House Electrics, Some Guidance Please

[CM4Me]

Hi Fellow TV members

We have a parcel of land, some 30kms out of town, which we are slowly developing into a small self sustaining organic farm. Eventually (when funds become available), we will build a suitable abode & move there permanently.

But for now we travel back & forth 6 out of 7 days. As a result we have decided to build a small 1 bedroom cottage for the occasional overnight stay, & later it can be used as a guests' cottage.

I intend to tell the builder our electrical requirements in detail, rather than rely on their questionable 'Thai way'. I'm more of a practical person than not, but have had no training as an electrician, I've just studied many of the articles here on TV, on other websites, & a book on building in Thailand. I have used Crossy's calculators for determining both the MD and cable size. But as I said I'm not an electrician & therefore respectfully ask the more knowledgeable TV members to advise, correct & or guide me through this maze.

Our land is somewhat isolated from the local village, & as a result we are the last consumer on this particular PEA single phase supply line. This line runs along our Soi on the opposite side, crosses the Soi directly in front of our property & ends.

At this time we have a 5/15 PEA Meter which the PEA advised, just this last week, can be changed to a 15/45 subject to their inspection of our main from the meter to the Main DB, & the Main DB itself. This 5/15 provides electricity to our small store, via an aerial cable, over a distance of 85m.

At this store there is a small DB which contains a 63A MCB 2 pole main switch, a 16 MCB & a 20 MCB. I calculate the MD as 13Amps based on 3 x lights & 3 x DPO (at 10Amps max each & each DPO counted as 2). This supply cable is 2.5sqmm.

At the point where the incoming supply line enters our property & almost at right angle to the line meter – store, & some 65m away, is where we plan to build the small cottage. Again the cable will be aerial.

I'm now assuming I will need to erect a pole adjacent to the PEA meter, just inside our boundary, on which will be fitted the Main DB, containing a Main Switch 63Amp MCB, & a 15Amp MCB(for the store) & a 20Amp MCB (for the small cottage - see my cal's following). If this is the case then I think the DBs at both the store & the small cottage will be known as Sub-DBs. This whole question of how to control & divide the incoming supply is my biggest unknown.

I calculate the MD for the small cottage to be 20 Amps, based on 14 x lights (which incls 2 x ceiling fans), 2 x 2500w instantaneous water heaters, & 20 x plugs (at 10 Amps max each & each DPO counted as 2). I believe the supply cable in this instance to be 4.0sqmm.

For the small cottage DB (or perhaps that should be called a Sub) I'm thinking of a 20Amp MCB Main Switch (not RCD),

1 x 10Amp MCB for lights/fans, )

2 x 20 Amp MCB for Power Outlets, ) RCD protected

2 x 20Amp MCB for the 2 water heaters )

1 x 20Amp MCB for dedicated fridge circuit (not RCD).

All POs will have PE back to the DB.

Within the cottage all cables will run in concealed electrical conduit, with cable being

Lights/fans 1.0sqmm 2 core - copper

All other electrical circuits 2.5sqmm 3 core - copper.

Main Earth 4sqmm, & run to an electrode 12.7mm copper clad steel buried 1.2m in the ground.

Am I on the right track? Constructive advice most welcome.

Clipsal is the only brand name that I'm familiar with, other recommendations, again, would be most welcome.

Tks, in anticipation

Kevin

Edited September 13, 2010 by CM4Me

[electau]

These caclulations are based on AS3000/2007. This may be of help to you Kevin.

Metering 1 x 10/45A.

Consumers mains 10sqmm min. copper to MSB.

Submains to existing store DSB from MSB. 10sqmm min.

Submain to proposed cottage DSB from MSB 10sqmm min.

Voltage drop based on 3% in the consumers mains and 3% in each sub main.

Consumers mains start at the point of termination of the service conductors.

You propose a pole/post to mount the Main Switch Board (MSB). the metering will be on the line side of the main switch. Each submain will be protected by a MCB 32A for the cottage and 32A for the store. Submains are proposed to be run in an aerial configuration.

Main earth and electrode will be located at the Main Switchboard.

A submain earth conductor and electrode at each DSB.

If you earth the neutral of the consumers mains, and each submain you will have an MEN installation. If you do not earth the neutrals your installation will be TT and ALL subcircuits must be protected by RCDs.

Each switchboard shall be fitted with a neutral link and earth bar.

Use Clipsal products if you can obtain them, you may have to use National for the socket outlets.

All socket outlets shall be 3 pin and earthed.

It would be recomended that all socket outlets are RCD protected.

You do not have to use conduit if the walls are hollow and a concealed ceiling space is available run TPS cables.

If you decide to run the submains underground you will run a separate earth conductors min 4 sqmm to each DSB. In this case you will not require the earth electrodes at the DSBs.

You cannot install RCDs on submains if the neutral is earthed. on the load side of the RCD. RCDs only on subcircuits.

Edited September 13, 2010 by electau

[Crossy]

Taking a pragmatic approach and mostly agreeing with electau.

PEA will want to see at least 16mm from their meter to your incomer for a 15/45 supply if your incomer is the normal 63A.

Since the supply to the shed has proved itself adequate (85m of 2.5 will drop 10% at 13A) fuse it down to 15A as you suggest. Certainly the existing 63A MCB is not protecting the 2.5 cable.

For the cottage you'll be needing at least 4mm (6% volt drop at 20A) but as it's a liveable structure and you're already at the end of a long line I'd go along with electau and use 10mm (4% drop at 20A). You can use up to a 40A breaker to protect the 10mm.

Both the above fuses / MCBs should be at your main DB (near the meter). Use a weatherproof DB or put it in a weatherproof enclosure (at least IP65) if you don't have a structure to house the DB.

In your location MEN is almost certainly NOT implemented, in that case you MUST use RCDs in both your remote DBs (with local earth rods) and do NOT link neutral to ground anywhere. Without the RCDs you are unlikely to get enough current to open the breakers in the event of a L-E fault.

Thoughts to think about.

Considering the location, I would check the supply voltage at the meter, both off load and with as much load as you can get (kettles are a good load to use, try to get to 20A+). Whilst not very scientific it will give you an idea what to expect in the way of supply variation and maybe save headaches later on. Try to do this check in the evening when everybody else is home and loading the system.

Do you have / need a water pump (for those shower heaters), depending upon its location we may need to increase the cable size to cope with the start current.

Do either of your aerials cross roads or other places where they may get damaged? If so consider including a 100mA RCD in the main DB to protect from shock in the event someone damages the feed.

[electau]

Just a note on my previous post. Cable sizes are minimum. Voltage drop based on 3% in the mains and sub-mains and 2% in the subcircuits. 5% max within the installation.

I have assumed that the consumers mains would be of short route length, from the point of attachment on the pole to the metering and main switch. 7 to 10 metres maximum.

Clearance from the ground to the aerial conductors should be 3 metres minimum.

Water heaters assumed to be the instantaneous type max demand 33.3% of FLA.

[fredge45]

CM4Me has asked that I send along his thanks for the good replies to his query.

While composing a response his computer (FRED) took the easy way out and died on him. As soon as he can get repairs he will respond, with even more questions I'm sure!!

[Anon999]

If you can find a small electrical retailer with a knowledgeable owner that could be a big help as he would know the situation in your neck of the woods. The other useful source is the local electricity supply company. I used both sources during the construction of a house.

Apart from Clipsal two other brands are Haco and Panasonic, I used Clipsal for the switches and Haco sockets or female plugs as the Thais call them.

What about a such things as an electric cooker, rice cooker, iron, washing machine, etc., as staying longer than the weekend may occur.

[CM4Me]

Firstly, I must apologize to one & all for my inability to participate in this post since I 1^st posted it. Unfortunately, my computers' mother board did a melt-down on me (as advised by my friend Fredge) & it's been away being repaired (& upgraded).

Secondly, thanks to those members that posted some invaluable advice.

So, considering all, my plan now is:

* To install a pole 3m max from the PEA Meter & mount a weatherproof MSB containing

A Main Switch, 2 pole, MCB 63A

A MCB 15A (to the store/shed)

A MCB 32 A (to the small cottage)

The Main Earth

Consumer mains to the MSB 16sqmm, max length 9m, aerial

* To install a DSB (at the cottage) containing

A Main Switch, 2 pole, MCB 32A

A MCB 10A, (light & Fans)

3 x 20A MCBs (power outlets)

2 x MCBs (H.W.)

All above RCBO protected

DSB Earth

Consumer sub-mains (MSB to the DSB) 10sqmm, 65m, aerial

* Supply means to the DSB (store/shed) to remain as is (i.e. 2.5sqmm for 85m, aerial), but with the MCB in the MSB fused down to 15A.

* All aerial cables to have 3m min clearance

* Earths will be 4sqmm, electrode 12.7m copper clad, buried 1.2m min.

A couple of things that are not clear to me are

1. The (amended) Amp rating for the DSB (store) Main Switch.

2. Main Earth (at the MSB) I assume this is connected to the incoming N supply line before the Main Switch.

Comments, suggestions, advice welcome. Again thanks in advance

Kevin

Edited September 27, 2010 by CM4Me

[electau]

For 3% voltage drop in the sub main to store (85m) for a max demand of 13amps you will require 10sqmm. Protect with a 16A MCB. Using 2.5sqmm the voltage drop would be 8.6%

The main earth connection will be at the main neutral link. PEA policy is to locate the main neutral link on the line side of the main switch.

Where one had 32A MCB for the store sub main it should be 16A.

[CM4Me]

electau, tks again for your advice.

Just one point for clarification - when you refer to 'main neutral line' do you mean the incomming line, the line after the PEA Meter & before my MSB Main Switch?

By the way, some advice I've been offered by Thais (incl a builder, a retail assistant in a very large building supply store etc) include

* No need to upgrade your meter, 5A for a small house is more than enough

* You don't need a MSB, save your money, just join the wires together.

* You don't need 'sigh din' (not sure of that spelling - but its refers to earthing), again save your money.

* MD, what's that?

But TIT, & obviously I've rejected the unsafe advice.

Kevin

Edited September 29, 2010 by CM4Me

[electau]

electau, tks again for your advice.

Just one point for clarification - when you refer to 'main neutral line' do you mean the incomming line, the line after the PEA Meter & before my MSB Main Switch?

By the way, some advice I've been offered by Thais (incl a builder, a retail assistant in a very large building supply store etc) include

* No need to upgrade your meter, 5A for a small house is more than enough

* You don't need a MSB, save your money, just join the wires together.

* You don't need 'sigh din' (not sure of that spelling - but its refers to earthing), again save your money.

* MD, what's that?

But TIT, & obviously I've rejected the unsafe advice.

Kevin

Yes, the main neutral refers to the incoming neutral conductor from the point of supply to the main switch board.

You max demand indicates that you will require a 15/45A meter. 45A is the max continuous rating. (The 15A is the test current for calibration purposes). The smaller meter is 5/15A.

You will require circuit protection for the submains so at this point you have a main switchboard. This is where the main switch is located.

You require earthing for safety.

MD is the maximum demand in amps, and is done by calculation or by the fixed current rating of a MCB.