2395 Written Question, Help please

[Joe Hyde]

Question ( worth 15 Marks )
Describe how a test for earth fault loop impedance, by direct measurement may be carried out on a circuit supplying a three-phase steamer .

My answer would be
I would not measure Zs on this circuit as it would contravene EAW Safe working practices. The value for Zs can be achieved without working near live conductors by R1+R2+Ze.

Comments :- I guess my answer would not get me 15 marks !

Can Anyone out there give me a Model answer to the question ? i.e. What are the examiners looking for ?

Thanks

JJ

 

[Jurasic Spark]

Ok, if they specifically want you describe a direct measurement as it says in your OP then measure it at the live side of the contactor. Then do R1 + R2 from bottom of contactor to motor and add it all together. You would need to do chapter and verse on instruments, expected readings, safety precautions etc to get the 15 pts.

I totally agree that there is no need to do it as a direct live test. It can be done dead and adding to Ze

 

[Joe Hyde]

Thanks,
I have my written Exam on the 12th Feb !
( % of candidates who passed the past paper June 2012 was only 24% !!!)
I have just found the Chief examiners report for this past paper , Their comments on the answers they recieved are below

Many candidates failed to consider the safety requirements when carrying out tests for Zs typically isolating the circuit to access live terminals and returning to energise without securing the test area. A large number of candidates carried out the test at the terminals of the equipment and not at the local isolator. Many failed to identify the need to confirm that test leads complied with GS 38 and a number could not correctly identify the test instrument. Some candidates appeared to be confused by the fact the circuit was for a three phase steamer. A worrying number of candidates carried out the test using a low resistance ohmmeter and subsequently score zero for this question.

 

[SirKit Breaker]

If 15 marks are on offer, than they want 15 different points to be mentioned. You will get marks for any of the points that you say so if you mention 7 you will get 7, and so on.

You will score zero with your answer, because it has specifically asked you to do it by DIRECT MEASUREMENT.

Cheers.........Howard

 

[SirKit Breaker]

Have a read of Joes post at the top.

You must mention

Seek permission to isolate.
Safe isolation procedure. Lock off tag off. post a notice
Prove dead using approved voltage indicator and proving unit.
expose terminals.
Calibrated Earth Fault loop impedance tester, visual inspection of condition.
Test leads to comply with GS38, and visual inspection of condition.
Make sure work area is safe prior to de isolation and energisation.
Explain the test procedure in detail, so on three phase you need to emphasise that you tested on each phase.
The test result and how you interpreted it and recorded it and confirmed it was or wasn't in spec.

This lot is not a comprehensive list, and it is not in the correct order, but you can see the depth of knowledge you need to demonstrate in you answer.

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