Does my Earth set-up look ok - 2 consumer units, 2 rods

[GavinK]

Hope the attached sketch helps - incoming supply goes to 2 separate consumer units - one upstairs, one downstairs (don't know why there's 2), each with its own main switch and RCBO. An earth cable goes from each Consumer unit and connects to the same earth rod. Also there is an outbuilding which is supplied from the first consumer unit (off an MCB) whose earth is connected to a second rod near that building. Is this set-up ok ? Thanks.

[Crossy]

Yeah, that works for me.

 

Make sure your outbuilding CU is covered by an RCBO as that building is TT but I think you're good to go.

 

Note - If your outbuilding is already covered by an RCBO in the house CU there's no real need for an additional one in the outbuilding.

[mahjongguy]

Let me ask, what if the outbuilding did not have its own ground; if instead it used a third wire running back to the ground connection in CU #1.

 

Would that be

- better?

- unnecessary?

- worse?

 

[Crossy]

52 minutes ago, mahjongguy said:

Would that be

- better?

- unnecessary?

- worse?

 

It could be all three ???? 

 

Assuming the main house is wired to the latest Thai standard (TN-C-S with MEN).

 

Better - Provides a metallic connection back to the transformer star-point, a L-E fault will open the MCB.

Unnecessary - RCBO provides shock protection anyway.

Worse - In the event of a neutral failure in the supply the supply "earth" could get well above true earth potential. If there's a water pipe or structural steel in the outbuilding that's at true earth you could have two "earthed" objects with a lethal potential between them. It's a particular problem with things like hot-tubs, lots of naked wet bodies standing on wet grass, you want any metalwork at true earth. Farm animals are also very vulnerable to shock between front and back legs so farm outbuildings are invariably TT with lots of local bonding.

[GavinK]

2 hours ago, Crossy said:

Yeah, that works for me.

 

Make sure your outbuilding CU is covered by an RCBO as that building is TT but I think you're good to go.

 

Note - If your outbuilding is already covered by an RCBO in the house CU there's no real need for an additional one in the outbuilding.

Thanks very much. I've noticed that there is no MEN in either Consumer unit. Do I need disconnect the neutral from the main switch and take it to the Earth busbar, then back to the main switch, in both consumer units ?

 

Also, the outgoing supply to the outbuilding (2x6mm) shares the same 25mm conduit as the incoming supply from the meter for 1.5m (just as it enters the house, to get to the consumer unit). Is this ok ? I guess there was no spare conduit to the consumer unit.

 

 

[Crossy]

Assuming you already have a permanent supply (about 4.5 Baht per unit) and don't have to pass the PEA inspection and if everything "risky" is protected by an RCD/RCBO somewhere then I'd leave the existing system alone, at least for now.

 

I wouldn't worry about the shared conduit, there's probably a regulation lurking somewhere but it's no hazard.

 

Making the system MEN would improve safety somewhat, but unless you KNOW that MEN is implemented locally I would still leave well alone. You can get an idea of whether your supply is MEN by looking at the supply poles, if the neutral (usually the top of the 4 LV wires) is grounded evert 3rd or 4th pole then you can be reasonably confident that you have MEN. If you're not sure, don't MEN.

 

 

 

[GavinK]

Thanks. Looks like it ain't broken so I won't fix it.

[mahjongguy]

3 hours ago, Crossy said:

 

It could be all three ???? 

 

Assuming the main house is wired to the latest Thai standard (TN-C-S with MEN).

 

Better - Provides a metallic connection back to the transformer star-point, a L-E fault will open the MCB.

Unnecessary - RCBO provides shock protection anyway.

Worse - In the event of a neutral failure in the supply the supply "earth" could get well above true earth potential. If there's a water pipe or structural steel in the outbuilding that's at true earth you could have two "earthed" objects with a lethal potential between them. It's a particular problem with things like hot-tubs, lots of naked wet bodies standing on wet grass, you want any metalwork at true earth. Farm animals are also very vulnerable to shock between front and back legs so farm outbuildings are invariably TT with lots of local bonding.

 

Well, that seems to cover the choices. Educational. Thx.

 

Given that I'm a belt-and-braces kind of guy, maybe I'd have a ground at the outbuilding and run back to the ground inside CU#1.

 

Any harm in that?

[Crossy]

5 minutes ago, mahjongguy said:

Any harm in that?

 

I would avoid it if there were any possibility of you being at "real" ground potential (stood on the ground in bare feet) whilst touching something (like your recharging EV) at mains ground potential. 

 

I'd bond the remote rod to any building steel too just to ensure no nasty voltages can occur.

[mahjongguy]

Thx again. I expect to be involved in something very much like that next year, and we take these things very seriously. Twenty years ago my partner's sister, mother of two young children, was electrocuted in her home.

[Crossy]

@mahjongguy sorry to hear that ???? 

 

There are still far too many electrical deaths here, including "sensible" farangs, 99% of which could have been prevented by a unit costing less than 500 Baht and half decent installation practices.

 

[xtrnuno41]

Why you think 2.5 meters dept of rods is enough? You need to measure for right working of ground.

Resistance should be low enough for proper safety working. 

In summertime when its dry , resistance gets higher, as the soil is getting drier.

At least use RCBO's then if you dont want to make ground properly working.

[millymoopoo]

Ensure both earth rods are driven into permanently damp ground, like beside a well or septic leach drain.

An earth rod driven into dry ground is as useless as tits on a bull.

Better still is to drive them into the ground water table.

Eg: if the water table starts at 3m then use 4m rods.!

[mahjongguy]

I just got this explanation. Someone might benefit.

 

Twenty years ago it was very common in rural Thailand, almost universal, that a signal booster was needed to get decent picture quality on the TV. There was a unit inside the house that injected low voltage into the coax antenna cable. This powered the high gain amplifier which was mounted at the top of the antenna mast. It seems that the indoor unit must have failed and was leaking 220vac to the amp and this bled to the mast (which was mounted low to the ground but insulated from it). Something like that, as she was killed when she touched the mast.