Author Topic: Electrical Test: Insulation, Continuity, RCCB, Polarity and Earth Electrode  (Read 6251 times)

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Offline Mechatrommer

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a friend came to ask about this. he think i'm the guy for this but it turn out to me scratching my head a bit. i googled some, but some aspect i need to ask...

i search for the tester device and i guess this is it...
http://www.ebay.com.my/itm/Megger-MIT310-Insulation-and-Continuity-Tester-Test-Lead-and-Crocodile-Clip-Set-/291852786363?hash=item43f3c81abb:g:dHQAAOSw-itXusm7
http://www.ebay.com.my/itm/UNI-T-RCD-LOOP-TESTER-MEGOHMMETER-MEGGER-UT593-RESISTANCE-IMPEDANCE-Earthing-OZ-/131327384801?hash=item1e93b8dce1:m:mI2o7hIMtPjPvwPIioFO8Wg

or cheaper option is this...
http://www.ebay.com.my/itm/UNI-T-UT525-Electrical-Insulation-Tester-RCD-Tester-Continuity-VAC-DC-4-in-1-/311577659097?hash=item488b79c6d9:g:~YwAAOSw8w1X-aej

but earth electrode test need another dedicated device:
http://www.ebay.com.my/itm/Proskit-8PK-ST1520-Digital-Earth-Resistance-Tester-/250944871538?hash=item3a6d7adc72:m:mNlsG-P4rTNjaj5oAH1NObQ

or this whooping GBP700+ device..
http://www.ebay.com.my/itm/Kewtech-KT65DL-Digital-8-in-1-17th-Edition-Multifunction-Tester-/252575618511?hash=item3aceae15cf:g:~AgAAOSwBLlU9bkJ

1) is RCCB test similar to RCD test? because i cant find an RCCB tester except some vintage model.
2) can i use insulation or continuity tester to check earth eletrode resistance? because we want to save cost on equipment testing.
3) if i want to buy only one device, i prefer the UNI-T-UT525 model above because it cheap. can it be used to test all as listed in the topic? or is it wise thing to do?

thanks.
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Offline Mechatrommer

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this is what i can come up with on earth electrode test, he used Kewtech KT65 @ 1:52 but thats darn expensive...

« Last Edit: October 10, 2016, 11:01:25 am by Mechatrommer »
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Offline Mechatrommer

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bump, in a busy traffic day...
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Offline Brumby

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1) is RCCB test similar to RCD test? because i cant find an RCCB tester except some vintage model.

This is easy to answer.

An RCCB is a Residual Current Circuit Breaker, the most common RCD (Residual Current Device) you will find.  In this context, you can consider them to be exactly the same thing.
 
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Offline Neilm

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Earth testing is different from continuity or insulation testing. Earth testing is done with 2, 3 or 4 stakes. It is like a 2, 3 or 4 terminal resistance measurement allowing compensation for resistances in the measurement leads. However, earth testing is done outside so the voltage limits are much lower than they might otherwise be. The leads will also be very long - the Megger DET4TD comes with 50 meter lengths of lead.

I do know that there are multi-functional testers (Fluke, Megger and Metral all make them). These combine continuity, insulation and RCD testers. I don't know of any that include Earth electrode test as well.
[edit]
I just followed that Kewtech link - I'm not sure but that "Earth Test" could be measuring the resistance of the earth at a socket NOT the earth electrode resistance.
[/edit]
« Last Edit: October 12, 2016, 05:46:21 am by Neilm »
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Offline Mechatrommer

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I do know that there are multi-functional testers (Fluke, Megger and Metral all make them). These combine continuity, insulation and RCD testers. I don't know of any that include Earth electrode test as well.
thanks for the reply i start to believe there are only few electricians left in this forum. btw, Uni-T has come into the game as i linked above. the famous name Megger price is quite reasonable, but Uni-T has come with 2-4X cheaper as an option. but not sure how they par up.

I just followed that Kewtech link - I'm not sure but that "Earth Test" could be measuring the resistance of the earth at a socket NOT the earth electrode resistance.
as video i linked in 2nd post, the person did it with Kewtech KT65, exactly like you said "Earth testing is done with 2, 3 or 4 stakes" outside the building. i believe it seems they want to build a good earth electrode for the building's earth connection, or just a demo there is.

i was just thinking if continuity or insulation tester can be done (hacked) is similar fashion... connect either R,Y or B to a stake far apart, and E to the existing building's earth ground electrode, apply some voltage maybe 400V or 1KV and measure the resistance.  :-// btw Kewtech is 8X the price of Uni-T or 2X the price of Megger, so it will be a hard decision if the returned profit is limited. but on the +ve side, i believe it can do all the required measurement mentioned above as a single unit.
« Last Edit: October 12, 2016, 06:13:30 am by Mechatrommer »
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Offline Neilm

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i was just thinking if continuity or insulation tester can be done (hacked) is similar fashion... connect either R,Y or B to a stake far apart, and E to the existing building's earth ground electrode, apply some voltage maybe 400V or 1KV and measure the resistance.  :-// btw Kewtech is 8X the price of Uni-T or 2X the price of Megger, so it will be a hard decision if the returned profit is limited. but on the +ve side, i believe it can do all the required measurement mentioned above as a single unit.

The trouble with "hacking" a continuity tester is the output voltage. Are you looking to put a new stake in, or are you measuring an existing stake? If the latter, you may want to look at something that can do ART (attached rod technique) measurements. This saves you having to detach the earth connection to do the test. There are also units that do "stakeless" tests. If you have a read of the DET4TC datasheet there is some information on those two.
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Offline Mechatrommer

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The trouble with "hacking" a continuity tester is the output voltage. Are you looking to put a new stake in, or are you measuring an existing stake?
from the friend's description... he want to measure existing building ground connection to earth. from the above video, there are 3 wires coming out of measurement device (Kewtech), one goes to earth electrode, 2 probes go to stakes buried few feet apart by his colleagues, i guess that 2 stakes is for "earth reference" in the measurement setup, i'm not sure though why 2 instead of only 1 stake. as they measured it, the guy keep punching the 1st earth electrode until resistance measurement within acceptable range ie below 200.

so in my friend's case, i believe he is going to measure existing earth installation in a building, to ensure the earth resistance to building electrical wiring (ground wires) will be in compliance to some standard, or within some acceptable value.

checking the DET4TC, the applied voltage is 25-50V, but for insulation/continuity test, MIT310 is applying 250V-1KV. so i guess this whole thing is just a V = IR test, ie we apply V, measure the I, and hence we will get R. in both cases of continuity/insulation test and earth electrode test. am i correct? or wrong? what confuse me actually or i believe i still dont have a clear picture, is why the need of 2, 3 or more stakes needed to do the earth measurement? beside the earth electrode under test.
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Online tautech

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Here (NZ) before a new installation is approved the earth stake test is done against a single short reference stake inserted some distance from the permanent earth stake ~10m IIRC.
That maybe because of our local clay soils (usually wet) and how it's done in other NZ areas I'm unsure.

That some authorities might require 2 reference stakes is not surprising, no doubt better accuracy or averaging can be obtained for the "record".
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Offline Mechatrommer

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checking the DET4TC, the applied voltage is 25-50V, but for insulation/continuity test, MIT310 is applying 250V-1KV.
i forgot to mention that i believe higher voltage test is better? because it will have higher sensitivity in resistance measurement, so i dont know what's so special about earth test (at lower test voltage).

yes tautech. i believe in my country too or everywhere, the compliance test should be done by professional before each building installation is approved for occupancy. i highly believe this will be for periodic/yearly/decade compliance test to ensure the system is not degraded or damaged.
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Online tautech

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i highly believe this will be for periodic/yearly/decade compliance test to ensure the system is not degraded or damaged.
This I have NEVER seen.
At commissioning yes, but never as a regular compliance test, not in NZ anyway.

It's something that to some extent does worry me as earth stakes DO degrade, I've pulled some that were decades old and were eroded to thin needles.  :o  :scared:
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Offline Mechatrommer

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well you just have. he even gave me the test form (in our language). of course this form can be the compliance test before commisioning but i guess the building owner needs assurance, who cares its their money. otoh earth electrode test is just a small part, 5 tests all. i will be surprised if you havent heard of periodic wiring continuity/insulation check. we have lot of rats going on above the ceiling where all the wiring go. and magic electrical tripping for no reason in many buildings in our place is common even in the place where i work.
« Last Edit: October 12, 2016, 08:45:00 am by Mechatrommer »
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Offline Neilm

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Before I start I should come clean, I am an electronics design engineer and I do actually work at Megger and I was on the team that designed the DET4TC, apologieses in advance if this starts sounding like an advert.

It is a case of R= V/I, but there is more subtlety.  The tester has to be able to compensate for the relatively high resistance of the test leads. For safety reasons there are limits to how much voltage an earth tester can output. This means you cannot just keep increasing the output. An insulation tester is limited to just now couple of mA, a continuity tester may output more but probably only at a few volts. Keep in mind the leads could easily be 100 ohms.

Megger produced a book called  "Getting Down to Earth" about earth testing. If I recall correctly  this does include test voltages. When looking for this, I found the MFT1735 which is an insulation, continuity and DVD tester which does include earth resistance testing ( I hadn't realised it was released yet).

The acceptable limits are defined by IEC61010, the performance of the earth tester is defined in IEC61557. Depending on the circumstances, your tester may have to meet these requirements, certainly for electrical work in the UK this would be the case.

The periodic testing you would not want to disconnect the wire, as this could cause more problems than it solves. I would look for a tester that supports art testing and / or stainless testing. The latter means you don't need to disconnect anything and use the existing installation.
« Last Edit: October 12, 2016, 08:43:47 am by Neilm »
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Offline Mechatrommer

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thanks for the advice Neilm, it is appreciated, no need for an apology. the fact that the friend came to me (both he and me are clueless unprofessionals) is that i guess the building owner (instead of hiring a professional) has a tight budget. so we (he) need to get this thing right i guess. i will check your reference, thanks.
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Online tautech

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i will be surprised if you havent heard of periodic wiring continuity/insulation check.
Not for domestic I haven't, however I own my residence.
For those that are being leased and commercial buildings it's understood they maybe be subject to different rules.
I'll ask my sparky mate......
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Offline Mechatrommer

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Not for domestic I haven't, however I own my residence.
For those that are being leased and commercial buildings it's understood they maybe be subject to different rules.
I'll ask my sparky mate......
not commercial premise, its a government building, dont ask further. :-[
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Offline ocw

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For related material on accuracy tests of some earth resistance and resistivity testers see:
https://www.eevblog.com/forum/metrology/earth-ground-resistance-resistivity-testers/
 

Online tautech

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i will be surprised if you havent heard of periodic wiring continuity/insulation check.
Not for domestic I haven't, however I own my residence.
For those that are being leased and commercial buildings it's understood they maybe be subject to different rules.
I'll ask my sparky mate......
There is no mandatory requirement here in NZ however on the odd occasion electrical "warrants of fitness" are performed but only at owners and tenants request.
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