2391 questions

[wrighty]

hey guys, 3 days and counting until i sit the dreaded.

just doing some revision and im stuck with a particular question so any help would be greatly appreciated.

here goes.....

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.

 

[trev]

Have a go at it first Wrighty

 

[wrighty]

do you just add them together? or what.

 

[Moses]

do you just add them together? or what.

You take the average.

 

[wrighty]

thats what i thought when i said add them up, is it really that simple, knew id feel a --- n it would be simple when id asked it, but hey its better to ask n be correct than presume n fail

 

[Moses]

thats what i thought when i said add them up, is it really that simple, knew id feel a --- n it would be simple when id asked it, but hey its better to ask n be correct than presume n fail

If you don't take the risk
You'll never get the kiss

 

[One_of_them]

are you sure you just take the average?

 

[ackbarthestar]

Have a look at GN3 page 49 and then back to us with your answer. Don't forget to show ALL calculations

edit: There must be more to this question because once you have got the answer, you would have to adjust the rods and take the measurements again, I suspect.

 

[JUD]

are you sure you just take the average?

Yes. As ackbarthestar says, it's all in GN3

 

[wrighty]

128+120+134 = 382

382/3 = 127.3333

?????

 

[Moses]

128+120+134 = 382

382/3 = 127.3333

?????

Correct.

 

[SJD]

GN3 says it is inadvisable to accept readings that differ by more than 5%. I have to admit I was never sure did this mean 5% between smallest and largest value (so a range of about 7 Ohm in this case), or did this mean +/-5% from mean (so about 120 to 134 Ohm is OK in this case)? In an exam, I'd just quote the GN3 wording, but to do it for real and know what I should accept ...?