Earth loop without neutral

[Guest123]

The way I see it, some guys have been testing this way for 20, 30, 40 years or more with no problems.

No **** from the NIC is going to make me change the way I do things just to suit them. If they have anything to say then I'll take my trade elsewhere.

Personally I feel it's quite insulting to all of us as they obviously dont have any faith in our competance to work safely.

 

[Sintra]

what about ewr? do they not get stroppy?

No because i am competent and use the correct procedures and have valid reasons for doing the live test.

 

[nickblake]

In order to make an accurate measurement of Zs at a remote end of a circuit, we must first understand what we are trying to measure. As in any test for earth-loop-impedance, the value we are attempting to evaluate is the impedance, in other words, the 'total opposition to an a.c. current'. In our case, this 'a.c. current' is our earth-fault current. For this measurement to carried out correctly we need to ensure that only the phase and cpc conductors are involved in the measurement process.
It follows then, that any additional fault paths in an electrical installation will have a detrimental effect on the measured Zs values of an installation.

 

[Jimmy Boy]

I did find it odd when I was on one of their Inspection and Testing courses that they made such a big issue of it, when you consider the NIC was formed what early 50's ? and the EAWR came into force on the 1st April 1990, why 20 Years after the legislation came in to force are they picking holes ?

 

[nickblake]

I always test Zs due to the fact that it is the only test that actually tests the complete circuit including MCB's, RCD's, Main switches etc which have been known to have high resistances.

Calculating from R1 + R2 and Ze can not detect this problem.

exactly my point in another post ,

 

[jam2020]

i quite agree lenny, but as i have my niceic dis assessment coming up i want to do everything by the book and not give them any reason to get stroppy.

 

[Spudnik]

There is no reason why you cannot test Zs at a light switch or rose.

Thats why the test leads are to GS38(?).

 

[Jimmy Boy]

http://www.electriciansforums.net/i...nfused-gs-38-leads.html?highlight=#post151596

 

[Jimmy Boy]

In other words they cant be GS 38 compliant to do a loop test, so we go un fused and do the business

 

[malcolmsanford]

i quite agree lenny, but as i have my niceic dis assessment coming up i want to do everything by the book and not give them any reason to get stroppy.

Problem is with the NIC it's not doing everything by the book, it's doing everything right by their book !!

I think if you are doing the Zs then it should be a live test. As far as I'm really concerned the R1 + R2 is a continuity/polarity test.

What are you looking for in that Zs test. It is the Earth fault path back to your protection device. The only time you will get a fault indication is when your installation is live and AFAIC I want to know what my EFLI is when the installation is working under normal conditions.

Remember if you do the Zs by calculation then you don't take into consideration all the parallel paths that will be involved when the installtion is in service. That is why normally a measured Zs is lower than a calculated one.

I find it a degrading attitude by some autohritive bodies in the UK to judge competancy on professional electricians. Do they think we are mad, no one wants to work live if they can help it, but by them advising that certain live tests should be done by calculation, when the calculation will give you a false result, is a worse scenario than live testing.

Zs and the PSCC test IMO are subject to parallel paths, they are both faults that occur when the installation is working under normal conditions, and therefore should be tested under those conditions, working and live.

 

[Graeme Harrold]

When I did my 2391, EWR was hammered home. The instructor who was also an assessor for NAPIT told us that testing was not treated the same as working live, as long as you are using GS38 test equipment, competant and follow the correct proceedures. We were shown methods of covering and shielding non-IP2X rated enclosures. Above all no enclosure is left open, unatended and live (IP2X or not) at any time. The minute you insert a tool into a live connection, you have moved from testing to working live.

 

[malcolmsanford]

That is NAPIT but other organisations within our industry are treating live tests as live working, and telling people, not advising mind you but telling, that you should not be doing live testing.

These organisations advise in their literature not to live test for Zs but in the field it is different as their assessors are telling you to do it by calcualtion, and calculation will not give you a correct reading.

 

[WayneL]

In other words they cant be GS 38 compliant to do a loop test, so we go un fused and do the business

Steve, you've lost me again.

Why can't you use fused leads to do a loop test - I do.


On the other matter, I really don't see what the fuss is about.

You have to test 'live' for Ze.
You have to test 'live' for RCD/RCBO tests.
You have to test 'live' for Supply Polarity.

So what's the difference - If you're competent to do these tests, surely you're competent to do Zs.

My worry, as I stated in the other thread, is that when you measure R1 + R2, the conductors are not terminated in the CU (if you want a true measurement)
Ze is measured with the 'Earthing Conductor' disconnected from the MET, so any 'resistance/termination' problem between the MET and the earth bar terminals will go un-noticed.

So, when you then terminate your CPCs into the earth bar, how do you know that each termination has made a sound, low-resistance joint?
You might just 'nick' a bit of insulation of one of the conductors.
Without a Zs test later on, this would go un-noticed.

You can do all the calculations that you like, but that won't tell you that your installation actually does comply to the 'design spec' and the 'Regs' - only testing can tell you this.

 

[Jimmy Boy]

Steve, you've lost me again.:

.

You seem to do that a lot try and keep up old chap.

To be truly GS38 compliant the leads must be fused to the appropriate rating for the test being carried out, normally this would be 500ma, this clearly would not be sufficient for a loop/pfc test so you would need to fuse the leads at a rating appropriate to the test, phone up Meggar tech and ask them why their leads they supply are not GS38 compliant ? The answer will be the tester has a HBC fuse in it, but it ain't 500ma !

 

[WayneL]

You seem to do that a lot try and keep up old chap.

To be truly GS38 compliant the leads must be fused to the appropriate rating for the test being carried out, normally this would be 500ma, this clearly would not be sufficient for a loop/pfc test so you would need to fuse the leads at a rating appropriate to the test, phone up Meggar tech and ask them why their leads they supply are not GS38 compliant ? The answer will be the tester has a HBC fuse in it, but it ain't 500ma !

You've either got a different version of GS 38 than me - or you are reading into it what you like.

I've just re-read GS38, and nowhere does it specify that the leads should be fused at 500mA for a loop test - that would be ridiculous.

The relevant section, as you pointed out, reads as follows:

15 Before testing begins it is essential to establish that the test device, including all leads, probes and connectors, is suitably rated for the voltages and currents which may be present on the system under test.

So why on earth would you loop test with 500mA fuses, sending 20A down the leads??

I have a Megger 1552, and although you don't have to use fused leads with this meter, Megger sell 10A fused leads for loop testing - go figure.

That makes 10A leads GS38 compliant for hi-current loop testing.