Retesting previous work

[chris013]

If you were to retest jobs that had been tested 5 years previously would you expect Ze to be lower or higher .RCD times to be lower or higher .Thanks Chris

 

[davesparks]

They should be the same

 

[Richard Burns]

A bit vague on the question I feel.
If nothing has changed on the installation then they should remain the same, however changes in network conditions external to the installation may raise (but probably lower) the Ze.

 

[DuaneMHunt1976]

50:50
Nothing stays the same and one meter is different from another (if i remember right a college of mine sent all their meters off for calabriation :53: any way .. they all tested on the same test board and got different results, roughly about the same but different) so the same test meter of today would give a different in 5yr im sure.
The other things is things change, bits get added and changed, even taking off a cover plate could add on resistace a fraction there and here.
Could also be your earthing, ground wet give you abit better. A pipe rusting or painted giving a bit more resistance to earth.

But it could also swing the other way, a new connection to ground or as said above the wet ground.

But over all i would say the resistance is more odds to go up over time, maybe 1ohm ever 5yr, but the test meter seeing it might see it as -2ohms or +10ohms. Its a Rough Figure .. Nothing is 1

Prim example is 1 apple and 1 apple is.. 2!! Apples if you look how reder is one apple over there other .. the taste .. the size ..the smell it gives off.. for some thing to be 1+1 it would have to be Perfection the same, but there will always be some difference just cant see them, seconds older, decay rate.

 

[davesparks]

50:50
Nothing stays the same and one meter is different from another (if i remember right a college of mine sent all their meters off for calabriation :53: any way .. they all tested on the same test board and got different results, roughly about the same but different) .

That is more likely incorrect operation of the testers than anything else. Incorrect nulling of test leads and poor contact pressure on the item being tested being likely culprits.

 

[DuaneMHunt1976]

He told me that they did COMPLAIN to the Calc Company and different makes have different tests.. it dose depend on how it dose things..

1 ohm is never 1 ohm .. it is 1.03449000400034 or some thing and if every meter is a bit different
one might see it as 1.03449000400035 and its differrent

Im not sure how it works on in a Meter, used to be a Wheat Stone Bridge
And if i was making one of them i would have it Perfect to have 3 Resisters all the same level


Nul Leads you can nul it can come back and look if there is any differences and 0.01 might pop up but odds on it will be 0.001 you just can see it as the machine will just ignore it, but this can Swing ever way



As i Explained above there is NOTHING perfect to give a Correct Reading, Rounding Down Rounding up, a machine maybe made not so perfect that for ever 10ohms it adds 0.01ohm

 

[Risteard]

Don't forget the measurement accuracy of test instruments. There is a few percentage legitimate margin of error.

They aren't anywhere near as accurate as some believe.

Plus Ze can change with the network.

 

[shanky887614]

Don't forget the measurement accuracy of test instruments. There is a few percentage legitimate margin of error.

They aren't anywhere near as accurate as some believe.

Plus Ze can change with the network.

5% is around the mark for calibration acurracy. my dmm is more accurate thab my mft

 

[Risteard]

5% is around the mark for calibration acurracy. my dmm is more accurate thab my mft

It depends. Different functions have different accuracy requirements.

A multimeter is unlikely to emit the correct current/voltage etc. though.

 

[Andy78]

It depends. Different functions have different accuracy requirements.

A multimeter is unlikely to emit the correct current/voltage etc. though.

Agreed. The use of a multimeter for any testing that is to be recorded on a certificate would likely not comply with the regs.

 

[shanky887614]

It depends. Different functions have different accuracy requirements.

A multimeter is unlikely to emit the correct current/voltage etc. though.

are you sure a benchtop multimeter is used to calibrate your mft

 

[shanky887614]

Agreed. The use of a multimeter for any testing that is to be recorded on a certificate would likely not comply with the regs.

i could use my fluke for the continuity tests as it has been calibrated so it would comply

 

[Andy78]

i could use my fluke for the continuity tests as it has been calibrated so it would comply

You might be right actually. I just checked the regs for the requirements of low resistance ohmeters. It seems they are a recommendation and not a requirement as I thought. I also thought that only equipment produced to BS61557 was to be used but can't find a reference to that either.
I'll let you off this time

 

[Risteard]

Well a battery and bell set could be used for some things (but certainly not all). However it all depends whether you want a value or simply a tick in a box. But the various parts of BS EN 61557 will specify all sorts of things which an ordinary multimeter would not meet.

 

[Risteard]

are you sure a benchtop multimeter is used to calibrate your mft

I think you will find that an instrument calibrator is quite a specific (and costly) instrument. It is not just an ordinary multimeter.