Question over Live/Neutral cable sizes - must they be the same?

[shoeless1963]

Firstly, my thanks to all those who post on here with advice: I’ve learned loads in the last three weeks and am grateful for the time and care you guys take to help the less knowledgeable. Especially me. I’m building – rather, having built – a house in the Phetchabun area and its going well in general as there are people in my wife’s family in the trade so they have done the plans, the structural work and an awful lot of the labour. My role has become chief whinger and it’s the electrics where I am now getting some problems. Answers to these questions welcomed and beer on offer to anyone who is in the area and fancies casting an eye over progress:

1. Wiring is in and I went for the electrical (yellow)conduit/embedded route, mainly for aesthetics. Nothing too fancy but managed to specify that power outlets and lights for example were on separate zones and we’ve gone full spec on breakers for items such as air cons and water heaters. Its radial design and I think we’re OK – based on the wise words here – for cables as its 2.5 mm2 for the electrical outlets (all three pin, earthed, some UK fitting most Thai style) and 6 mm2 for the air con units, all wired back to a breaker panel in the kitchen. So far so good…
2. … although the water heaters were more of an issue and in the end I’ve gone for one 6kW (single point) and one 9.5 kW (multipoint) in the two bathrooms. The latter type appears on other forums as a long debate and as it’s a c. 20m run from the main panel to the wall breaker, I went over-spec on cable and bought 10 mm2 and 6 mm2 for the smaller unit. The excess of the 10 mm2 cable (bought a 50m roll, single core PVC protected seven mini-cores) was intended to feed the little electric two-ring hob and be used for an oven point although not yet purchased.

Sadly, I made the fatal mistake of having to be out of town for a few days and the electrician – yet another relative theoretically but one about to be disinherited – has elected to chop up my lovely 10 mm2 cable into short lengths and use it instead as individual earthing wire for the water heaters. We’ve also a main earth point, ground spike, etc. outside the back of the kitchen connected to the breaker of course. So, to the questions – and apologies as these may be very straightforward:

1. Not content with downgrading the cabling to 6 mm2 for the larger heater – this is probably OK – he has elected to run just a single 6 mm2 for the Live and only a 2.5 mm2 for the Neutral. I have read for hours on here to try and find out whether the L and N should be the same diameter or whether the N can be lower spec and apologise as I don’t get the logic. Obviously, it’s a single phase supply/design…my gut feel is that they should be the same cable but before I get him to rip it out and do it properly, does it actually need to be replaced? The guys at HomePro where we bought the water heater thought not, but to be fair they are no more electricians than me
2. This idea of having local earths straight into the ground for the water heaters (and I think he’s going to do the same for the air-cons but we are still on first fix inside the house) is new to me. It’ll salve my soul slightly if it is a good option – means the 10mm2 cable isn’t wasted and it was only the price of a ticket to a Premier League match anyway – but wanted the advice, please.
3. He was going to wire the house in zones, where the wall electrics and the lights were back to the same breaker. Apparently that is the ‘fashion’ (!) here in Thailand. I have explained that I want the wall sockets and the lights on separate circuits (and zoned) – but as he’s proven inclined to do what he wants anyway, are there any specific views/regulations around this just in case?
4. I am keeping the kitchen a separate zone again (thanks to Crossy’s site and also for the tip to keep outside circuits on a separate breaker). I’m of the understanding though that I can plug in the fridge and washing machine to standard wall sockets – the fridge is ordinary UK sized, not the walk-in wardrobe US sized fridge. Is that right or again should they have a separate circuit

As I said, many thanks for the erudite postings on here and apologies if these questions are answered anywhere else. Incidentally, Phetchabun is a lovely little town - OK, I like 'Field of Dreams' so I have a corn fetish already - but if anyone can recommend a pukka electrical contractor in the area, I'd be really grateful. Obviously, a falang can't work in that line but I bet they could drink a lot of beer

[Forkinhades]

1. Cables really should be 10mm, and most definetly of the same size (major Fire Risk if not), however you can the 2.5 as your earth which should be taken back to the DB.

2. Really not a good idea, this can create potential diferences in voltage (Risk of electric shock), You have a new install at first fix stage, all your earths should be taken back to the DB!

3. Personal preference really, as long as you have calculated the loads and do not exceed the values, and correct cables used.

4. If your going the radial route, then I suggest 2 4mm radial circuits on 20A MCB's, or 6mm on a 32A

[bankruatsteve]

" as he’s proven inclined to do what he wants anyway, are there any specific views/regulations around this just in case?"

Any 'spark' that thinks it's OK to use different size wire between L & N on the same circuit should not be allowed to do what he wants. Tell him he will do what you want.

[Forkinhades]

Point to add is that you should only have one earth rod, and that is the main one, with a 16mm cable to your DB.

Dont forget your MEN connection. The PEA will advice on that .

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[Crossy]

1. Cables really should be 10mm, and most definetly of the same size (major Fire Risk if not), however you can the 2.5 as your earth which should be taken back to the DB.

2. Really not a good idea, this can create potential diferences in voltage (Risk of electric shock), You have a new install at first fix stage, all your earths should be taken back to the DB!

3. Personal preference really, as long as you have calculated the loads and do not exceed the values, and correct cables used.

4. If your going the radial route, then I suggest 2 4mm radial circuits on 20A MCB's, or 6mm on a 32A

Agree, with one exception.

Unless there are very long runs I wouldn't bother going over 2.5 and use a 20A breaker on outlet radials, if you have lots of outlets split them between circuits.

Reasoning is thus (and follows Aussie rules), the outlets are rated at 16A and are un-fused, if you have a 20A breaker it is unlikely that you will seriously stress a 16A outlet before the breaker opens. If you have a 32A breaker you could pull 40A+ (uncle's welder) from an outlet before it opened, I'm not convinced any Thai outlet would survive that.

EDIT For your MEN connection, follow the scheme in forky's pinned thread (routing the incoming neutral via the ground bar) as that's how the MEA / PEA man is going to expect it to be wired.

[thomasteve]

What cable cross-section sizes are readily available in Thailand is there a 4mm2 ? as well as 2.5, 6.0 and 10sq.mm ?

I would have thought 2.5 sq.mm is ok for radial power sockets and lights in one or two rooms as it can carry up to approx.30 amps ? as a quick rule of thumb as most sockets are now used for small loads except in the kitchen.

It also seems to be the preferred size used for the smaller air-cons and shower heaters (up to 7kW).

EDIT : Crossy's post crossed with mine !!

Edited May 30, 2014 by thomasteve

[Crossy]

All the regular metric sizes are available, 1, 1.5, 2.5, 4, 6, 10, 16, 25 ........ in singles, twin, and twin with earth.

Current ratings are on the Bangkok Cables website (they've recently re-organised the site so none of my links work, grrrr).

I wouldn't go over a heater 3.5kW on 2.5mm cable, most aircons will be fine on 2.5. That said, our water heaters are on 6mm and aircon on 4.

[Forkinhades]

^ Indeed, I forgot about uncle

I have Schneider sockets installed in my house, which are a German company, and the sockets are only rated 13A!

Dont have any Thai brand sockets to hand, and don't know their claims!

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[thomasteve]

^ Indeed, I forgot about uncle

I have Schneider sockets installed in my house, which are a German company, and the sockets are only rated 13A!

Dont have any Thai brand sockets to hand, and don't know their claims!

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Some of the cheaper brands, especially extension and multi sockets, are made from as little poor quality brass as possible and plugs are a loose fit so anything more than about 1 Amp might be risky !!

[Forkinhades]

What cable cross-section sizes are readily available in Thailand is there a 4mm2 ? as well as 2.5, 6.0 and 10sq.mm ?

I would have thought 2.5 sq.mm is ok for radial power sockets and lights in one or two rooms as it can carry up to approx.30 amps ? as a quick rule of thumb as most sockets are now used for small loads except in the kitchen.

It also seems to be the preferred size used for the smaller air-cons and shower heaters (up to 7kW).

EDIT : Crossy's post crossed with mine !!

I would not use 2.5mm on circuits over 20A. 2.5mm can carry about 22A, depending on how circuits are wired and type of cable used. Also here you have ambient temperature to deal with which will derate the cable by 0.9

^ just from memory

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[Crossy]

BKK ratings for VAF-G http://www.bangkokcable.com/bcc_catalog/backoffice/file_upload/131007_32-300!300V%2070C%20VAF-G%202C.pdf

2.5mm clipped direct 23A

[thomasteve]

BKK ratings for VAF-G http://www.bangkokcable.com/bcc_catalog/backoffice/file_upload/131007_32-300!300V%2070C%20VAF-G%202C.pdf

2.5mm clipped direct 23A

Good points as ambient temperatures in most roof spaces are very high and it's also in conduit so you should derate 2.5sq.mm copper conductors down to possibly under 20 Amps at a guess - without doing the calculation.

Just noticed from Crossy's pdf link though that their sheathed cable should not be installed in conduit (or buried).

Edited May 30, 2014 by thomasteve

[Forkinhades]

Many types of different install, and the 'swing' of the current carrying capacity can be 30%

Dont know whether they have used ambient temperature in their calculations.

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[Forkinhades]

BKK ratings for VAF-G http://www.bangkokcable.com/bcc_catalog/backoffice/file_upload/131007_32-300!300V%2070C%20VAF-G%202C.pdf

2.5mm clipped direct 23A

Good points as ambient temperatures in most roof spaces are very high and it's also in conduit so you should derate 2.5sq.mm copper conductors down to possibly under 20 Amps at a guess - without doing the calculation.

Just noticed from Crossy's pdf link though that their sheathed cable should not be installed in conduit (or buried).

I have had 3 sockets installed for the outside utility room, the run actually went over my kitchen , in the ceiling void. Then installed in conduits, it was calculated to use 4mm on a 20A.

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[thomasteve]

BKK ratings for VAF-G http://www.bangkokcable.com/bcc_catalog/backoffice/file_upload/131007_32-300!300V%2070C%20VAF-G%202C.pdf

2.5mm clipped direct 23A

Good points as ambient temperatures in most roof spaces are very high and it's also in conduit so you should derate 2.5sq.mm copper conductors down to possibly under 20 Amps at a guess - without doing the calculation.

Just noticed from Crossy's pdf link though that their sheathed cable should not be installed in conduit (or buried).

I have had 3 sockets installed for the outside utility room, the run actually went over my kitchen , in the ceiling void. Then installed in conduits, it was calculated to use 4mm on a 20A.

Sent from my SM-G900F using Thaivisa Connect Thailand mobile app

It is best to do 4mm2 for such locations as all 3 sockets could be heavily loaded with washing machines,etc. (and in conduit)

For areas such as bedrooms and living - rooms with light loads and no conduit 2.5 mm2 seems to be in common use, although it could also be attributed to usual cost-cutting.

Incidentally, what is the current :-) recommended size of earth conductors for circuits such as lights, sockets, showers, air-cons ?

Should they now be the same size as L & N or are thinner ones OK as UK used (still do ? ) with their 2.5 T&E cables and larger sizes.

[Forkinhades]

Indeed sir, other circuits in bedrooms and the like can be 2.5mm

The 3 core cable that is akin to twin and earth back home. The circuit protective conductor will be smaller. I would just go with what is available.

Also, as already stated a 2.5mm earth would be adequate for a 10mm supply for a instantaneous water heater.

I have actually done a pdf of this before, it's on here somewhere.

Will try and locate it.

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[Forkinhades]

If the 10mm was run singularly and not grouped with other circuits (not in parrallel) then a 2.5mm is fine, if it was grouped (run in parrallel) then a 4mm would need to be used.

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[thomasteve]

If the 10mm was run singularly and not grouped with other circuits (not in parrallel) then a 2.5mm is fine, if it was grouped (run in parrallel) then a 4mm would need to be used.

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thanks, Forky.

[shoeless1963]

Gentlemen:

Thanks for taking the time to come back... I left it until late tonight to close this off just in case there were some subsequent posts. You have (all) confirmed what I thought which is that L and N need to be the same cable. Just to show that I did listen...

...we had 'uncle' back over this evening and explained that the mad falang husband wants to have a second 6mm2 cable installed on the important runs (two water heaters and one cooker and one hob point). Looking eternally on the bright side, the 2.5mm2 that he ran as the original neutral can now become the earth cable and runs back to the main DB as suggested. Luckily labour is cheap and we caught this, thanks to your help, before the ceiling went in. If I may then, a few final questions:

1. I note the comments that earths should run all the way back to the DB and that there should be one single earthing point, which is to the ground spike. Mother-in-law has already procured this for us. (NB you did not see my earlier comments privately and I daren't repeat them in the open forum but hmmm... did I marry the right generation remains a key question). Anyway, is it really a bad idea to have local earths for the heater units? Could I go belt and braces and have both?

2. I'm going to risk the 6mm2 pair for the larger water heater. I've disassembled that already and the cabling inside - which surprisingly used AWG wiring - suggests that a 6 mm2 pair will be OK, as does the wiring diagram provided by the manufacturer (Mex). Its borderline but the 9.5 kw unit actually consists of one 5.0kW and one 4.5kW element wired in parallel so I think that, coupled with the fact that I will have dual breakers - the ghastly wall mounted version outside the bathroom that Mrs Shoeless insists upon and then the individual breaker in the DB - is OK. Any reasons that this is not going to work?

3. Loathe to cheat and start a new debate but forgot to ask... we are going to install down lights and dimmers in a couple of places (lounge, kitchen, main bedroom). The maximum dimmer I can find locally is a horrible old 500W thing and all the rest are 300W. I've seen though in houses in civilisation - well, Pattaya anyway - 900W dimmers. Any ideas were I can find these here in Thailand?

Last question is back to cable loading.

I now have the remnants of a 50m 10mm2 cable run that cost me around 3,500 baht.

I need to calculate the load capacity of this cable...

...specifically how high off the ground do I hang 'uncle'? I'd hate to think of the cable stretching as he dangled there and his feet still being able to touch the ground.