zs as stated in 7671 ,,, i.e 7.67

Hi Eddie,so no orther reason for lower values to be inserted on certs? As ive done some testing for a large electrical company and sent certs in with higher values from regs and they have sent them back to me to sign with lower values on certs?

 

[eddielarge]

Hi Eddie,so no orther reason for lower values to be inserted on certs? As ive done some testing for a large electrical company and sent certs in with higher values from regs and they have sent them back to me to sign with lower values on certs?

We did a testing contract a few months back and this arguement arose , because 4 other testers always put the 80% value. how i see it is that the cert is asking you for the max Zs.

I phoned the nic on this subject and they said that it it the max zs and not the 80% ..

 

[sixfingers]

Also ive noted they have put 5s max disconnection time down on circuits with 6,10,16 mcbs fitted and 0.4s for circuits with 32s fitted?

 

[cornburn]

Also ive noted they have put 5s max disconnection time down on circuits with 6,10,16 mcbs fitted and 0.4s for circuits with 32s fitted?

Sounds like someone's got their wires crossed there

A thank you..............

 

[Amp David]

I always see it as this, the cert is asking for the MAX VALUE of Zs as stated in 7671.

So you put the value stated 7671.

Easy. Think the large electrical company are a little off the beaten track IMHO

 

[kung]

The max Zs figure in bs7671 was taken when the conductors were heated up to about 70deg c when we test our conductors are at room temp or just above thats why we use the rule of thumb method and reduce the tabulated values in bs7671 to the 80% and its this figure we use to compare our test figures to and use the max figure in bs7671 on cert as stated they ask for max Zs on cert.

 

[Des 56]

To another tester reading the certificate,the mcb rating and type are there,so its not too important which figure is used

State max as in brb or the 80% that I use with that 80% note written in the title box ,at least then the results can be a straight comparison with whats written

 

[dfitzplugs]

I'm under the impression that the max disconnection times are 5 sec for sub mains and 0.4 for all other circuits, is this correct ?

 

[eddielarge]

To another tester reading the certificate,the mcb rating and type are there,so its not too important which figure is used

State max as in brb or the 80% that I use with that 80% note written in the title box ,at least then the results can be a straight comparison with whats written[/QUOTE


It states max zs according to 7671 no the 80% , i know you write this on the cert but why not just put max and be done with it

 

[Des 56]

To another tester reading the certificate,the mcb rating and type are there,so its not too important which figure is used

State max as in brb or the 80% that I use with that 80% note written in the title box ,at least then the results can be a straight comparison with whats written[/QUOTE


It states max zs according to 7671 no the 80% , i know you write this on the cert but why not just put max and be done with it

Why do you see this as a problem ?
The certificate gives information obtained,that information would be read by another person who should have sufficient knoledge to understand whats written

There is no ambiguity with either method
Whatever is written can be understood by the devices used
To me its a column on a sheet of information that makes little difference whatever figure is used

 

[nickblake]

All circuits up to 32 amps should be 0.4

 

[Des 56]

All circuits up to 32 amps should be 0.4

You missed out the words final circuit

Final circuits exceeding 32 amp and distribution circuits are 5 s