3 phase wiring for Thai hotel

29 Jul 2006
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United Kingdom
Hi, I'm a British guy building a small bungalow resort in Phuket, Thailand. My builders and Thai electrician have been working to a set of plans drawn up by a competent architect. The electrician has just completed the internal wiring for each bungalow, (lights, water heater etc), and this all looks ok.

However, he has now done a runner! So I need to bring in another person to complete the external wiring. I want to try to understand the circuit plan so that I can advise him, or spot any errors before we have problems!

I've studied the overall site circuit plan, which is basically a three phase input from the 33KV supply, stepped down via a transformer to 400V/230V. Then the supply is run via the various main breakers before it is distributed across the hotel site to the bungalows etc.

I want to understand the coding of the cables shown on my plan. All external cables are NYY type, (that is, sheathed in black PVC). But I'm having problems understanding the coding on the plan.

For example, the main 3 phase input from the transformer seconday is marked '4-2.5 sq mm nyy pvc dia 2" '. OK, that seems to mean 4 cores (3 phase plus neutral), each of 2.5 square millimetres, with an overall external diameter of the pvc cable of 2 inches.

But what about some of the distribution cables? These are typically marked '4-2.5, 1-2.5 g sq mm nyy pvc 3/4" ' Now that seems to suggest 4 cores at 2.5 square millimetres and 1 core of 2.5 square millimetres. I'm not sure what the 'g' means!

In any case, why do you need 5 wires? I can understand three for the 3 phases, plus a wire for the neutral. Or maybe they mean 4 wires for the 3 phase plus neutral, and 1 wire for an earth. (Ah ha, maybe the 'g' means ground...)

Additionally, I can't understand why the plan implements distribution of three phases to my bungalows. Surely single phase should be supplied to the buildings, with a few buildings connected to phase 1, some to phase 2 and some to phase 3 - so that you get a balanced load across all 3 phases.

If I run three phase NYY cable, then that's pretty expensive to buy! I would prefer to run single phase, and balance the loads/phases as mentioned above.

Any comments, advice, questions appreciated!

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Two observations:

I can't see how a 4 x 2.5mm cable is going to have an outside diameter of 2 inches. I wonder if it could be circumference or duct size? Could it have been 4 x 25mm armoured, with a design current of 100A or so, as it is the supply from your transformer?

3-phase supply is often used for high load appliances like air conditioners or cookers (a) in Australia where long overhead cables are common (b) in US where the voltage is only 110. In both cases it is to keep the amps-per-phase down. It sounds like you are only distributing 20A to each bungalow if it uses 2.5mm.

On balance, I think you need to consult a competent local person who's familar with regulations and common working practices. I bet they don't even use rings over there! ;)
Hi JohnD, thanks for your reply.

No, they don't know what ring-circuits are here...

I agree with you re the diameters quoted. They are too large for the core sizes. On reflection, I think they are refering to the diameter of the trunking in which the cable will run.

The quoted loads for the cable sizes to each set of buildings are shown as:

4-2.5, 1-1.5 g 5KVA
4-8, 1-4 g 15KVA
3-16, 1-10, 1-8 g 30KVA

I have 5 bungalows, each with 2 bedrooms and bathrooms. Each bedroom has standard lights and powerpoints, as well as an aircon unit. The bathroom has an instant water heater. The plan indicates breakers of 16A for the aircon, 16A for the powerpoints, 10A for the lighting, with use of a main 16A breaker in the consumer unit. The water heater has a breaker of 20A and is not wired via the CU.

What is not shown is how these bungalows should be 'fed' with the 3 phase so as to balance everything out. I could, for example, feed phase 1 to room 1 CU, and phase 2 to room 1 water heater. Then phase 3 to room 2 CU and phase 1 to room 2 water heater . . .and so on.

Since I have no idea which rooms will be occupied and which equipments in these rooms will be used at whatever time, what is the best wiring configuration so as to balance the 3 phases?

Or does it really matter all that much? (We are installing a dedicated transformer to connect to the nearby 33KV line)


seeing as you dont know, and we can only guess why not ask the architect?

It would be better than getting it wrong
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Having seen some of the supply distribution set-ups in Phuket I would say you are lucky they are not specifying a piece of wet string. Sorry I know this does not help, but you can really only go by what your architect says. Have you looked at any other developments or spoken to other ex-pat developers?
The Commercial department of the British Consulate might be a useful source names of or routes to reliable local people.

Some are helpful , some are not.
jj4091 & bernardgreen, dont bother i bet its all done now since it was posted in July
Hi JohnD and Simon43,
I am new to this site and realise that this topic is aged!
However, John, you are close. I am building a bungalow in Roi-Et, Thailand. I designed two ring mains, 1 for the kitchen and one for the remainder of the house. I had to literally draw the circuits showing the complete loop before the sparky (sharky) would do the job properly. He claimed that ring mains were old fashioned!
For you, Simon, can't help too much with the spec you gave. John got most of it right but I suspect that the 2" figure might well be plastic conduit, but can't be sure. With regard to 3 phase distribution. The 3 phases will have to go right round the resort. Phase 1 (red) will tap off to chalet 1, phase 2 (yellow) to chalet 2, phase 3 (blue) to chalet 3. Then, phase 1 to chalet 4 etc. Therefore all 3 phases will go al the way round.
As I said I am having great difficulty with my electrician - fortunately I am in the trade.
Hope I have been of some help. Perhaps you can email me your diagram.
[email protected]
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