Seems peculiar to me...

[sparkinlee]

One of the things I've got for tomorrow is to advise on the likely costs of dealing with urgent items identified on a recent PIR done by another electrician on a church hall. Haven't seen the premises yet, but have been sent the PIR.

This identifies 'No mains earthing' and 'No equipotential bondings (gas/water)', as well as 'No access to fuse box'.

Despite this there is a recorded measured Ze value on the test results of 0.20 and Zs readings on the circuits of about 0.4.

So I'm curious where the return path is going to get these readings. Hopefully I will find out tomorrow, but in the meantime what's your best guess...?

 

[Deleted member 26818]

It's possible that the Ze was obtained through enquiry, and that the Zs were measured. Although I would expect the recorded Ze if obtained through enquiry to be either 0.8Ω or 0.35Ω.

 

[Engineer54]

If TN-S, ...Ze may have been obtained by using the lead sheath of the incoming DNO cable

 

[IQ Electrical]

One of the things I've got for tomorrow is to advise on the likely costs of dealing with urgent items identified on a recent PIR done by another electrician on a church hall. Haven't seen the premises yet, but have been sent the PIR.

This identifies 'No mains earthing' and 'No equipotential bondings (gas/water)', as well as 'No access to fuse box'.

Despite this there is a recorded measured Ze value on the test results of 0.20 and Zs readings on the circuits of about 0.4.

So I'm curious where the return path is going to get these readings. Hopefully I will find out tomorrow, but in the meantime what's your best guess...?

It's possible that the earth conductor from the MET to the consumer unit was missing and the Ze measurement was measured to the MET.

Even in apparently simple 'insulated' installations, parallel paths exist (maybe a boiler supply etc.) and a return path will be formed for Zs values.

Any tester/inspector worth his salt would not have carried out any live testing on finding a missing 'main earth' of course.

As for 'no access to fuse box' it doesn't sound like a particularly valuable PIR does it?

Nothing new there then......

 

[sparkinlee]

Well it turns out...

There is literally no apparent earth connection - no MET, no TNS strap on incomer, no TN-C-S.

There may be an earth rod connected straight into the fuse box, but it's impossible to get the front off the fuse box (boxing has been built around it since installation) to find out, so not sure how Ze was measured.

It's equally unclear whether there's any effective gas & water bonding but there is some G/Y connections onto metal trunking which goes down beneath floor level, which I guess allows some Zs reading if nothing else.

At least they are taking the inspection seriously - the DNO is already booked to come in to renew the service head and provide an earth connection, after which I'm hoping to get the job to renew the CU and conduct some proper tests!

 

[robsparky1975]

If i was booked to do a pir and could not get the cover off the CU,i would advise to the need and revisit,as cant see why the original tester didnt bother to do so.

 

[IQ Electrical]

If i was booked to do a pir and could not get the cover off the CU,i would advise to the need and revisit,as cant see why the original tester didnt bother to do so.

This is an 'inspector' who carried out Zs testing on an installation without a main earth conductor.....

 

[daiplayer]

How can you get a Zs without a main earthing conductor ?

 

[sparkinlee]

Well there was no TNS or TN-C-S connection, so I guess there must have been some form of 'TT', either by way of an earth rod (of unknown location) or via trunking going underground... or both.

I've now got the job of dismantling the boxing around the fuse box and replacing it, so I'll find out...

 

[Engineer54]

As i said, If the systems TN-S and if the previous guy did indeed take a Ze test, then he must have gone directly onto the sheath of the DNOs cable. Not the most sensible thing to do, but feasible...

One also has to ask, if this is a TN-S earth system, ....Why had the DNO left this installation without an earthing point from the cable??

 

[IQ Electrical]

How can you get a Zs without a main earthing conductor ?

There are a few ways, one being parallel paths-even on the most basic apparently 'all insulated' installation, there are numerous connections to 'earthy' services etc.

The favourite is any supply to a heating system, all pipework connected to a metallic conductive manifold then you take a cpc to the boiler-voilà!

 

[oldtimer]

I was asked to look at a job and a new head end was put in 7 years before the customer was then told to get their main earth looked at I posted this on the forum a couple of months ago along with the pics but as I said then I would not walk away and leave it in fact I put a 16mm earth lead in free of charge as i would not sleep at night knowing there was no earth. But does this post surprise me well now if I am asked to do a PIR and there is no earth in I will put it in so that I can continue with the task in hand but sadly we are now getting a air sucking through peoples teeth and saying this is not my job and out of interest me thinks for them to complete the PIR they must have put in a temporary lead

 

[Engineer54]

I was asked to look at a job and a new head end was put in 7 years before the customer was then told to get their main earth looked at I posted this on the forum a couple of months ago along with the pics but as I said then I would not walk away and leave it in fact I put a 16mm earth lead in free of charge as i would not sleep at night knowing there was no earth. But does this post surprise me well now if I am asked to do a PIR and there is no earth in I will put it in so that I can continue with the task in hand but sadly we are now getting a air sucking through peoples teeth and saying this is not my job and out of interest me thinks for them to complete the PIR they must have put in a temporary lead

A Gentleman Spark...