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Posted By Topic: A question from an Australian skills test

DougP
May 18 2018 09:25

This is a question from an Australian skills maintenance test.

In some states, the support riser is bonded to the incoming neutral rather than the installation earthing system (which actually seems like a good idea).

Note that the wording of the question and the picture don\'t match..

Anyone know what the answer could be? The options seem to defy logic, and apparently the third option is not the correct answer.

http://iforce.co.nz/i/30c3whru.dqh.jpg
   

Satobsat
May 18 2018 10:47

I would answer with \"the results of the test will be invalid\"

But re-reading it \"I would say the answer is the 2nd one \"neutral conductors will be energised\" due to other installations operating on the local network.

Which would also mean that the \"results of the test will be invalid\" so what do you answer with?

Like my tutor used to say \"stop over thinking it and answer with what they want you to say.\" 2nd answer.

Bit of a trick question but the pertinent point in the question is \"with the supply energised\"

   

DougP
May 18 2018 16:06

As far as I can see, the 4th answer can\'t be right. The third option I\'m told isn\'t right.
The second option can\'t be determined from the information provided.

So the only possible answer must be the first one. I think it should say \"MEN connection must NOT be disconnected\".

It seems to be very badly written. Possibly there is mistakes in the question or answers.
   

pluto
May 18 2018 17:58

I\'ve looked at copies of the VIC (Australia) service rules and the only item being connected to the neutral conductor is the bracket itself and it is NOT earthed back to the earth bar of the installation.

The only valid answer must be that you have not done the mains polarity testing as described in the service rules.
   

Sarmajor
May 18 2018 19:48

You only get to choose from the 4 answer choices.

From where I am sitting I can’t even understand the question in an NZ context.
   

DougP
May 18 2018 22:17

I know what you\'re saying Sarmajor.
But it\'s the same MEN system.
They bond their brackets to the incoming Neutral.
But who knows what their polarity test procedure is.

From what I\'ve heard from them, it differs depending if it\'s a linesman, or an electrician. But I\'ve never seen a linesman doing any testing in NZ. So who knows...
   

pluto
May 19 2018 13:04

I did a bit more searching on AU Electrical Safety Regulators Office websites and some older material which described how to do the polarity testing at the mains entry point which was there a few years ago has been removed.

However I did fimnd some material on the AU Institute Electrical Inspectors website on an allied subject of verifying polarity within an electrical installation; which says that the system used in NZ for polarity checking on mains and electrical installations is one that should now be used.

That is make yourself a temporary earth (some distance away from the main earth electroode position), long trailing lead nd use a voltmeter to verify the active conductor is 230 V approx to the mass of earth and the neutral is almost 0 volts to the mass of earth. Ensure that the measurement is made on the end of the conductor when the installation turned off, thia is prevent any load on the installation making the measured voltage measurements invaild.
   

Sarmajor
May 19 2018 16:00

Which is all well and good but what is the correct answer to the quiz question as far as the Examiner is concerned.

As far as I can tell the bonding of the service support conductor should have no effect on the polarity test unless the house is steel framed.
If the house was steel framed and the polarity at the supply end of the service main was incorrect testing using the NZ trailing earth method should pick it up.

There would also be a measurable amount of current flowing in the service support bonding conductor but probably not enough to blow the service fuse.

   

AlecK
May 20 2018 08:11

Forget the \"extra\" info (ie what is not included in the question) about some states earthing the btracket to incoming mains N.
Look again at the picture, and note it shows a \"disconnected\" bonding conductor while the questions is about what happens if it hadn\'t been disconnected.
The conductor is clearly entering the mains entry, so it will be connected to the E bar and has been disconnected from the bracket (NOT from the incoming service mains N)
   

AlecK
May 20 2018 09:11

The alternative is that the bracket / conduit is earthed to the N terminal of the connection box,

either way it doesn\'t alter the answer.
Nor does whether the earth wire is disconnected as shown in the picture, or not as asked in the question.
I think Satobsat is correct: it\'s a trick question.

The only thing you know for sure is that the mains are energised. So answer two is correct regardless of which system of earthing the bracket is used, and regardless of whether that earthing connection is disconnected or not.

Answer 1 can\'t be correct, as there is NO accepted method of testing polarity of energised mains that doesn\'t require the MEN to be opened.

Answer 4 can\'t be correct. The polaritymay be reversed, or not - that\'s what the test is supposed to be finding out - and it can\'t depend on whether or not that earthing connection has been disconnected.

Answer 3 may be true, depending on the test method used. We aren\'t told that - but should assume it\'s a method specified in \"3017\". The normal & accepted test method for a \"live\" test involves an independent earth AND opening the MEN. The results won\'t vary with how the bracket is or isn\'t earthed. A test method that depends on whether or not the bracket is connected to anything is NOT a reliable method. So that answer can\'t be correct.

Which I suspect is the point of the question; to see whether people understand that disconnecting the bracket\'s earth is simply not relevant to polarity testing. Those who think disconnecting such an earth will make a difference clearly don\'t understand the MEN system and don\'t know how to do a proper test.





   

DougP
May 20 2018 10:19

Your explanation sounds perfectly reasonable Alec.

But what do they mean by \"neutral conductors will be energised\"? And what difference would the service bonding conductor being disconnected or not make?

There is only 1 occurrence of the word \"energised\" in 3017 (none in 3000). 3017 3.4.2(b) which is transposition of conductors - but in the skills question, we\'re not told if the polarity is correct or not - so I\'m not sure how any of the answers be determined?
   

pluto
May 20 2018 11:34

My guess is that in QLD where the question came from (look at top line of the question photo for the source) there is an complete need to do testing with no supply applied for all testing. If want to work on live electrical equipment you have to do a detailed HSAW study before doing any work, then have a very high level safe work procedures + an assistant to pull you off live parts if your work procedure does NOT work out and you touch live parts by accident.

Other states in AU are now joining this thrust with VIC and WA being recent additions to the NO LIVE work group.

This being so the second bullet point is the correct answer.

You will note that AS/NZS 3017 shows testing of consumer mains testing and that shows that tsting would require the supply has to be disconnected to carry out polarity checking of the consumer mains.
   

daniel2
May 20 2018 14:10

I’m trying to get my head around the answer (b - neutral is energised). Please explain this answer. I can understand there will be voltage present if it’s disconnected; but when it’s connected?
   

SaintAlan
May 20 2018 14:49

Steel framing is widely used in Australian housing, and aluminium cladding. That would mean the bracket is effectively earthed through the structure, so connecting it to N would add another MEN point and some most unreliable test conditions.
The NZ practice of bonding steelwork to earth is more reliable.
   

AlecK
May 21 2018 09:45

We\'re told that the supply is energised, and that condition applies to all conductors, not just to the (presumed) active(s). This one fact gives the answer to the question, and all the rest is distraction - including the bit about disconnecting the \"service bonding conductor\". It will make zero difference - but many people would not know that and some could believe that disconnecting is necessary in order to get a valid result on the test.

The very fact that you are testing for polarity of incoming supply means there\'s a chance of reverse polarity; and if that does prove to be the case the (presumed) N will be not only a \"live conductor\" but at some voltage to earth (\"some\" because if the MEN link is in place, it will be somewhere less than nominal voltage).

When testing anything, we have to cast aside all assumptions, and prove everything from first principles. Including that the presumed neutral is in fact neutral; and of course starting with proving that our voltage tester and other test instruments are actually functioning.

SaintAlan\'s point about possibility of other earth paths is valid, but again can\'t be assumed but instead must be tested for (insulation resistance test).


Also calling this a bonding wire (as the question does) is fundamentally wrong. It\'s NOT there for equipotential bonding. It\'s there for (earth) fault protection and therefore is a protective earthing conductor.



   

Satobsat
May 21 2018 10:01

The neutral conductor is considered a live conductor. It is also connected to other installations in the vicinity that will be energising the neutral under normal use. It is the what I was taught.
   

pluto
May 21 2018 11:06

You all need to be careful what the system of supply at the point of connection, it is TN-C therefore you DO NOT use the earthing descriptions typically used inside an installation.

From my observations made in AU over many years in domestic housing, the service bracket is NOT earthed or bonded to the electrical installation earth bar,and also not be metallic framing, it uses the line works type construction of using the neutral as an PEN conductor as would be used on a distribution power pole to earth metal that needs to bonded to earth for protection /safety purposes.
   

mowgli
May 22 2018 07:13

\"Answer 1 can\'t be correct, as there is NO accepted method of testing polarity of energised mains [that doesn\'t require the MEN to be opened].\"

AlecK I would not have added the last bit in brackets as 3017 only describes one polarity test for consumer mains and that\'s de-energised.

The fact that the question includes that mains is energised suggests maintenance/troubleshooting rather than new install verification/testing to 3017. So an independent trailing earth with the MEN connected would be reasonable and give a reliable indication of mains transposition.

If transposition was present then removing the MEN link while energised would be opening 230V to ground. That could get exciting.
   

AlecK
May 22 2018 09:16

Yes the fact it\'s already connected & energised suggests an existing rather than a new installation.
That\'s partly why I didn\'t cite \"3017\"; which is specifically aimed at verifying new work and not at fault-finding.

And yes opening the MEN for any reason, including for using the \"independent earth\" test method to check polarity, can be exciting. Polarity reversal being only one of several conditions that can make it so. Opening an MEN should ALWAYS be treated as if it were live work, even on an isolated installation. Same for disconnecting / connecting MECs (the idea that an earth conductor connected to the mass of earth can\'t bite is simply wrong).

But fact remains that the MEN (or equivalent) has to be opened in order for the test results to be valid.

\"3017\" and \"3019\" are about to be reviewed, and I\'d like to see more test methods added, including this one (yes I know it\'s there for submains to an outbuilding; though that specifies disconnecting the N rather than opening the DB\'s MEN). I don\'t know of any good reference for fault-finding methodologies and (especially) sequences; and methods designed primarily for verifying new work are often not appropriate or practicable for fault-finding / verifying existing in-service installations.

But given the fact that several States in Oz now forbid live work, in at least one case absolutely; I doubt we\'ll be able to get any live testing methods added. May struggle to have the existing live test methods (EFLI, RCDs, earth electrodes) retained.

What the HSW zealots don\'t realise, in their blind (and futile) pursuit of completely eliminating all risk, is that you can\'t completely eliminate live testing unless you outlaw use of electricity. A distinction needs to be made between doing installation and repair work, which should (almost) always be done de-energised; and verification / fault-finding, some of which needs to be done live.
(Rant over)

Any suggestions for improvement of either \"3017\" or \"3019\" should be submitted to SNZ urgently; if you don\'t ask for it it won\'t happen unless the Committee think of it for themselves. So get in now at the start, rather than waiting for a draft amendment to be released for public comment.

   

dbuckley
May 22 2018 11:08

Hold hard a mo: the diagram says \"Service bonding conductor disconnected\" and the question text says (my emphasis) \"if the service support conductor is NOT disconnected\"

Surely that is contradictory? Have I gone mad??
   

Andrew
May 22 2018 12:09

The aim of the question appears to be to throw a bunch of distracting detail at you, part of which is a diagram showing one situation, and the question asking about a different situation, neither of which is relevant to the answer.
   

daniel2
May 22 2018 13:23

I think I would have failed this test as I spent half an hour too long on one question.
   

DougP
May 22 2018 13:56

Exactly. They need to realise this isn\'t an application to MENSA.

It\'s just a refresher test for a tradesman.
   

AlecK
May 22 2018 14:32

I never wanted to work in QLD anyway.

But surely being able to \'see the wood for the trees\' (ie decide which info is relevant) is an essential part of our job?
   

Satobsat
May 22 2018 14:34

Quite the discussion you started there Doug. Did you get the correct answer to the question at the end of the test?
   

DougP
May 22 2018 15:08

It wasn\'t my test. I\'ll have to check back with the person who asked the question originally.

It was quite a long discussion on the other Q&A board as well!

And it\'s a lot warmer in Qld than in Dunedin Alec!
If you can put up with the mosquitos.

   

dbuckley
May 22 2018 15:52

Andrew notes

> The aim of the question appears to be to throw a bunch of distracting detail at
> you, part of which is a diagram showing one situation, and the question asking about
> a different situation, neither of which is relevant to the answer.

Ok..... now I understand.

This clip from My Cousin Vinny springs to mind (slightly NSFW language)

https://www.youtube.com/watch?v=CFdJza0AbeA

Marisa Tomei picked up the gong for Best Supporting Actress for her role in this movie, and this clip gives a hint as to why.
   

AlecK
May 22 2018 17:24

and cyclones
   

Satobsat
May 22 2018 18:16

Don\'t forget all the West Islanders Aleck
   

DougP
May 23 2018 08:36

Correct answer is B
   

mf51to1
May 23 2018 22:04

The other question (departing slightly from the OP) is why they don’t run a seperate PEC from the earth bar?
I’m sure a 6mm earth would also fit up the service riser bracket. No functional difference but would bring it more inline with 3000.
   

pluto
May 24 2018 07:39

Remember the system of supply at the point of attachment is an TN-C so the system of earthing using the earth bar of the electrical installation of the support bracket is NOT applicable.

Bonding the bracket to the PEN (neutral conductor) at the point of attachment is the correct method and will have the lowest impedance fault loop.
   

AlecK
May 24 2018 10:20

Yes the supply is TN-C at any point up to the MEN.
But that does NOT make any difference to the requirements of \"3000\".
True earthing to the incoming PEN conductor is likely to provide better earthing; but it is non-compliant with \"3000\" unless done as a \"Part 1 solution\".

In NZ, generally the POS is upstream of the situation in question, so the bracket is part of the installation, and earthing to the PEN conductor is NOT the \"correct\" method. For domestic, it\'s non-compliant - because Part 1 isn\'t permitted.

In another jurisdiction, where a different definition of \"installation\" and / or \'point of supply\" may apply; or in NZ where the POS is downstream of the situation illustrated; then this support bracket could be treated as \"works\". In which case Pluto\'s assessment would be correct.
   

DougP
May 24 2018 21:43

In quite a number of areas in Australia they use unprotected consumer mains.

So earthing of these supports and some metering enclosures, is by connection to the main neutral as per 5.5.3.5
   

AlecK
May 25 2018 12:16

Well spotted DougP.

In NZ we (technically) don\'t have unprotected consumer mains, because of ESR 32.
However that\'s only because of our definition of \"mains\", ie they start at POS.
So where the POS is within a meterbox or MSB, we can have exposed conductive at risk of being contacted by the supply cables upstream of the short circuit / fault protection device(exactly like the Ozzy \"unprotected consumer mains\"; but because the conductors are upstream of POS, they (technically) aren\'t \"mains\". So ESR 32 doesn\'t require them to have protection.

I believe that in such circumstances we should earth those parts as if they were \"unprotected consumer mains; ie use a heavier PEC and (depending on configuration) a heavier MEN link. These need to be of equal size to the incoming N, instead of the usual approx half the size (as per Table 5.1).

   

DougP
May 25 2018 12:23

Thanks for that Alec.

ESR32 - well I hadn\'t noticed that before. I guess I need to read the whole thing again :(
   

rkirman
Sep 17 2019 13:40

Sorry for unearthing an old thread, but it seems this was the only worthwhile result to my search for "service support bonding".
i too faced this confusing question and a few others in my skills test.. but finally passed it.
but my question is in the real world, should my service support be connected to the earth bar? it recently had energex bond it to the incoming neutral. and my house being hardwood frame and concrete tile means the service support is effectively insulated from the rest of the installation.
   

AlecK
Sep 18 2019 08:15

The answer may differ depending on where you are, each State having there own regulation.
For NZ, the answer depends on whether the bracket in question is upstream or downstream of the PoS.

For a typical house, PoS will be where the supply crosses the boundary; and the bracket supporting the house end of the aerial conductors (which is what I presume you mean by "service support") is supporting "mains" which are part of the installation.
ESRs require all installations to comply with AS/NZS 3000; where the earthing requirements are in Section 5.
Basically if double insulation is maintained, you don't need to earth the bracket. If not, it must be earthed to the earth bar.

That's not to say connecting to N is unsafe, just that for installations it's non-compliant with Part 2. For non-domestic, connecting to incoming N could be OK as a "Part 1 solution"; but would need to be fully documented in a "certified design".
   

DougP
Sep 18 2019 08:29

rkirman your answer will be in your local service rules (SIRs)
   

molsiol10
Oct 07 2019 07:16

If there is a transformer inside, find out the secondary voltage and current at the load. If it passes through the rectifier, also get the DC values. See if you can get a standard AC or DC power supply for connection and install a wall outlet in the charger to match the power supply. I did this when I installed a mobile casino https://greatcasino.co.nz/online-casino/spin-palace/. Then just tag the power supply. If it is a switching power supply, this may complicate the work a little.