Am2 fault finding help!!

[Peterpedroo]

Recently took my am2 and passed everything but fault finding. I fount 7/7 faults but I worded three of them wrong could. 

For example I got a bad insulation resistance reading on one of the circuits and I didn't know if it was a short circuit or not. 

Could anyone help me on what readings I would be getting with either the continuity or insulation resistance test if it was a dead short? 

 

[roys]

Hi Peter

It would be productive if you you tell us what readings and why you think you should get, then we will help / guide you in the right direction if you are of the mark.

 

[Peterpedroo]

Last time I had a insulation fault on the co2 circuit from the spur between line and earth. The reading was very low on the insulation resistance fault and I put it down as a short circuit, does that sound about right? 

Thanks

 

[apprentice87]

Not that i have ever done this test, but i would never have put "short circuit" I would have put "L/E fault, xxx ohms"

john..

 

[Peterpedroo]

I think I have to say if it is a short circuit or a high resistant joint etc 

 

[apprentice87]

It is not right for me to comment as i am not qualified and have never done this test, but it would hardly be a "high resistance joint" as you should obviously not have any joints L/E

You would not have a "short circuit" L/E either as you would hardly have any sort of circuit that involved L/E other than a fault path.

You said you found an "insulation fault, L/E" What was wrong with putting that as the answer?? Seems a perfectly good answer to me!!

The others [that know what they are on about] will be along soon, they wil be able to help you.

john..

 

[Tony S]

High and low resistance have a value measured in ohms, for any test you state the value. Be it micro ohms µΩ to tera ohms TΩ they all have a value.

As an apprentice I got my arse kicked by my mentor for putting IR & CR OK on a motor test report. In big red letters was “WHAT DOES OK EQUATE TO?”

 

[apprentice87]

Hi Tony,

What you think though?? I think the OP just had a bit of a crisis of confidence.. If he had just put what he thought in the first place "Insulation fault L/E" and the value as you state, then he would have passed?? What you think??

john..

 

[Peterpedroo]

I didn't actually write the result and when I retake it again. It would help if I knew just to put L and E fault 

 

[apprentice87]

Yes, but describe what the fault is, and any value associated with it [as Tony said] as in "insulation fault L/E [500k ohms]" or whatever

[That is what i would do anyway]

With exams in general, always show workings out for mathematical questions. This means that even is the answer was wrong, but the examiner can see that you know how to do the workings out, but that you just made a simple mistake, you could well still get marks.

and in written answers, try to word them so that the reader can work out what the original question was, so if asked what is an OCPD? You would say "An OCPD is a device for limiting overcurrents such as overload and/or fault currents in a circuit"

john..

 

[Peterpedroo]

Thanks mate I will write the recordings down. What would be a example of a short circuit on a ring circuit how would I find it? 

 

[apprentice87]

A L/N fault caused by whatever..

Simple IR test between L and N would give a reading off the low end of the scale of the meter like 0.0 ohms. [as the meter would be trying to read in M ohms] If you then tried the meter on the continuity [low ohms] range, it would give a reading of whatever the conductor resistance was out to the fault and back, plus the resistance of the fault itself. Could/would be a reading of either 10's of m ohms [note little "m"] or a few ohms depending on cable length and fault.

You would have to break the circuit down into sections and test each length of cable to pinpoint the faulty length.

john

 

[roys]

If you clip your leads together on your insulation tester and press test you will see what your meter shows for a dead short.

Next hold your leads apart you will see what your meter will read for a "perfect" insulation result.

There will of course be results in between these two extremes, and it is learning what is acceptable, what will get better and what will get worse that will come with experience and a bit of mentoring.

Feel free to keep asking, as I know what it feels like when something is not sinking in.

 

[Tony S]

Hi Tony,

What you think though?? I think the OP just had a bit of a crisis of confidence.. If he had just put what he thought in the first place "Insulation fault L/E" and the value as you state, then he would have passed?? What you think??

john..

xΩ L→E which is below the minimum of xMΩ required.

For a satisfactory IR test what ever you do don't write ∞ (infinity), give it a value <499MΩ or whatever your meter goes up to,

As to how you find the fault is a different matter. My test procedures won’t be in line with the prescribed methods required by the C&G.

 

[apprentice87]

Hi Tony,

Got to be fair that is an excellent "model answer"

john..