2391 exam question?

[Flakey]

hi there.
had a question in the exam just wanted to see if the answer was correct or not .
Q : earth electrode was tested 3 figures obtained were as followed: 158 ohm, 160 ohm, 162 ohm
A: 158,160,162/3 = 160 ohm?

the figures may not have been right but is this the method? I know the (Rt) reciprocal method but thought that because they stated it was an earth electrode then you take the mean of the three resistances that are taken i.e with t1 test rod 10x distance away based on the length of the earth rod and t2 in between Earth rod and t1 take reading. than with t2 6 meters further away from the earth rod take reading. than t2 6 meters nearer earth rod take reading.

many thanks

James

 

[cossie400]

Yep, add the 3 values together and divide by 3

 

[Flakey]

Yep, add the 3 values together and divide by 3

Phew cheers mate thought i was trying to be too clever .

 

[Flakey]

If anyone can recite any of the questions would be great as all is a blur once you leave the exam

Another question:
Q what is the purpose of the earth fault loop impedance test.
my answer : the purpose of the EFLI test is to confirm that the test result is satisfactory to allow current to flow so the protective device will operate withing the desired time!

i think my wording was crud to be honest but hope that explains it in some way for a few points

 

[SirKit Breaker]

If anyone can recite any of the questions would be great as all is a blur once you leave the exam

Another question:
Q what is the purpose of the earth fault loop impedance test.
my answer : the purpose of the EFLI test is to confirm that the test result is satisfactory to allow current to flow so the protective device will operate withing the desired time!

i think my wording was crud to be honest but hope that explains it in some way for a few points

Sounds Ok, you could have added, that it confirms an earth path, but i wouldnt lose any sleep over it.

Cheers............Howard

 

[loop3]

To ensure that the efli is sufficiently low, (the max value permissible is tabulated according to the protective device) to allow enough of the PFC to flow under fault conditions, thus activating the protective device within the time specified by bs7671. Note. Several factors affect the disconnection time.

 

[loop3]

You'll miss points for not being specific. But you'll still score where you were right. My mate works for cg.