Maximum Zs

[oldtimer]

Guys I have made up quick reference laminated sheets so that I do not wear out the tables on the books and as I am still learning T&I I must admit I am confused as my course at select said that I was to factor in the 80% rule of thumb from the red bok the OSG has this figure factored in but when a company came to my work to do our PIRs they paperwork referenced ZS max from the red book ?

So for clarification what figure do I use the max in the red book or the 80% figure in OSG ?

Another point also is when you meaure Ze you disconnect parallel paths so as Zs is the sum of Ze and R1+R2
then when doing this test does the parallel paths have to be disconnected to obtain a true figure ?

One last also if anybody want a copy of these tables I would be happy to pass a copy on even for some feedback

 

[Guest123]

Hi.

The figures in BS 7671 are what is inserted on the test forms as this is what they ask for, the readings you obtain however should be no more than the 80% rule of thumb found in the OSG.

When you measure Ze obviously the whole installation is de-energised and the main earthing conductor disconnected to carry out the test.

The measured Zs is what you would find under normal serviceable conditions i.e ALL conductors connected and measured at the extremity of each circuit.

 

[james king]

just wish that SOME of the expericend sparks will help with people threads and not just say u should not being doing it u r not approved there for go work in tesco for exapmle. just puts the less sparks down. every one does not know every thing about anything no matter. if u are just here to tell people how crap they are then why post??

agreed that people on here are very helpful so thank u to those

 

[brucelee]

hi
just wanted to ask where the max zs values are for the older bs3871 mcb s are, can you use the values for bs 60898 and 61009 this is what i was told is this correct and then i x by 0.8 to get 80% values cheers

 

[pevvers]

I know that 3871 3's and 60898 C's are the same characteristics, 4's and D's I've heard can be interchanged but I have never seen a Zs table for a 3871 type 4. 3871 types 1+2 are not interchangeable with any of the 60898 tables....

But I always stand to be corrected!