2391 Past Exam Paper

[spark 68]

or Zs measured < Zs/1.2 tabulated

other ambient temperature correction factors are

0 - 0.96
5 - 0.98
10 - 1
20 - 1.04
25 - 1.06
30 - 1.08

as you can see you add 0.02 per 5 degrees rise in ambient temperature.

 

[Spazz]

I will stick with the 0.8 rule as well as I am still lost - I will see if the tutor can explain it so I can understand it

 

[spark 68]

For the 2391 you need to show your working out and use the method they ask for, so you really need to know both.

 

[telectrix]

the 0.8 factor is to compensate for the difference in resistance of the cable between the 20deg.C. that you measure at , and the 70deg.C. max. operating temperature of the cable.

 

[spark 68]

Yes Tel, but the 0.8 is a multiplier, the rating factors are divisors

 

[brucelee]

for the question multiply you max 100% BS 7671 tabulated value by 0.8 to get the maximum measured value of 80% of bs7671 to compare your test results to if its lower than the 80% max measured values then circuit complies the OSG and GN£ have the 80% values and the regs has the 100% values

so eg

1.07 x 0.8 = 0.856 so if the mesured value less than this then complies

 

[Spazz]

Can someone give me an example of the faumula I need to use please.

Im not with it much today and really not in the mood to be doing this - but it has to be done - exam in 3 weeks

 

[brucelee]

the 1.2 correction factor is for a cable bunched or incorporated in a multicore 70C PVC cable
Xlpe is 1.26 or 1.28 depending on max temp

 

[Spazz]

formula please?

 

[brucelee]

draw a simple table with

max Bs761 measured values max measured 80% Ok or not

1.07 0.8 0.856 Zs complies


or


1.07 x 0.8 = 0.856ohms > 0.85ohms if thats what your measured was acceptable

I will dig my noted out of to colleg now lol

 

[spark 68]

To calculate Max Zs for MCB's, without the BGB or OSG, rule of thumb method


for example, 32A B type MCB

Types
B = X5
C = X10
D = X20

Uo = 230V


(Uo/(Type X In)) X 0.8

In X B =
32 X 5 = 160
Uo / 160
230/160 = 1.4375 = 1.44 ( to 2dp) two decimal places
1.44 X 0.8 = 1.152 = 1.15 ( to 2dp)

 

[Spazz]

Dont forget all I have in the exam is the table on the sheet and my memory and I cant remember the whole table as well.

Thanks everyone - I will look at it again tomorrow as I not going to college tonight!

Im off for the night as well - bloody customers not paying me and I don't know what the hell Im going to do!

 

[Silly Sausage]

Dont forget all I have in the exam is the table on the sheet and my memory and I cant remember the whole table as well.

Thanks everyone - I will look at it again tomorrow as I not going to college tonight!

Im off for the night as well - bloody customers not paying me and I don't know what the hell Im going to do!

Good Morning Nicholas...

As Ze has been given in the question, for the 1st part you need to remember and use the formula given on page 113 (old GN3) after the 2nd highlighted block. You need to memorize this and the one below (I'm sure both formulas can be simplified, swear I did it once, see if I can find it!)
You don't need to remember the correct factors, they've given you one.

The 2nd part is the 'Rule of Thumb' method


Understand & remember the above, it's an easy & quick 15 marks if it comes up in the exam, happy days!

 

[needasparks]

Also another one - I don't do an 3 phase work hardly

Am I right in saying the test voltage of an IR test on 400V three-phase kiln is 500v DC?

Interested in when you would test at 1000V and what on.