confusing figures between net and regbook

[martin mcguinness]

Hiya lads a stupid query (maybe )
i was filling in an EICR for a mate and had left my on site guide and reg book at home so i decided to check the net for max zs values for 60898 type b mcbs 6a. 16a, 32a, and 40a but the figures didnt match up with the ones in the reg book. so question what sites do the lads recommend as i was dong it on a mobile device so ended up giving in and waiting till i got hame

thanks
mad spark

 

[Taylortwocities]

Most guides (and that includes the OSG and the Internet) may have a "rule of thumb" percentage of 80% calculated on the 'regs' table Zs values.
That may account for the difference.

Also the Zs figures recently have changed in the Bible, but the Internet will rely on people like you and me to keep it up to date. And I CBA!

 

[martin mcguinness]

i think keep a photocopy of max zs tables in folder with the certs (have to fill in by hand as dont want to pay for software )

 

[westward10]

Got them in my head.

 

[Wilko]

Got them in my head.

There are pills for that you know ...

 

[Ian1981]

Hiya lads a stupid query (maybe )
i was filling in an EICR for a mate and had left my on site guide and reg book at home so i decided to check the net for max zs values for 60898 type b mcbs 6a. 16a, 32a, and 40a but the figures didnt match up with the ones in the reg book. so question what sites do the lads recommend as i was dong it on a mobile device so ended up giving in and waiting till i got hame

thanks
mad spark

Easy way to work out type b mcbs is 218.5 volts divided by 5x their rated current
10x for type c
20x type D
Saves you needing to look it up if you've forgotten your books
Fuses ...... not so easy with out a reference to hand

 

[westward10]

For mcbs just memorise a few. For example if you know a 10A you can easily work out a 20A, 40A by just doubling the 10A value. Must admit I knew nearly all of them off by heart until the values changed and my brain now struggles to adapt

 

[Rpa07]

Easy way to work out type b mcbs is 218.5 volts divided by 5x their rated current
10x for type c
20x type D
Saves you needing to look it up if you've forgotten your books
Fuses ...... not so easy with out a reference to hand

Where did you get that gem from?
Didn't I say that you were a clue'd up spark!

 

[Ian1981]

Where did you get that gem from?
Didn't I say that you were a clue'd up spark!

230v x cmin 0.95= 218.5v
32 type b x5 is 160amps
218.5/160= 1.37 ohms.

 

[Rpa07]

Lovely - data inputted - thanks a lot. Sometimes when you look at the mathematics of stuff it's like poetry.

 

[Ian1981]

230v x cmin 0.95= 218.5v
32 type b x5 is 160amps
218.5/160= 1.37 ohms.

230v x cmin 0.95= 218.5v
32 type b x5 is 160amps
218.5/160= 1.37 ohms

Lovely - data inputted - thanks a lot. Sometimes when you look at the mathematics of stuff it's like poetry.

Yeah it's just the basics ohms law v/IR
Think the old bs 3871 where
Type 2 x 7rated current
Type 3 x10 rated current

 

[telectrix]

and these calcs. go out the window when voltage is more like 240V, and generally, cables will never be operating at their max. temp. of 70 deg.

 

[Ian1981]

and these calcs. go out the window when voltage is more like 240V, and generally, cables will never be operating at their max. temp. of 70 deg.

This is true however the max values are based on a worst case scenario as bs 7671 tends to er on the safe side of things.