meggers

[spanner51]

Re: meggers

garn wrote:
if I m correct if There Are Other Appliances On The Same Ring the best Way Is to isolate The Appliance That your Working On loop test from Another Socket Record Thre Reading. Then re test the loop With the Appliance On.

I may be wrong BUT. An Earth Loop Impedence test has nothing to do with an appliance. You are only testing the integrity of the socket earth.

This may help explain it http://www.tlc-direct.co.uk/Book/5.3.1.htm

[Alex]

Re: meggers

spanner51 wrote:I may be wrong BUT. An Earth Loop Impedence test has nothing to do with an appliance. You are only testing the integrity of the socket earth.

This may help explain it http://www.tlc-direct.co.uk/Book/5.3.1.htm

Earth loop impedance will read the earth path on the property system as you say, however the flying lead on the loop tester is then employed after the house frame test to confirm the appliance is suitably earthed.

Test 1: Taken from mains point back, maximum reading should not exceed 1.1 ohms. that is the integrity of the installation.

Test 2: Use the flying lead to an exposed metal part of the appliance frame, and test again. This time you will get the appliance reading plus the original as in test 1 and the appliance earth which needs to be to be below 0.1 ohms. Thus the sum should be no more than test 1 plus 0.1 ohms.

In summary; If Test 1 is 1.1 ohms, and test 2 is 1.19 ohms the installation and appliance have both passed. The appliance reading was 0.09 ohms in this case.

This should be applied before you carry out any work, and again after completion.

Also the insulation resistance test, using a 500v megger. A maximum reading of 2 megohms on the appliance is required. Some electronic machines now will pick up error codes on heaters even if they are as good as 5 megohms, yet they pass the legal criteria.

Alex

[Martin]

Re: meggers

spanner51 wrote:This may help explain it http://www.tlc-direct.co.uk/Book/5.3.1.htm

Hmmmmm?…not sure we need to go there spanner51 at this point to be honest? An example of which is……

tlc-direct.co.uk wrote:The earth fault loop impedance can be used with the supply voltage to calculate the earth-fault current.
IF =
Uo
Zs
where
IF = fault current, A
Uo = phase voltage, V
Zs = loop impedance

For example, if a 240 V circuit is protected by a 15 A semi-enclosed fuse and has an earth-fault loop impedance of 1.6 Ohms, the earth-fault current in the event of a zero impedance earth fault will he:
IF =
Uo =
240 A
= 150 A
Zs
1.6

A far far better option to take on board is what Alex has just posted. That being a more down to earth, positive and direct approach to earth loop testing, I would suggest.

I would hope at some point in the not too distant future to apply those same techniques toward a more concise, simplistic form using words and photographic illustrations that relate directly to our trade. (i.e. Showing the various megger and earth loop stages required in order to carry out repairs to built in ovens, hobs, dishwashers etc etc.

[lee8]

Re: meggers

Whats the point of testing an appliance if the return to the safety devices are faulty :rolls:

So you test the whole equation, i.e the whole circuit from safety devices to the appliance. 😉

[Martin]

Re: meggers

lee8 wrote:Whats the point of testing an appliance if the return to the safety devices are faulty :rolls:

I swear to god this is a wind up isn’t it?:)

lee8 wrote:So you test the whole equation, i.e the whole circuit from safety devices to the appliance. 😉

Lee your a lovely knowledgeable fella, I must say first off here, but, come on, what do you mean by “safety devices?” lets try it from there…….GO! 8)

[spanner51]

Re: meggers

Martin wrote:
Hmmmmm?…not sure we need to go there spanner51

I agree

But if you click elsewhere on the tlc web site, (5.3.4) it gives typical values of Earth loop Impedance

32amp fused circuit 1.09ohms max

32amp mcb circuit 1.88ohms max

What I was trying to be helpful about is :- that if an engineer doing the test doesn’t understand what he or she is testing, then there is no point in doing it

[lee8]

Re: meggers

Martin wrote:Lee your a lovely knowledgeable fella, I must say first off here, but, come on, what do you mean by “safety devices?” lets try it from there…….GO! 8)

You know, those bits of wire near the main switches by the front door or under the stairs. 😉

Or is it the one in the power station. 😥

[Martin]

Re: meggers

lee8 wrote:You know, those bits of wire near the main switches by the front door or under the stairs. 😉

Or is it the one in the power station. 😥

Oh I get you now Lee and it’s the first one on your list here.:rotl:

I had to chuckle at that and knew you were pulling my leg all along. 😀

By the way on the Megger.pdf thing…..3 more Hotmail requests bounced back so clearly if you have a Hotmail email address it just won’t work. Hotmail should be called NOTmail I reckon…sorry guys! 🙁

I think if you can’t use an alternative email address I might have to put the pdf on one of those FREE pdf file downloading sites? Not ideal but I can’t figure any other way over the problem can you? 😕

[lee8]

Re: meggers

Cant it be placed on this site.

I`m sure a huge disclaimer will secure UKW liability from any resulting deaths.

[Brains]

Re: meggers

Martin

The EFLI data you have supplied refers to a TN systems (i.e TN-S or TN-C-S). You need to take into account TT systems that use earth-rods. Also, if there is an 30mA RCD providing additional protection then max allowable EFLI can go up to 1667 ohms.

I would like to suggest that if EFLI testig is carried out then, the RCD trip times should be verified. I know that this is extra work, but, is a key part of safety testing and takes just a few minutes with an appropriate tester.

Also, with an installation that is RCD protected, checking Fault Loop Impedance from L-N (ZL-N) will provide a good ‘sanity check’ to ensure MCB disconnection within the required time for line to neutral fault.

Hope this helps

Regards

[Martin]

Re: meggers

lee8 wrote:Cant it be placed on this site.

I`m sure a huge disclaimer will secure UKW liability from any resulting deaths.

That’s a possibility I suppose?…leave it with me on that one and I will have a word with Ken to see if he can do this for us?

I’ll get back to you in the fullness of time……………. 🙂

[Martin]

Re: meggers

Brains wrote:Martin

The EFLI data you have supplied refers to a TN systems (i.e TN-S or TN-C-S). You need to take into account TT systems that use earth-rods. Also, if there is an 30mA RCD providing additional protection then max allowable EFLI can go up to 1667 ohms.

I would like to suggest that if EFLI testig is carried out then, the RCD trip times should be verified. I know that this is extra work, but, is a key part of safety testing and takes just a few minutes with an appropriate tester.

Also, with an installation that is RCD protected, checking Fault Loop Impedance from L-N (ZL-N) will provide a good ‘sanity check’ to ensure MCB disconnection within the required time for line to neutral fault.

Hope this helps

Regards

Whoa boy!…..easy their Brains…don’t want to put folks off the testing subject over those technical variables right now do we? Please do bear in mind we are talking BASIC’s here at this stage. In-depth stuff is, to say the least, is way over the top and best avoided. Having said that I appreciate your comments and welcome your future input.

But I would add that I am fully aware of the variables with regard to earth loop testing. All the way from overhead power line supplies lines right down to earth rod resistance potential. Even down to the fact that impedance readings can change in relation to ambient temperatures and so on. The point being that too much information at this stage and to an audience such as this is really and truly best avoided TBH.:wink:

Besides, and in my humble opinion I would far rather create an enthusiastic audience toward the very basic and much required standards field service work demands rather than blind anyone with the science of the subject and put them right off!:(

No ‘mathematical formulae’ or ‘what if’ at this point is the way forward. Preaching to the converted may well follow but that’s way way ahead of what I would suggest is best for us all right now….. 🙂

But hey…thats just my opinion.:oops:

[Brains]

Re: meggers

Sorry Martin

Don’t want to put anyone off testing.

Just wanted to remind everyone of the variables.

May I also suggest our colleagues to inspect the method of earthing and circuit protection first prior to testing.

Reasons: First to ensure that there is a Main Earth Connection. In a lot of older properties it is not uncommon to identify no Main Earth or ‘Water-Pipe’ earths (not Main Protective Bonding – another subject for another day?). This is to prevent inadvertent /elevated shock risks to people within the property.

Also, to prevent inadvertent tripping of RCDs – annoying to the customer if they are using a PC elsewhere in the house and if they do not know how to reset timeswitches.

I would also suggest that you inform the customer prior to carrying out these measurement.

If you want me to contribute further techno-babble let me know & I would be happy to do so. 😉

Regards

[lee8]

Re: meggers

Also avoid it if the fridge/consumer unit is in the locked garage that the mother in law has no key for and happens to be full of xmas food.

And the owners left for the weekend away via Easyjet.

Its never happened tooooo me, but you have to be aware. 😳

[leavemetogetonwithit]

Re: meggers

Blimey, I’m up for improving my knowledge and practice of safety but does it mean I’m going to need a third toolbag? (At the moment my gear all fits in two bags which hook onto my pannier rack.)
Can we try and establish what my legal obligations are and take it from there? Gotta be a happy medium somewhere. Really don’t want to end up taking responsibility for the customer’s total electrical installation!
Mike.

[Author]

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