Max Zs

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Robbo

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Settle a conflict of opinions here for me will ya...

What are the maximum earth fault loop impedance readings permitted for a BS 60898 type B mcb for a 6, 20 ans 32 Amp circuits?

Go on, help me win a free egg and sausage roll in morning !

 
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Settle a conflict of opinions here for me will ya...What are the maximum earth fault loop impedance readings permitted for a BS 60898 type B mcb for a 6, 20 ans 32 Amp circuits?

Go on, help me win a free egg and sausage roll in morning !
well table 41.3, Pg 49 of the big red book says..

6A - 7.67ohm

20A - 2.3ohm

32A - 1.44ohm

@ normal operating temperatue!

if not adjusted re Apendix 14.

 

stringy

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i think robbo should give us a bite of his free butty, il splitt mine with you special location lol

 

Robbo

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Ta very much so why may I ask is my pal quoting me page 103 of the little red book (osg) and coming up with other nonsence?

 

stringy

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Ta very much so why may I ask is my pal quoting me page 103 of the little red book (osg) and coming up with other nonsence?
the figures quoted in the osg are lower because they are a lower temprature than the regs.

osg 10 degrees c

regs normal operating temp

 
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Ta very much so why may I ask is my pal quoting me page 103 of the little red book (osg) and coming up with other nonsence?
The values in the little red book OSG

are the "rule-of-thumb" 80% values..

that allow for increased heat in a conductor during earth fault!

NICEIC quote these 80% values as the max value when testing cold conductors..

as it is generally accepted that if cold less than 80% of max from Big book..

then in the event of a fault the big book max will not be exceeded!

{remember cables will heat up during fault!}

& thus the MCB will still trip fast enough!

BUT the value that goes on your certificate IS the BIG book value NOT osg! ;)

as I was corrected by mr NICEIC man on a previous inspection! :|

 

stringy

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I thought exactly the same as specs and stringy :p Do i get a bite aswell then? ]:)
better make it a large butty robbo your not going to have any left at this rate

 

Robbo

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What does it say for a 16A?

(Up the parents house, not got my regs book sorry)

 

stringy

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The values in the little red book OSG are the "rule-of-thumb" 80% values..

that allow for increased heat in a conductor during earth fault!

NICEIC quote these 80% values as the max value when testing cold conductors..

as it is generally accepted that if cold less than 80% of max from Big book..

then in the event of a fault the big book max will not be exceeded!

{remember cables will heat up during fault!}

& thus the MCB will still trip fast enough!

BUT the value that goes on your certificate IS the BIG book value NOT osg! ;)

as I was corrected by mr NICEIC man on a previous inspection! :|
ooops ive been putting the osg values down Blushing

you would have thought my boss would have noticed that, hmm i wonder if he even checks them lol

 

stringy

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What does it say for a 16A?(Up the parents house, not got my regs book sorry)
16a 2.87 in the big red book

16a 2.32 in the small red book

:^O

 

Shakey

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The values in the little red book OSG are the "rule-of-thumb" 80% values..

that allow for increased heat in a conductor during earth fault!

NICEIC quote these 80% values as the max value when testing cold conductors..

as it is generally accepted that if cold less than 80% of max from Big book..

then in the event of a fault the big book max will not be exceeded!

{remember cables will heat up during fault!}

& thus the MCB will still trip fast enough!

BUT the value that goes on your certificate IS the BIG book value NOT osg! ;)

as I was corrected by mr NICEIC man on a previous inspection! :|
surely the value that goes on the cert is the value you measured or calculated? ;)

you COMPARE that with the value in the book

 

Shakey

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The values in the little red book OSG are the "rule-of-thumb" 80% values..

that allow for increased heat in a conductor during earth fault!

NICEIC quote these 80% values as the max value when testing cold conductors..

as it is generally accepted that if cold less than 80% of max from Big book..

then in the event of a fault the big book max will not be exceeded!

{remember cables will heat up during fault!}

& thus the MCB will still trip fast enough!

BUT the value that goes on your certificate IS the BIG book value NOT osg! ;)

as I was corrected by mr NICEIC man on a previous inspection! :|
additionally the rule of thumb allows for the fact that when measuring the Zs the circuit is cold, and the resistance will be 'artificially' low, and pre-supposes that the circuit will be at normal operating temperatue when the fault happens

of course it is pretty much irrelevent unfer the 17th edition anyway, as most circuits need only be lower than 1667 ohms (can opened, worms everywhere)

but of course i am not a real electrician so i am only guessing:^O

 

Monkeyboy

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of course it is pretty much irrelevent unfer the 17th edition anyway, as most circuits need only be lower than 1667 ohms (can opened, worms everywhere)

but of course i am not a real electrician so i am only guessing:^O
I love you Shakey! and that is why we are all on THIS forum now

 
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