Basic domestic testing Qs

[newtothis]

I'm just look for confirmation thoughts on this first point.

I think when IR testing on an existing installation and it’s not practical to remove all vulnerable equipment. I can connect L to N to earth and test at 500V on the circuit I’m testing.


The question is if I do the above, could it result in, or contribute to; the measured ZE + R1+R2 not equalling the measured ZS ?


In my case it’s the downstairs RFC it includes the kitchen. It's hard to without causing a bit of damage to access a FCU with a neon to the cooker hood which has an extractor fan and 4 light bulbs.

Thanks in advance for any help, and there's no need for undue diplomacy, or softly softly language, if I'm barking up the wrong tree. :bucktooth: I'd rather know straight !

 

[newtothis]

L to N combined to E

 

[Simonslimline]

I'm just look for confirmation thoughts on this first point.

I think when IR testing on an existing installation and it’s not practical to remove all vulnerable equipment. I can connect L to N to earth and test at 500V on the circuit I’m testing. (Yes this is acceptable)


The question is if I do the above, could it result in, or contribute to; the measured ZE + R1+R2 not equalling the measured ZS ? (Not sure what you mean by this)


In my case it’s the downstairs RFC it includes the kitchen. It's hard to without causing a bit of damage to access a FCU with a neon to the cooker hood which has an extractor fan and 4 light bulbs. (The FCU should be accessible)

Thanks in advance for any help, and there's no need for undue diplomacy, or softly softly language, if I'm barking up the wrong tree. :bucktooth: I'd rather know straight !

See my replies in Blue mate.

 

[newtothis]

Thanks for your reply, appreciate it mate !

(Not sure what you mean by this)

I'll use my cooker radial as an example all measured values
[FONT=&amp]ZE 0.14ohm TNS R1+R2 0.12ohm ZS is 0.67ohm should it be 0.26ohm or close.
Tearing what little hair I have left out LOL

Added
6-2.5 mm2 cable
32A Type B MCB

I know the R1+R2 is right from looking up the OSG - 10.49 PM it tallies with the length of the cable.

Checked the ZE several times.
[/FONT]

 

[Simonslimline]

You are doing a high current test aren't you?

What tester are you using?

Is it in calibration?

 

[Pete999]

IR testing is a test to ensure the IR complies, it will have no bearing on RI+R2 these are the resistances of the line conductor and the cpc in series added together using a low resistance ohmmeter, continuity on you MFT

 

[newtothis]

You are doing a high current test aren't you?

What tester are you using?

Is it in calibration?

Yes for the ZE no for the ZS because of the RCDs
Tester is in callibration.

 

[Simonslimline]

Are you familiar with the alternative Zs method?

Doing a No trip test is not very accurate to be honest.

 

[newtothis]

IR testing is a test to ensure the IR complies, it will have no bearing on RI+R2 these are the resistances of the line conductor and the cpc in series added together using a low resistance ohmmeter, continuity on you MFT

Thanks Pete.

 

[Simonslimline]

Actually not really sure if you can apply this test to a RFC.

 

[newtothis]

Are you familiar with the alternative Zs method?

Doing a No trip test is not very accurate to be honest.

Not familiar, have you got a link to an explanation please, soz to be a pain

 

[Simonslimline]

Safely isolate circuit under test.

Link Line & CPC at furthest point of circuit.

Test at the DB across the (isolated) load side of the Circuit breaker and the live supply side of the RCD.

Carry out test, record result.

 

[Pete999]

Actually not really sure if you can apply this test to a RFC.

What tests are you referring to mate????

 

[Simonslimline]

What tests are you referring to mate????

Alternative Zs which by bypasses the RCD mate.

Obviously no trouble with a radial circuit but in this case it's an RFC.

 

[Pete999]

Alternative Zs which by bypasses the RCD mate.

Obviously no trouble with a radial circuit but in this case it's an RFC.

Sorry thought you was talking about something else, that'll teach me

 

[newtothis]

Safely isolate circuit under test.
Do you mean just isolate to make Line and CPC connection, then energise ?

Link Line & CPC at furthest point of circuit.

Test at the DB across the (isolated) load side of the Circuit breaker and the live supply side of the RCD.

Carry out test, record result.

Put a Q in blue

 

[Simonslimline]

Put a Q in blue

Isolate the MCB. Then test from the isolated side of MCB and Live supply side of RCD. This way you are performing the exact same EFLI test except bypassing the RCD so a high current test can be carried out which is more accurate.

The line is connected to earth at the end of the circuit. So you have a PD between the isolated Circuit breaker and the 230 on the supply of the RCD.

 

[Simonslimline]

Put a Q in blue

Don't Re-energise the circuit until you have removed the temp link and terminated conductors back to there respective terminals.

 

[newtothis]

Ye haaw, Thanks mate, I've got it !

 

[Simonslimline]

Ye haaw, Thanks mate, I've got it !

And if in doubt just draw it out. This way you will see the path the test current takes.

 

[newtothis]

what was confusing me is I knew it was a live test, and the supply L side is live even if the board isolated.

So in summary, can I say if my measured ZS doesn't exactly equal (or is a significantly out) with my R1+R2 + ZE
Using the low current ZS test can be a factor, along with user error on the testing and loose connections, poor design on the circuit ?

Failure on the IR test is not a contributor to the above, if it's down to something that should have been disconnected?

 

[Simonslimline]

Generally a low current loop test is not that accurate and it is better to perform a high current test whenever possible.

If anything, the measured Zs would normally be lower than the calculated value due to parallel paths via bonding etc.

User error could play a part and not making good contact on the terminals when carrying out the test could contribute to higher than calculated reading.

 

[newtothis]

Thanks very much Simonslimline, I'm driven to get this right. I'm going to slow down and double check everying I do.

I have mates who are sparkies and seem mega competent. They admit their knowledge of testing is a bit sketchy.
I'm also working with sparks at the moment who are very well up on testing, but don't take too seriously.
Telling me stories about skipping parts of the testing cos they didn't like the person they were testing for etc etc...
I'm laughing with them at their stories, but inside I don't agree. :teeth_smile:

 

[Simonslimline]

Thanks very much Simonslimline, I'm driven to get this right. I'm going to slow down and double check everying I do.

I have mates who are sparkies and seem mega competent. They admit their knowledge of testing is a bit sketchy.
I'm also working with sparks at the moment who are very well up on testing, but don't take too seriously.
Telling me stories about skipping parts of the testing cos they didn't like the person they were testing for etc etc...
I'm laughing with them at their stories, but inside I don't agree. :teeth_smile:

Sadly you will see this when onsite, depending where though i guess. I have seen this attitude and it all comes down to wanting to be finished faster and being a lazy T@£$%.
If it's there --- in court then its there problem i guess.

Personally i couldn't sleep without knowing i had done my job correctly and verified the safety of my work.

Chris kitcher does a great book on Inspection & testing, well worth a purchase.

 

[Richard Burns]

Remember when testing Zs normally you are also testing through the RCD and the MCB which are not included in the Ze test or the R1+R2 test and occasionally these items can exhibit a noticeable added resistance to the test. This may be what you are experiencing.

A poor design of circuit would not contribute to a variance between ZS and Ze+(R1+R2); if the circuit were poorly designed then they would both be high.

An IR test failure would not affect a Zs / ZXe(R1+R2) variance, although a really bad fail where any conductors were touching could reduce the measured value in both cases; although other factors would come into play before you could do the live test!:sorcerer:

A small diagram for the alt Zs test.