2391 question

[i=p/u]

15. An earth electrode resistance test has been carried out, and the following results were obtained: 128Ohms, 120Ohms and 134Ohms. Determine the value of RA to be recorded on the certificate. Show all calculations.

il get by with a little help, ty

id say add them together and divide by 3 to get awnser... i dont think it wants you to go into the effectiveness of the values given..help help i think

 

[i=p/u]

anyone

 

[Deleted member 26818]

The value of Ra is the mean or average of the of the three readings.
So yes, add the three readings together, and divide by three.

 

[i=p/u]

just there is more than 5% on some of them and we were taught about deviation and a longer sum... but im sure they just looking for the average ty

 

[i=p/u]

10 State the effect each of the following would have on the measured insulation resistance of a conductor.

a) decrease in length increase

b) decrease in CSA none

c) decrease in temperature none

 

[spark 68]

Except a) = increase

That almost looks like a mixture of two different 2391 questions

 

[Deleted member 26818]

Why do you believe that a decrease in conductor length will result in a decrease in insulation resistance?
What do you believe causes an increase or decrease in insulation resistance?

 

[i=p/u]

19 A 200mA general purpose RCD to BSEN 61008 is to be tested to ensure it operates within specification. State the

a) test instrument to be used rcd tester

b) the maximum test current to be applied during the test 500mA

c) the maximum acceptable tripping time during the test in b) above 40ms min 150 max

 

[i=p/u]

things like length of circuits , testing more than 1 ciruit at a time

Why do you believe that a decrease in conductor length will result in a decrease in insulation resistance?
What do you believe causes an increase or decrease in insulation resistance?

 

[spark 68]

RCD question

b) 200mA
c) 300ms

only 30mA (or less) RCDs used for additional protection are tested @ 5X I delta n

general purpose RCD to BSEN 61008 max = 300ms

general purpose others max = 200ms

 

[i=p/u]

kk spark, i see its not in book as such but you use your noggin and follow suit

 

[spark 68]

things like length of circuits , testing more than 1 ciruit at a time

Tip: read the question, it mentions a conductor, not a circuit

as the length is less, you will have less leakage so a Higher IR reading

 

[Deleted member 26818]

In general, the greater the area of insulation there is, the lower the resistance.
As such all of the answers should be 'increase'.

 

[i=p/u]

weeeeeeeeeeeeee:77:

 

[spark 68]

As such all of the answers should be 'increase'

are you sure spin ?, I did mine in December, and Iam almost sure we were told the Csa had no effect on an IR test.

I will stand to be corrected, and bow to superior knowledge

 

[i=p/u]

but would it not be proportional ahhhh ok i do get what you saying

In general, the greater the area of insulation there is, the lower the resistance.
As such all of the answers should be 'increase'.

 

[i=p/u]

i thought changing csa didnt matter about insulation resistance so who right, me me me

 

[Deleted member 26818]

I think you will have to decide yourselves.
Consider why insulation resistance would decrease, then apply it to the various scenarios in the question.

 

[ringer]

RCD question

b) 200mA
c) 300ms

only 30mA (or less) RCDs used for additional protection are tested @ 5X I delta n

general purpose RCD to BSEN 61008 max = 300ms

general purpose others max = 200ms

Spark, where did you get this information from regarding testing at 5X ?
And the 300ms for BSEN61008, all others at 200ms ?

 

[spark 68]

Hi Ringer,

general purpose RCD to BSEN 61008 max = 300ms

general purpose others max = 200ms

This is in the OSG, but excludes S types and the types which are 30mA or less which trip in the 40ms required @ 5 X I delta n for additional protection.

Spark, where did you get this information from regarding testing at 5X

This is also in the OSG, but I got the info. from elsewhere, which escapes me at the minute.

red OSG (cos I haven't got the green one yet) pages 91 and 92 sections 11.2, 11.3, 11.4 and 11.5