Maximum Zs

[riccer]

I am filling out my first domestic electrical installation form to the 17th edition.

And I cannot seem find out what the maximum Zs permitted by BS 7671 value is.

Could you please help me with this.

 

[willosparky]

maximum Zs or maximum Ze

 

[ian.settle1]

I am filling out my first domestic electrical installation form to the 17th edition.

And I cannot seem find out what the maximum Zs permitted by BS 7671 value is.

Could you please help me with this.

Zs for what type of protective device?

As said in one of your previous postings if you don't know what you are doing leave it alone before you hurt your self or kill someone else.

 

[Ballcock]

I am filling out my first domestic electrical installation form to the 17th edition.

And I cannot seem find out what the maximum Zs permitted by BS 7671 value is.

Could you please help me with this.

After the un-helpful replies you have received, you will find what you need in App. 2 of the on-site guide.

hope this helps

 

[Amp David]

Use the index, thats what its for, that is if you've got a copy of the regs?

 

[solo2771]

Maz Zs varies wth the type of protection used ie fuse, mcb
we were told to use the tables in the regs book and as a rule of thumb multiply it by 0.8.
If using mcb's the higher the value the lower the max Zs

 

[Mac]

I am filling out my first domestic electrical installation form to the 17th edition.

And I cannot seem find out what the maximum Zs permitted by BS 7671 value is.

Could you please help me with this.

17th Edition Maximum Ze & Zs Values Good luck mate.Too many grumps on the forum

 

[Ballcock]

Use the index, thats what its for, that is if you've got a copy of the regs?

Didn't you once have to learn?
I joined this forum with the hope of passing on some information, and in turn learning a bit , yes that's right, I'm an electrician of 25 years that's still learning.
Wouldn't you rather someone had the sense to ask, instead of diving in and getting hurt?

Yours
Vinnie

Apologies for the language Mods, sometimes it's the only way

 

[scotsparky]

Try page 103 on OSG the figures are pre calulated at 80%

 

[pevvers]

The fact that it says maximum Zs permitted by BS7671 should give you a clue that the corrected 80% values should not be used for this column.

All the tables that you require for this column you'll find in part 4 of BS7671.

 

[Spudnik]

This forum is for EVERYONE to use, therefore i would respectfully ask that answers are kept civil.

If you do not wish to help then DO NOT POST.

 

[brucelee]

17th Edition Maximum Ze & Zs Values Good luck mate.Too many grumps on the forum

just want to say cheers for posting this link mac its a good reference.saves time pouring over regs a lot quicker , easier to find what your looking for nice one mac

 

[promaxia]

with the new requirments 17th all consumer units require mcbs to bs 60898 or rcbos to bs 61009.BS 7671 deals with the magnatization effect of the breakers.Its not rocket science to know off your head the values of the 9 sizes of breakers 6,10,16,20,25,32,40,50,and 63.learn all of these on b type then for c type its half and then for d type its half again.What is valuable to know that for any circuit with a dissconnection time of 5 sec.ie 40a 50a 63a and a sub distribution circuit yoy can use the thermal characteristics of the breaker .this would be a departure from bs 7671 but its still within electricity at works regs 1989.

 

[wislum]

Hi Riccer,
I have trained a number of so called electricians and the have come up short on testing most think they know it all and cant be taught anything new. Those generally fail the 2391 at least 3 times. What I am trying to saqy is IF IN DOUBT ASK which is just what you have done and good on you for it.
The answer to your question is use the figures in the big red book page 48 and 49 for table 41.2 forfuses with a dis time of 0.4secs and table41.3 for MCBs and table 41.4 for fuses with a dis time of 5 secs. The 80% isue is the reading you get must not exceed that 80% of Max figure to be safe( 80% allows for sme correction factors such as temperature)

I train and I am still learning the only way to adapt to changes

 

[sugarman]

I am filling out my first domestic electrical installation form to the 17th edition.

And I cannot seem find out what the maximum Zs permitted by BS 7671 value is.

Could you please help me with this.

look on page 49 of our big red book my friend ,,,,looking under what type of protective device you have,,,,ie....a 60898 type b mcb rated at 32amps is ,,,,,1.44 ohms.....
check it out...... good luck..

 

[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!