Checking New Electrics: Two Questions

[anatta]

I'm checking the electrics of our new house and have managed to carry out some of the tests prescribed on Crossy's excellent site, but with only very limited technical knowledge I need advice on two matters.

1. The two main supply wires are spliced (bound with bulging tape) inside the consumer unit some 15 cm before reaching the main CB/ELCB. I haven't yet had a chance to ask the electrician if this is because he originally cut them too short, but that is my best guess. Question: Is this dangerous and therefore unacceptable?

2. The house has 12 (double) socket outlets, but I notice only four earth wires (apart from the ground spike wire) joining the earth bar in the CU. I've tried to measure the resistance from the earth bar to each of the socket outlet earth contacts, and get readings of 6 or 7 ohms for all of them - but my multimeter doesn't seem very reliable (and I may be misguided even to think it can be used for such a test!). Question: Is a ratio of one earth wire to three (/six) socket outlets acceptable? (And if the 6-7 ohms is accurate, is it within acceptable limits?)

Thanks.

[lopburi3]

I would be concerned about the taped connections. If same wire type and bound by a split bolt of the same material suspect it might be safe but no way for you to check it without removal of tape on a hot line (don't do it). Incoming mains should be direct to breaker screws so they can be tightened there (and even there you should not do yourself).

I would be more concerned with checking each and every outlet for full hot voltage to ground and neutral and no voltage from neutral to ground. But again if you are not comfortable on using meter with live voltage have the electrician made the checks and you just watch the meter readings. You likely have twist connections on the ground lines and they can be bad (or become bad). I would make them use split bolts at such connections as they are much more reliable than a pliers twist.

[electau]

You should carry out a visual check first of the PE conductor on all socket outlets.

Then with a continuity tester check the continuity of the PE conductor from each outlet.

The main earth conductor should not exceed 0.5ohms and the PE conductors should not exceed 0.5ohms.

6 to 7 ohms is too high you should check your multimeter for accuracy. Remember the test voltage for a multimeter is generally 300mV.

Minimum size of the PE conductor should be 2.5sqmm.

Edited December 12, 2010 by electau

[anatta]

Thanks electau and lopburi3. We've now remedied some of the doubtful things. When the electrician showed visible disbelief I looked with him through relevant sections of a 43-page booklet I had got from the local electricity company entitled คู่มือการฅิดฅั้งระบบไฟฟ้าภายในที่อยู่อาศัย (roughly,'Guide to Installing Domestic Electrics').

[citizen33]

Another person's tuppence worth, before we hear from the real experts.

1. The taped cables are unlikely to be safe. One solution, if the leads are too short but can be brought out outside the consumer unit, is to fit an additional good-quality double pole switch (about 100 amp) on the supply into the house (i.e. the existing cables coming into the CU) and then bring new leads from this into the consumer unit. If you don't have an RCD in the consumer unit, the new switch could be an RCD, or alternatively you could replace the main switch in the consumer unit with an RCD and have an external main switch. Obviously you'll need to get somebody to disconnect the leads at the meter before you do this (so you are not working with live cables).

2. A resistance test to earth with a multimeter is unreliable. You need a 'megger' (with more current) or a more sophisticated earth resistance tester to test an earth. However the multimeter continuity test will tell you if the earth connectors in the sockets are connected to the earth stake, which is a start. Google 'earth resistance test' to see what I am talking about.

[Crossy]

Thanks electau and lopburi3. We've now remedied some of the doubtful things. When the electrician showed visible disbelief I looked with him through relevant sections of a 43-page booklet I had got from the local electricity company entitled คู่มือการฅิดฅั้งระบบไฟฟ้าภายในที่อยู่อาศัย (roughly,'Guide to Installing Domestic Electrics').

Can you please post a scan of the electricity company document? These things are always very handy to have as references to point-and-shoot at with your Thai sparks.

[Forkinhades]

You really do need proper test equipment to carry out a full range of tests, which will cost around 50,000 baht.

You need to test your earth spike

You need to test insulation resistance (especially if you have taped joints)

You need to test the earth loop at every accessory

You need to check continuity of all cables

You need to test the ELCB tripping time, less than 400 milli seconds

You need to test for polarity at every accessory

check for insulation of live parts

check for correct size of cables, mcb's

check cables have been routed in prescibed zones

check for functional testing of assemblies

check for connection of single pole devices for protection or switching in line conductors

that is about a third of it............................

remember this is serious stuff, and should really be left to the experts, if you want to safe from electrical fire/electrocution !

[Crossy]

Yup ^^^ and I have it (one of these http://www.bis.fm/products/Robin_KTS1620.asp a UK 16th Edition installation tester)

Sadly none of the Thai domestic sparkies I've ever spoken to have anything more than a cheap multimeter (and they don't know how to do much with it)

[Forkinhades]

Yup ^^^ and I have it (a UK 16th Edition installation tester)

Sadly none of the Thai domestic sparkies I've ever spoken to have anything more than a cheap multimeter (and they don't know how to do much with it)

you should know me by now crossy

and 17th Edition thank you

[Crossy]

Yup ^^^ and I have it (a UK 16th Edition installation tester)

Sadly none of the Thai domestic sparkies I've ever spoken to have anything more than a cheap multimeter (and they don't know how to do much with it)

you should know me by now crossy

and 17th Edition thank you

Indeed But the 17th goes way OTT in so many respects and is probably going to be more trouble than it's worth here trying to install to it here particularly when the supply authority has such a cavalier attitude to such things as properly grounding TT and TNCS systems.

16th is 1,000,000 times better than anything we get here (in domestic installations anyway).

[Forkinhades]

Yup ^^^ and I have it (a UK 16th Edition installation tester)

Sadly none of the Thai domestic sparkies I've ever spoken to have anything more than a cheap multimeter (and they don't know how to do much with it)

you should know me by now crossy

and 17th Edition thank you

Indeed But the 17th goes way OTT in so many respects and is probably going to be more trouble than it's worth here trying to install to it here particularly when the supply authority has such a cavalier attitude to such things as properly grounding TT and TNCS systems.

16th is 1,000,000 times better than anything we get here (in domestic installations anyway).

Indeed, but the 17th states that any circuit within a wet area needs to be protected by an RCD, ie lighting in a shower/bathroom, which I fully agree with, and be applied very easily.

The IET code (Thailands) is quite stringent, but as you say nobody takes any notice of it, or indeed fails to understand it

[Crossy]

Yup ^^^ and I have it (a UK 16th Edition installation tester)

Sadly none of the Thai domestic sparkies I've ever spoken to have anything more than a cheap multimeter (and they don't know how to do much with it)

you should know me by now crossy

and 17th Edition thank you

Indeed But the 17th goes way OTT in so many respects and is probably going to be more trouble than it's worth here trying to install to it here particularly when the supply authority has such a cavalier attitude to such things as properly grounding TT and TNCS systems.

16th is 1,000,000 times better than anything we get here (in domestic installations anyway).

Indeed, but the 17th states that any circuit within a wet area needs to be protected by an RCD, ie lighting in a shower/bathroom, which I fully agree with, and be applied very easily.

The IET code (Thailands) is quite stringent, but as you say nobody takes any notice of it, or indeed fails to understand it

No arguments FinH I also note that the 17th now permits socket outlets in bathrooms, something that until now was a massive no-no in the UK.

Do you have a copy of the Thai code? Many members would be interested in seeing what it actually says.