hey everyone.. quick question.

[robinson]

Hey everyone sorry i havent been on here recently!

wondered if anyone could help i have my level 3 exam tomorow,

ive took the week of revise to REVISE HARD! which i have been! although i have been doing cable calcs for ages and can normally do them. Although i just done a practice paper ( in which i have to answer sheet to compare)

and i have the mcb size wrong??

whats going on heres the question

A 230v, 6 kW single phase load is supplied by single core pvc cables in high impact pvc conduit fixed to the surface of a brick wall over a distance of 20 metres. The circuit is protected by a type C circuit breaker. The temperature is 35 degrees Celsius.

Determine

a. the design current (1 mark)

b. the installation method (1 mark)

c. the circuit breaker rating (1 mark)

d. the correction factor (1 mark)

e. the minimum cable rating (1 mark)

f. the minimum cable size. (1 mark)

heres the answers... it says

a. 6000/230 =26 A

b. from table 4a1 method 3. (here i would normally look on page 259 in my regs book, but i cant find method 3 or find the table in my on site guide? whats it on about?

c.32A ( i chose a 30 A, why have they chose 32)

d. from table 4c1 0.94 ( i got this but again wheres this table)

e 32/0.94= 34 A ( got wrong cause i chose a 30A breaker)

f From table 4d1a col 4 6mm2 41A ( again i got this wrong choosing the wrong breaker? and if i chose a 30 A its a 4mm cable so whos right? also where is this table lol!

any help would be really greatfull ive done loads of practice papers! and this has only just happened!

Really appreciate any help.

 

[ianmacd]

B) its method 20 from 4A2 (ref C)

c) MCB's are 32A (or maybe 25A but that would just nuisance trip). 30A would be rewireables etc.. MCB's tend to be in sizes 6,10,16,20,25,32,40,45.

d) 4B1

f) 4d1a col6 pg 274

Although that doesn't check for voltage drop. You sure its a 17th edition question?

 

[dariusthemead]

lot of working out for 6 marks, leave it while last, if youve got enough marks for a pass etc dont worry about it.

 

[ianmacd]

To be honest this should be something that becomes second nature and (IMO anyway) is not that onerous to work out.

As I said above too, not sure why they are avoiding the VD issue there since they did specify the length.

 

[meerkat]

a. 6000/230 =26 A Correct

b. from table 4a1 method 3. (here i would normally look on page 259 in my regs book, but i cant find method 3 or find the table in my on site guide? whats it on about? Pge 261 BRB 7671 REF METHOD B

c.32A ( i chose a 30 A, why have they chose 32) Pge 49 Type C (BSEN 60898 MCB) next size up from 26Amps, In = 32 Amp, there is no 30A type C MCB listed.

d. from table 4c1 0.94 ( i got this but again wheres this table) Pge 267 BRB 7671, Ca for 35C = 0.94.

e 32/0.94= 34 A ( got wrong cause i chose a 30A breaker)

f From table 4d1a col 4 6mm2 41A ( again i got this wrong choosing the wrong breaker? and if i chose a 30 A its a 4mm cable so whos right? also where is this table lol! Table 4D1A, Column 4 Ref Method B, It = In /Ca = 32/0.94 = 34 Amps, Table 4D1A Column 4 next up from 34 Amp is the 41Amp of the 6mm Cable.

Remember to use the Fault protection Formula, Ib < In < Iz to comply with BRB 7671 in this case Ib =26a < In =32a < Iz =41a, I hope this helps (MEERKAT)

 

[robinson]

cheers everyone! as always i get a 5* answer!!! thank you appriciate it!!!

another two questions im struggling on ill post them up in ten mins

---------- Post Auto-Merged at 19:48 ---------- Previous post was made at 19:22 ----------

anoter two....

identify the devices used in a 400ka three phase four wire 400v insallation (tn-c-s) with a rated short circuit at the intake of 46ka to provide

a.) overcurrent protection

b.) earth fault protection

c.) isolation

cheers!

second

a schedule of test results is to be completed for a ring final circuit. The resistance values of the phase and cpc loops are measured as 0.6 ohms and 1 ohm respectively. The value of Ze is 0.35ohms.

a.) deteermine the expected value of R1+R2 to be compared with the test reading.

b.) Determine the expected value of Zs

c.) indicate the symbol to be inserted on the schedule of test results for the ring final circuit only

many thanks

 

[steptoe]

BS88 fuses

0.6 + 1.0 / 4

no idea what 2 c is,

 

[ianmacd]

no idea what 2 c is,

A tick in the ring column?

 

[robinson]

hey thank you!! yeah c is a tick! haha they tryin to trick me! got the exam tonight ray just one more qucik question

it maybe easy n just acting stupid but

whats tyhe different between a switch fuse and a fuse switch?

---------- Post Auto-Merged at 15:13 ---------- Previous post was made at 13:49 ----------

iknow now thanks! headbang

 

[meerkat]

Hi Robinson,

A fuse switch is generally found at the start of an industrial/commercial system, the fuse sits on a carriage and the whole carriage is thrown in or out by the operation of the switch itself.

With a switch fuse the fuse remains in place and a connector makes or breaks the supply to the circuit.

I hope this helps, (MEERKAT)