one of many to follow Im sure but ......

[lofty84]

A circuit is protected by a 32A type B breaker. if the value of Ze is 0.8 ohms what will be the maximum allowable value for (R1+R2)


how do I go about finding this in the IEE regs (red one) please ......

 

[telectrix]

your max. value for Zs is 1.44ohms ( table 41.3. 32A type MCB). therefore use Zs=Ze+(R1+R2)

 

[SimpleSimon]

Its in the regs table 41.3 pg. 56. These values are given at fault conductor operating temp. Where as the ones in OSG are at 80% compared to the regs which are given at normal operating temp.

Sent from my GT-I9100 using Tapatalk

 

[lofty84]

cheers telectrix and Si jacc ;-).

So with those details the maximum allowable R1+R2 value is going to be 0.64 ohms

1.44 - 0.8 = 0.64 ohms



well that was nice and easy

 

[malcolmsanford]

cheers telectrix and Si jacc ;-).

So with those details the maximum allowable R1+R2 value is going to be 0.64 ohms

1.44 - 0.8 = 0.64



well that was nice and easy

Not quite try again

 

[lardy]

1.44 x 0.8 = 1.152

 

[i=p/u]

32A x 5 = 160 230/160=1.44 x0.8 =115 ohms is you max allowed take away 0.8 = 0.35 / by cable in table 9A osg will = your length

 

[lofty84]

I thought if u x by 0.8 you had to divide by pie

 

[telectrix]

why use the 0.8 value. the question asks for the max. value. the max. value for Zs is 1.44.

 

[lofty84]

my answer sheet says the correct answer is 0.64 ohms and that worked with what telectric and SI were saying. i = P/u u have just messed that up lol, how come you are timesing the 32A breaker by 5 snd doing all the other maths.......

 

[darren]

my answer sheet says the correct answer is 0.64 ohms and that worked with what telectric and SI were saying. i = P/u u have just messed that up lol, how come you are timesing the 32A breaker by 5 snd doing all the other maths.......

.64 ohms if the ze measured is .8 , max r1+r2 depends on what the measured ze is??

 

[i=p/u]

Cause im good an like to teach you fully and will be teaching electrics when im 55 probably

 

[telectrix]

.64 ohms if the ze measured is .8 , max r1+r2 depends on what the measured ze is??

if you don't have the brb to hand, you can calc. the max. ZS for any MCB . it's 230/( 5 x In ) for a B type, for c and d types the factor 5 becomes 10 and 20 respectively.

 

[lofty84]

So whos right ....

 

[lofty84]

I see so if I had a 40 A type d breaker and I wanted to know the max zs I can go

230/40X20 = 0.2875

doesnt sound right to me ...

 

[i=p/u]

X 20 for d

 

[malcolmsanford]

No lofty a type d would be 20 times so it would be 40*20 = 800 and then 230/800 = 0.2875 and table 41.3 is 0.29

 

[lofty84]

In the event of an earth fault on the HV side of a substation the LV instillation may be affected by

a)V
b)U
c)I
d)Isqt

im trying to use the contents page in the brb page 3 to find something to go on but cant ...

 

[lofty84]

found substations in the index and under reg 442.2 it says either Uf U1 or U2 so it must me U. what does U represent again please ..

 

[malcolmsanford]

It is no good us giving you the answers really but a guide have a look and read of section 442 of the BRB