Cable size meter to building 72M

[Crossy]

7 minutes ago, regedit said:

You mean run a cable from the roof steel to the rod (so 2 cables will finally be attached to the rod) ? 5 of the earths will pass through the roof space so adding one more attached to the steel down to the control room will be doable.

 

What size cable for CU to rod and roof steel to rod ? Mains supply will be on 4x32mm.

 

Yeah, our roof steel actually tests better (by a factor of 4) than the 2.5m rod.

 

From the main CU to the rod, 16mm² minimum, if you've got some 32 spare that's your stuff, but for all grounds, basically the bigger the better.

[Robin]

Reading all this has got me thinking.

Where in Thailand can you buy 2 core +earth cable for domestic wiring.  When my house (in Phayao) was built, I had to bring a drum of 2+ earth from UK as every electrical shop I asked at was "why you want 3 wires.? Only use 2 in Thailand."  

My experience of Thai electricians has been that earths wires are not considered to be important, more like a waste of money.  All vry keen to sell me a 'safety cut' (ELCB) but cannot understand why an earth wire is needed.

My observation of  (overhead) wiring in my village is that we have 3 phases and a earth, which is also the neutral or return.  Any experts here care to comment on this.  I am not an electrician, but just try to use common sense when coping with Thai wiring:-

1.  Make sure that the live is switched, not the neutral.

2.  Make sure that all screw connections are done up tightly; do not rely on wires twisted together.

3.  The correct wire for the connection is the one that will carry the current used, not the smallest that will work for 5 mins. (until the electrician is of the site.)

 

[sometimewoodworker]

42 minutes ago, Robin said:

Where in Thailand can you buy 2 core +earth cable for domestic wiring. 

Well it’s really difficult but how about; Global House, DoHome, Thai Watsadu, HomeHub, HomePro and every electrical supplier. I’ve seen it in all of them and bought from some of them.

 

[sometimewoodworker]

46 minutes ago, Robin said:

My observation of  (overhead) wiring in my village is that we have 3 phases and a earth, which is also the neutral or return.

It will be the neutral, in a lot of places it is earthed at about every 3 pole as in MEN but you need to check as it may not be.

[Crossy]

@Robin

 

Common sense is indeed the way to go.

 

If that cable from the UK is the regular T&E with the reduced size, bare earth core then it technically does not meet the Thai regulations which require a full size, insulated earth core, it's perfectly safe of course (I hope it's not wired as a "ring main" on a 32A breaker). The equivalent here is VAF-G (the G designates it has the earth core). This is the stuff you'd use for outlets 

https://www.homepro.co.th/p/1018377 

 

 

It did used to be as common as hen's teeth but is now readily available as is 3-core flex, often in Black, White, Brown (I use the brown for earth).

 

Thailand local supplies are 3-phase, 4 wire, 220V Phase-Neutral (230V in Bangkok) supposedly TN-C-S with MEN (look for the earthed neutral on the supply poles). A MEN link between a local earth rod and neutral is required in your consumer unit. Many get alarmed at this link, but much of the UK is the same apart from the link being hidden in the service head.

 

A handy PEA document Groundwire Mk2 book-Manual.pdf 

 

And the important diagram with translations, note the routing of the incoming neutral via the earth bar to implement the MEN link.

 

 

 

 

 

[Yellowtail]

Is what looks like wire-rope strung across the top the ground/earth?

 

The high voltage lines only have three and a ground, correct?

[Crossy]

28 minutes ago, Yellowtail said:

Is what looks like wire-rope strung across the top the ground/earth?

The high voltage lines only have three and a ground, correct?

 

The "wire rope" on top of the HV poles is lightning protection, it's not a service conductor although it is earthed. 

HV lines are 3-phases only plus that lightning protection.

 

The 4 LV lines usually have the neutral at the top and it's bare (and also looks like wire rope), the phases themselves are insulated.

 

The neutral is usually earthed every 3rd pole or so making it MEN (multiple earthed neutral) and there's also a link between the neutral and earth (and your local rod) inside your consumer unit, making the service TN-C-S with MEN.

 

Wiki has a good discussion of earthing systems 

https://en.wikipedia.org/wiki/Earthing_system 

Thailand is generally TN-C-S with MEN or TT.

 

 

[regedit]

On 11/20/2020 at 5:17 PM, Crossy said:

 

Yeah, our roof steel actually tests better (by a factor of 4) than the 2.5m rod.

 

From the main CU to the rod, 16mm² minimum, if you've got some 32 spare that's your stuff, but for all grounds, basically the bigger the better.

Would it be wrong to go instead from the roof steel to the earth busbar in the big distribution board, and then have only 1 cable from the busbar to the earth rod?

[Crossy]

6 minutes ago, regedit said:

Would it be wrong to go instead from the roof steel to the earth busbar in the big distribution board, and then have only 1 cable from the busbar to the earth rod?

 

My only reservation would be if your roof took a lightning hit the current would all be going via your ground bar.

[Yellowtail]

20 minutes ago, Crossy said:

 

My only reservation would be if your roof took a lightning hit the current would all be going via your ground bar.

 

Lightning in Thailand?

[Crossy]

33 minutes ago, Yellowtail said:

Lightning in Thailand?

 

It would seem so.

 

 

 

 

[Yellowtail]

I was working setting up a Himalaya ride in Buffalo NY back in the late '70s and it got hit by lighting. That's some hairy s--- right there...

[regedit]

On 11/13/2020 at 4:43 PM, Crossy said:

Do you intend metering each room? Probably worth it for monitoring if not billing. A lot of options on aliExpress including ones with RS485 or wifi.

 

 

I’ve seen those digital DIN rail meters - would those work for monitoring usage and billing for each room ? Do they have internal batteries to keep the current reading during a black out ? I was thinking I could have them all fitted in the utility room, after the master breaker for each room, before running to the consumer unit in each individual room. 

[Crossy]

3 minutes ago, regedit said:

I’ve seen those digital DIN rail meters - would those work for monitoring usage and billing for each room ? Do they have internal batteries to keep the current reading during a black out ? I was thinking I could have them all fitted in the utility room, after the master breaker for each room, before running to the consumer unit in each individual room. 

 

The units we have monitoring our solar remember over power failures, not sure it they have batteries or store the data in FLASH, either way they would be ideal for your purposes.

[regedit]

2 hours ago, Crossy said:

 

The units we have monitoring our solar remember over power failures, not sure it they have batteries or store the data in FLASH, either way they would be ideal for your purposes.

Do you have a photo or link to the unit/ brand you are using ? I've not bought the main switches or housing box yet. Thanks.

[Crossy]

3 minutes ago, regedit said:

Do you have a photo or link to the unit/ brand you are using ? I've not bought the main switches or housing box yet. Thanks.

 

I have these https://www.aliexpress.com/item/32919001382.html

 

Many options available.