basic bad practice

[Stevesplatto]

Found this on a large testing companies website:

'Where the mains supply is connected, as will be the case for periodic testing, the protective and equipotential conductors must not be disconnected because if a fault occurs these conductors may rise to a high potential above earth. In this case, an earth-fault loop tester can be used to verify the integrity of the protective system.'

So wrong, I wonder how many wrongly measured Ze readings they've reported (parallel paths). I emailed them suggesting they might consider turning of the main isolator to reduce the risk of the conductors rising to 'a high potential above earth' before disconnecting the main earth for a real Ze test..
Big company as well..

Ride em cowboy!

 

[ringer]

I disagree with what you say. I believe that they are referring to sites which run 24/7 and cannot be switched off entirely. They are not proposing to measure Ze, but Zs. Measuring Zs will , assuming acceptable results, confirm adequate earthing for protective devices to operate. They mention the protective system, which is the combination of the distributor's earthing system and the bonding (in parallel).

 

[Silly Sausage]

NEVER disconnect the earthing from an installation with people in it!

 

[jase]

Found this on a large testing companies website:

'Where the mains supply is connected, as will be the case for periodic testing, the protective and equipotential conductors must not be disconnected because if a fault occurs these conductors may rise to a high potential above earth. In this case, an earth-fault loop tester can be used to verify the integrity of the protective system.'

So wrong, I wonder how many wrongly measured Ze readings they've reported (parallel paths). I emailed them suggesting they might consider turning of the main isolator to reduce the risk of the conductors rising to 'a high potential above earth' before disconnecting the main earth for a real Ze test..
Big company as well..

Ride em cowboy!

doesnt say anything about measuring Ze there, what they are saying is that instead of measuring Ze on an energised circuit it is ok to use a EFLI tester to measure Zs, this would determine that earthing arrangements of that circuit are adequate, have they emailed you back yet????

 

[Brightspark2]

As said turning off a large installation that runs 24/7 is not going to happen. 95% of EICR I do are like this. Massive warehouses that dont stop or data centres that CANNOT be turned off.

You couldnt walk into a food production factory like walkers where downtime cost thousands and ask them could I switch the main switch off so I can gain an accurate Ze, its not going to happen.

 

[SirKit Breaker]

NEVER disconnect the earthing from an installation with people in it!

And never energise an Installation with the main earthing conductor disconnected.

 

[Stevesplatto]

No this isnt talking about a food factory that can't be shut down...

This is a general description of testing procedures. Normal practice is to obviously isolate the supply for continuity tests.

I'm not sure how a Zs test alone can fully verify the integrity of the protective conductors without an R1/R2 (dead test) as suggested. Suppose the Ze could be determined by enquiry but it's not ideal...

Interesting how instead of seeing this as a general procedure and thus flawed some people saw this instead as a description of how to proceed when isolation isnt possible, which it wasnt, and rose to it's defence. Looked for ways it could be right. Guess I should have pasted the entire article!

Cheers
s

PS I did gt a eply asking for the page URL

 

[Farmelectrics]

doing a ze test were you cant switch of the supply is known as zdb which as im led to belive is acceptable were it is not practable to isolate supply due to bussiness requirments

 

[Stevesplatto]

How would you be able to ascertain the value of the supply earth (Ze) if you can't isolate it from protective bonding?

 

[roukel01]

By enquiry

 

[Wayne Watts]

Farmelectrics is right on! Stop worrying about other peoples bad practice and worry about getting your own correct! The point of the inspection is to affirm the safety and integrity of the installation. If you haven't got the understanding of the agreed limitations then your in trouble. Zdb if fine! No bad practice there!

 

[Stevesplatto]

Yeah right! The regs do say 'by enquiry'. Ever tried to get a Ze spec in writing out of a supplier? And what if you suspect a problem with say a suppliers TN-S strap clamp (which I did just recently) they will ask you what the Ze is before they'll come out!

 

[roukel01]

If you see a problem, thats a different scenario all together, doing Zs is fine otherwise surely?

 

[Stevesplatto]

To be frank I don't very often come across situations where I can't isolate the supply and carry out a Ze loop test and check continuity of the protective conductors. The situation I illustrated, a malfunction clamp, is a real situation which would not have shown up with a zs loop test with all protective conductors connected because of parallel paths... Where's my bad practice?
cheers
s

 

[Wayne Watts]

You don't have one bud! Just these threads alway nit pick to some degree. It's quite funny really! Every install needs to be assessed on its own merit. I do think your concern about Parallel earth path is less worry tho. If you loose the ze i would expect zdb to be just to high (ohm or two) and that's what your testing for eh? Enjoy.