different test results on IPF readings

[MarcP]

I am a newly qualified and practicing for my enrolment on competent person scheme (on a "friendly", allready safe installation etc  etc).

Whilst repeating prospective fault current and short circuit fault current tests (using a kewtech 63 multimeter), I

get similar but not identical readings. Does it matter? examples are 3.396 Ka, 3.234 Ka, etc, The same disparity occurs om short circuit testing.

Am I worrying too much about this?

 

[binky]

this is not unusual, I've never worked out why it always varies slightly, but it does.

 

[MarcP]

Thanks Binky, appreciate this.

 

[Doc Hudson]

I am a newly qualified and practicing for my enrolment on competent person scheme (on a "friendly", allready safe installation etc  etc).

Whilst repeating prospective fault current and short circuit fault current tests (using a kewtech 63 multimeter), I

get similar but not identical readings. Does it matter? examples are 3.396 Ka, 3.234 Ka, etc, The same disparity occurs om short circuit testing.

Am I worrying too much about this?

You need to remember you are trying to establish what magnitude of current could flow if you stick a dead short across the circuit. So the voltage potential between the conductors, (which can fluctuate) and the impedance path along the circuit, through to your meter probes and meter. Which can also fluctuate depending upon how good a connection you have between leads and circuit. Imagine what happens if the voltage fluctuates up a bit and the continuity of your probe terminations goes down a bit, or vice-versa?  You also have the tolerance accuracy of the test meter itself between readings.  The sort of variations you describe don't sound that unusual to me. If it was a massive difference, (e.g.  1.234kA and 5.678kA, that would be a bit more concerning). Do the values look appropriate for the Ze and voltages on your test installation?  Your main concern is that the largest value you read is within the breaking capacity of your protective devices so it doesn't all go bang! 

Doc H. 

 

[binky]

Only time to get concerned is odd PSCC readings - I've had this twice, turned out to be a faulty Neutral out in the road. 

 

[MarcP]

You need to remember you are trying to establish what magnitude of current could flow if you stick a dead short across the circuit. So the voltage potential between the conductors, (which can fluctuate) and the impedance path along the circuit, through to your meter probes and meter. Which can also fluctuate depending upon how good a connection you have between leads and circuit. Imagine what happens if the voltage fluctuates up a bit and the continuity of your probe terminations goes down a bit, or vice-versa?  You also have the tolerance accuracy of the test meter itself between readings.  The sort of variations you describe don't sound that unusual to me. If it was a massive difference, (e.g.  1.234kA and 5.678kA, that would be a bit more concerning). Do the values look appropriate for the Ze and voltages on your test installation?  Your main concern is that the largest value you read is within the breaking capacity of your protective devices so it doesn't all go bang! 

Doc H. 

Very helpful, thanks for the explanation. It makes sense to me now.

Only time to get concerned is odd PSCC readings - I've had this twice, turned out to be a faulty Neutral out in the road. 

Wow, I hope that NEVER happens to me. Thanks for the tip though, I would always first suspect my workmanship or my testing kit. It would not occur to me that the system itself had a fault but now you've highlighted it, I'll bear it in mind. Thanks again