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i hope all you electrical experts out there can help me with this one. We are currently building a large new house of approximately 400M2 indoor living space. We also have a (existing) smaller 2 bedroom, 1 living room, 1 bathroom cottage. Also building a seperate kitchen (European spec and appliances) area with bathroom and entertainment area. I would like to know the best way to supply all 3 buildings from our 1 incoming supply. I have done some homework on this and will feed the main house with a pair of 35mm2 NYY cables which will be buried in a 100mm conduit, to our main distribution panel (consumer unit). Cottage and kitchen will have their own consumer units fed from the main board. Each is to be fed by a pair of 16mm2 NYY cables, buried in 50mm conduit. All 3 boards will be earthed to a ground spike. All electrical accessories will be British 3 pin type sockets etc. Been told that I have to upgrade the incoming supply. All above has been suggested by a Thai Electrical Engineer. If anybody can verify for me or suggest better / proper way to install I would be very grateful. Regards,Tas

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You should have a talk with PEA and see what's available power wise from the incoming supply. How far are you from the transformer serving your property? Are you having voltage drop problems with your existing cottage? Have you worked out a total demand estimate? Of course you need a larger supply and meter. What size meter do you have now, 15(45)?

Edited by InterestedObserver
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How far is the run from power meter to your load center?

35 mm wire is fine if the run is not too long & will handle 100 amps.

But you are going to need a 30/100 amp meter at a minimum.

16 mm branches are fine. I would want my underground runs to be waterproof using silicone etc.

The PEA's mandate is to supply customers the current they require. If that means adding a transformer so be it. It sux to be a monopoly.

As poster above stated calculate your maximum demand.

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You should keep your max demand to less than 100Amps per phase.

Your voltage drop should not exceed 5% from the point of connection of the service conductors to the consumers mains to any point in the electrical installation.

You should have a maximum demand calculation done first before you approach the PEA.

If the PEA have to upgrade their transformer you may be required to supply some of the capital cost of the upgrade.

Installing a MCB as a main switch is one method of setting the max demand, the second method is by calculation. The second method is the one usually done for domestic/residential installations.

Edited by electau
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As noted above, do a maximum demand calculation. It doesn't have to be exhaustive for a domestic installation, just to get a ball-park idea of consumption. Make sure you include all your big consumers (aircon, water heaters, stove etc. etc.)

Some Points to Ponder.

Is 3-phase available to your property (if not you are limited to 100A single-phase maximum, and that is not available in all areas, next down would be 45A maximum)

How far from the local transformer is your property (those cables have volt drop too) and how big is the transformer (will PEA have to upgrade).

Is MEN/PME implemented (this will determine how your system is grounded and protected).

Distance is not your friend. As Electau says, calculate your volt drop on each run and size your cable appropriately.

NOTE. If you have aircons and waterpumps you should use at least 2x the run current when calculating your volt drop to account for start-up surge.

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