Domestic Instal in Thailand - Phase 2 - Testing

[Thai Amateur]

At last I've been able to complete theelectrical installation of the bungalow. Taken so long because I'vehad to fix so many problems with the building work left by my earlierlocals.
So now I've done some preliminarytesting and YES I am going to get a local professional in to do thefinal testing but I want to make sure that I haven't made any majorerrors. Plus I want to make sure that any local I get really doesknow how to test properly.
I have a Kyoritsu model 6010A multitester.
1. Tested continuity – OK.
2. Tested conductor resistance R1 + R2.Compared result with recommended length of cable for voltage dropmultiplied by the resistance for the cable size. Problem with spurs Iadded to water pump and car port but overcame this with anothercircuit. All R1 + R2 well within the recommended parameter.
3. Test Insulation (at 500v).
Here I seem to have a problem althoughI can't see why. I have 2 consumer units supplied from a single main(3 pole) disconnecter switch.
First I connected L-N and tested L-E.
Unit 1 – 160 Mohms
Unit 2 – 80 Mohms
Next I removed the link and tested L-N,L-E, N-E.
Unit 1
L-N - 0.11 MOhms
L-E – 140 MOhms
N-E – 195 Mohms
Unit 2
L-N - 0.08 MOhms
L-E – 60 MOhms
N-E – 70 Mohms


First time I've done anything like thisso any advice would be most appreciated.

 

[Des 56]

and your question is ?

 

[Thai Amateur]

I don't understand why L-N readings are so low.
Also when taking a reading should I keep the button on the meter down or just press and let go? If I keep it depressed the reading (except L-N) just keep going up.

 

[Des 56]

The insulation resistance test has precautions that must be taken before carrying out that test
If they are not taken,there can be damage caused to electronic equipment

The reading you are getting will probably be caused by not ensuring adequate precautions have been carried out prior to the test

Your electrician will do the insulation resistance test and the low reading you are now getting will most probably be of little concern

 

[Engineer54]

IR testing of a new installation needs to be conducted without anything in circuit such as lamps, fluescent ballasts, or other such consumables, this includes CU/DB RCD's and combined socket outlet RCD/GFCI devices, wall thermostats, or other electronic devices. Any of which will knock your IR values for six and can damage or kill those electronic elements you're injecting 500 volts into. Individual circuit value's will give considerably higher values than an overall CU/DB value.

 

[Thai Amateur]

My main problem is that I cannot trust the local electricians absolutely. I am in Thailand and there are very different rules out here. So I really need to understand the cause of my problem so that I can then evaluate what my local "expert" says when he does the testing.

 

[Thai Amateur]

OK. I tested to each MCB with connection in place but only that MCB closed. Should I remove the connections to each MCB and then test directly from the live conductor?
Definitely no thing connected to the system.

 

[Engineer54]

If you have an RCD device in circuit, be it within CU or as a combined socket outlet then these must be disconnected before testing. May be a good idea to go round and release wall outlets etc from wall and ceiling roses etc from ceilings and check if any conductors are being pinched by retaining screws etc. Basically you are testing the installation wiring ONLY, ...nothing else, so remove, isolate or disconnect anything other than wall ceiling accessories.


How about a posting a few photo's of your CU/DB's and installation as a whole. Pictures speak a thousand words... lol!!

 

[Thai Amateur]

Thanks. Some of the socket connections are a bit tight where I have radial plus spur (plus TV in the same socket) so will check through those.
Night time here but will try to get photos tomorrow.

 

[Thai Amateur]

If you have an RCD device in circuit, be it within CU or as a combined socket outlet then these must be disconnected before testing. May be a good idea to go round and release wall outlets etc from wall and ceiling roses etc from ceilings and check if any conductors are being pinched by retaining screws etc. Basically you are testing the installation wiring ONLY, ...nothing else, so remove, isolate or disconnect anything other than wall ceiling accessories.


How about a posting a few photo's of your CU/DB's and installation as a whole. Pictures speak a thousand words... lol!!

Retested the insulation with all conductors disconnected. Got OL (over 200MOhms) on all circuits apart from 2 which both read 150 MOhms.

Will now try to post images.

 

[Thai Amateur]

Left is 100 Amp 3 pole switch to be isolator for 2 CUs

 

[Thai Amateur]

Both CUs are 63 Amp with RCBO and 8 MCBs. 1 spare on each CU.

 

[Thai Amateur]

Oven Switch 2 Pole
Hob (left) and oven connections. Connection method not determined yet as undecided between sep hob and oven or combind. Hob will be gas either way.

Light Switches - Combined socket with TV - Socket with sep TV - Water Heater switch

Nothing screwed down yet. Will do that after the walls are painted. For now I just want to make sure that the system is OK before I get the suspended ceiling in place. No way I want to work in the loft after that.
I'll also do another full test after everything is screwed down just in case I put a screw through a cable.

 

[Thai Amateur]

Both CUs came with 32 Amp and 20 Amp MCBs. I've sized my theoretical maximum consumption on each circuit and come up with 20, 16 and 6 Amp requirements using the next size MCB up from the maximum amps any circuit might draw. Well within the limits of any cables.
20 Amp are Oven, Water Heaters, biggest Air Con and the Kitchen socket circuit. 16 Amp are the main circuits to living ad bedroom areas. 6 Amp a the lighting and wall and ceiling Fan circuits.
These sound to be to much closer to the old fashioned fuses I used to have in UK.

 

[Engineer54]

Retested the insulation with all conductors disconnected. Got OL (over 200MOhms) on all circuits apart from 2 which both read 150 MOhms.

Will now try to post images.

Those figures are far more acceptable, that's 200 million and 150 million ohms respectively...lol!! Now take care dressing the cable back into the back boxes when you fit the wall accessories back to walls and ceilings.

Not too keen on those multi choice plug outlets you've used, but then we are talking about Thailand. I see that you have run a separate earth wire with some cables, could you not find cable with incorporated earth?? What material is used for your main water incoming water supply, metal or PVC/plastic?? If metal, you'll need to bond that incoming water pipe to the Main Earthing Terminal of your installation. But i'm guessing that it will be a Plastic/PVC pipe....

So what sort of values did you eventually achieve for your earth rods to this property??